JP2009512985A - Continuous pulse traveling wave accelerator - Google Patents

Abstract

[Solution]
Two or more pulse forming lines, each having a switch for generating a short acceleration pulse along the short length of the beam tube, and said charge traversing axially to continuously energize the particle beam A continuous pulse traveling wave compact accelerator comprising: a trigger mechanism for continuously triggering the switch so that an axial electric field is generated along the beam tube in synchronization with the pulsed beam of particles;
[Selection] Figure 1

Description

  The US government has rights to this invention in accordance with the W-7405-ENG-48 agreement between the US Department of Energy and the University of California in the work of Lawrence Livermore National Laboratory.

  This application is a portion of prior application No. 11 / 036,431 filed on Jan. 14, 2005 claiming the benefit of provisional application No. 60 / 536,943 filed on Jan. 15, 2004. This is a continuation application and is filed in US provisional applications 60 / 730,128, 60 / 730,129, 60 / 730,161 and 2006 filed on October 24, 2005. It also claims the benefit of US Provisional Application No. 60 / 798,016, filed May 4, all of which are hereby incorporated by reference.

  The present invention relates to a linear accelerator, and more specifically, travels along the beam tube of the accelerator in synchronism with the pulsed beam of charged particles traversing in the axial direction to continuously energize the charged particles. A continuous pulse traveling wave linear accelerator that continuously triggers a switch to differentially propagate an electrical wavefront through a linear accelerator pulse forming line so that an axial electric field is generated .

  Particle accelerators are used to increase the energy of charged atomic particles, such as electrons, protons, or charged nuclei, so that they can be studied by atomic physicists and particle physicists. The particles of high energy charged atoms are accelerated to collide with target atoms and the resulting product is observed using a detector. At very high energy, charged particles can destroy the nuclei of target atoms and interact with other basic units of matter. Particle accelerators are also an important tool in developing fusion devices and in medical applications for cancer treatment.

  One type of particle accelerator is disclosed in Carder US Pat. No. 5,757,146, incorporated herein by reference, which is a method for generating fast electrical pulses for acceleration of charged particles. I will provide a. Carder shows a dielectric wall accelerator (DWA) system consisting of a series of stacked circular modules that generate high voltages when switched. Each of these modules is called an asymmetric bloom line, which is described in US Pat. No. 2,465,840, which is incorporated herein by reference. As best seen in the Carder patents FIGS. 4A-4B, the bloom line consists of two different dielectric layers. On each surface and between the dielectric layers are conductors that form two parallel plate radial transmission lines. One side of the structure is called the low speed line and the other side is called the high speed line. The center electrode between the high speed line and the low speed line is first charged to a high potential. Since the two lines are of opposite polarity, there is no net voltage across the inner diameter (ID) of the bloom line. Shorting the outer ends of the structure with a surface flashover or similar switch generates two opposite polarity waves that propagate radially inward toward the Bloomline ID. The wave in the high speed line reaches the structure ID before the wave arrives in the low speed line. When the fast wave reaches the structure ID, the polarity at the arrival point is reversed only at that line, thereby creating a net voltage across the ID of the asymmetric bloom line. This high voltage lasts until the wave on the slow line finally reaches ID. In the case of an accelerator, it can be accelerated by injecting a charged particle beam during this time. In this way, the DWA accelerator in the Carder patent provides an axial acceleration electric field that continues throughout the structure to obtain a high acceleration gradient.

  However, existing dielectric wall accelerators such as Carder's DWA have certain unique problems that can affect beam quality and performance. Specifically, several problems exist in the Carder DWA disk-like geometry, which makes the entire device more than optimal for the intended use of accelerating charged particles. Get smaller. A flat planar conductor having a central hole focuses the propagating wavefront radially toward the central hole. In such a geometry, the wavefront experiences a varying impedance, which distorts the output pulse and may not give a predetermined time-dependent energy gain to the charged particle beam across the electric field. Alternatively, a charged particle beam that traverses the electric field formed by such a structure experiences a time-varying energy gain that allows the acceleration system to properly transport such a beam for such limited applications. Forming the beam can be prevented.

  Also, the impedance of such a structure may be significantly lower than the required impedance. For example, it is often highly desirable to produce a beam on the order of sub-milliamperes while maintaining the required acceleration gradient. Carder's disk-like bloom line structure can cause excessive levels of electrical energy to be stored in the system. Beyond the apparent electrical inefficiency, any energy that is not delivered to the beam when the system is activated can remain in the structure. Such excessive energy can adversely affect the overall performance and reliability of the device, thereby leading to premature system failure.

  Further, the large extension of the outer periphery of the electrode is peculiar to a flat planar conductor (for example, a disk shape) having a center hole. As a result, the number of parallel switches for activating the structure is determined by its circumference. For example, a 6 inch diameter device used to generate pulses of less than 10 ns generally requires at least 10 switch sites per disk-shaped asymmetric bloom line layer. This problem becomes even more problematic when long acceleration pulses are required. This is because the output pulse length of this disc-shaped bloom line structure is directly related to the radial range from the center hole. Therefore, if a long pulse width is required, more switch sites are required accordingly. If the preferred embodiment for activating the switch is the use of a laser or other similar device, a very complex distribution system is required. Also, the long pulse structure requires a large dielectric sheet that is difficult to manufacture. This can increase the weight of such structures. For example, in the current configuration, a device supplying 50 ns pulses can weigh as much as several tons per meter. Some of the short pulse disadvantages can be mitigated by using spiral grooves in all three conductors in the asymmetric bloom line, which can result in destructive interferometric interlayer coupling that can interfere with operation. There is. That is, a significantly reduced pulse amplitude (and hence energy) from stage to stage can appear at the output of the structure.

  Various types of accelerators have also been developed for specific applications in medical treatment such as cancer treatment using proton beams. For example, US Pat. No. 4,879,287 to Cole et al. Discloses a multi-station proton beam treatment system for use at the Loma Linda University proton accelerator facility in Loma Linda, California. In this system, particle source generation occurs at one location within the facility and acceleration occurs at other locations within the facility, but the patient is located at another location within the facility. Because the particle source, acceleration, and target are far away from each other, particle transport is achieved using a complex gantry system with a large and bulky deflecting magnet. Other exemplary systems known in medical treatment are also disclosed in Bertsche US Pat. No. 6,407,505 and Blosser et al US Pat. No. 4,507,616. Bertsch shows a standing wave RF linac, and Blosser shows a superconducting cyclotron rotatably mounted on a support structure.

  Also known are ion sources that form a plasma discharge from low pressure gas in a certain volume. From this volume, ions are extracted and collimated into the accelerator for acceleration. These systems are generally limited to extracted current densities below 0.25 A / cm2. This low current density is due in part to the intensity of the plasma discharge at the extraction interface. One example of an ion source known in the art is disclosed in US Pat. No. 6,985,553 to Leung et al. Having an extraction system configured to generate ultrashort ion pulses. Another example is in U.S. Pat. No. 6,795,807 to Wahlin, which discloses a multi-grid ion beam source having an extraction grid, an acceleration grid, a focusing grid, and a shield grid to produce a highly collimated ion beam. It is shown.

  According to a first aspect of the present invention, there is provided a dielectric beam tube having a length L surrounding an acceleration axis and at least two pulse forming lines connected to the beam tube in a direction crossing the dielectric tube. The line propagates at least one electrical wavefront through the pulse forming line independently of the other pulse forming lines to transmit an acceleration pulse with a short pulse width τ along the corresponding minor axis length δL of the beam tube. Synchronized with at least two pulse forming lines having a switch connectable to a high voltage potential to generate and a pulse beam of said charged particles traversing axially to continuously energize the charged particles. And a means for continuously controlling the switch so that an electric field in the direction of the traveling axis is generated along the beam tube.

  Another aspect of the invention is a plurality of pulse forming lines extending to the lateral acceleration axis, each pulse forming line passing through the pulse forming line independently of the other pulse forming lines. A plurality of pulse forming lines having a switch connectable to a high voltage potential to propagate a typical wavefront and generate a short acceleration pulse adjacent to the corresponding short axis length of the acceleration axis, and for charged particles Operable to continuously control the switch to generate an electric field in the direction of the traveling axis along the acceleration axis in synchronism with the pulsed beam of charged particles traversing in the axial direction in order to provide energy continuously. A continuous pulse traveling wave linear accelerator with a connected trigger.

  Another aspect of the invention is a dielectric beam tube of length L surrounding an acceleration axis and at least two bloom line modules each forming a pulse forming line perpendicular to the acceleration axis, each bloom line A first conductor having a first end and a second end connected to the beam tube; a first end adjacent to the first conductor and switchable to a high voltage potential; A second conductor having a second end connected to the beam tube; and a third conductor having a first end adjacent to the second conductor and connected to the beam tube and a second end connected to the beam tube. A first dielectric member having a first dielectric constant and filling a space between the first conductor and the second conductor; a second conductor having a second dielectric constant; And a second dielectric member that fills a space between the third conductor and the first and second dielectric constants. At least two Bloomline modules smaller than the dielectric constant of the tube, each Bloomline module propagating at least one electrical wavefront through the Bloomline module independently of the other Bloomline modules. At least two bloom line modules having at least one switch connectable to a high voltage potential to generate an acceleration pulse with a short pulse width τ along the corresponding minor axis length δL of the beam tube; Operates to continuously trigger the switch to generate an axial electric field along the beam tube in synchrony with the pulsed beam of charged particles traversing in the axial direction to provide energy continuously. A continuous pulse traveling wave linear accelerator with a connected controller.

  The accompanying drawings, which are incorporated in and form a part of the disclosure, are as follows.

A. Compact Accelerator with Banded Bloom Lines Referring now to the drawings, FIGS. 1-12 guide a wavefront propagating between a first end and a second end and a second end Fig. 2 shows a compact linear accelerator used in the present invention with at least one strip-shaped Bloomline module for controlling the output pulses. Each bloom line module has first, second and third planar conductor strips, a first dielectric strip between the first conductor strip and the second conductor strip, and a second A second dielectric strip is provided between the first conductor strip and the third conductor strip. The compact linear accelerator also includes a high voltage power source connected to charge the second conductor strip to a high potential, and at least one of the first and third conductor strips to increase the high potential in the second conductor strip. And a switch that causes a propagating reverse polarity wavefront in the corresponding dielectric strip.

  The compact linear accelerator has at least one strip-shaped bloom line module that guides the propagating wavefront between a first end and a second end and controls the output pulse at the second end. . Each bloom line module has first, second and third planar conductor strips, a first dielectric strip between the first conductor strip and the second conductor strip, and a second A second dielectric strip is provided between the first conductor strip and the third conductor strip. The compact linear accelerator also includes a high voltage power source connected to charge the second conductor strip to a high potential, and at least one of the first and third conductor strips to increase the high potential in the second conductor strip. And a switch that causes a propagating reverse polarity wavefront in the corresponding dielectric strip.

  FIGS. 1 and 2 show a first exemplary embodiment of a compact linear accelerator, generally designated by reference numeral 10, comprising a single bloom line module 36 connected to a switch 18. The compact accelerator also includes a suitable high voltage power supply (not shown) that supplies a high voltage potential to the bloom line module 36 via the switch 18. In general, bloom line modules are typically in the form of strips of uniform width but not necessarily, ie long and narrow geometric shapes. The specific bloom line module 11 shown in FIGS. 1 and 2 extends between the first end 11 and the second end 12 and has a relatively narrow width wn (FIG. 2) compared to the length l. , 4) in the form of an elongated beam or a plate-like straight line. This strip-like form of the bloom line module guides the propagating electrical signal wave from the first end 11 to the second end 12 and thereby controls the output pulse at the second end. Works. Specifically, the shape of the wavefront may be controlled by appropriately configuring the width of the module, for example by gradually reducing the width as shown in FIG. Due to the strip configuration, the compact accelerator can overcome the variable impedance of the propagating wavefront that can occur when directed radially to focus on the center hole, as discussed in the background for Carder's disk-shaped module. . In this way, a flat output (voltage) pulse can be generated by the strip or beam-like form of the module 10 without destroying the pulse, so that the particle beam does not suffer from an aging energy gain. Can be. As used herein and in the claims, the first end 11 is characterized as an end connected to a switch, for example a switch 18, and the second end 12 is a particle. An end adjacent to a load region such as an output pulse region for acceleration.

  As shown in FIGS. 1 and 2, the narrow beam-like structure of the basic bloom line module 10 is formed as a thin strip, both elongated but also shown as a thicker strip. 3 plane conductors separated by. Specifically, the first planar conductor strip 13 and the middle second planar conductor strip 15 are separated by a first dielectric member 14 that fills the space between them. The second planar conductor strip 15 and the third planar conductor strip 16 are separated by the second dielectric member 17 that fills the space between them. The separation made by the dielectric members is preferably positioned so that the planar conductor strips 13, 15, 16 are parallel to each other as shown. Further shown is a third dielectric member 19 connected to the planar conductor strip and dielectric strip 13-17 to cover these ends. The third dielectric member 19 serves to combine the waves so that only a pulse voltage is applied across the vacuum wall, thereby reducing the time during which the wall is stressed and even higher. A gradient is possible. The third dielectric member can also be used as a region for deforming the wave before applying the wave to the accelerator, that is, increasing the voltage and changing the impedance. Accordingly, the third dielectric member 19 and the second end 12 are generally shown adjacent to the load region indicated by the arrow 20. Specifically, the arrow 20 represents the acceleration axis of the particle accelerator that faces the direction of particle acceleration. As explained in the background art, it goes without saying that the direction of acceleration depends on the path of the fast and slow transmission lines through the two dielectric strips.

  In FIG. 1, the switch 18 is shown connected to each of the planar conductor strips 13, 15, 16 at the first end, ie, at the first end 11 of the module 36. The switch initially serves to connect the outer planar conductor strips 13, 16 to ground potential and the middle conductor strip 15 to a high voltage source (not shown). Thereafter, the switch 18 operates to short-circuit at the first end, thereby causing a voltage wavefront to propagate through the Bloomline module and generating an output pulse at the second end. Specifically, the switch 18 has a propagating reverse polarity wavefront in at least one of the dielectrics depending on whether the Bloom line module is configured for symmetric or asymmetric operation. It can be raised from the first end to the second end. When configured for asymmetric operation, as shown in FIGS. 1 and 2, the Bloomline module is configured in a manner similar to that described by Carder in the dielectric constants and thicknesses of the dielectric layers 14,17. (D1 ≠ d2) is different. The asymmetrical operation of the Bloom line makes the propagation wave velocity through the dielectric layer different. However, if the Bloom line module is configured for symmetrical operation as shown in FIG. 12, the dielectric strips 95, 98 have the same dielectric constant and the same width and thickness (d1 = d2). become. Also, as shown in FIG. 12, the magnetic member is also placed in close proximity to the second dielectric strip 98, thereby preventing wavefront propagation within the strip. In this way, the switch causes a propagation reverse polarity wavefront only in the first dielectric strip 95. It will be appreciated that the switch 18 is a switch suitable for asymmetric or symmetric Bloom line module operation, such as a gas discharge occlusion switch, surface flash over occlusion switch, solid state switch, photoconductive switch, and the like. Also, the switch / dielectric member type / dimension selection can be appropriately selected to allow the compact accelerator to operate at various acceleration gradients including, for example, gradients in excess of 20 megavolts / m. However, it goes without saying that even lower gradients can be achieved as a matter of design.

  In one preferred embodiment, the width w1 of the second planar conductor is defined by the characteristic impedance Z1 = k1g1 (w1, d1) across the first dielectric strip. k1 is the electrical constant of the first vacuum of the first dielectric strip defined by the square root of the ratio of the transmittance to the dielectric constant of the first dielectric member, and g1 is defined by the shape effect of the adjacent conductor. D1 is the thickness of the first dielectric strip. The thickness of the second dielectric strip is defined by the characteristic impedance Z2 = k2g2 (w2, d2) across the second dielectric strip. Where k2 is the electrical constant of the second vacuum of the second dielectric member, g2 is a function defined by the shape effect of the adjacent conductor, and w2 is the width of the second planar conductor strip. , D2 is the thickness of the second dielectric strip. In this way, different dielectrics provide different impedances, as required in asymmetric bloom line modules, so that the impedance can be kept constant by adjusting the width of the associated line. Therefore, more energy is transmitted to the load.

  4 and 5 show bloom lines having first and second planar conductor strips 41, 42 and a second planar conductor strip 42 that is narrower than the widths of the first and second dielectric strips 44, 45. FIG. 2 shows an exemplary embodiment of a module. In this particular form, the extension of the electrodes 41, 43 makes it difficult for the electrode 42 to couple energy to the previous or subsequent bloom line, which is counterbalanced as described in the background art. Interferometric interlayer coupling is prevented. Also, the modules of other exemplary embodiments are preferably configured so that their width varies along the length direction l (see FIGS. 2 and 4), thereby controlling the shape of the output pulse. This is shown in FIG. 6, which shows the taper as the module extends radially inward toward the central load region. In another preferred embodiment, the dimensions of the bloom line module and the dielectric member are selected such that Z1 is approximately equal to Z2. As already explained, when the impedance is matched, the formation of the waves forming the vibration output is prevented.

  Also preferably, in the asymmetric bloom line configuration, the second dielectric strip 17 has a much lower propagation velocity than the first dielectric strip 14, such as 3: 1. In this case, the propagation speed is defined by v2 and v1, respectively. Here, v2 = (μ2ε2) −0.5, v1 = (μ1ε1) −0.5, the transmittance μ1 and the dielectric constant ε1 are the material constants of the first dielectric member, and the transmittance μ2 And dielectric constant ε2 is a material constant of the second dielectric member. This can be obtained by selecting a member for the second dielectric strip that has a dielectric constant or μ1ε1 greater than that of the first dielectric strip, ie μ2ε2. As shown in FIG. 1, for example, the thickness of the first dielectric strip is shown as d1, the thickness of the second dielectric strip is shown as d2, and d2 is shown to be greater than d1. ing. By setting d2 greater than d1, the combination of different arrangements and different dielectric constants results in the same characteristic impedance Z on both sides of the second planar conductor strip 15. It should be noted that the characteristic impedance may be the same in both halves, but the propagation speed of the signal passing through each half is not necessarily the same. Although the dielectric constant and thickness of the dielectric strip may be appropriately selected to provide different propagation velocities, the elongated strip-like structure and configuration is an asymmetric Bloomline concept, i.e., the dielectric is dielectric constant and thickness However, it goes without saying that it is not always necessary to use different ideas. In other exemplary embodiments, the advantages of the control waveform are enabled by the elongated beam-like shape and form of the Bloomline module, not by a specific method that produces high acceleration gradients. A switching structure, such as the switching structure described with respect to FIG. 12 with symmetric Bloom line operation, can be used.

  Alternatively, the compact accelerator may be configured to have two or more elongated bloom line modules that are stacked in alignment with each other. For example, FIG. 3 shows a compact accelerator 21 having two bloom line modules stacked in alignment with each other. The two bloom line modules form alternating laminates 24-32 of planar conductor strips and dielectric strips, which are common to both modules. The conductor strip is connected to the switch 33 at the first end 22 of the laminated module. A dielectric wall 34 is also provided adjacent to the load region indicated by the acceleration axis arrow 35 and covering the second end 23 of the stacked module.

  The compact accelerator may be configured with at least two bloom line modules positioned so as to surround the central load area. Each of the surrounding modules may further include one or more additional bloom line modules that are stacked to be aligned with the first module. FIG. 6 shows an exemplary embodiment of a compact accelerator 50 having, for example, two bloom line module stacks 51, 53, with the two stacks surrounding a central load region 56. Each module stack is shown as a stack of four independently operating Bloomline modules (FIG. 7) and is separately connected to the associated switches 52,54. It goes without saying that the coverage of the segments increases along the acceleration axis by stacking the bloom line modules in alignment with each other.

  8 and 9 show a compact accelerator having two or more conductor strips 61, 63, for example conductive strips 61, 63 each connected at their second end by a ring electrode, indicated by 65. Another exemplary embodiment is indicated by reference numeral 60. The ring electrode configuration provides orientation averaging that may occur in structures such as FIGS. 6 and 7 in which one or more of the surrounding modules extends toward the central load region without completely surrounding the central load region. Act to overcome. As best shown in FIG. 9, each module stack represented by 61, 62 is connected to an associated switch 62, 64, respectively. 8 and 9 show an insulator sleeve 68 disposed along the inner diameter of the ring electrode. Alternatively, a separate insulator member 69 is also shown disposed between the ring electrodes 65. Alternatively, alternating layers of conductive foil 66 and insulating foil 66 'may be used as an alternative to the dielectric member used between the conductor strips. The alternating layers may be formed as a laminated structure instead of a monolithic dielectric strip.

  FIGS. 10 and 11 also show two further exemplary embodiments of the compact accelerator, which is indicated generally by the reference numeral 70 in FIG. 10 and generally in FIG. Reference numeral 80 indicates. Each compact accelerator has a bloom line module in the form of a non-linear strip. Here, the non-linear belt-like form is shown as a curved shape or a meandering shape. In FIG. 10, the accelerator 70 comprises four modules 71, 73, 75, 77 shown surrounding the central region and extending toward the central region. Each module 71, 73, 75, 77 is connected to an associated switch 72, 74, 76, 78, respectively. As can be seen from this structure, the direct radial distance between the first and second ends of each module is shorter than the overall length of the nonlinear module, thereby increasing the power transmission path and the accelerator. Can be made compact. FIG. 11 shows a structure similar to that of FIG. 10, and the accelerator 80 has four modules 81, 83, 85, 87 shown to surround the central region and extend toward the central region. ing. Each module 81, 83, 85, 87 is connected to an associated switch 82, 84, 86, 88, respectively. Also, the radially inner end of the module, i.e., the second end, is connected to each other by a ring electrode 89, thereby providing the advantages described in FIG.

B. Continuous Pulse Traveling Wave Acceleration Mode A dormant induction linear accelerator (LIA) is shorted along its entire length. Thus, acceleration of charged particles depends on the ability of the structure to form a transient electric field gradient and to separate a series of consecutive applied acceleration pulses from adjacent pulse forming lines. In prior art LIAs, this method is preferably performed by causing the pulse forming lines to emerge from the interior of the structure as a series of stacked voltage sources over the transition period when a charged particle beam is present. A typical means for creating this acceleration gradient to achieve the required separation is to use the magnetic core in the accelerator and the elapsed time of the pulse forming line itself. The latter includes the addition of length by optionally connecting cables. After transient acceleration occurs, the system is again shorted along its length due to saturation of the magnetic core. The disadvantages of such prior art systems are that the acceleration range is very low (˜0.2-0.5 MV / m) due to the limited spatial extent of the acceleration region, and the magnetic member is expensive. It is a big point. Also, even a good magnetic member can not respond to high speed pulses without severe loss of electrical energy, and so when a core is needed, forming this type of high gradient accelerator is At best, it cannot be practical, and in the worst case it is technically impossible.

  FIG. 25 shows a schematic diagram of a continuous pulse traveling wave accelerator of the present invention, indicated generally by the reference numeral 160 and of length l. Each transmission line of the accelerator is shown to be ΔR in length and δl in width, and the beam tube is d in diameter. An acceleration pulse whose electrical length (that is, pulse width) is τ is used to continuously excite the short axis length δl of the beam tube to generate a single virtual traveling wave 164 along the length direction of the acceleration axis. A trigger controller 161 is provided that continuously triggers the switch set 162 for generation. Specifically, the continuous trigger / controller can continuously trigger the switch, thereby synchronizing the pulse beam of charged particles traversing in the axial direction to continuously provide energy to the particles. A traveling axial electric field surrounding the acceleration axis is generated along the beam tube. The trigger controller 161 may trigger each switch individually. Alternatively, the trigger controller may simultaneously switch at least two adjacent transmission lines forming a block to switch adjacent blocks continuously, whereby an acceleration pulse is formed through each block. In this way, a block of two or more switch / transmission lines excites the short axis length nδl of the beam tube wall. δl is the minor axis length of the beam tube wall corresponding to the excited line, and n is the number of adjacent excitation lines at any time instant (n ≧ 1).

  Some numerical examples for illustrative purposes: d = 8 cm, τ = several nanoseconds (eg 1-5 nanoseconds for proton acceleration, 100 picoseconds to several nanoseconds for electron acceleration), v = c / 2 (C = speed of light). However, it goes without saying that the present invention can be expanded and contracted to almost any size. Preferably, the beam tube diameter d and length l satisfy the criterion l> 4d in order to reduce the fringing field at the input and output ends of the dielectric beam tube. The beam tube preferably satisfies the standard, that is, γτv> d / 0.6. Where v is the wave velocity on the beam tube wall, d is the beam tube diameter, and τ is:

で表わされるパルス幅、γは、下式：

Is expressed by the following equation:

で表わされるローレンツ係数である。なお、ΔＲはパルス形成ラインの長さであり、μは比透過率（通常＝１）であり、εｒは比誘電率である。このように、加速軸に沿って生成されるパルス高勾配は、少なくとも約３０ＭｅＶ／ｍであり、最大でも約１５０ＭｅＶ／ｍである。

Is the Lorentz coefficient. Note that ΔR is the length of the pulse forming line, μ is the relative transmittance (usually = 1), and εr is the relative dielectric constant. Thus, the pulse height gradient generated along the acceleration axis is at least about 30 MeV / m and at most about 150 MeV / m.

  Unlike many such accelerator systems that require a core to form an acceleration gradient, the accelerator system of the present invention operates without a core. This is because when the criterion nδl <l is satisfied, the electrical activation of the beam tube occurs along a small area of the beam tube at a time and a short circuit is avoided. By not using a core, the present invention provides a variety of cores associated with the use of the core, such as limited acceleration due to the voltage obtained in the case of Vt = AΔB, where A is the cross-sectional area of the core, limited by ΔB. To avoid problems. The use of the core also serves to limit the number of times the accelerator is repeated. This is because a pulse power supply is required to reset the core. The pulsed acceleration at a given nδl is separated from the conductive housing by the transient isolation characteristics of the unexcited transmission line adjacent to the given axial segment. Needless to say, parasitic waves arise from the incomplete transient isolation characteristics of the unexcited transmission line because a portion of the switch current is shunted to the unexcited transmission line. Of course, this happens without magnetic core separation to prevent this shunt from flowing. Under certain conditions, parasitic waves may be advantageously used, for example as shown in the examples below. In the form of an open circuit bloom line stack consisting of asymmetric strip bloom lines where only high speed / high impedance (low dielectric constant) lines are switched, the parasitic waves generated in the unexcited transmission line will cause higher voltages in the unexcited lines. Generating and increasing its voltage beyond the initial charge state, while increasing the voltage by a smaller amount in the slow line. This is because the two lines appear successively as a voltage divider that receives the same injected current. At this time, the wave appearing on the accelerator wall is increased to a value larger than the initially charged value, thereby obtaining a higher acceleration gradient.

  FIG. 26 and FIG. 27 show the difference in gradient produced by the length L beam tube. FIG. 26 shows a single pulse traveling wave having a width vτ smaller than the length L. In contrast, FIG. 27 shows a typical operation of a stacked bloom line module where all transmission lines are triggered simultaneously to produce a gradient over the entire length L of the accelerator. Here, vτ is not less than the length L.

C. Charged Particle Generator: Integrated Pulsed Ion Source and Injector FIG. 13 is a typical of charged particle generator 110 of the present invention having a pulsed ion source 112 and an injector 113 integrated into a single unit. The embodiment is shown. In order to generate an intense pulsed ion beam, modulation of the extracted beam and subsequent cluster is required. Initially, the particle generator operates to form an intense pulsed ion beam using a pulsed ion source 112 that uses a surface flashover discharge to generate a very dense plasma. The estimated plasma density exceeds 7 atmospheres and such discharge is fast. This makes it possible to form extremely short pulses. Conventional ion sources form a plasma discharge from a low pressure gas within a predetermined volume. From this volume, ions are extracted and collimated into the accelerator for acceleration. These systems are generally limited so that the extracted current density is below 0.25 A / cm2. This low current density is due in part to the intensity of the plasma discharge at the extraction interface.

  The pulsed ion source of the present invention has at least two electrodes that are bridged using an insulator. The gas species of interest is dissolved in the metal electrode or is in a solid state between the two electrodes. This geometry causes the spark formed over the insulator to receive and discharge the material and become ionized for extraction into the beam. Preferably, the at least two electrodes are bridged using an insulating member, a semi-insulating member, or a semi-conductive member, so that a spark discharge is formed between these two electrodes. The member contains a desired ionic species in an atomic form or a molecular form in or near the electrode. Preferably, the material containing the desired ionic species is an isotope of hydrogen, such as H2 or carbon. Also preferably, at least one of the electrodes is semi-porous and a reservoir underneath that electrode contains the desired ionic species in atomic or molecular form. 14 and 15 illustrate an exemplary embodiment of a pulsed ion source, generally designated by reference numeral 112. A ceramic 121 is shown having a cathode 124 and an anode 123 on the surface of the ceramic. The cathode is shown surrounding a palladium centerpiece 124 that covers the underlying H2 reservoir 114. Of course, the cathode and anode may be reversed. Further, the opening plate, that is, the gate electrode 115 is positioned in a state where the opening is aligned with the palladium top hat 124.

  As shown in FIG. 15, a high voltage is applied between the cathode electrode and the anode electrode to generate electron emission. Since these electrodes are initially close to a vacuum state at a sufficiently high voltage, electrons are field-emitted from the cathode. These electrons traverse the space toward the anode and cause local heating upon impact with the anode. This heating releases the molecules, which then collide with the electrons, causing the molecules to become ionized. These molecules may or may not be the desired species. The ionized gas molecules (ions) accelerate and return to the cathode, where they collide with the Pd top hat and cause heating. Pd has the property of allowing gas, specifically hydrogen, to pass through the member when heated. That is, since heating with ions is sufficient to cause hydrogen gas to leak locally into the volume, these leaked molecules are ionized by electrons to form a plasma. Also, when the plasma is increased to a sufficient density, a free-standing arc is formed. Thus, using a negatively charged electrode placed on the opposite side of the aperture plate, ions can be extracted and injected into the accelerator. If there is no extraction electrode, ions can be extracted using an electric field of appropriate polarity as well. Also, the gas is deionized when the arc is stopped. If the electrode is formed of a gettering member, the gas is then absorbed into the metal electrode to be used for the next cycle. Gas that is not reabsorbed is delivered by a vacuum system. The advantage of this type of source is that the gas load in the vacuum system is minimized in pulsed applications.

  Charged particle extraction, focusing, and transport from the pulsed ion source 112 to the input of the linear accelerator is performed by an integrated injector section 113 shown in FIG. Specifically, the charged particle generator injector section 113 serves to focus the charged ion beam onto the target. The target may be a patient in a charged particle therapy facility, or may be a target for isotope production or any other suitable target for a charged particle beam. Also, the integrated injector of the present invention allows the charged particle generator to transport the beam and focus it on the patient using only the electric focusing field. There are no magnets in the system. The system can provide a wide range of beam current, energy, and spot size independently.

  FIG. 13 shows a schematic arrangement of the injector 113 with respect to the pulsed ion source 112, and FIG. 21 shows a schematic diagram of the charged particle generator 132 combined with the linear accelerator 131. The beam extraction, transport, and focusing of the compact high gradient accelerator are all controlled by an injector comprising a gate electrode 115, an extraction electrode 116, a focusing electrode 117, and a grid electrode 119, which are charged particles. Located between the source and the high gradient accelerator. However, a minimal transport system should consist of an extraction electrode, a focusing electrode, and a grid electrode. If necessary, a plurality of electrodes can be used for each function. All electrodes can also be formed to optimize system performance, as shown in FIG. The gate electrode 115 with a high-speed pulse voltage is used to turn on / off the charged particle beam within a few nanoseconds. A simulated extracted beam current as a function of gate voltage in a high gradient accelerator designed for proton therapy is shown in FIG. 17, and the final beam spot at various gate voltages is shown in FIG. Yes. In the simulation performed by the inventor, the nominal gate electrode voltage is 9 kV, the extraction electrode is 980 kV, the focusing electrode is 90 kV, the grid electrode is 980 kV, and the high gradient accelerator has an acceleration gradient. 100 MV / m. Since FIG. 16 shows that the final spot size is not affected by the voltage setting of the gate electrode, the gate voltage is a simple knob for turning on / off the beam current as shown in FIG.

  High gradient accelerator system injectors use a gate electrode and an extraction electrode to extract and capture a space charge dominated beam whose current is determined by the voltage at the extraction electrode. The accelerator system uses a set of at least one focusing electrode 117 to focus the beam to the target. The potential contour plot shown in FIG. 18 shows how the extraction and focusing electrodes function. Here, a minimal focusing / transport system is used, ie one extraction electrode and one focusing electrode. The voltages at the extraction, focusing, and grid electrodes at the entrance of the high gradient accelerator are 980 kV, 90 kV, and 980 kV. FIG. 18 shows that the voltage of the shaped extraction electrode sets a gap voltage between the gate electrode and the extraction electrode. Also, FIG. 18 shows that the voltage at the shaped extraction electrode, shaped focusing electrode, and grid electrode gives a strong net focusing force to the electrostatic focused-unfocused-focused region, ie the charged particle beam. It also shows the formation of an Einzel lens.

  Although focusing the beam using an Einzel lens is not new, the accelerator system of the present invention does not use a focusing magnet at all. In addition, the present invention combines the Einzel lens with another electrode so that the beam spot size at the target can be adjusted regardless of the beam current and energy. A grid electrode 119 is present at the injector outlet or the high gradient accelerator inlet. The extraction electrode and the grid electrode are set to the same voltage. By making the grid electrode voltage the same as the extraction electrode voltage, the energy of the beam injected into the accelerator remains the same regardless of the voltage setting at the shaped focusing electrode. Therefore, when the voltage at the regular focusing electrode is changed, only the intensity of the Einzel lens changes, and the beam energy does not change. Since the beam current is determined by the voltage of the extraction electrode, the final spot can be freely adjusted by adjusting the voltage of the shaped focusing electrode independent of the beam current and energy. In such a system, it goes without saying that further focusing can be achieved with a suitable gradient in the axial electric field (ie dEZ / dz) and consequently the time rate of change of the electric field (ie dE / z at z = z0). dt).

  A simulation of the beam envelope for beam transport through a 250 MeV proton high gradient accelerator without magnets with various focusing electrode voltage settings is shown in FIG. These plots clearly show that the spot size of the 250-MeV proton beam at the target can be easily adjusted by adjusting the focusing electrode voltage, although their corresponding focusing electrode voltages are given on the left side. Yes. Also, a plot of spot size versus focusing electrode voltage at various proton beam energies is shown in FIG. Two curves are plotted for each proton energy. The upper curve shows the edge radius of the beam and the lower curve shows the core radius. These plots show a wide range of spot sizes (2 mm-2 cm diameter) for a 70-250 MeV, 100 mA proton beam by adjusting the focusing electrode voltage in a high gradient proton therapy accelerator using an acceleration gradient of 100 MV. It shows that you can.

  A compact high gradient accelerator system using such an integrated charged particle generator can independently provide a wide range of beam currents, energies, and spot sizes. The accelerator beam extraction, transport and focusing are all controlled by a gate electrode, a shaped extraction electrode, a shaped focusing electrode and a grid electrode located between the charged particle source and the high gradient accelerator. The voltage setting of the extraction electrode and the grid electrode is the same. The shaped focusing electrode between these electrodes is set to a low voltage, thereby forming an Einzel lens and providing an adjustment knob for the spot size. The minimum transport system consists of an extraction electrode, a focusing electrode and a grid electrode, but if the system requires a very strong focusing force, an additional Einzel lens using an alternating voltage can be connected to the regular focusing electrode and the grid electrode. Can be added between.

D. FIG. 21 is an integral view of an input end of a compact linear accelerator 131 for forming a charged particle beam and injecting the beam along the acceleration axis into the compact accelerator. FIG. 2 shows a schematic diagram of an exemplary operable compact accelerator system 130 of the present invention with a charged particle generator 132 located at the end. By integrating the charged particle generator with the accelerator in this way, a relatively compact size for the unit structure can be achieved, and the actuator mechanism 134 can be moved unit by unit as indicated by the arrow 135. , Beams 136-138 are obtained. In previous systems, due to their scale size, magnets were required to transport the beam from a remote location. On the other hand, in the present invention, since the scale size is considerably reduced, a beam such as a proton beam can be generated and controlled without using a magnet, and all can be transported to the immediate vicinity of a desired target position. it can. Such a compact system is ideal for use in medical therapy accelerator applications, for example.

  Such unit-type devices are configured to operate an integrated particle generator-linear accelerator to directly control the position of the charged particle beam and the beam spot formed thereby, indicated generally at 133. It may be mounted on a support structure. Various configurations for mounting a unitary combination of a compact accelerator and a charged particle source are shown in FIGS. 22-24, but are not limited thereto. Specifically, FIGS. 22-24 are exemplary of the present invention showing a combined compact accelerator / charged particle source mounted on various types of support structures to be operable to control beam positioning. The embodiment is shown. The accelerator and charged particle source may be suspended and articulated from a fixed stand and directed to the patient (FIGS. 22 and 23). In FIG. 22, unitary operation is possible by rotating the unit device about the center of gravity indicated by 143. As shown in FIG. 22, the integrated compact generator-accelerator is preferably pivotable about its center of gravity to reduce the energy required to direct the accelerated beam. It may be activated. However, it will be appreciated that other mounting configurations and support structures for operating such a compact unit-type combination of a compact accelerator and a charged particle source are possible within the scope of the present invention.

  It goes without saying that various accelerator architectures for integration with charged particle generators that allow a compact and operable structure may be used. For example, the accelerator architecture may use two transmission lines in the Bloomline module structure described above. The transmission line is preferably a parallel plate transmission line. Moreover, it is preferable that a transmission line is a strip | belt shape as FIG. 1-12 shows. Also, various types of high voltage switches with fast occlusion time (nanoseconds), such as SiC photoconductive switches, gas switches, or oil switches may be used.

  Also, various actuator mechanisms and system control methods known in the art may be used to control the operation and operation of the accelerator system. For example, simple ball screws, stepping motors, solenoids, electrically operated translators and / or pneumatics, etc. may be used to control the positioning and movement of the accelerator beam. This allows the beam path programming to be very similar if not identical to the programming language widely used in CNC machines. It goes without saying that the actuator mechanism functions to control the acceleration beam direction and beam spot position with the integrated particle generator-accelerator in mechanical action or operation. In this regard, the system has at least one degree of rotational freedom (eg, for rotation about the center of mass), but as known in the art, the displacement or deformation position of the body or system. Preferably, it has six degrees of freedom (DOF), which is a set of independent displacements including three translations and three rotations that completely specify Translation represents the ability to move in each of the three dimensions, and rotation represents that the angle can be changed around three vertical axes.

  The accuracy of the acceleration beam parameters is determined by the feedback positioning system (eg, a monitor located on the patient 145) configured in the active positioning system, the monitoring system, and the accelerator control and positioning system represented by the measurement box 147 in FIG. Can be controlled by. Also shown is a system controller 146 that controls the accelerator system, which includes at least one of the following parameters: beam direction, beam spot position, beam spot size, dose, beam intensity, and beam energy. One may be based. The depth is controlled relatively accurately by the energy based on the Bragg peak. The system controller preferably also includes a feedforward system for monitoring and providing feedforward data relating to at least one of the parameters. The beam formed by the charged particles and the accelerator may also be configured to form a vibration projection on the patient. Preferably, in one embodiment, the vibration projection is a circle with a continuously changing radius. In any case, the application of the beam may be actively controlled based on one or a combination of position, dose, spot size, beam intensity, beam energy.

  Although specific operation sequences, materials, temperatures, parameters, and specific embodiments have been described or illustrated, they are not intended to be limiting. Improvements and modifications will be apparent to those skilled in the art, and the present invention is limited only by the scope of the appended claims.

1 is a side view of a first exemplary embodiment of a single bloom line module of a compact accelerator of the present invention. FIG. FIG. 2 is a plan view of the single bloom line module of FIG. 1. FIG. 6 is a side view of a second exemplary embodiment of a compact accelerator with two bloom line modules stacked on top of each other. FIG. 9 is a plan view of a third exemplary embodiment of a single bloom line module of the present invention, where the width of the middle conductive strip is smaller than the other layers of the module. FIG. 5 is an enlarged cross-sectional view taken along line 4 in FIG. 4. FIG. 6 is a plan view of another exemplary embodiment of a compact accelerator shown with two bloom line modules surrounding the central acceleration region and extending radially toward the central acceleration region. It is sectional drawing which follows the line 7 of FIG. With two bloom line modules surrounding the central acceleration region and extending radially toward the central acceleration region, and one module's planar conductor strip rings against the corresponding planar conductor strip of the other module FIG. 6 is a plan view of another exemplary embodiment of a compact accelerator shown connected by electrodes. It is sectional drawing which follows the line 9 of FIG. FIG. 6 is a plan view of another exemplary embodiment of the present invention in which four non-linear Bloomline modules are each connected to an associated switch. FIG. 11 is a plan view of another exemplary embodiment of the present invention similar to FIG. 10 including a ring electrode connecting each of the four non-linear Bloom line modules at its second end. FIG. 4 is another exemplary embodiment of the present invention similar to FIG. 1, wherein the dielectric constant and thickness of the first dielectric strip and the second dielectric strip are the same for symmetrical Bloomline operation. It is a side view of a thing. 1 is a schematic diagram of an exemplary embodiment of a charged particle generator of the present invention. FIG. 14 is an enlarged schematic diagram along circle 14 of FIG. 13 showing an exemplary embodiment of a pulsed ion source of the present invention. The progress of the pulse ion generation by the pulse ion source of FIG. 14 is shown. Shown are multiple screenshots of the final spot size on the target at various gate electrode voltages. Figure 5 shows a graph of extracted proton beam current as a function of gate electrode voltage in a high gradient proton beam accelerator. 2 shows two graphs showing potential contour lines in the charged particle generator of the present invention. FIG. 5 is a comparative diagram of beam transport in a 250 MeV high gradient proton accelerator without magnets at various focusing electrode voltage settings. It is a comparison figure of four graphs of the edge beam radius (upper curve) and the core radius (lower curve) on the target side with respect to the focusing electrode voltage in 250 MeV, 150 MeV, 100 MeV, and 70 MeV proton beams. 1 is a schematic view of an actuable compact acceleration system of the present invention having an integrated unit-type charged particle generator and linear accelerator. FIG. FIG. 2 is a side view of a typical mounting arrangement of a unit compact accelerator / charged particle source of the present invention, illustrating medical treatment applications. 1 is a perspective view of an exemplary vertical mounting arrangement of a unit compact accelerator / charged particle source of the present invention. FIG. 1 is a perspective view of a typical hub-spoke mounting arrangement of a unit compact accelerator / charged particle source of the present invention. FIG. 1 is a schematic diagram of a continuous pulse traveling wave accelerator of the present invention. FIG. FIG. 26 is a schematic diagram showing the movement of a short pulse traveling wave of the continuous pulse traveling wave accelerator of FIG. 25. FIG. 6 is a schematic diagram illustrating the long pulse motion of a typical cell of a conventional dielectric wall accelerator.

Claims (15)

A dielectric beam tube of length L surrounding the acceleration axis;
At least two pulse forming lines connected to and transverse to the beam tube, each pulse forming line passing through the pulse forming line independently of the other pulse forming lines. At least two switches having a switch connectable to a high voltage potential in order to propagate an electrical wavefront and generate an acceleration pulse with a short pulse width τ along the corresponding minor axis length δL of the beam tube A pulse forming line;
In order to continuously energize the charged particles, the switch is continuously operated so that an electric field in the traveling axial direction is generated along the beam tube in synchronization with the pulse beam of the charged particles traversing in the axial direction. Means for controlling;
A short pulse dielectric wall accelerator comprising: Each pulse forming line is
A first conductor having a first end and a second end adjacent to the acceleration axis;
A second conductor adjacent to the first conductor, the first conductor having a first end switchable to a high voltage potential and a second end adjacent to the acceleration axis. When,
A third conductor adjacent to the second conductor, the first conductor having a first end and a second end adjacent to the acceleration axis;
A first dielectric material having a first dielectric constant and filling a space between the first conductor and the second conductor;
A second dielectric material having a second dielectric constant and filling a space between the second conductor and the third conductor;
The short pulse dielectric wall accelerator of claim 1, wherein the short pulse dielectric wall accelerator is a bloom line module.   The first, second and third conductors, and the first and second dielectric members have a parallel strip structure extending from the first end to the second end. The short pulse dielectric wall accelerator according to claim 2.   The short pulse dielectric wall accelerator of claim 2, wherein the dielectric beam tube has a larger dielectric constant than the first and second dielectric members.   The short pulse dielectric wall accelerator according to claim 4, wherein the dielectric beam tube includes alternating layers of a conductor and a dielectric in a plane perpendicular to the acceleration axis.   Said means for continuously controlling the switch can simultaneously switch at least two adjacent pulse forming lines forming one block, and can switch adjacent blocks continuously, whereby each The short pulse dielectric wall accelerator of claim 1, wherein acceleration pulses are continuously formed through the block.   The short pulse dielectric wall accelerator of claim 1, wherein the diameter d and length L of the beam tube satisfy a criterion L> 4d in order to reduce the fringing magnetic field at the input and output ends of the dielectric beam tube. Beam tube is standard γτv> d / 0.6
Where v is the velocity of the wave on the beam tube wall, d is the diameter of the beam tube, and τ is:

Is expressed by the following equation:

The short pulse dielectric wall accelerator according to claim 1, satisfying a Lorentz coefficient represented by: A plurality of pulse forming lines extending to the lateral acceleration axis, each pulse forming line propagating through the pulse forming line independently of the other pulse forming lines through at least one electrical wavefront; A plurality of pulse forming lines having a switch connectable to a high voltage potential to generate a short acceleration pulse adjacent to a corresponding short axis length of the acceleration axis;
In order to continuously give energy to the charged particles, the switch is continuously operated so that an electric field in the traveling axis direction is generated along the acceleration axis in synchronization with the pulse beam of the charged particles traversing in the axial direction. A trigger operatively connected to control;
A continuous pulse traveling wave linear accelerator. Each pulse forming line is
A first conductor having a first end and a second end adjacent to the acceleration axis;
A second conductor adjacent to the first conductor, the second conductor having a first end switchable to a high voltage potential and a second end adjacent to the acceleration axis; ,
A third conductor adjacent to the second conductor, the first conductor having a first end and a second end adjacent to the acceleration axis;
A first dielectric material having a first dielectric constant and filling a space between the first conductor and the second conductor;
A second dielectric material having a second dielectric constant and filling a space between the second conductor and the third conductor;
The continuous pulse traveling wave linear accelerator according to claim 9, wherein the continuous pulse traveling wave linear accelerator is a Bloom line module.   The first, second and third conductors, and the first and second dielectric members have a parallel strip structure extending from the first end to the second end. A continuous pulse traveling wave linear accelerator according to claim 10.   Said means for continuously controlling the switch can simultaneously switch at least two adjacent pulse forming lines forming one block, and can switch adjacent blocks continuously, whereby each 10. A continuous pulse traveling wave linear accelerator according to claim 9, wherein acceleration pulses are continuously formed through the block. A dielectric beam tube of length L surrounding the acceleration axis;
At least two bloom line modules, each forming a pulse forming line transverse to the acceleration axis and having a first end and a second end connected to the beam tube A first conductor having an end, a second conductor adjacent to the first conductor, the first end being switchable to a high voltage potential, and a second conductor connected to the beam tube A second conductor having an end, a third conductor adjacent to the second conductor, the first conductor having a first end and a second end connected to the beam tube However, the third conductor has a first dielectric constant, has a first dielectric member that fills a space between the first conductor and the second conductor, and has a second dielectric constant. A second dielectric member filling a space between the second conductor and the third conductor, the first and Second dielectric constant smaller than the dielectric constant of the beam tube,
Each Bloomline module propagates at least one electrical wavefront through the Bloomline module independently of the other Bloomline modules, so that an acceleration pulse with a short pulse width τ is applied to the corresponding short axis length of the beam tube. at least two bloom line modules having at least one switch connectable to a high voltage potential to generate along δL;
In order to continuously give energy to the charged particles, the switch is continuously operated so that an electric field in the traveling axis direction is generated along the beam tube in synchronization with the pulse beam of the charged particles traversing in the axial direction. A continuous pulse traveling wave linear accelerator with a controller operatively connected to trigger the system.   The continuous pulse traveling wave linear accelerator of claim 13, wherein the Bloomline module is a symmetric Bloomline with equal first and second dielectric constants.   14. The continuous pulse traveling wave linear accelerator of claim 13, wherein the Bloom line module is an asymmetric Bloom line with unequal first and second dielectric constants.

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