WO2002071817A1 - Accelerateur a resonance cyclotron comportant des cavites a etages multiples - Google Patents

Accelerateur a resonance cyclotron comportant des cavites a etages multiples Download PDF

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Publication number
WO2002071817A1
WO2002071817A1 PCT/US2001/024499 US0124499W WO02071817A1 WO 2002071817 A1 WO2002071817 A1 WO 2002071817A1 US 0124499 W US0124499 W US 0124499W WO 02071817 A1 WO02071817 A1 WO 02071817A1
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WIPO (PCT)
Prior art keywords
cavity
cavities
frequency
charged particles
successive
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Application number
PCT/US2001/024499
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English (en)
Inventor
Robert Spencer Symons
Jay L. Hirshfield
Wang Changbiao
Original Assignee
Northrop Grumman Corporation
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Filing date
Publication date
Priority claimed from US09/797,434 external-priority patent/US6617810B2/en
Application filed by Northrop Grumman Corporation filed Critical Northrop Grumman Corporation
Priority to JP2002570593A priority Critical patent/JP2004530260A/ja
Priority to EP01963795A priority patent/EP1316246A1/fr
Publication of WO2002071817A1 publication Critical patent/WO2002071817A1/fr

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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H9/00—Linear accelerators
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H7/00—Details of devices of the types covered by groups H05H9/00, H05H11/00, H05H13/00
    • H05H7/14—Vacuum chambers
    • H05H7/18—Cavities; Resonators

Definitions

  • Jory and Trivelpiece accelerated electrons with 1000 volts of energy traveling along the axis of a TE-m circular waveguide cavity to 500,000 volts of energy with momentum directed primarily in the circumferential direction. They used these electrons to generate millimeter wavelength radiation in another circular waveguide supporting a higher order mode.
  • a high-current, high- gradient, high-efficiency, multi-stage cavity cyclotron resonance accelerator provides energy gains of over 50MeV/stage, at an acceleration gradient that exceeds 20MeV/m, in room temperature cavities.
  • the multi-stage cavity cyclotron resonance accelerator includes a charged particle source, a plurality of end-to-end rotating mode room-temperature cavities, and a solenoid coil.
  • the solenoid coil encompasses the cavities and provides a substantially uniform magnetic field that threads through the cavities.
  • the MCCRA is provided with a constant magnetic field sufficient to produce a cyclotron frequency a little higher than the RF of the accelerating electric field.
  • a plurality of input feeds, each of which are respectively coupled to a cavity, are also provided.
  • the beam from the first cavity passes through a cutoff drift tube and is accelerated further with a cavity supporting a still lower radio-frequency electric field.
  • the charged particles are emitted in pulses in correspondence with the difference frequency.
  • MCCRA multi-stage cavity cyclotron resonance accelerator
  • Fig. 1 illustrates two stages in multi-stage high-gradient cavity proton accelerator
  • Fig. 2 illustrates the computed variations of mean proton energy
  • Fig. 3c illustrates the projection in a longitudinal plane of the orbit of a proton undergoing acceleration as in Figs. 3a and 3b;
  • Fig. 4 illustrates the normalized mean energy and axial velocity for muons in a two-cavity cyclotron accelerator
  • Fig. 7 is a chart illustrating a calculation of power for an eleven cavity accelerator having spaced cavity frequencies
  • Fig. 8 illustrates the influence of finite bunch width on rms energy spread
  • Fig. 9 illustrates acceleration history and evolution of rms energy spread in a two- cavity proton accelerator for three values of relative initial phase between fields in the two cavities
  • the accelerator includes an ion source 1 , end-to-end TE T H rotating mode room-temperature cavities 2, 3, and a solenoid coil 4.
  • Input feeds 6, 7 are coupled to the cavities 2, 3, respectively.
  • the solenoid coil 4 provides the substantially uniform magnetic field that threads through the cavities 2, 3.
  • a DC voltage source 8 provides an accelerating voltage to the ion source 1 on the order of several kilovolts.
  • the magnetic field in the accelerator must be substantially uniform across all stages, since an increasing field would lead to an undesirable loss of axial momentum and stalling, while a decreasing field would lead to an unmanageable increase in the orbit radius of the charged particle.
  • the accelerator shown in Fig. 1 is simplified for ease of explanation, and that an actual accelerator may have many more cavity stages than the two shown in the figure.
  • the first cavity 2 is driven with 10 MW of RF power at 100 MHz (fi)
  • the second cavity 3 is driven with 7.7 MW at 94 MHz (f 2 ), via the respective input feeds 6, 7. It is important that successive cavity stages of the accelerator operate at successively-lower RF frequencies in order to maintain approximate resonance as the particle mass increases.
  • Particle acceleration from 10 keV to 1GeV requires an aggregate frequency reduction between the first and last cavity states of approximately a factor of two.
  • the beam power after the second stage is 13.4 MW.
  • the strong axial acceleration gradient is possible since the protons make a large number of gyrations, and follow a long path moving nearly parallel to the rotating RF electric field. For this example, the protons execute about 48 turns in the first cavity, and reach a final gyration radius of about 17 cm.
  • This rapid, efficient cyclotron resonance acceleration of protons in a TE U 1 cavity with a uniform magnetic field is reminiscent of similar results reported for electrons by Jory and Trivelpiece, who showed evidence of acceleration by hundreds of keV.
  • Fig. 3a shows the energy gain and axial velocity for two exemplary cavities operated in tandem.
  • the second cavity operating at 94 GHz, has a radius of 110 cm and a length of 302 cm.
  • the relative phase difference between fields in the first and second cavities is set at OJO , the value that was found to maximize energy gain in the second cavity.
  • Figs. 3b and 3c show projections in the transverse (x-y) and longitudinal (x-z) planes of the orbit of a single proton during the course of its acceleration. Specifically, Fig. 3b illustrates a projection in the transverse plane of the orbit of a proton undergoing acceleration as in Fig. 3a. Fig. 3c illustrates a projection in the longitudinal plane of the orbit of a proton undergoing acceleration as in Figs. 3a and 3b. The proton executes about 90 turns during acceleration.
  • an alternative embodiment of the invention may provide muon acceleration at cyclotron resonance using cavities in a strong uniform magnetic field.
  • the 100 MHz and 94 MHz TE ul cavities for the example of the first two stages of the proton accelerator shown in Figs. 2-4 have diameters of 220 cm, yet the maximum proton orbit diameters are 34 and 44 cm. At least in these first stages, most of the cavity volume is not traversed by the proton beam, but is permeated with magnetic flux lines from the surrounding solenoid coils.
  • the required 67 kG cryomagnet would need a room-temperature bore diameter of perhaps 240 cm (to allow room for the RF feeds, as shown in Fig. 1). While this is probably within the present state-of-the-art, it would be highly desirable to reduce this bore diameter.
  • the cavity diameters are reduced by using dielectric loading in the form of thick coaxial dielectric liners 9, 10.
  • Analysis of the dispersion relation for the HEM ⁇ mode showed, for example, that a 100 MHz cavity with TE ⁇ -like fields in the interior vacuum hole could have a significantly reduced overall diameter.
  • Successive cavities would of course be larger, as their resonant frequencies decrease and as their hole diameters increase to accommodate the increasing radius of the gyrating beam.
  • a drawback of the presence of alumina within a high-power cavity structure is that it could lead to breakdown problems, and the extreme weight and cost of such large alumina elements would also be disadvantageous.
  • radial vanes 62 are employed in the cavity that provide capacitive loading and thereby reduce the cutoff frequency for the desired dipole modes. It should be noted that only one-half of the structure is shown in Fig. 6, after cutting along the vertical axis of symmetry. When four symmetric vanes are used, the two dipole modes are 90° out of time and spatial phase with respect to one another. To obtain a rotating (i.e., circularly polarized) field, these two dipole modes are excited in time-quadrature.
  • the structure can be labeled a radio- frequency double-dipole (RFDD).
  • RFDD radio- frequency double-dipole
  • the cutoff frequency for the dipole mode was found to be 73.7 MHz, while the cutoff frequency for the quadrupole mode was found to be 78.97 MHz.
  • a section of RFDD structure 222 cm in length would have a dipole resonance frequency of 100 MHz and a quadrupole resonance frequency of 104 MHz. Operation with Q L of the order of 1,000- 10,000 should thus be possible purely in the dipole mode, without significant coupling by the beam to the quadrupole mode.
  • protons drift from one TE U 1 cavity to the next, but successive cavities must have lower resonance frequencies in order to effect cumulative acceleration since the imposed axial magnetic field is uniform and the effective proton mass is increasing.
  • acceleration through a cascade of cavities provided the phases for fields in each cavity are properly adjusted. Specifically, as the proton bunch arrives at each cavity, maximum acceleration is achieved if the orientation of the electric vector of the rotating TE 1 U mode is parallel to the proton momentum.
  • uniform acceleration of a train of proton bunches can occur only if the phases of disparate frequencies in successive cavities are judiciously sequenced to insure that all bunches have identical histories as they progress through the cascade.
  • the cavity frequencies are arranged to decrease in equal increments.
  • the frequency decrease increment may be selected to be 5 MHz, and the cavity frequencies may be selected to be 100, 95, 90, 85,
  • the proton beam would be pulsed at the difference frequency between successive cavities (e.g., 5 MHz) such that bunches of protons enter each cavity at a time in which the electromagnetic fields in the cavity have aligned in a certain way.
  • the initial phases of the fields in each cavity may thus be arranged to provide optimized cumulative acceleration to the first proton bunch. If successive bunches are injected at time intervals corresponding to the inverse of the difference frequency (e.g., 5 MHz "1 or 200 nsec), then the fields seen by each bunch would be identical to those seen by the first bunch. This is because after each 200 nsec Interval, fields in the respective cavities will have advanced by precisely 20, 19, 18, 17, 16, ...
  • the cavity cascade has features in common with a conventional RF linear accelerator, or linac, that generates a beam of highly energized particles by propelling them in a straight line with energy from an electromagnetic field.
  • Fig. 7 provides a chart that illustrates a calculation of power for an eleven cavity accelerator having spaced cavity frequencies as described in the above example. For each cavity, the chart shows the initial and final proton energy ( ⁇ ), the proton velocity ( ⁇ ), the beam load, the total beam power, and the orbit radius. At the beam power levels identified in the chart, the cyclotron frequency will be closest to the cavity frequency at any point within the device.
  • Fig. 8 illustrates the effects of finite proton bunch width.
  • acceleration is independent of the time of injection. But, due to the phase dependence of acceleration in the second cavity, energy spread increases with pulse width.
  • parameters for the first cavity at 100 MHz are as described above with respect to Figs. 2-3c.
  • parameters for the second cavity at 94 MHz are also as described above, except for small variations in Q L and final average beam energy.
  • Q L would be 13,200, 13,600 and 17,000, respectively
  • final average beam energy would be 116.2, 116.0 and 114.0 MeV, respectively.
  • the relative initial phase difference between fields in the two cavities is 0.70 ⁇ .
  • the final energy spread is approximately 2%.
  • the particles are seen to lie along a nearly straight line approximately 4.8 cm long, with a deviation from linearity of less than 0.4 mm. These particle loci can be contrasted with the trace in x-z for the first particle during its final 4.8 cm of travel, which is a half-cycle of oscillation with radius of approximately 17 cm, as shown in Fig. 3c.
  • the proton bunch advances in the z direction and rotates about the z axis nearly as a straight rigid object.
  • the small deviations from linearity arise from phase slip between proton momenta and the RF electric field, and from small energy differences between the head and tail of the bunch.
  • the near uniformity of the axial charge distribution within such a long bunch should mitigate against longitudinal instability.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Particle Accelerators (AREA)

Abstract

L'invention concerne un accélérateur à résonance cyclotron comportant des cavités à étages multiples (MCCRA) haute intensité, à gradient élevé et haut rendement, qui fournit des gains d'énergie supérieurs à 50MeV/étage, à un gradient d'accélération supérieur à 20MeV/m, dans des cavités à température ambiante. Cet accélérateur à résonance cyclotron comprend une source de particules chargées, une pluralité de cavités à température ambiante à mode de rotation placées bout à bout, et une bobine de solénoïde. La bobine de solénoïde produit un champ magnétique sensiblement uniforme qui traverse les cavités. Spécifiquement, le MCCRA présente un champ magnétique constant suffisant pour produire une fréquence de cyclotron légèrement supérieure à la RF du champ électrique d'accélération. Une pluralité de charges d'entrée sont couplées chacune respectivement à une cavité. Dans une forme de réalisation de invention, le faisceau provenant de la première cavité traverse un tube de glissement à fréquence de transition et est accéléré davantage à l'aide d'une cavité à champ électrique radiofréquence encore inférieur. Cette forme de réalisation permet de produire efficacement un faisceau de protons de plusieurs milliampères pour un gigavolt. Cette cavité unique transfère environ 70 % de l'énergie radiofréquence au faisceau. L'invention concerne un accélérateur à cavités multiples, qui présente sur toute sa longueur un champ magnétique statique constant ou légèrement décroissant et utilise des tubes de glissement à fréquence de transition entre les cavités, qui fonctionnent à des fréquences progressivement décroissantes ; chacune de celles-ci étant quelque peu inférieure à la fréquence locale de cyclotron relativiste du faisceau de cette cavité. Cet accélérateur à énergie moyenne est extrêmement efficace, compact et fonctionne en continu. Dans une autre forme de réalisation, les fréquences progressivement décroissantes sont sélectionnées de manière à décroître selon des incréments sensiblement égaux qui correspondent à une fréquence différentielle. Les particules chargées sont émises en pulsations correspondant à la fréquence différentielle.
PCT/US2001/024499 2000-07-31 2001-07-31 Accelerateur a resonance cyclotron comportant des cavites a etages multiples WO2002071817A1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
JP2002570593A JP2004530260A (ja) 2001-03-01 2001-07-31 多段空洞サイクロトロン共鳴加速器
EP01963795A EP1316246A1 (fr) 2000-07-31 2001-07-31 Accelerateur a resonance cyclotron comportant des cavites a etages multiples

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
US09/797,434 2001-03-01
US09/797,434 US6617810B2 (en) 2000-03-01 2001-03-01 Multi-stage cavity cyclotron resonance accelerators
US22168901P 2001-07-31 2001-07-31
US60/221,689 2001-07-31

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WO2002071817A1 true WO2002071817A1 (fr) 2002-09-12

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Cited By (2)

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Publication number Priority date Publication date Assignee Title
CN103347363A (zh) * 2007-11-30 2013-10-09 梅维昂医疗系统股份有限公司 间断粒子源
KR20200095278A (ko) * 2019-01-31 2020-08-10 성균관대학교산학협력단 다중 캐비티를 포함하는 사이클로트론 시스템

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP7497870B2 (ja) 2020-09-07 2024-06-11 国立大学法人大阪大学 荷電粒子加速装置及び荷電粒子加速方法

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103347363A (zh) * 2007-11-30 2013-10-09 梅维昂医疗系统股份有限公司 间断粒子源
CN103347363B (zh) * 2007-11-30 2016-06-01 梅维昂医疗系统股份有限公司 间断粒子源
KR20200095278A (ko) * 2019-01-31 2020-08-10 성균관대학교산학협력단 다중 캐비티를 포함하는 사이클로트론 시스템
KR102165370B1 (ko) 2019-01-31 2020-10-14 성균관대학교산학협력단 다중 캐비티를 포함하는 사이클로트론 시스템

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