High-power Accelerators Research Articles

A comparison of rat SPECT images obtained using 99mTc derived from 99Mo produced by an electron accelerator with that from a reactor

Recent shortages of molybdenum-99 (99Mo) have led to an examination of alternate production methods that could contribute to a more robust supply. An electron accelerator and the photoneutron reaction were used to produce 99Mo from which technetium-99m (99mTc) is extracted. SPECT images of rat anatomy obtained using the accelerator-produced 99mTc with those obtained using 99mTc from a commercial generator were compared. Disks of 100Mo were irradiated with x-rays produced by a 35 MeV electron beam to generate about 1110 MBq (30 mCi) of 99Mo per disk. After target dissolution, a NorthStar ARSII unit was used to separate the 99mTc, which was subsequently used to tag pharmaceuticals suitable for cardiac and bone imaging. SPECT images were acquired for three rats and compared to images for the same three rats obtained using 99mTc from a standard reactor 99Mo generator. The efficiency of 99Mo–99mTc separation was typically greater than 90%. This study demonstrated the delivery of 99mTc from the end of beam to the end user of approximately 30 h. Images obtained using the heart and bone scanning agents using reactor and linac-produced 99mTc were comparable. High-power electron accelerators are an attractive option for producing 99Mo on a national scale.

Evolution of Beam Distribution in Crossing a Walkinshaw Resonance

The third-integer coupling resonance at ν(x)-2ν(z)=ℓ, known as the Walkinshaw resonance, is important in high-power accelerators. We find that, when the betatron tunes ramp through a Walkinshaw resonance the fractional emittance growth (FEG) is a universal function of the effective resonance strength: G(1,-2,ℓ)√[ε(xi)]|Δ(ν(x)-2ν(z))/Δn|(-1/2), where G(1,-2,ℓ) is the resonance strength; ε(xi) and ε(zi) are the initial horizontal and vertical emittances, respectively; and |Δ(ν(x)-2ν(z))/Δn| is the resonance crossing rate per revolution. At large effective resonance strengths, the FEG reaches an asymptotic maximum value (FEG)(max)~2ε(xi)/ε(zi) for ε(xi)>>1/2ε(zi) or ε(zi)/(2ε(xi)) for ε(xi)<<1/2ε(zi). There is little emittance exchange at ε(xi)=1/2ε(z), which can be used to minimize emittance growth in crossing a Walkinshaw resonance.

High-energy proton beam accelerators for subcritical nuclear reactors

Schemes for high-power accelerators to be used in electronuclear facilities are reviewed. The possibilities of the electronuclear method of obtaining energy and using accelerators for the transmutation of radioactive wastes as well as in reactor materials engineering are reviewed briefly. The parameters of accelerators which are currently operating, under construction or being designed in the world for subcritical reactor schemes, complexes for salvaging wastes and power neutron generators are presented.

Plasma-Wall Interactions in the Cesiated SNS H− Ion Source

High-current H− ion beams are needed to drive high-power accelerators as well as to heat future fusion reactors with neutral beams. The most productive H− sources enhance the production of H− ions with caesium. Cs lowers the work functions of the metal walls, which increases the probability of ions to capture a second electron when bouncing back from the metal plasma walls. However, caesium also causes voltage break downs that can be severe and cause significant downtime. SNS has developed a frugal caesium management, which uses a single injection of ~4 mg of caesium to produce ~50 mA of H− beam without decay for up to 6 weeks. This paper presents calculations and experimental data, which suggest the persistence of the caesium enhanced H− beams are due to 1) thermally limiting the Cs emission, and 2) conditioning for high purity hydrogen plasma, which eliminates the sputtering of Cs by non-hydrogen ions, and 3) hydrogen ions being too light to sputter Cs.

Estimation of acceptable beam-trip frequencies of accelerators for accelerator-driven systems and comparison with existing performance data

Frequent beam trips as experienced in the existing high-power proton accelerators may cause thermal fatigue in accelerator-driven system (ADS) components, which may lead to degradation of their structural integrity and reduction of their lifetime. In this study, acceptable beam-trip frequencies of the ADS accelerator were evaluated and compared with the performance of the ADS accelerator, which was estimated based on the operational data on existing accelerators. Thermal transient analyses were performed to investigate the effects of beam trips on the reactor components, with the objective of determining the feasibility of engineering the ADS and the reliability of the accelerator. These analyses were based on the thermal responses of the following reactor components: the beam window, the fuel cladding, the inner barrel and the reactor vessel. Assuming that the annual plant availability was 70%, our results indicated three acceptable beam-trip frequencies, depending on the beam-trip duration, τ b : 2 × 104 times per year for 0 10 s; 2 × 103 times per year for 10 s 5 min; and 42 times per year for τ b > 5 min. In order to consider methods to reduce beam-trip frequency, we compared the acceptable beam-trip frequency with the performance of the ADS accelerator, which was estimated based on the operational data on existing accelerators. The comparison showed that for beam trips with a duration of 10 s or less, the beam-trip frequency was acceptable. On the other hand, for beam trips with durations of 10 s 5 min and τ b > 5 min, it was necessary to reduce the beam-trip frequencies to about 1/6 and 1/35, respectively.

Transport of intense ion beams and space charge compensation issues in low energy beam lines (invited)

Over the last few years, the interest of the international scientific community for high power accelerators in the megawatt range has been increasing. For such machines, the ion source has to deliver a beam intensity that ranges from several tens up to a hundred of mA. One of the major challenges is to extract and transport the beam while minimizing the emittance growth and optimizing its injection into the radio frequency quadrupole. Consequently, it is crucial to perform precise simulations and cautious design of the low energy beam transport (LEBT) line. In particular, the beam dynamics calculations have to take into account not only the space charge effects but also the space charge compensation of the beam induced by ionization of the residual gas. The physical phenomena occurring in a high intensity LEBT and their possible effects on the beam are presented, with a particular emphasis on space charge compensation. Then, beam transport issues in different kind of LEBTs are briefly reviewed. The SOLMAXP particle-in-cell code dedicated to the modeling of the transport of charge particles under a space charge compensation regime is described. Finally, beam dynamics simulations results obtained with SOLMAXP are presented in the case of international fusion materials irradiation facility injector.

Magnetic Field Shielding by Vacuum Chambers of Magnetic Material for Beam Loss Reduction

One of the reasons of a beam loss in a high power accelerator is leakage magnetic field from a magnet at a close beam line, which distorts the beam orbit and makes the beam hit the wall of the beam pipe. The most effective way to shield such leakage field is to cover the beam by the magnetic materials at the nearest space. This means that beam pipes and bellows be made of the magnetic materials. We plan to apply this method to the vacuum chambers of the beam extraction section of the J-PARC 3 GeV synchrotron, where the effect of the leakage magnetic field to the beam orbit is evident. However, there is few proven evidence of the vacuum chambers made of magnetic materials. Therefore we clarify the problems in producing beam pipes and bellows, which satisfy the magnetic and vacuum performance. In this article, we deliver the over view of the magnetic shielding project and our approaches to the problems in producing the vacuum chambers of magnetic materials.

High-power Accelerator for Environmental Applications

High-power Accelerator for Environmental Applications

A tunable waveguide to cavity coupler for high power accelerator cavities

The end iris ridge waveguide couplers are used to couple power to accelerator cavities through a reduced size coupling port. However, higher electric and magnetic fields due to reduced size lead to strict requirements on dimensional tolerances during coupler fabrication process. It is shown by detailed parametric analysis that even small dimensional changes during manufacturing or operation can lead to undesired shift in design frequency and deterioration of return loss. Hence, transmitted power testing of two couplers connected back to back without an intermediate cavity cannot be carried out. Here, we propose cylindrical static tuners on impedance matching section to relax the dimensional tolerance requirements. It is also shown that an iris coupled coupler-cavity system is more tolerant towards coupler dimensional changes than a stand-alone coupler. However, same tuners can find use for tuning the coupling coefficient of coupler-cavity system. The proposed tuning scheme is expected to reduce the coupler manufacturing costs and provide an useful alternative for coupling coefficient tuning over iris machining.

Present Status and Perspectives of RIBF

The RIKEN Radioactive Isotope Beam Factory (RIBF) is a top world-class RIB facility, which was constructed to establish new framework of nuclear physics, to elucidate the origin of elements, and to explore new applications with fast RIBs. To achieve these goals, the RIBF facility consists of a high-power accelerator complex, a large-acceptance in-flight separator and unique devices to cover various experimental programs. As illustrated in Fig. 1, the accelerator complex consists of the old facility and a newly constructed one [1]. The old facility has a K540-MeV ring cyclotron (RRC) and two injectors, a variable-frequency heavy-ion linac (RILAC) and a K70-MeV AVF cyclotron. A new highpower heavy-ion booster system consisting of three ring cyclotrons with K = 570 MeV (fixed frequency, fRC), 980 MeV (intermediate stage, IRC), and 2600 MeV (superconducting, SRC), respectively, boost energies of the RRC beams up to 440 A MeV for light ions and 350 A MeV for very heavy ions. The goal of the primary beam intensity is set to be 1 pμA. At the end of 2006, the first primary beam was successfully accelerated at and extracted from SRC. The new in-flight separator BigRIPS [2] is to convert the SRC primary beams into RIBs. Combination of the high-power accelerator complex and the in-flight separator makes it possible to explore the limit of of nuclei and provides high yield rates of exotic nuclei. The RIBF facility has started delivering RI beams since 2007. In 2007, the first commissioning with a 350A MeV U beam successfully produced and identified two new isotopes, Pd, even with a low intensity of 0.03 pnA [3]. In November 2008, the second attempt to search for new isotopes was performed by utilizing the U beam with a 10 times higher intensity of 0.3 pnA and more than 40 of new isotopes were produced

Development of novel positron emitters for medical applications: nuclear and radiochemical aspects

AbstractIn molecular imaging, the importance of novel longer lived positron emitters, also termed as non-standard or innovative PET radionuclides, has been constantly increasing, especially because they allow studies on slow metabolic processes and in some cases furnish the possibility of quantification of radiation dose in internal radiotherapy. Considerable efforts have been invested worldwide and about 25 positron emitters have been developed. Those efforts relate to interdisciplinary studies dealing with basic nuclear data, high current charged particle irradiation, efficient radiochemical separation and quality control of the desired radionuclide, and recovery of the enriched target material for reuse. In this review all those aspects are briefly discussed, with particular reference to three radionuclides, namely64Cu,124I and86Y, which are presently in great demand. For each radionuclide several nuclear routes were investigated but the (p,n) reaction on an enriched target isotope was found to be the best for use at a small-sized cyclotron. Some other positron emitting radionuclides, such as55Co,76Br,89Zr,82mRb,94mTc,120I,etc., were also producedviathe low-energy (p,n), (p,α) or (d,n) reaction. On the other hand, the production of radionuclides52Fe,73Se,83Sr,etc.using intermediate energy (p,xn) or (d,xn) reactions needs special consideration, the nuclear data and chemical processing methods being of key importance. In a few special cases, a high intensity3He- orα-particle beam could be an added advantage. The production of some potentially interesting positron emittersviagenerator systems, for example44Ti/44Sc,72Se/72As and140N d/140Pr is considered. The significance of new generation high power accelerators is briefly discussed.

ILU-14 industrial electron linear accelerator with a modular structure

A new high-power (up to 100 kW) industrial electron linear accelerator ILU-14 for energies of 7.5–10.0 MeV has been developed by the Budker Institute of Nuclear Physics. The operating frequency of the accelerator is 176 MHz, and the total efficiency is 26%. Owing to the modular structure of the accelerator, the electron energy and the beam power can be varied within certain limits by changing the modular arrangement. A 5-MeV prototype of this accelerator has been produced and successfully tested. Its design parameters verified in the experiments are as follows: the beam current averaged over the RF period is 600 mA, the beam pulse power is 2.5 MW, and the electron efficiency of the accelerating structure is 68%. By applying an additional RF voltage to the electron gun cathode-grid gap, a 96% transmittance of the beam current has been attained at a minor beam energy spread. The prototype of the ILU-14 accelerator can be used as an accelerator with a beam power of 50 kW.

An air scintillator

A method for bremsstrahlung dosimetry by air luminescence at high-power pulsed electron accelerators is considered. Light emitted in an air scintillator is focused by the lens at the tip of a quartz optical fiber and transmitted to the photocathode of a photomultiplier tube. The sensitivity of the measuring channel is determined using a standard ribbon lamp. Bremsstrahlung pulses producing an exposure of 0.18 C/kg at the bremsstrahlung beam axis in a ∼20-ns time interval are detected at the ЛИУ-30 electron accelerator with a high accuracy. This exposure corresponds to an absorbed dose rate, integrated over the beam diameter, of 7.5 × 107 Gy m/s.

Ionizing wave via high-power HF acceleration

Recent ionospheric modification experiments with the 3.6 MW transmitter at the High Frequency Active Auroral Research Program (HAARP) facility in Alaska led to discovery of artificial ionization descending from the nominal interaction altitude in the background F-region ionosphere by ~60 km. This paper presents a physical model of an ionizing wavefront created by suprathermal electrons accelerated by the HF-excited plasma turbulence.

三阴极强流加速器研制

三阴极强流加速器研制

Multipactoring suppression by fine grooving of conductor surfaces of coaxial-line input couplers for high beam current storage rings

Input couplers for radio-frequency accelerating cavities with heavy beam loading undergo many multipactoring zones due to the wide range of input powers. Furthermore, regular coaxial lines have more multipactoring than rectangular waveguides because of more uniformity of the electromagnetic field. Grooving conductor surfaces of coaxial lines is expected to be a promising method for suppressing multipactoring under any conditions with heavy beam loading. In this paper, we present a method for designing practical fine grooves on conductor surfaces of coaxial lines to suppress multipactoring, based on multipactoring zone maps, and demonstrate the suppressive power both in high-power tests and accelerator operations.

Studies of dual-harmonic acceleration at CSNS- II

The Rapid Cycling Synchrotron RCS) of the China Spallation Neutron Source (CSNS) complex is designed to provide 1.56×1013 protons per pulse (ppp) during the initial stage, and it is upgradeable to 3.12×1013 ppp during the second stage and 6.24×1013 ppp during the ultimate stage. The high beam intensity in the RCS requires alleviation of space charge effects to reduce beam losses, which is key in such high beam power accelerators. With higher intensities in the upgrading phases, a dual-harmonic RF system is planned to produce flat-topped bunches that are useful to reduce the space charge effects. We have studied different schemes to apply the dual-harmonic acceleration in CSNS- II, and have calculated the main parameters of the RF systems, which are presented in this paper.

Analyses of high power negative ion accelerators for ITER neutral beam injector (invited)

In JAEA, research and developments to realize high power accelerator (1 MeV, 40 AD(-) ion beams for 3600 s) for ITER have been carried out experimentally and numerically utilizing a five stage MAMuG (Multiaperture, Multigrid) accelerator. In this paper, the extension of the gap length, which is required to improve the voltage holding capability, is examined in two dimensional beam optics analyses and also from view point of stripping loss of ions. In order to suppress excess power loadings due to the direct interception of negative ions, which is issued in long pulse tests, the beamlet deflection is analyzed in three dimensional multibeamlet analyses. The necessary modifications shown above are applied to the MAMuG accelerator for coming long pulse tests in JAEA and ITER.

Review on high current 2.45 GHz electron cyclotron resonance sources (invited)

The suitable source for the production of intense beams for high power accelerators must obey to the request of high brightness, stability, and reliability. The 2.45 GHz off-resonance microwave discharge sources are the ideal device to generate the requested beams, as they produce multimilliampere beams of protons, deuterons, and monocharged ions, remaining stable for several weeks without maintenance. A description of different technical designs will be given, analyzing their strength, and weakness, with regard to the extraction system and low energy beam transport line, as the presence of beam halo is detrimental for the accelerator.

Simulation of the Residual Activity Induced by High-Energy Heavy Ions

Quantification of residual activity is an important issue for high-power accelerator facilities like the Facility for Antiprotons and Ion Research (FAIR). While beam losses of 1 W/m are at present accepted for proton machines as a tolerable level for ensuring “hands-on” maintenance, the beam-loss tolerances for high-energy heavy-ion accelerators have not yet been quantified. The Monte Carlo particle transport codes FLUKA and SHIELD were used to simulate the irradiation of copper and stainless steel by different ions (1H, 4He, 12C, 20Ne, 40Ar, 84Kr, 132Xe, 197Au, and 238U) with energies typical for FAIR machines. Copper and stainless steel were chosen as common materials for accelerator structures. The isotope inventory contributing >90% to the total residual activity does not depend on the projectile species; it depends only on the target material and projectile energy. The activity per watt induced by a 1 GeV/u heavy ion is lower than the activity per watt induced by a 1-GeV proton. A tolerable beam-loss level for a 1 GeV/u 238U beam was found to be ˜5 W/m.