The use of the Wien filter to eliminate object slit scattering in MeV ion nanobeam systems

One of the fundamental limitations in the performance of MeV ion microbeam focusing systems is the effect of ion scattering at the edges of the object aperture. As the aperture is reduced in the search for smaller spot sizes, the fraction of scattered to unscattered beam increases. The scattered beam contains lower energy particles which can be transmitted through the system to create a halo of over-focused particles surrounding the final image. Removal of this halo is critical to achieving small spot sizes, especially in single ion applications.In this paper, we discuss the use of a Wien filter (crossed magnetic and electrostatic fields) to deflect the reduced energy scattered particles and ensure that only ions with the correct energy are accepted into the lens. This paper reviews the beam optics of Wien filter systems and presents calculations of the parameters required to obtain useful energy dispersion.     

Experiments on the acceleration and extraction of ions in a cyclotron with an azimuthally varying magnetic field and adjustable energy

Questions concerning the shaping and shimming of magnetic fields are discussed. Results of investigations of the ion acceleration process are presented. Results of experiments on extraction of the accelerated ion beam are reported. The construction of a deflecting system which fully compensates for the field dispersion effect is described. Ion energy adjustment was carried out for a magnetic field interval from 5 to 17 koe. The maximum deuteron energy in the extracted beam was 31.5 mev. The energy spread of the accelerated ions was ±1%.The experiments were carried out on the one and one-half meter cyclotron at the I. V. Kurchatov Order of Lenin Institute of Atomic Energy Academy of Sciences USSR [1].In conclusion the authors express deep gratitude to L. F. Kondrashev, N. Z. Kubyshkin and S. I. Prokof' ev for their great aid in the preparation of the experiments and also to all the service personnel of the cyclotron installation and to the machine shop workers.     

Cyclotron instability in ogra

Conclusions The experimental results reported here indicate that a cyclotron instability can and does develop in Ogra. Furthermore, at the present time, as far as we know there is no other possible explanation for the anomalous magnitude and the dependence of electric field (at the cyclotron frequency) on plasma density observed experimentally. The presence of density waves with different phase velocities can cause electron heating and electron loss. In this regard, the fact that the electrons can interact with the electric waves seems to be indicated by experiments with an electron beam carried out by Yu. A. Kucheryaev and D. A. Panov [9]; these experiments indicate that an electron beam passing through a plasma along the magnetic field loses or gains energy by virtue of interaction with waves at the cyclotron frequencies corresponding to H ₂ ⁺ and H ₁ ⁺ ions.On the one hand, the effect of the cyclotron instability can cause ions to form bunches as a result of nonlinear effects, and these can lead to a more effective interaction, with the dissipation and exchange of energy. On the other hand, the existence of electric fields perpendicular to the magnetic field can cause ion drift across the magnetic field when the phase velocity of these waves is approximately equal to the ion velocity. As is evident from the table, this situation can arise in certain modes of operation. For a more detailed explanation of the effect of the cyclotron instability on ion loss and electron loss, it will be necessary to carry out further investigations. The author wishes to take this opportunity to thank I. N. Golovin for his continued interest in this work and for a number of valuable comments offered in discussions of the experimental results. E. P. Velikhov for help in carrying out the calculations, and A. N. Karkhov and V. F. Nefedov for help in carrying out the measurements with Ogra. Fruitful discussions of the experiments and the results of the calculations with colleagues working with Ogra were very helpful in determining the physical pattern of these effects.Translated from Atomnaya Énergiya, Vol. 14, No. 1, pp. 72–81, January, 1963     

Measurement of Ion Cyclotron Emissions by Using High-Frequency Magnetic Probes in the LHD

Two pairs of high-frequency magnetic probes were installed in the Large Helical Device (LHD). During the injection of a perpendicular neutral beam, ion cyclotron emissions (ICEs) with the fundamental frequency corresponding to the ion cyclotron frequency at the plasma edge were detected, which are the same type of ICE as measured with the former spare ion cyclotron range of frequencies (ICRF) heating antennas. This type of ICE was further investigated with regard to the phase and intensity of signals. Another type of ICE was found in the LHD, and these ICEs were synchronized with bursts of toroidicity induced Alfv¶en eigenmodes (TAE) and the rise of intensity of lost ion °ux. Therefore the source of these ICEs was thought to be the particles transferred from the core to the outer region of plasma by the TAE bursts. The frequency of ICEs induced by the TAE bursts increases linearly with the magnetic ¯eld strength, since the ion cyclotron frequency increases with the magnetic ¯eld strength.     

Investigation of the confinement of high energy non-neutral proton beam in a bent magnetic mirror

By using the particle-in-cell (PIC) simulation method, we studied how the proton beam is confined in a bent magnetic mirror. It is found that the loss rate of the charged particles in a bent mirror is less than that in the axi-symmetric mirror. For a special bent mirror with the deflection angle of the coils α = 45°, it is found that the loss rate reaches maximum value at certain ion number density where the ion electrostatic oscillation frequency is equal to the ion cyclotron frequency. In addition, the loss rate is irrelevant to the direction of the proton beam. Our results may be helpful to devise a mirror. In order to obtain the least loss rate, we may choose an appropriate deflection angle, and have to avoid a certain ion number density at which the ion electrostatic oscillation frequency is equal to the ion cyclotron frequency.     

Estimation of the sheath power dissipation induced by ion cyclotron resonance heating

During ion cyclotron resonance heating, the sheath power dissipation caused by ion acceleration in the radio frequency(RF) sheath is one of the main causes of RF power loss in the tokamak edge region. To estimate the power dissipation of an RF sheath in the ion cyclotron range of frequency(ICRF), a 1 D fluid model for the multi-component plasma sheath driven by a sinusoidal disturbance current in the ICRF is presented. By investigation of the sheath potential and ion flux at the wall, it is shown that the larger frequency and lower amplitude of the disturbance current can cause smaller sheath power dissipation. The effect of the energetic ion on the sheath power dissipation depends on the disturbance current. For large amplitude of disturbance current, the increase in the concentration and energy of the energetic ion leads to a decrease in sheath power dissipation. While for a small disturbance current, the sheath power dissipation demonstrates non-monotonic variation with the concentration and energy of the energetic ion. In addition, the sheath power dissipation is found to have a small increase in the presence of light impurity ions with low valence.     

高能重离子在聚合物中的辐照效应研究

Ion irradiation of polymers can induce irreversible changes in their macroscopic properties such as electrical and optical properties and the surface-related mechanical properties. Electronic excitation, ionization, chains scission, cross-links and mass losses are accepted as the fundamental events that give rise to the observed macroscopic changes. Detailed and systematic study of radiation induced effects in polymers enriches not only the knowledge of ion-material interactions but also supplies new bases for polymeric materials synthesis through ion-beam technologies. Previous work has concentrated mainly on effects induced by low-ionization particles such as γ-rays and electrons. Since 1980,s the application of high energy heavy ion accelerators enables the use of high energy heavy ion as an irradiation source, and many new and exciting effects and phenomena have been revealed.Energetic heavy ions in matter lose energy mainly through electronic excitation and ionization. Compared to low-ionization particles, high energy heavy ion possesses higher LET(linear energy transfer) values which can reach several to several tens keV/nm. As most of the primary ionizations and excitations occur close to the ion trajectory in a core of a few nanometers in diameter, a continuous damaged zone along the ion path can be induced,in which all bonds inside the zone can be destroyed due to the high rate energy deposition. Studies on this particularity of high energy heavy ion irradiation and its effects in materials will cause great influence on industry as well as on our daily life.The previous work has revealed the great difference in the effects induced by high energy heavy ions compared to the other particles. It has been shown that under irradiation with lower LET particles gas release depends on molecular structure and material composition, whereas under irradiation with high LET particles, such as high energy heavy ions, it is not the case. Some materials that undergo degradation under γ-irradiation can be cross-linked by irradiation with high energy heavy ions. In some cases new molecular structures were induced by high energy heavy ions with sufficiently high LET values. In recent years we have irradiated polyethylterephthalate (PET), polystyrene (PS), polycarbonate (PC) and polyimide (PI) with high energy Ar, Kr, Xe and U ion beams.Chemical and physical changes of the materials induced by the high energy heavy ion beams were investigated by Fourier-transform infrared ray spectroscopy, ultraviolet and visible transmission spectroscopy and X-ray diffraction measurements, from which damage cross-sections of various functional groups were determined[1]. An energy loss threshold for damage of phenyl ring in PET has been derived and difference in amorphization of PET under high and low LET irradiations was observed. It is found that alkyne end groups can be induced in all the materials above a certain electronic energy loss threshold, which is found to be about 0.8 keV/nm for PS and 0.4 keV/nm for PC. The production cross-section of alkyne end group increases with increasing electronic energy loss and shows saturation at high electronic energy loss values.     

用于硼中子俘获治疗的强流质子回旋加速器中心区结构优化设计

中国原子能科学研究院目前正在研制用于硼中子俘获治疗（BNCT）的强流质子回旋加速器,该加速器设计引出能量14 MeV、质子束流强大于1 mA。相比引出流强为400 μA的PET回旋加速器,BNCT强流质子回旋加速器对中心区相位接收度和轴向聚焦的要求更高。为实现mA量级的束流的加速和引出,BNCT强流质子回旋加速器采取了增加负氢束流注入能量、增大磁铁镶条孔径、使用用于增大Dee盒头部张角的阶梯状结构及调整加速间隙的入口和出口高度等一系列中心区结构优化设计,有效地提高了中心区的相位接收度,改善了轴向电聚焦。在新的离子源注入能量下通过数值计算得到实测场下的轴向电聚焦和间隙高度的关系,选取合适的间隙高度获得最佳的轴向聚焦,从而确定了mA量级束流的注入和加速的中心区结构。同时在设计中考虑空间电荷效应的影响,计算了不同流强下的束流尺寸变化。中心区结构在实测磁场下的优化设计计算结果表明,BNCT强流质子回旋加速器中心区的束流对中好于0.5 mm,相位接收度大于40°,中心区最高可接收流强3 mA。目前,新的中心区结构已进入机械加工阶段。     

On the decrease of the ion pulse duration and ion pulse rate in a cyclotron

Results of calculations and experiments dealing with shortening of the duration of ion pulses on the target of a cyclotron are presented. The possibility of changing the ion pulse rate by deflecting with a high frequency potential applied to an electrode inside the dee, which draws off the ions on the first half turn is discussed.Calculations and experiments were made for the condition of deuteron acceleration up to 10 Mev in the one and one-half meter cyclotron [1].The authors deeply thank N. A. Vlasov, S. P. Kalinin, B. V. Rybakov, and V. A. Sidorov for sustained interest in the work and their joint discussion of it; N. I. Chumakov, V. P. Konyaev, and G. N. Golovanov for making a series of calculations; Yu. V. Korshunov, A. V. Antonov, and E. A. Meleshko for the deisgn and adjustment of the electronic apparatus for the control electrode supply.     

Energy loss of degrader in SC200 proton therapy facility

The proton beam energy determines the range of particles and thus where the dose is deposited. According to the depth of tumors, an energy degrader is needed to modulate the proton beam energy in proton therapy facilities based on cyclotrons, because the energy of beam extracted from the cyclotron is fixed. The energy loss was simulated for the graphite degrader used in the beamline at the superconducting cyclotron of 200 MeV in Hefei(SC200). After adjusting the mean excitation energy of the graphite used in the degrader to 76 eV, we observed an accurate match between the simulations and measurements.We also simulated the energy spread of the degraded beam and the transmission of the degrader using theoretical formulae. The results agree well with the Monte Carlo simulation.     

Cyclotron with a magnetic field traveling in the radial direction

In this paper we consider the design of a cyclotron with a magnetic field which travels in the radial direction; a machine of this kind had been proposed by the author. By means of circular windings which are fed by ac generators it is possible to produce one or more concentrated magnetic fields which travel in the radial direction in the gap.Two versions are proposed. In the first, the traveling wave is the field in-which the particles are accelerated. In the second, the traveling wave is superimposed on the usual fixed magnetic field and acceleration takes place by virtue of the combined fields. The spatial distribution of the field in the wave makes it possible to obtain a stability region(1 > n > 0) which is displaced in the radial direction with the radial velocity of the particles. A stability region is also obtained in the case in which the absolute value of the magnetic field of the acceleration region increases in the radial direction.In principle, the system proposed here makes it possible to build cyclotrons with energies as high as desired. In spite of the cyclic-action characteristics of the acceleration, because of the improved focusing, there is reason to believe that the mean intensity can be larger than that which is obtained in the fm cyclotron.Typical calculations are given for accelerators of various energies. These calculations indicate that the weight and size of these accelerators may be much smaller than other accelerators of the same energy.     

Isotope separation in a magnetized sheet plasma by ion cyclotron resonance

The isotope separation experiment in a sheet plasma has been studied by using ion cyclotron resonance heating. The sheet plasma flowed into two parallel plate electrodes to which an rf electric field with a frequency equal to an ion cyclotron for the desired isotopic species was applied. The observed resonance frequency is 180 kHz, however, the ion cyclotron frequency of Ar ion is 65 kHz. This discrepancy may be explained in terms of plasma space potential in the sheet plasma. The ion saturation current in a Langmuir probe gives a maximum value of 6.7 V/cm and 2.3 kG.     

千兆电子伏重离子加速器——兰州冷却储存环

能量达千兆电子伏的兰州重离子加速器冷却储存环HIRFL-CSR,是一个集加速、累积、电子冷却及内外靶实验于一体的多功能双冷却储存环同步加速器系统,由主环CSRm和实验环CSRe构成,并以兰州重离子回旋加速器系统HIRFL作注入器。CSR将重离子束的能量从兆电子伏提高到千兆电子伏,同时利用空心电子束冷却技术将束流的动量分散及发射度降低1~2个数量级,并提供多种类的高电荷态重离子束以及放射性次级束(RIBs),以开展更高精度的物理实验及更广范围的应用研究。兰州冷却储存环于2006年建成并投入运行,实现了剥离注入与多圈注入、空心电子束对重离子束的冷却与累积、变谐波宽能区同步加速、等时性环型谱仪、RIBs的产生与收集以及重离子束的快慢引出,并实现了高能重离子束的空心电子束冷却,使得重离子束的动量分散降低到10^-5量级,而发射度收缩到0.1πmm•mrad以下。同时,完成了短寿命近滴线核素的高分辨质量测量物理实验及高能重离子束深层治癌的临床应用实验。     

Heavy Ion Acceleration at Cyclone (Belgium)

CYCLONE is an isochronous cyclotron in operation in Louvain-la-Neuve (Belgium). It is equipped with a P. I. G. hot cathode heavy ion source and accelerates various ions up to energies of 110 MeV Q2/A with extracted beam intensities reaching 10 ?A in the 4+ state. The source is described and some performance parameters are given. In order to reach higher charge states an injector cyclotron is projected which will allow a final energy of 27 MeV/nucleon up to neon decreasing to 6 MeV/nucleon for xenon. Extracted intensities vary between 5 × 1013 and 109 pps depending on particle and energy. Some design aspects are described which will allow the cost of the project to be quite low.     

The Plastic Ball ? a Multi-Detector, Large Solid Angle Spectrometer with Charged Particle Identification for the Bevalac

For the study of central relativistic nuclear heavy ion collisions, which are characterized by the emission of a large number of particles, one needs a detector which covers a large solid angle ? 4? if possible ? and which is capable of identifying charged particles. The high multiplicity requires a large number of detectors, and the need for charged-particle identification requires a measurement of the energy loss, and the total energy for each particle detected. The spectrometer consists of 815 detector modules, which cover 94% of 4?. The geometry of these modules has been taken from the Stanford crystal ball detector for ?-rays ? with minor modifications. This geometry is suited for the high multiplicities of particles emitted in relativistic heavy ion collisions. The dimension of the individual elements have been chosen to stop 240 MeV protons. Above this energy reaction losses start to dominate, so that the light output of a scintillator would no longer be a true indication of the energy. Out of 100 charged particles, 94 will hit the Plastic Ball, 87 will fire a detector element, and 80 will be identified uniquely. For the individual detector modules we have used the "Phoswich" idea, by gluing a 4 mm thick CaF2 scintillator to a 35 cm thick plastic scintillator (NE114) with the shape of a truncated pyramid, which is viewed by one photomultiplier tube (PM2202B).     

A Small "Cold-Cathode" High-Intensity Cyclotron Ion Source

High beam currents have been achieved with a radial source which fits into the 2-inch gap of a 30-inch cyclotron. The geometry is that of a cold-cathode or P. I. G. source. However, the cathodes are heated to thermionic temperatures by ion bombardment rather than a conventional high-current heated filament. The source is now in use and produces intense beams of H+, D+, He3, and alpha particles. Internal beams of H+ or D+ of more than one mA are obtained routinely at extraction radius. In addition, 30 ?A of H- or D- are obtained at a stripping foil by merely reversing the magnetic field of the cyclotron.     

Acceleration of ions in a cyclotron with an azimuthally varying magnetic field

This article describes experiments on the acceleration of charged particles in an azimuthally varying magnetic field on the 1 1/2f-meter cyclotron of the Atomic Energy Institute, of the Academy of Sciences, USSR [1].The production of a magnetic field of the sector type with a coarse variation of ±15% at a potential of 15 kv between the dees made it possible to accelerate deuterons to an energy of 19 Mev. Investigation of the motion of the ions at the final orbits showed that it was possible to eject a large part of the ion beam with an energy considerably exceeding 20–22 Mev by means of an electrostatic deflecting system. Curves characterizing the acceleration process in an azimuthally varying magnetic field were plotted. Valuable data was obtained on the correction to the form of the magnetic field by current coils distributed inside the accelerating chamber.In conclusion, the authors thank N. D. Fedorov, A. P. Babichev, A. S. Knyazyatov, and V. K. Anokhin for taking part in the magnetic measurements, S. I. Prokof'ev for active aid in the preparation of the covers of the accelerating chamber, N. N. Khaldin for valuable advice and participation in the fabrication planning, N. I. Venkov and all personnel servicing the cyclotron setup, I. M. Shnaptsev and H. G. Yadykin for making the vacuum tests, ML A. Egorov, V. M. Komarov, V. I. Andreev, and V. S. Kalyaev for their outstanding work on assembling the mechanical parts.     

A Source for Multiply-Charged Ions and Acceleration of C, N and O Ions by IPCR Cyclotron

The design and performance of the ion source which is now used in the IPCR variable energy cyclotron are described. The source is of the electron-bombarded hot cathode type having two cylindrical cathodes of tungsten and a water-cooled copper anode containing a replaceable molybdenum slit plate. The arc discharge is established continuously but not pulsed. The source is usually operated very stably under an arc power of 1.5 to 3kW with a gas flow rate of 1 to 2 cc/min. The lifetime of the source is mainly limited by the erosion of the upper tungsten cathode at about 24 hours. At present, C4+, N4+, O4+, N5+ and O5+ ions are accelerated up to 48~100, 56~1100, 70~95, 56~125 and 70~125 MeV respectively, and a few micro-amperes of these ions are extracted from the cyclotron. The vacuum obtainable in the accelerating chamber is usually 2 ~ 4 × 10-6 mHg, and the loss of ion beam by the charge exchange effect is comparatively small. Extracted ion beams are used in several experiments for about 1900 hours in a year.     

Results of ICRF Heating Experiments from the EAST 2010 Campaign

Radio frequency(RF) plasma heating in ion cyclotron range of frequencies(ICRF)was successfully performed on the Experimental Advanced Superconducting Tokamak(EAST).This is mainly because lithium wall conditioning was routinely used to reduce both impurity and hydrogen(H) recycling and to improve the ICRF power absorption.Mainly ICRF heating of the H minority regime at 27 MHz has been applied in deuterium plasmas.The ion cyclotron resonance heating(ICRH) is found to depend strongly on plasma preheating.The ICRH efficiency can be much improved in conjunction with the lower hybrid wave(LHW).Effective ion and electron heating was observed with the H minority heating mode.The increase of the stored energy reached30 kJ in L-mode plasma by using the ICRF power of 1.0 MW alone when the H cyclotron resonance layer was at plasma center.