Beam Acceleration Tests Research Articles

Superconducting Linac Booster for Super-Heavy Element Experiments at RIKEN Radioactive Isotope Beam Factory

The Rikagaku Kenkyūjo (RIKEN) heavy-ion linac was upgraded by introducing a new super-conducting linac-booster to advance the super-heavy elements synthesis program beyond nihonium at the RIKEN Radioactive Isotope Beam Factory (RIBF). The total acceleration voltage was upgraded from 25 MV with 12 room temperature drift-tube-linacs (DTLs) to 39 MV by introducing a superconducting linac booster, SRILAC. The upgrade of the beam intensity is realized by a newly constructed superconducting electron-cyclotron resonance ion source (SC-ECRIS). The construction of SRILAC and the SC-ECRIS started in FY2017. After the hardware installation and commissioning, the first beam acceleration test was successfully conducted at the end of FY2019, and user beam service was started in FY2020. This article provides an overview of the upgrade and its present performance.

High Power Density Beam Measurement of a Single Beamlet Multi-Grid Prototype H- Negative Ion Accelerator

Beam optics of the ITER prototype accelerator with 88 mm acceleration gap length has been examined through H- beam acceleration tests at the ITER target beam perveance. The beam optics has been examined for beam energies up to 790 keV under the ITER target perveance. The total grid heat load was successfully reduced to 10 %, which was lower than the allowable value of 15 %. The beam emittance of the ITER perveance has been measured for the first time by using newly developed emittance measurement system consisting of carbon-fiber-composite (CFC) plate with pin-holes. The emittance of 790 keV H- beam shows the divergence angle of the beam core is satisfied with the ITER requirement of <7 mrad. Measurement at the beam periphery was made possible by modifying the pin-hole size of pepper-pot apertures, and the observed divergent components were 20 mrad. The ratio of the diverged beam became lower with the increase of the beam energy. This result contributes the design of the ITER accelerator and the beam line components.

Commercialization of an S-band standing-wave electron accelerator for industrial applications

An electron accelerator system has been developed for use in industrial, as well as possible medical, applications. Based on our experiences achieved during prototype system development and various electron beam acceleration tests, we have built a stable and compact system for sales purposes. We have integrated a self-developed accelerating cavity, an E-gun pulse driver, a radio-frequency (RF) power system, a vacuum system, a cooling system, etc. into a frame with a size of 1800 × 1000 × 1500 mm3. The accelerating structure is a side-coupled standing-wave type operating in the π/2 mode (tuned to~3 GHz). The RF power is provided by using a magnetron driven by a solid-state modulator. The electron gun is a triode type with a dispenser cathode (diameter of 11 mm). The system is capable of delivering a maximum 900-W average electron beam power with tight focusing at the target. Until now, we have performed various electron beam tests and X-ray beam tests after having built the system, have completed the beam assessment for commercializations, and have been preparing full-fledged sales activity. This article reports on our system development processes and on some of our early test results for commercializations.

Development of C⁶⁺ laser ion source and RFQ linac for carbon ion radiotherapy.

A prototype C(6+) injector using a laser ion source has been developed for a compact synchrotron dedicated to carbon ion radiotherapy. The injector consists of a laser ion source and a 4-vane radio-frequency quadrupole (RFQ) linac. Ion beams are extracted from plasma and directly injected into the RFQ. A solenoid guides the low-energy beams into the RFQ. The RFQ is designed to accelerate high-intensity pulsed beams. A structure of monolithic vanes and cavities is adopted to reduce its power consumption. In beam acceleration tests, a solenoidal magnetic field set between the laser ion source and the RFQ helped increase both the peak currents before and after the RFQ by a factor of 4.

Development of high intensity linear accelerator for heavy ion inertial fusion driver

In order to verify the direct plasma injection scheme (DPIS), an acceleration test was carried out in 2001 using a radio frequency quadrupole (RFQ) heavy ion linear accelerator (linac) and a CO2-laser ion source (LIS) (Okamura et al., 2002) [1]. The accelerated carbon beam was observed successfully and the obtained current was 9.22mA for C4+. To confirm the capability of the DPIS, we succeeded in accelerating 60mA carbon ions with the DPIS in 2004 (Okamura et al., 2004; Kashiwagi and Hattori, 2004) [2,3]. We have studied a multi-beam type RFQ with an interdigital-H (IH) cavity that has a power-efficient structure in the low energy region. We designed and manufactured a two-beam type RFQ linac as a prototype for the multi-beam type linac; the beam acceleration test of carbon beams showed that it successfully accelerated from 5keV/u up to 60keV/u with an output current of 108mA (2×54mA/channel) (Ishibashi et al., 2011) [4]. We believe that the acceleration techniques of DPIS and the multi-beam type IH-RFQ linac are technical breakthroughs for heavy-ion inertial confinement fusion (HIF). The conceptual design of the RF linac with these techniques for HIF is studied. New accelerator-systems using these techniques for the HIF basic experiment are being designed to accelerate 400mA carbon ions using four-beam type IH-RFQ linacs with DPIS. A model with a four-beam acceleration cavity was designed and manufactured to establish the proof of principle (PoP) of the accelerator.

Multiple-energy operation with extended flattops at HIMAC

Multiple-energy operation with extended flattops for synchrotron accelerators is being developed at HIMAC. This operation uses synchrotron operation-patterns having a stepwise flattop. With these patterns, a beam would be initially accelerated to the maximum energy, and then successively decelerated to lower energies. Having extended the flattops and extracted beams during these flattops, heavy ions with various energies can be provided in a single synchrotron cycle. Since the extraction energy can be quickly changed by the accelerator, itself, no energy degrader will be required to control the depth dose-distribution. By applying this multiple-energy operation to our fast raster-scanning irradiation, we can considerably reduce the total irradiation time, and concurrently obtain excellent depth dose-distributions. Beam acceleration and extraction tests using this operation were made. Successful results of the tests proved the effectiveness of this multiple-energy operation with extended flattops in heavy-ion therapy.

Achievement and improvement of the JT-60U negative ion source for JT-60 Super Advanced (invited)

Developments of the large negative ion source have been progressed in the high-energy, high-power, and long-pulse neutral beam injector for JT-60 Super Advanced. Countermeasures have been studied and tested for critical issues of grid heat load and voltage holding capability. As for the heat load of the acceleration grids, direct interception of D- ions was reduced by adjusting the beamlet steering. As a result, the heat load was reduced below an allowable level for long-pulse injections. As for the voltage holding capability, local electric field was mitigated by tuning gap lengths between large-area acceleration grids in the accelerator. As a result, the voltage holding capability was improved up to the rated value of 500 kV. To investigate the voltage holding capability during beam acceleration, the beam acceleration test is ongoing with new extended gap.

Superconductivity and cryogenics for linear accelerator programme at IUAC, New Delhi

The Inter-University Accelerator Center, New Delhi is involved in commissioning a superconducting linear accelerator (LINAC) as a booster to its existing 15 UD Pelletron accelerator. The booster consists of three LINAC modules, each containing eight superconducting Nb quarter wave resonators and a superconducting solenoid magnet. The first LINAC module preceded by a superbuncher with one cavity and followed by a rebuncher cryostat with two cavities was installed in 0° beam line of Pelletron and has been under operation for some time at the Center. The module is integrated with a liquid helium (LHe) refrigerator through a cryogen valve box and the distribution line. The performance tests of each component like the RF cavity, the cryomodule and the liquid helium distribution line were carried out independently prior to the beam acceleration test. After having many trial runs on this integrated cryonetwork system, beam acceleration tests were performed during 2007. The energy of silicon beam with charge state of +10 has been enhanced approximately from 130MeV to 158MeV using the first module with seven effective cavities and the accelerated beam was delivered at user’s scattering chamber. The present paper highlights the performance of the first module producing an accelerating beam duly bunched in the rebuncher. The performance of first LINAC cryomodule along with problems and the solution associated with the cryogenic system and the cavities encountered during the beam runs are presented in this paper.

Effects of voltage errors caused by gap-voltage and automatic-frequency tuning in an alternating-phase-focused linac

A compact injector for a heavy-ion medical-accelerator complex was developed. It consists of an electron-cyclotron-resonance ion-source (ECRIS) and two linacs, which are a radio-frequency-quadrupole (RFQ) linac and an Interdigital H-mode drift-tube-linac (IH-DTL). Beam acceleration tests of the compact injector were performed, and the designed beam quality was verified by the measured results, as reported earlier. Because the method of alternating-phase-focusing (APF) was used for beam focusing of the IH-DTL, the motion of beam ions would be sensitive to gap-voltage errors, caused during tuning of the gap-voltage distribution and by automatic-frequency tuning in actual operation. To study the effects of voltage errors to beam quality, further measurements were performed during acceleration tests. In this report, the effects of voltage errors for the APF IH-DTL are discussed.

Acceleration of ampere class H− ion beam by MeV accelerator

The H(-) ion accelerator R&D to realize the international thermonuclear experimental reactor neutral beam is ongoing at Japan Atomic Energy Agency (JAEA). The required performance for the prototype MeV accelerator developed at JAEA is 1 MeV, 500 mA (current density of 200 A/m(2)) H(-) ion beam at the beamlet divergence angle of less than 7 mrad. Up to 2005, 836 keV, 146 A/m(2) H(-) ion beam was successfully accelerated as the highest record of the current density at MeV class energy beams. In the present work, high current negative ion beam acceleration test was performed by increasing the beam extraction apertures from 3 x 3 (9 apertures) to 3 x 5 (15 apertures). By fixing the air leak at the source chamber due to backstream ions as well as the improvement of voltage holding capability by a new fiber reinforced plastic insulator ring, the performance of the MeV accelerator was improved. So far, H(-) ion beam of 320 mA was successfully accelerated up to 796 keV with the beam divergence angle of 5.5 mrad. The accelerated drain current including the electron reaches close to the power supply limit for the MeV test facility. The heat flux by the backstream ion during the above beam acceleration was estimated to be 360 W/cm(2). The Cs leakage to the accelerator during the test campaign (Cs total input of 5.0 g) was 0.26 mg (7.0 microg/cm(2)). This is considered to be the allowable level from the viewpoint of voltage holding.

33.7 MHz heavy-ion radio frequency quadrupole linac at VECC Kolkata

A 33.7 MHz heavy-ion radio frequency quadrupole (RFQ) linear accelerator has been designed, built, and tested. It is a four-rod-type RFQ designed for acceleration of 1.38 keVu, qA> or =116 ions to about 29 keVu. Transmission efficiencies of about 85% and 80% have been measured for the unanalyzed and analyzed beams, respectively, of oxygen ((16)O(2+), (16)O(3+), (16)O(4+)), nitrogen ((14)N(3+), (14)N(4+)), and argon ((40)Ar(4+)). The system design and measurements along with results of beam acceleration test will be presented.

Performance of a compact injector for heavy-ion medical accelerators

A compact injector, designed for a heavy-ion medical accelerator complex, was constructed. It consists of an Electron-Cyclotron-Resonance Ion-Source (ECRIS) and two linacs, which are a Radio-Frequency-Quadrupole linac and an Interdigital H-mode Drift-Tube-Linac (IH-DTL) having the same operating frequency of 200 MHz. For beam focusing of the IH-DTL, the method of Alternating-Phase-Focusing (APF) was employed. The compact injector can accelerate heavy ions having a charge-to-mass ratio of q m = 1 3 up to 4.0 MeV / u . Use of the APF IH-DTL and operating frequency of 200 MHz allowed us to design compact linacs; the total length of the two linacs is less than 6 m. Beam-acceleration tests of the compact injector system were performed. The measured intensity of accelerated C 4 + 12 beams with the compact injector was 380 e μ A . Beam transmission of the APF IH-DTL was estimated to be as high as 96%, which is comparable to the value calculated by a simulation code. Transverse phase-space and energy distributions of accelerated beams were measured and compared with those calculated by the simulation code, and we found that they were agreed well with each other.

Superconducting RFQs

At INFN-Legnaro the heavy ion injector PIAVE, based on two superconducting RFQ and eight quarter wave resonators (QWR), is at an advanced stage of beam commissioning. The RFQs (SRFQ1 and SRFQ2), built in full Nb within a stiffening Ti jacket, are 0.8 m in diameter and 1.4 and 0.8 m long respectively, with a resonant frequency of 80 MHz. The PIAVE beam is bunched by a normal conducting 3-harmonic buncher upstream the SRFQs. The SRFQs are specified to work at a peak surface field of 25.5 MV/m, a value which was exceeded in the test phase and has been recently confirmed in on-line tests. Phase and amplitude locking, versus both microphonics and pressure variations of the liquid helium bath, is the main issue. Since November 2004, the two SRFQs have been used quite extensively, for beam acceleration tests in PIAVE, showing a high degree of reliability. A 16O 3+ pilot beam, received from an ECR ion source located on a high voltage platform, was used in the tests. The typical ion beam current was a few hundreds nA, even though it could be raised up to a few μA without any inconveniences. Beam tests with 132Xe 18+ were made too. The paper reports the more recent results of on-line SRFQ tests and beam operation.

Flattop acceleration system in the RIKEN AVF cyclotron

A flattop acceleration system has been developed and installed in the RIKEN Azimuthally Varying Field (AVF) cyclotron in order to improve the transmission efficiency and energy spread of beams. The flattop accelerating voltage is generated by a superposition of voltages of the fundamental and third harmonics on the dee, by attaching an additional resonator capacitively coupled to the main resonator. The flattop voltage could be generated from 36 to 63 MHz corresponding to the third harmonic of the operating frequency range of 12–21 MHz. A beam acceleration test was carried out and beam emittance in the longitudinal phase space was measured using a spectrometer. With this flattop system, the single-turn extraction was achieved more easily and the momentum spread was reduced to one-third. The beam transmission efficiency through the AVF cyclotron as well as the RIKEN Ring Cyclotron (RRC) has also been improved.

Development of a continuously variable energy radio frequency quadrupole accelerator for SiC power semiconductor device fabrication

High energy ion implantation is an important process for controlling deep junction conductivity of SiC semiconductor devices. An radio frequency quadraupole (RFQ) accelerator can accelerate high current ions, but the conventional RFQ accelerator is unable to accelerate various ions with different energies. In order to form the box profile with a low number of defects, a high current MeV ion implanter was constructed using a newly designed continuously variable energy RFQ accelerator and high temperature ion implantation chamber. Results of the experiment showed that the resonance frequency varied from 11.7 to 29.3 MHz, so the output beam energy could be changed over a range of about 6.3 times. The results also showed a higher Q-value of over 5000 compared with that of a conventional machine of 1500. Beam acceleration tests were performed using Al ions, and beams were accelerated from 20 to 750 keV using an radio frequency power of 15 kW. The ions were implanted into 4H-SiC, and the projected ranged was 0.76 μm measured by secondary ion mass spectroscopy.

The electron accelerator Ridgetron for industrial irradiation

A compact electron accelerator, the Ridgetron, with a ridged cavity resonator has been developed for industrial irradiation. It is of a recirculating acceleration type and is intended to have an energy range of 0.5–10 MeV and a beam power of 1–25 kW. The operating frequency is in a VHF band. In this band, a RF amplifier by use of a transmitting tube can be operated in cw mode. A prototype system with an energy of 2.5 MeV and a beam power of 6.5 kW was constructed to confirm the feasibility. The beam acceleration test with a low current beam was performed in the pulse mode operation.

Acceleration of heavy ions by the JAERI tandem superconducting booster

An independently phased heavy ion linac composed of 46 superconducting quarter wave resonators has been built as a booster for the tandem accelerator at Japan Atomic Energy Research Institute, Tokai. Several kinds of heavy ions from Si to Au have been accelerated. The performances of the resonators and the cryogenic system, the method of setting resonator phases and the results of the beam acceleration tests are described.

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.

Initial Operation of the Argonne Superconducting Heavy-Ion Linac

Initial operation and recent development of the Argonne superconducting heavy-ion linac are discussed. The linac has been developed in order to demonstrate a cost-effective means of extending the performance of electrostatic tandem accelerators. The results of beam acceleration tests which began in June '78 are described. At present 7 of a planned array of 22 resonators are operating on-line, and the linac system provides an effective accelerating potential of 7.5 MV. Although some technical problems remain, the level of performance and reliability is sufficient that appreciable beam time is becoming available to users.