JP2010251275A - Ion collective accelerator and application thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of collective acceleration of various ion species by a compact and extremely strong hollow electron bunch. <P>SOLUTION: A high-density hollow electron cloud or electron ring which contains heavy ions is momentarily generated by such a special and new technique of laser irradiation, or the like, and the hollow electron cloud is momentarily drawn together with the heavy ions by a direct RF electric field to be accelerated, so that an accelerator which is extremely small and inexpensive with high acceleration efficiency can be achieved. It is possible to achieve a microminiature table top heavy ion accelerator of heavy particles which can be installed in size of existing hospitals, as one application thereof which is strongly desired. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

In the present invention, various ion ^* groups (ion bunches) are confined in an electron group (electron bunches), and high-density electron bunches with high strength are generated and accelerated, so that the ion group confined in the electron bunches is 100 MV / m. The present invention relates to a collective acceleration device that accelerates with the above electric field strength and its application.

Several researchers have been working since mid 1950 to accelerate a charged population (charge bunches) limited in time and space to high energies exceeding several GeV in a short distance by an electron population with high beam intensity (electron bunches). Various variations of inventions and proposals have been made. (The first electron collective acceleration method was suggested by Bennett in the United States, but it was the former Soviet Beksler that first made a clear and easy-to-understand proposal.)
W. H. Bennett, Phys. Rev. 45,890 (1934)
V. I. Veksler, Proc. CERN Symposium on High Energy Accelerators and Pion Physics 2, 80-83 (CERN, Geneva, Switzerland; 1956).
G. I. Budker, Relative Stabilized Electron Beams, CERN Symposium on High Energy Accelerators, Vol. 1,68 (1956)
In 1956, the first Accelerator International Conference was held in Geneva, Switzerland, where the former Soviet Union Dubna Bexler, Moscow Academy of Sciences Budkar and others were charged particles. As a new acceleration method, the theory and experiment on ion acceleration by high-intensity and high-density electron bunches are reported. Bexler also announced at the Accelerator Conference in Cambridge in 1967 about the production of an induction linac (induction linear accelerator) aimed at accelerating 10 billion protons per bunch to 1 GeV at a distance of 15 m.
V. I. Veksler et al. , Proc. VI. International Conference on High Energy Accelerators, Cambridge Electron Accelerator, Cambridge, 1967, p. 289.
^* (Ion here means all charged particles including protons, but when called heavy ions, it means charged particles that are heavier than helium in the element table.)

This innovative method of accelerating electron ensembles captures the minds of researchers at the forefront of accelerators in Europe and the United States, and intensive research into theory and experiment has begun at major research laboratories in the world. In particular, LBL (Lawrence Berkeley Laboratories) in the United States started the theory, experiment and research of the demonstration test accelerator as an electron ring accelerator system (ERA system).
D. Keefe et al. Phys. Rev. Letters 22, 558 (1969)
Similar research has also begun at Reiser at the University of Maryland, which is also the mecca of research on high-intensity electron beams.
D. L. Nelson and H.C. Kim, Studios on Formation of an Electron Ring Using Cylindrical Hollow Beam, Proc. of VII International Conf. on High Energy Accelerators, Yerevan, August 1969,
D. L. Nelson, The Formation of an Electron Ring in a Static Magnetic Field, Ph. D. Thesis, August 1970, Department of Physics & Astronomy, University of Maryland, College Park, Maryland

Furthermore, using this electronic ring and induction linac, the inventor Christfilos started a fusion project at the Lawrence Livermore National Laboratory, a national military institute. Researchers' expectations for the accelerator (ERA) method have increased.
N. C. Christfilos, Phys. Rev. Lett. 22,830 (1969)

The large current ERA mainly employs the betatron system, but the problem of beam instability has gradually become apparent. On the other hand, since the era of high energy physics was the time when the demand for the early realization of proton accelerators of several hundred GeV was increasing, the study of a large synchrotron system that is technically easier and more feasible was also promoted. Garren, “lattice of the NAL proton synchrotron”, PAC1969
The proton synchrotron was selected as the high-energy proton accelerator, and it moved to the construction of the syncrontron of CERN (European Nuclear Research Institute) SPS and Fermilab (Fermental accelerator laboratory).

Although LBL withdrew early, efforts continued to achieve ERA at various laboratories such as Garching in Germany and the Dobna Institute in the former Soviet era.
D. W. Huggings et al. , “Traping of cust-injected, non neutral, electro rings with resistive walls and static mirror coil, Physical review letter, volume 40, volume 40, volume 40,
C. Andelfinger et al. , “Of the experimental and theoretical innovations in the Garching Electron Accelerator”, IEEE Transaction on Nuclear Science, 1979.
E. B. Abubakirov et al. , “Generation and acceleration of high-current annual electron beam in linear induction accelerator and microwave from Cherenkov TWT”, EPAC 1990.
Higher energies can be achieved with the LEP (Large Electron Postron) accelerator of the super-large electron synchrotron with a circumference of 27 km and the Fermilab Tevatron and CERN of the superconducting magnet, and the LHC (Large) of the superconducting magnet with higher energy and higher magnetic field. Hadron Collider) headed for the synchrotron system. The next-generation high-energy accelerator of LHC is ILC (International Linear Collider), which is a collider of linear electrons and positrons, and a policy of accelerating several hundred GeV or TeV region with electrons and positrons is adopted. ERA research and development gradually declined.

The ion acceleration method by ERA can be either (1) a weak focusing method of the LBL method or a betatron method with one-turn incidence to generate an axial magnetic field that changes with time, or (2) a Laslet-Sessler method. Either a large electron ring is created at the cathode and incident on a static axial magnetic field that decreases in the axial direction, or (3) a large hollow electron beam is generated at the riser-type cathode at the University of Maryland and converted into a cusp magnetic field. The mainstream method is to form an electron ring by shortening in the axial direction by any method such as incidence. In either case, however, various beam instabilities occur due to the high amount of current required. Initially, according to Budkar and others, this stability was claimed to be controllable, but the stabilization of the electronic bunch was Extremely difficult.
J. et al. Lasslett, A.M. Sessler, “a method of static-field compression in an electro-ring accelerator”, UCRL-18589, PAC1969,
A. Sessler, “collective field acceleration”, UCRL-19242, VII international conference on high energy accelerator, Yerevan, USSR, 1969,
J. et al. Lasslett, A.M. Sessler, “a method of static-field compression in an electro-ring accelerator”, UCRL-18589, PAC1969.
A. Sessler, “collective field acceleration”, UCRL-19242, VII international conference on high energy accelerator, Yerevan, USSR, 1969.

The present invention provides a collective acceleration method for various ion species using a compact and large-strength hollow electron bunch, which has been unsolved in the past, instead of the above-described method which has the problem of beam instability of a high-current electron ring. It is what we propose.

As the latest application, irradiation of heavy particle beam with high biological effect (RBE) about 3 times that of proton beam at the same time as Bragg Peak that induces a steep ionization phenomenon at a distance according to the energy of ion. To realize a table top treatment accelerator for radiation resistant tumor treatment. (The size of the table top accelerator here means the size of the device that fits in the radiation room of an existing hospital). For the proton beam, the development of the table top is MIT / Still River Systems's Monarch250PBRT and the HiArt / Livermore Laboratory's DWA (Dielectric Wall Accelerator), but even the heavy ion beam is a table top accelerator proposal It hasn't been done yet.
http: // www. stillriverssystems. com / (many are veiled with secrets)
Caporaso et al. , High gradient induction accelerator, Particle Accelerator Conference, 2007. PAC. IEEE Volume, Issue, 25-29 June 2007 Page (s): 857-861

In the present invention, in order to avoid the instability of the high-intensity electron beam, a method of instantaneously generating an electron population (electron bunch, electron cloud) is adopted. That is, it is not a slow method in which electrons are generated at the cathode of an electron gun and then injected into a vacuum vessel as in the conventional method, but has a structure in which ions are captured in the vicinity of an electron generation source corresponding to an electron gun. A compact electron population is generated from the generation process. This method eliminates the need for a complicated injection process such as an LBL electronic ring.

The electron population is in the form of a hollow electron ring or a hollow cylindrical electron cloud. Both ends of the electron cloud are closed or open. Ions to be accelerated in this hollow part are captured with a strong Coulomb potential. This is hereinafter referred to as “hollow electron cloud”. When the cylindrical length is short, it matches the conventional ERA type electronic ring shape. The hollow electron cloud and the trapped ions are instantaneously extracted and accelerated by a high electric field RF electric field or the like, and then the electron cloud and ions are electromagnetically separated by a method proposed by Bexler et al.

The generation of such a hollow electron cloud was finally made possible by recent advances in ultrashort pulse high power technology such as high power lasers, and in the 60s and 70s when ERA research and development was incandescent. Technically impossible.
Three specific methods for realizing the hollow electron cloud are listed below. The method shown below basically uses the method presented by Bexler. However, this is an improvement over many important points as described below. The difference from Bexler is the method of generating electron beams and ions. An electronic ring accompanying device, for example, a coil for compression (axial compression) of an electronic ring by a magnetic field, etc. is mounted.

The first method is a method for generating a hollow static cylindrical electron cloud (hollow beam) ion beam having a concentric generation structure of electrons and ions. The outer part of the concentric circle draws a large-current electron beam by an electrostatic field with the cathode electrode shaped like a ring. A high-current hollow beam source with no generation of ions in the cathode body has already been experimentally verified, and is realized by a CBS (Cold Beam Synchrotron Source) type electronic cooling unit according to the present invention. By using a hollow electron ring, the space charge effect restriction can be relaxed, and a stronger and higher current hollow beam can be realized.
E. Levichev, V.M. Kiselev, V.M. Parkhomchuk, V.M. Reva, S .; Sinyatkin, V.M. VOSTRIKOV, LATTICE STUDY FOR THE CARBON ION SYNCHROTRON FOR CANCER THERAPY WITH ELECTRON COOLING, EPAC08
E. B. Levichev et al. "Carbon Ion Accelerator Facility for Cancer Therapy", Proceedings of RuPAC, 2006, Novosibirsk, Russia, pp. 363-365.
Masayuki Kumada, Vasili V. Parkhomchuk, B.M. I. Grishanov, E .; B. Levichev, F.M. V. Podgorny, S.M. A. Rastigeev, V.M. B. Reva, A .; N. Skrinsky, V.M. A. VESTRIKO, THE CBS-THE MOST COST EFFECTIVE AND HIGH PERFORMANCE CARBON BEAM SOURCE DEDICTED FOR A NEW GENERATION CANCER THERAPY, PAC 205, Koxville
The ion bunch to be accelerated inserts a micro ion source in the center of the cathode. With this structure, the generation timing of ions and the generation of electron rings can be adjusted.

In the second method, the hollow electron cloud of the driving beam and the ion bunch of the driven beam are generated by independent high-power lasers. In this case, the laser target electrode preferably has a concentric circular structure, and a solid material serving as an ion generation source is disposed inside and a photocathode material serving as an electron beam generation source is disposed outside. It is desirable to use two independent lasers with different wavelengths suitable for the generation of ions and the wavelength of electrons. In order to generate a hollow beam for generating an electron beam, a laser beam having a weak distribution centering on the intensity distribution of the cross section of the laser beam is used. Hollow laser beams are possible by appropriate design of lens material and geometric structure. The spatial and temporal positional relationship between the electron cloud and ions is set by the time and spatial structure of the two laser beams. The hollow electron cloud in which the generated ions are confined can be instantaneously accelerated to the speed of light in the same manner as that for extracting electrons with an RF electron gun. The energy of the ions at this time is determined mainly by the holding potential of the ions determined by the number of electrons in the electron cloud.

The third method is a method of irradiating a thin film (foil) with a laser beam according to the method of a laser driven accelerator of a high energy electron beam. These have already begun to realize GeV class high-quality electron beams with the energy of electrons. In these methods, it is possible to accelerate ions by irradiating the foil with a high-power laser. However, only a few MeV protons have been obtained, and no practical energy has been obtained.
C. -M. Ma et al. , Development of a laser-drive proton accelerator for cancer therapy, Laser physics, ISSN 1054-660X (print) 1555-6611 (Online), Volume 646, 39 6
These ion accelerations are also considered as a kind of collective acceleration. In the present invention, as in the second method, an electron ring beam is generated by irradiating a foil with a ring-shaped laser beam having a beam cross-sectional intensity. Is the first time. At this time, one laser beam may be used, but the cross-sectional intensity distribution may have a structure in which the central intensity is not necessarily zero but weak and the intensity of the outer circumferential portion is strong. A similar effect can be expected by making the laser beam intensity distribution uniform and providing a thickness distribution toward the target portion of the foil.
Since the ERA method is adopted for the laser-driven accelerator in this way, this method is different from the conventional force-driven laser-driven proton beam method, and the acceleration efficiency can be greatly improved due to the electron ring structure. Therefore, less laser power is required and the entire device including the laser is made compact.

電荷および誘電率の値を代入して

本発明で可能と考えられるパラメター、Ｒ＝０．４６ｃｍ，ａ＝０．１ｃｍ，Ｎ＝１０^１３を代入するとＥ_ｍａｘ＝１，０００ＭＶ／ｍを得る。これは電子雲の保持力の電場に対応し、これに閉じ込められたイオンのエネルギーの最大値を示す。イオンを内蔵した電子リングの加速は従来提案されている直接引き出しのＲＦ電場またはｍａｇｎｅｔｉｃ ｅｘｐａｎｓｉｏｎ ａｃｃｅｌｅｒａｔｉｏｎのいずれかあるいは両方を用いる。
また、実際には、電子リング中の電子の分布が一様でない影響などもあり、有効電場はフォームファクターｆ（ｆ〜１／２）を乗じた値が妥当である。
電荷と質量の比が２の場合には例えば、完全電離の炭素イオンの場合では、５００ＭＶ／ｍの電場に相当し加速される炭素イオンのエネルギーは１ｍの長さにて核子あたり２５０ＭｅＶ／ｕ／ｍ程度のイオンエネルギーが得られる。Magnitude of the electric field which can in which more compact electronic rings generated in any manner, for example, the electron ring when major radius of the donut rings R, minor radius a, the number of electrons in the bunch, and N _e E _max (also called holding power or holding power)

Substituting charge and dielectric constant values

Substituting parameters considered possible in the present invention, R = 0.46 cm, a = 0.1 cm, N = 10 ¹³ , gives E _max = 1,000 MV / m. This corresponds to the electric field of the coercive force of the electron cloud and indicates the maximum value of the energy of ions confined in this. Acceleration of an electron ring containing ions uses either a direct extraction RF field or a magnetic expansion acceleration, which has been conventionally proposed, or both.
In practice, the distribution of electrons in the electron ring is not uniform, and the effective electric field is a value obtained by multiplying the form factor f (f to 1/2).
When the charge to mass ratio is 2, for example, in the case of a fully ionized carbon ion, the energy of the accelerated carbon ion corresponding to an electric field of 500 MV / m is 250 MeV / u / n per nucleon at a length of 1 m. An ion energy of about m can be obtained.

The present invention is suitable for a human cancer treatment apparatus with a very short accelerator length. For heavy-dose radiotherapy of radiation-resistant tumors in the deep part of the body (less than 30 cm), the energy of the heavy-particle beam per nucleon should be 400 MeV / u or more, so when the accelerator of this method is completed, The length of the part is about 2m. For this reason, by strengthening radiation shielding, it is possible to install a heavy particle beam therapy system in an existing hospital. Further, since the acceleration device is a linac system, the number of repetitions of ion beam extraction can be increased, and as a result, the number of particles per pulse may be small. It is possible to reduce the influence of beam loading, which contributes to reducing the strength of the acceleration electric field.

As described above, in the present invention, a compact high-density electron ring, which is difficult with the conventional method, is instantaneously generated by a high-power laser whose intensity distribution has a ring-type laser beam output form, and ions are generated in a potential field with strong electron ringing. Three specific methods of collective acceleration that confine traps and place ions in the electron cloud and accelerate in the axial direction instantly to avoid instability are described, enabling the realization of a tabletop device for heavy ion radiotherapy for cancer Explained how to do.

In addition, the apparatus can switch between heavy particle beams and electron beams independently. From this, it is possible to generate X-rays from an electron beam by irradiating it to the target, which can be applied to position confirmation, position monitoring, organ movement monitoring, etc. 1) positioning, 2) during treatment Real-time monitoring 3) It has the feature of giving three functions of treatment.

Finally, a general table top accelerator device is mainly a rotating gantry system that rotates around a patient. These have one irradiation device for one accelerator. In contrast, the conventional cyclotron or synchrotron system can be equipped with a plurality of irradiation chambers, and the use of expensive devices is increased by increasing the number of treatment rooms. In this case, when increasing the irradiation chamber with a fixed beam, a beam line using a deflecting electromagnet is required, so each requires a large radius of curvature, and the significant cost of the beam line is added to deflect the ion beam. It must be done. This system is similar to a short and lightweight linear accelerator (electronic linac), so it is not only easy to make a rotating gantry, but it can easily rotate itself on a flat surface, so no deflection electromagnet is used for the fixed beam line. It has the great advantage of saving.

Claims (7)

Accelerator and its application to accelerate ions with high-density compact electron population generated instantaneously. The ion collective acceleration device according to claim 1, wherein a hollow electron population is instantaneously generated by a ring-shaped cathode having an extremely small ion source in the center, and a direct RF electric field or electron ring accelerator (ERA) is used. High-energy ion extraction and acceleration can be realized by a magnetic expansion acceleration method. The ion accelerating device according to claim 1 is formed by two different types of independent lasers having different wavelengths: a laser having a hollow intensity distribution with zero light intensity at the center and a laser filling the center. Irradiate a solid cathode material with a photocathode on the outside and an ion on the inside to generate a hollow electron cloud with a hollow structure. The electron cloud containing ions is directly applied to an RF electric field or electron ring accelerator. High energy ion extraction / acceleration is realized by a magnetic expansion acceleration method (ERA). A hollow electron having a hollow structure can be obtained by irradiating a plastic foil or the like with the collective acceleration device for ions according to claim 1 by a laser having a hollow intensity distribution similar to that of claim 3 or a laser beam having a weak central light intensity. High energy ion extraction / acceleration can be realized by a magnetic field expansion acceleration method using an RF electric field or electron ring accelerator (ERA) that directly generates clouds. Alternatively, the same effect can be expected by making the intensity distribution of the cross section of the laser light uniform and providing a thickness distribution on the foil side. The ion collective acceleration apparatus according to claim 1 is applied as a cancer treatment apparatus having a high QOL (Quality Of Life) by accurately irradiating a malignant tumor. The ion collective acceleration device according to claim 1 can also be used in the position adjustment of cancer patients, the dynamic monitoring of movement during treatment of tumors, or the CT diagnostic device by using the strong electron beam as an X-ray source. . The collective acceleration device for ions according to claim 1 has a high degree of freedom of rotation on a plane and can be easily rotated because of its light weight and compact size, and can be rotated in any direction of 360 degrees around its rotation axis. Because the particle beam can be emitted, unlike the case of circular accelerators such as synchrotrons and cyclotrons, the beam course can be switched to multiple treatment rooms in a short time without using a deflecting electromagnet, etc. Make it available.