Narrowing of the electron energy spectrum in the ILU-10 accelerator

Results of numerical and experimental investigations of electron energy spectrum narrowing by applying an external boosting HF voltage to the grid-cathode gap of a triode HF gun in the ILU-10 single-cavity pulsed accelerator (electron energy, 5 MeV; mean beam power, 50 kW; operating frequency, 116.3 MHz) are described. These results showed that, without a booster HF voltage, 62% of the beam power is within 5% of the energy spread and, after a booster voltage of the operating frequency is applied, as much as 74% of the beam power falls within these limits. Finally, at a booster voltage of the third harmonic, 93% of the beam power lies within 5% of the energy spread.     

An ILU-8 pulsed high-frequency electron linear accelerator

An ILU-8 single-cavity electron linear accelerator has been designed for use in industrial radiation technology systems for electron irradiation of materials and products. Experimental data of accelerator adjustment and results of measurements of the accelerated beam parameters in modes characteristic of industrial applications are presented. The main parameters of the accelerator are as follows: the electron energies are 0.7–1.0 MeV and the beam power is 20 kW at an average current of up to 25 mA. The accelerator operates in a pulsed mode: the pulse duration is 800 μs, and the pulse repetition frequency is 50 (60) Hz. The cavity is excited by a single-stage self-excited oscillator based on a GI-50A tube with feedback via the cavity at a frequency of 175.6 MHz. The accelerating cavity, together with a system of beam extraction into the atmosphere, can be located inside the biological shielding composed of steel slabs with a total mass of 76 t.     

A 1.2-MeV Two-Section Continuous Wave Linear Electron Accelerator with 50-mA Average Beam Current

A 1.2-MeV compact two-section continuous wave linear electron accelerator with an average beam current of 50 mA and beam power of 60 kW is described. A simulation of the beam dynamics, accelerating structure, and RF system was carried out. Measured beam parameters are close to the design objectives: 1.15 MeV, 44 mA, and 50.6 kW.     

A Continuous-Wave Linear Accelerator with an Output Electron Energy of 600 keV (Average Beam Current of 50 mA)

We describe a compact continuous-wave linear accelerator for industrial applications with an output electron energy of 600 keV, average beam current of 50 mA, and average beam power of 30 kW. The electron gun, beam dynamics, accelerating structure, and the RF-system design were modeled. After manufacturing, assembling, and tuning, the accelerator was started and the design parameters were achieved.     

Surface plasma source with saddle antenna radio frequency plasma generator

A prototype RF H(-) surface plasma source (SPS) with saddle (SA) RF antenna is developed which will provide better power efficiency for high pulsed and average current, higher brightness with longer lifetime and higher reliability. Several versions of new plasma generators with small AlN discharge chambers and different antennas and magnetic field configurations were tested in the plasma source test stand. A prototype SA SPS was installed in the Spallation Neutron Source (SNS) ion source test stand with a larger, normal-sized SNS AlN chamber that achieved unanalyzed peak currents of up to 67 mA with an apparent efficiency up to 1.6 mA∕kW. Control experiments with H(-) beam produced by SNS SPS with internal and external antennas were conducted. A new version of the RF triggering plasma gun has been designed. A saddle antenna SPS with water cooling is fabricated for high duty factor testing.     

A high-current nanosecond electron accelerator with a semiconductor opening switch

A compact nanosecond electron accelerator with an output energy of up to 4000 keV, a pulsed power of 100–180 MW, a beam current of 0.25–1.1 kA, and a pulse energy of 5–7 J is described. The accelerator operates with a pulse repetition rate of 200 Hz and ensures an average beam power of up to 1 kW. A nanosecond generator with a solid-state switching system, which is based on magnetic stages of pulse compression and a semiconductor opening switch, is used as a supplying device. The design and electric circuit of the accelerator are described, and test results are presented.     

Development of a plasma generator for a long pulse ion source for neutral beam injectors

A plasma generator for a long pulse H(+)/D(+) ion source has been developed. The plasma generator was designed to produce 65 A H(+)/D(+) beams at an energy of 120 keV from an ion extraction area of 12 cm in width and 45 cm in length. Configuration of the plasma generator is a multi-cusp bucket type with SmCo permanent magnets. Dimension of a plasma chamber is 25 cm in width, 59 cm in length, and 32.5 cm in depth. The plasma generator was designed and fabricated at Japan Atomic Energy Agency. Source plasma generation and beam extraction tests for hydrogen coupling with an accelerator of the KSTAR ion source have been performed at the KSTAR neutral beam test stand under the agreement of Japan-Korea collaborative experiment. Spatial uniformity of the source plasma at the extraction region was measured using Langmuir probes and ±7% of the deviation from an averaged ion saturation current density was obtained. A long pulse test of the plasma generation up to 200 s with an arc discharge power of 70 kW has been successfully demonstrated. The arc discharge power satisfies the requirement of the beam production for the KSTAR NBI. A 70 keV, 41 A, 5 s hydrogen ion beam has been extracted with a high arc efficiency of 0.9 -1.1 A/kW at a beam extraction experiment. A deuteron yield of 77% was measured even at a low beam current density of 73 mA/cm(2).     

H- radio frequency source development at the Spallation Neutron Source

The Spallation Neutron Source (SNS) now routinely operates nearly 1 MW of beam power on target with a highly persistent ～38 mA peak current in the linac and an availability of ～90%. H(-) beam pulses (～1 ms, 60 Hz) are produced by a Cs-enhanced, multicusp ion source closely coupled with an electrostatic low energy beam transport (LEBT), which focuses the 65 kV beam into a radio frequency quadrupole accelerator. The source plasma is generated by RF excitation (2 MHz, ～60 kW) of a copper antenna that has been encased with a thickness of ～0.7 mm of porcelain enamel and immersed into the plasma chamber. The ion source and LEBT normally have a combined availability of ～99%. Recent increases in duty-factor and RF power have made antenna failures a leading cause of downtime. This report first identifies the physical mechanism of antenna failure from a statistical inspection of ～75 antennas which ran at the SNS, scanning electron microscopy studies of antenna surface, and cross sectional cuts and analysis of calorimetric heating measurements. Failure mitigation efforts are then described which include modifying the antenna geometry and our acceptance∕installation criteria. Progress and status of the development of the SNS external antenna source, a long-term solution to the internal antenna problem, are then discussed. Currently, this source is capable of delivering comparable beam currents to the baseline source to the SNS and, an earlier version, has briefly demonstrated unanalyzed currents up to ～100 mA (1 ms, 60 Hz) on the test stand. In particular, this paper discusses plasma ignition (dc and RF plasma guns), antenna reliability, magnet overheating, and insufficient beam persistence.     

AУPT-1M accelerator for radiation technologies

AУPT-1M modernized electron accelerator with an accelerating voltage up to 1 MV, a 1-kW electron beam power, and a 100-ns pulse duration is described. As compared to the prototype (УPT-1 accelerator), the layout of assemblies is changed in it, allowing one to place it in rooms with heights up to 2.5 m. It uses Murata capacitors and a ТQPи1–10k/75 thyratron with a cold cathode for switching. The computer-aided parameter-monitoring system is created. A metal-ceramic cathode consisting of several elements with ～15% nonuniform current density distribution of the electron beam on the exit foil was used to obtain an electron beam with a width of up to 400 mm. The accelerator can be used in radiation technologies in layers with a thickness of up to 0.3 g/cm².     

Complex diagnostics of a high-current accelerator during generation of high-power bremsstrahlung

A diagnostic system has been developed for the YHH-10 high-current electron accelerator with a beam current of ≤ 60 kA, an electron energy of ≤4 MeV, and a pulse duration of ≤80 ns. The X-ray diagnostic method is used in the diagnostic system to determine the energy of accelerated electrons at the entrance into the converter target. A measuring transducer of the electron energy is based on determining the static transfer characteristic of the converter target, which relates (under the known conditions) the energy of accelerated electrons to the beam current and the dose rate at a selected point of the bremsstrahlung field on the electron beam transport axis. Physically, the transducer is located in the target unit of the accelerator.     

Linear induction accelerators made from pulse-line cavities with external pulse injection

Two types of linear induction accelerator have been reported previously. In one, unidirectional voltage pulses are generated outside the accelerator and injected into the accelerator cavity modules, which contain ferromagnetic material to reduce energy losses in the form of currents induced, in parallel with the beam, in the cavity structure. In the other type, the accelerator cavity modules are themselves pulse-forming lines with energy storage and switches; parallel current losses are made zero by the use of circuits that generate bidirectional acceleration waveforms with a zero voltage-time integral. In a third type of design described here, the cavities are externally driven, and 100% efficient coupling of energy to the beam is obtained by designing the external pulse generators to produce bidirectional voltage waveforms with zero voltage-time integral. A design for such a pulse generator is described that is itself one hundred percent efficient and which is well suited to existing pulse power techniques. Two accelerator cavity designs are described that can couple the pulse from such a generator to the beam; one of these designs provides voltage doubling. Comparison is made between the accelerating gradients that can be obtained with this and the preceding types of induction accelerator.     

First neutral beam injection experiments on KSTAR tokamak

The first neutral beam (NB) injection system of the Korea Superconducting Tokamak Advanced Research (KSTAR) tokamak was partially completed in 2010 with only 1∕3 of its full design capability, and NB heating experiments were carried out during the 2010 KSTAR operation campaign. The ion source is composed of a JAEA bucket plasma generator and a KAERI large multi-aperture accelerator assembly, which is designed to deliver a 1.5 MW, NB power of deuterium at 95 keV. Before the beam injection experiments, discharge, and beam extraction characteristics of the ion source were investigated. The ion source has good beam optics in a broad range of beam perveance. The optimum perveance is 1.1-1.3 μP, and the minimum beam divergence angle measured by the Doppler shift spectroscopy is 0.8°. The ion species ratio is D(+):D(2)(+):D(3)(+) = 75:20:5 at beam current density of 85 mA/cm(2). The arc efficiency is more than 1.0 A∕kW. In the 2010 KSTAR campaign, a deuterium NB power of 0.7-1.5 MW was successfully injected into the KSTAR plasma with a beam energy of 70-90 keV. L-H transitions were observed within a wide range of beam powers relative to a threshold value. The edge pedestal formation in the T(i) and T(e) profiles was verified through CES and electron cyclotron emission diagnostics. In every deuterium NB injection, a burst of D-D neutrons was recorded, and increases in the ion temperature and plasma stored energy were found.     

Status of the plasma generator of the superconducting proton linac

In the framework of the superconducting proton linac (SPL) study at CERN, a new non-cesiated H(-) plasma generator driven by an external 2 MHz RF antenna has been developed and successfully operated at repetition rates of 50 Hz, pulse lengths of up to 3 ms, and average RF powers of up to 3 kW. The coupling efficiency of RF power into the plasma was determined by the cooling water temperatures and the analysis of the RF forward and reflected power and the antenna current and amounts to 50%-60%. The plasma resistance increases between 10 kW and 40 kW RF power from about 0.45 Ω to 0.65 Ω. Measurements of RF power dissipated in the ferrites and the magnets on a test bench show a 5-fold decrease of the power losses for the magnets when they are contained in a Cu box, thus validating the strategy of shielding the magnets with a high electrical conductivity material. An air cooling system was installed in the SPL plasma generator to control the temperatures of the ferrites despite hysteresis losses of several Watts.     

Simulations of slow positron production using a low-energy electron accelerator

Monte Carlo simulations of slow positron production via energetic electron interaction with a solid target have been performed. The aim of the simulations was to determine the expected slow positron beam intensity from a low-energy, high-current electron accelerator. By simulating (a) the fast positron production from a tantalum electron-positron converter and (b) the positron depth deposition profile in a tungsten moderator, the slow positron production probability per incident electron was estimated. Normalizing the calculated result to the measured slow positron yield at the present AIST linear accelerator, the expected slow positron yield as a function of energy was determined. For an electron beam energy of 5 MeV (10 MeV) and current 240 μA (30 μA), production of a slow positron beam of intensity 5 × 10(6) s(-1) is predicted. The simulation also calculates the average energy deposited in the converter per electron, allowing an estimate of the beam heating at a given electron energy and current. For low-energy, high-current operation the maximum obtainable positron beam intensity will be limited by this beam heating.     

Performance and operation of advanced superconducting electron cyclotron resonance ion source SECRAL at 24 GHz

SECRAL (superconducting ECR ion source with advanced design in Lanzhou) ion source has been in routine operation for Heavy Ion Research Facility in Lanzhou (HIRFL) accelerator complex since May 2007. To further enhance the SECRAL performance in order to satisfy the increasing demand for intensive highly charged ion beams, 3-5 kW high power 24 GHz single frequency and 24 GHz +18 GHz double frequency with an aluminum plasma chamber were tested, and some exciting results were produced with quite a few new record highly charged ion beam intensities, such as (129)Xe(35+) of 64 eμA, (129)Xe(42+) of 3 eμA, (209)Bi(41+) of 50 eμA, (209)Bi(50+) of 4.3 eμA and (209)Bi(54+) of 0.2 eμA. In most cases SECRAL is operated at 18 GHz to deliver highly charged heavy ion beams for the HIRFL accelerator, only for those very high charge states and very heavy ion beams such as (209)Bi(36+) and (209)Bi(41+), SECRAL has been operated at 24 GHz. The total operation beam time provided by SECRAL up to July 2011 has exceeded 7720 hours. In this paper, the latest performance, development, and operation status of SECRAL ion source are presented. The latest results and reliable long-term operation for the HIRFL accelerator have demonstrated that SECRAL performance for production of highly charged heavy ion beams remains improving at higher RF power with optimized tuning.     

A high-current subnanosecond electron accelerator with a gas-filled former

A subnanosecond electron accelerator prototype based on the ARSA small-size accelerator with a gas-filled former (nitrogen ~4 MPa) has been developed and studied. The operation principle of the former involves charging of a short storage line and its discharge to a stepped line with an accelerating tube that generates electrons. The recorded electron-beam current pulse length was t_0.5 = 0.3 ns, the current amplitude was at least 1.5 kA, and the maximum electron energy was ~850 keV.     

Design and tuning of a 40-MeV electron linear accelerator

The 40-MeV electron linear accelerator RELUS-6 with a 100-mA pulse current has been designed. The standing wave accelerator with a biperiodic accelerating structure is composed of four sections and is powered from two 6-MW pulse klystrons. The operating frequency is 2856 MHz. The total length of the accelerating structure is 2.73 m. Calculations have been performed with the aim of selecting the lengths of the first three cells in the first accelerating section and the values of the accelerating field in them, so that the width of the energy spectrum at the end of the accelerator is 2%. The geometry of the accelerating structure and the power input cells has been designed. Four accelerating structures have been manufactured based on the simulation results. The structures have been tuned to the operating frequency, the predetermined accelerating field distribution, and a fixed coupling between the feed waveguide and the accelerating section.     

High power solid state rf amplifier for proton accelerator

A 1.5 kW solid state rf amplifier at 352 MHz has been developed and tested at RRCAT. This rf source for cw operation will be used as a part of rf system of 100 MeV proton linear accelerator. A rf power of 1.5 kW has been achieved by combining output power from eight 220 W rf amplifier modules. Amplifier modules, eight-way power combiner and divider, and directional coupler were designed indigenously for this development. High efficiency, ease of fabrication, and low cost are the main features of this design.     

基于SiC器件的高效率功率因数校正电源研究

针对传统有桥Boost功率因数校正电路效率不高的问题,分析了Boost功率因数校正电路的基本结构以及控制方法,Si C器件的特点和发展历程,提出了使用Si C器件来提升其功率密度的方案。介绍了功率因数校正电路中重要参数的设计,简述了一种适用于PFC功率电感的设计方法以及主要设计步骤,并分析了传统有桥功率因数校正电路的损耗分布情况。选取了数家公司生产的不同材料的MOSFET,搭建了对应的1.2 kW实验样机,并测量了各个样机效率。研究结果表明,在115 V交流输入下,相比infineon公司最新的具有超结结构的Cool MOS,ROHM公司的大电流Si MOSFET,使用SiC MOSFET能够提升有桥功率因数电路的工作效率。     

A High-Current Nanosecond Electron Accelerator with Inductive Energy Storage

A nanosecond electron accelerator with an output energy as great as 600 keV, a beam current of 16 kA, and an accelerating voltage half-height duration of ～180 ns is described. The accelerator is based on an inductive energy storage composed of two coils. A wire explosive current chopper is used in the inductive storage as a release. The circuit diagram of the accelerator is shown, the design for the accelerator is described, and results from its testing are presented.