Accelerator Beam Current Research Articles

Direct current measurements of the SPIDER beam: a comparison to existing beam diagnostics

For negative ion beam sources there are several methods of measuring the accelerated beam current, most commonly electrical measurements at the power supply and calorimetric measurements. On SPIDER, the ITER Heating Neutral Beam full-scale beam source prototype, electrical measurements at the acceleration grid power supply (AGPS) are complemented by polarizing the diagnostic calorimeter STRIKE to provide an additional electrical measurement of the accelerated current. This is in addition to the calorimetric measurements provided by STRIKE. These diagnostics give differing measurements of the beam current. Exploiting the reduced number of open apertures on SPIDER a new beam diagnostic has been installed to measure the individual beamlet currents directly. The so called Beamlet Current Monitor (BCM) has been used to measure the current of five beamlets during the most recent SPIDER campaign. This work compares the BCM current to the electrical measurements at the AGPS and STRIKE. The average BCM current agrees well with the STRIKE electrical measurements, indicating that the AGPS overestimates the beam current. The individual beamlets are compared to the STRIKE calorimetric measurements, showing similar current trends with the source parameters.

Beam commissioning of the coupled RFQ-SFRFQ cavity

We developed a novel compact structure, called a Coupled RFQ-SFRFQ (CRS), to accelerate a 0.8 MeV helium beam for a materials irradiation project. A high accelerating efficiency was achieved by replacing the accelerating section of the radio frequency quadrupole (RFQ) with a separated-function radio frequency quadrupole (SFRFQ) structure, in a single cavity. Following the electromagnetic simulations, RF measurement of the CRS cavity was performed, including low RF power and high RF power measurement. Recently, beam experiments on the CRS linac indicated that the maximum accelerated beam current could reach 2 mA with an energy of 0.8 MeV and energy spread (FWHM) of 3.1%. The experimental measurement results showed good consistency with the beam dynamics simulations.

POWER SUPPLY SYSTEM FOR THE HELIUM IONS LINAC’S INJECTOR

This paper presents compact power supply system for the helium ion linac’s injector. The system consists of high-voltage modulator, power supplies of cathode filament, solenoid and arc modulator. It is designed on modern semi-conductor base. Using of the designed power supply system allowed to decrease the power consumption and to get rid of spurious capacitances and pickups. As a result of improving the continuous adjustment modulator and high-voltage pulse stabilization scheme, the accelerated beam current has increased twice.

Low-energy beam transport studies supporting the spallation neutron source 1-MW beam operation

The H(-) injector consisting of a cesium enhanced RF-driven ion source and a 2-lens electrostatic low-energy beam transport (LEBT) system supports the spallation neutron source 1 MW beam operation with ∼38 mA beam current in the linac at 60 Hz with a pulse length of up to ∼1.0 ms. In this work, two important issues associated with the low-energy beam transport are discussed: (1) inconsistent dependence of the post-radio frequency quadrupole accelerator beam current on the ion source tilt angle and (2) high power beam losses on the LEBT electrodes under some off-nominal conditions compromising their reliability.

Time structure of an accelerated beam using a radio-frequency quadrupole linac with direct plasma injection scheme

In direct plasma injection scheme, the relation between the ion current from a laser ion source and the accelerated beam current by a radio-frequency quadrupole (RFQ) linac was studied by a series of the following analyses. First, ion current at beam extraction was calculated from measured plasma parameters using a scaling law. Second, the beam emittance at the entrance of acceleration electrode region was evaluated by the simulation of the ion extraction out of the ion source plasma using the result of the first calculation. Last, the accelerated beam current could be reproduced by the simulation of beam acceleration using the results of the second. The second calculation revealed the time variation in the injected beam parameter to the RFQ linac. Then it was proved that the time structure of the accelerated beam was different from that of the injection beam because the degree of the matching between the injected beam emittance and the RFQ acceptance varied with time.

RF Set Point Determination of the PEFP RFQ by Measuring the Beam Current

One of the goals of the Proton Engineering Frontier Project (PEFP) is to construct a 100-MeV proton accelerator. A 3-MeV radio frequency quadrupole (RFQ) has been designed, fabricated and installed and is being tested at the Korea Atomic Energy Research Institute (KAERI) site as a front-end system for the 100-MeV accelerator. The RF power set point should be determined during the initial tests of the RFQ to operate the machine properly. We determined the RF set point by comparing the measured output beam current of the RFQ with the calculated results. By measuring only the accelerated beam current, this method provides a direct method for determining of the RF set point with less ambiguity or complexity compared with other methods. The results showed that the determined set point was about 4 % higher than the designed one.

Development and construction of a neutron beam line for accelerator-based boron neutron capture synovectomy

A potential application of the 10B(n, alpha)7Li nuclear reaction for the treatment of rheumatoid arthritis, termed Boron Neutron Capture Synovectomy (BNCS), is under investigation. In an arthritic joint, the synovial lining becomes inflamed and is a source of great pain and discomfort for the afflicted patient. The goal of BNCS is to ablate the synovium, thereby eliminating the symptoms of the arthritis. A BNCS treatment would consist of an intra-articular injection of boron followed by neutron irradiation of the joint. Monte Carlo radiation transport calculations have been used to develop an accelerator-based epithermal neutron beam line for BNCS treatments. The model includes a moderator/reflector assembly, neutron producing target, target cooling system, and arthritic joint phantom. Single and parallel opposed beam irradiations have been modeled for the human knee, human finger, and rabbit knee joints. Additional reflectors, placed to the side and back of the joint, have been added to the model and have been shown to improve treatment times and skin doses by about a factor of 2. Several neutron-producing charged particle reactions have been examined for BNCS, including the 9Be(p,n) reaction at proton energies of 4 and 3.7 MeV, the 9Be(d,n) reaction at deuteron energies of 1.5 and 2.6 MeV, and the 7Li(p,n) reaction at a proton energy of 2.5 MeV. For an accelerator beam current of 1 mA and synovial boron uptake of 1000 ppm, the time to deliver a therapy dose of 10,000 RBEcGy ranges from 3 to 48 min, depending on the treated joint and the neutron producing charged particle reaction. The whole-body effective dose that a human would incur during a knee treatment has been estimated to be 3.6 rem or 0.75 rem, for 1000 ppm or 19,000 ppm synovial boron uptake, respectively, although the shielding configuration has not yet been optimized. The Monte Carlo design process culminated in the construction, installation, and testing of a dedicated BNCS beam line on the high-current tandem electrostatic accelerator at the Laboratory for Accelerator Beam Applications at the Massachusetts Institute of Technology.

2.45 GHz synchronised polarised electron injection at MAMI

A semiconductor modelocked diode laser has been used to produce picosecond spin-polarised electron bunches from strained GaAsP photocathodes and inject them into MAMI, synchronised to the 2.45 GHz accelerating field. The laser meets the operational requirements of MAMI producing stable electron beams, with a polarisation purity of 72% and a transmission efficiency of 52% at an accelerated beam current of 10.1 μA.

Acceleration of high current heavy ions using a variable energy radio-frequency quadrupole linac and measurement of the input beam emittance

A high current ion beam injection system and a variable energy radio-frequency quadrupole (RFQ) accelerator with an external LC resonance circuit are tested. A four-rod RFQ electrode of 2.3 m length is newly designed to obtain a milliampere class MeV ion beam. To increase accelerated beam current, injected beam emittance into the RFQ is measured and compared with the designed RFQ acceptance. Injected beam emittance tends to increase with the beam current increase. The beam acceleration tests are carried out with a cw rf power supply of 100 kW (10–30 MHz, continuously variable). Results show that the time-averaged beam currents of N+ and Ar2+ are 1.1 mA (0.4 MeV) and 1.03 mA (1.0 MeV), respectively, and that the peak current of these beams is about 5 mA. As representative ion species for fabricating semiconductor devices, P+ and P2+ are accelerated, and the time-averaged beam current of 0.48 mA (0.56 MeV) and 0.28 mA (0.81 MeV) are obtained, respectively. This high current MeV ion implanter has great potential for application to high-dose implantation and high throughput production of semiconductor devices and material surface modifications.

Energy control of the IMPELA TM series of industrial accelerators

Electron accelerator sources of radiation for industrial processes must maintain constant and reproducible irradiation parameters in order to provide satisfactory dose quality assurance. The advanced control system used in AECL's IMPELA TM series of accelerators ensures this by making it possible to decouple the primary accelerator variables, beam energy and beam current. Beam energy is made independent of current by controlling the field amplitude in the standing-wave structure during a relatively long pulse (50–500 μs) and an energy stability similar to that of dc machines is achieved. Experiments with the calibration linac facility at Chalk River show that the beam energy can be held constant to within ± 2% on an absolute basis. This eliminates the requirement for the complex beam analysis after acceleration used on short-pulse linacs. Methods for the measurement of energy at the users site and at the calibration facility are described.

Magnetic properties of CoZr amorphous films prepared by low energy ion beam sputtering

In this paper, magnetic properties of CoZr amorphous films prepared using low-energy ion-beam sputtering are investigated by varying the accelerator voltage and beam current of a single-grid ion-beam sputtering system. It is shown that CoZr films become amorphous with a lower Zr content when the films are prepared with lower accelerator voltage or lower ion-beam current. It is also clarified that the saturation magnetostriction constant of amorphous CoZr film becomes smaller as the Zr content becomes smaller ; a film with a Zr content of approximately 3.3at% has a magnetostriction constant of zero without adding a third element such as Nb, Ta or Re. CoZr amorphous films with a saturation magnetization of more than 1.5T, a coercive force of less than 0.2Oe and a magnetostriction constant of zero could be obtained using low-energy ion-beam sputtering with an accelerator voltage of less than 300V.

Transverse Instabilities in the LIL

In view of a Beam Break Up (BBU) study, we have calculated and identified series of transverse deflecting modes in the S band sections of the LEP Injector Linacs (LIL). In these TW quasi-constant gradient structures with various iris diameters from 18 to 26 mm, only it-modes of the C band of the HEM11, having negative group velocities and phase velocities around c will lead to cumulative BBU. These deflecting ?-modes occur at frequencies in the range from 4558 to 4290 MHz for diameters from 18 to 26 mm. Frequency variation with iris diameter is -15 MHz for each added mm for calculated and measured 0-modes and about twice that value for ?-modes. Levels for starting transverse instabilities have been determined for various accelerated Beam Currents with different pulse widthes.

Performance of the Intense Pulsed Neutron Source Accelerator System

The Intense Pulsed Neutron Source (IPNS) facility has now been operating in a routine way for outside users since November 1, 1981. From that date through December of 1982, the accelerator system was scheduled for neutron science for 4500 hours. During this time the accelerator achieved its short-term goals by delivering about 380,000,000 pulses of beam totaling over 6 × 1020 protons. The changes in equipment and operating practices that evolved during this period of intense running are described. The intensity related instability threshold was increased by a factor of two and the accelerator beam current has been ion source limited. Plans to increase the accelerator intensity are also described. Initial operating results with a new H- ion source are discussed.

Reduction of the Apparent Impedance of Wide Band Accelerating Cavities by RF Feedback

In the CERN SPS proton synchrotron the four accelerating cavities are of the travelling wave structure type. At the 10 GeV/c injection energy the cavities present to the beam an impedance very similar to that of a detuned RLC cavity with the result that strong dipole and quadrupole instabilities occur. The SPS accelerated beam current was limited by the combined action of these two effects to 2.5 X 10/sup 13/ protons which resulted in capture losses increasing with the injected beam intensity. Among the solutions possible for this problem, the RF feedback, which would alleviate both transient beam loading and instability effects, looked to the authors to be the most promising. In such a system the total voltage seen by the beam is reinjected into the feedback cavity via its power amplifier. Without any delay in the system the cavity impedance seen by the beam could be greatly reduced. Unfortunately the long delay in the system severely limits the bandwidth and the RF feedback could hardly correct more than the n = O beam loading component. The authors circumvented this problem by observing that they needed a large gain only in the vicinities of the RF frequencies. Outside these bandsmore » the phase rotation due to the long delay is unimportant if the gain is made low enough. If, in addition, the total delay of the system is made exactly equal to one machine turn, the open loop phase of the feedback system is always zero for each RF frequency. The two ingredients needed to make the RF feedback work for n not too small are therefore a transfer function with comb filter shape and a total delay of one machine turn. In this paper these ingredients are derived.« less

Multistage linear electron acceleration using pulsed transmission lines

A four-stage linear electron accelerator is described which uses pulsed radial transmission lines as the basic accelerating units. An annular electron beam produced by a foilless diode is guided through the accelerator by a strong axial magnetic field. Synchronous firing of the injector and the acccelerating modules is accomplished with self-breaking oil switches. The device has accelerated beam currents of 25 kA to kinetic energies of 9 MV, with 90% current transport efficiency. The average accelerating gradient is 3 MV/m.

A Rotatable Cold Cathode Penning ion Source

A rotatable cold cathode Penning ion source has been designed and is now operating in the Oak Ridge Isochronous Cyclotron (ORIC). Previous sources for positive heavy ions have been severely limited in life-time by cathode sputtering and buildup of sputtered cathode material. The new ion source extends the cathode lifetime by a factor of ~ 6. The source cathodes are discs of tantalum, 7/8 in. in diameter and 3/8 in. thick. Upon completion of an ion source burn at one position on the circular edge of the cathode discs, each disc is rotated to an unused position for the next burn. Provision exists for continuous rotation of the cathodes. The plasma collimating holes, where the sputtered cathode tantalum is deposited, also are on discs with six possible positions. The new source has resulted in increased accelerated beam currents and greater stability for heavy ions. The source has also been used to produce light ion beams (H, D, ?) over a wide range of intensities.

Integrator and meter with low input impedance for accelerator beam current

A current integrator with low input impedance working in the range 10 −8 - 10 −4 A has been designed with solid state operational amplifiers for the measurement of the beam current of a Van de Graaff accelerator. The first part of the integrator can be used as a current meter working in an increased range 10 −9 -10 t-4 A.