Continuous Wave Radio Frequency Quadrupole Research Articles

Physical design and multi-physics analysis of a 200 MHz continuous wave radio frequency quadrupole accelerator for a proton accelerator facility

Based on the platform of a proton accelerator facility, a 200 MHz high intensity continuous wave (CW) radio frequency quadrupole (RFQ) accelerator has been designed at the Sino-French Institute of Nuclear Engineering and Technology of Sun Yat-Sen University, China. Employing the conventional four-vane structure, the RFQ can accelerate 20 mA proton beam from 20 keV to 2.5 MeV. In the beam dynamics design, the simulated transmission efficiency reaches 99.5% and the vane length is less than 4 m. In the electromagnetic design, for the long-term stable operation, Pi-mode Stabilizer Loops (PISLs) are utilized to achieve more than 10 MHz mode frequency separation and to decrease the effects of dipole modes. The 48 tuners are optimized to provide a range of ± 2 MHz frequency tuning. Additionally, the undercuts are optimized to ensure a good field flatness along the longitudinal direction. Based on the coolant channel design, the multi-physics analysis is performed to investigate the deformation and stress resulting from the dissipation of RF power within the cavity, as well as determine the temperature tuning coefficients of the coolants within the vane and wall. The entire design and analysis of PAFA-RFQ has been completed, and the scheme of the design can also be applied to the design of other RFQ cavities.

Beam commissioning and analysis of a continuous-wave window-type deuteron radio-frequency quadrupole

As high-intensity beams are required for various applications, high-power, high-current, continuous-wave (CW) radio-frequency quadrupole (RFQ) accelerators have become a research focus in recent years and also a direction for development in the future. To master and accumulate the advanced technology in design, fabrication and operation of high-current CW RFQs, the RFQ group at Peking University has built a window-type CW RFQ, operating at 162.5[Formula: see text]MHz, to accelerate a 50-mA deuteron beam from 50[Formula: see text]keV to 1[Formula: see text]MeV. It is the first relatively high-frequency window-type CW RFQ in the world. A [Formula: see text] ion beam extracted from an electron cyclotron resonance (ECR) ion source was used for the beam commissioning because deuteron beam acceleration will produce a serious radiation risk. We compared and analyzed the measurement results obtained during the beam commissioning with simulations. The data show good consistency in many respects. For the discrepancies, we explain the issues in detail. We achieved stable and robust acceleration of about 1.5[Formula: see text]mA CW [Formula: see text] for 1[Formula: see text]h. Finally, we discuss the differences between [Formula: see text] ion beam acceleration and deuteron beam acceleration.

Development and beam commissioning of a continuous-wave four-vane heavy ion radio-frequency quadrupole accelerator based on stable operation

Abstract A continuous-wave (CW) heavy ion radio frequency quadrupole (RFQ) accelerator was developed for the Low Energy Accelerator Facility (LEAF) at IMP. The RFQ accelerator is the most effective accelerator for accelerating the low energy high intensity beam, but there are challenges achieving the stable CW operation. This paper presents the development of the LEAF RFQ based on the stable CW operation. In the beam dynamics design, a multi-harmonic buncher is utilized to reduce the longitudinal emittance and the constant-voltage design is applied for low RF power loss. In the radio frequency (RF) design, the constant-voltage four-vane RFQ is selected to reduce the power dissipation. The π -mode stabilizing loop (PISL) is employed to reduce the admixture of the dipole field. In order to ensure the stability of the cavity structure, the multi-physics of the cavity are analysed. The resonant frequency sensitivities of the cooling water temperature are studied to tune the cavity frequency during operation. Through low power test and tuning, the resonance frequency and field distributions are optimized. The beam commissioning ( 4He 1 + , 14N 2 + and 86Kr 13 + ) and some radiation experiments have been performed. The entire processes of the LEAF RFQ development, such as, beam dynamics design, RF design, multi-physics analysis, low power test, high power conditioning, beam commissioning and some radiation experiments, will be detailed presented in this paper. The results of testing and commissioning indicate that the development of the LEAF RFQ has succeeded. And the design scheme for RFQ with stable CW operation in this work can be applied to other future CW RFQs.

Installation of a Four-Vane Radio-Frequency Quadrupole Accelerator for the Rare Isotope Science Project

A radio-frequency quadrupole (RFQ) linear accelerator has been fabricated and installed as the injector for the superconducting linear accelerator of the Rare Isotope Science Project (RISP) to accelerate particles from protons to uranium ions. In this paper, a new continuous-wave (CW) 4-vane RFQ with a low operational frequency of 81.25 MHz and a ramped inter-vane voltage profile was realized. A RFQ with octagonal cross section is composed entirely of oxygen-free electronic (OFE) copper and is fabricated using a three-step brazing process. The cavity length is 5 meters and the diameter is 1 meter. The RFQ consists of nine modules, and the length of each module is 0.56 meter, which was determined in consideration of the facility’s capability. The machining tolerance and the final gaps between vanes were checked using pin gauges and a 3D coordinate measurement system (CMM) as the errors were less than ±30 μm and ±50 μm respectively. The fabrication technology experiences in this work can be applied to future heavy-ion CW RFQs.

RF tuning and beam commissioning of CW RFQ for China-ADS Injector-I

A 325-MHz continuous-wave (CW) four-vane radiofrequency quadrupole (RFQ) is employed in Injector-I of the China Accelerator-Driven Subcritical System. The radiofrequency tuning and beam commissioning were performed from January 2014 to January 2017. In a cold test, a stability study showed that the design of the segmented resonantly coupling and dipole stabilizer rods can shift the harmful quadrupole and dipole mode from the fundamental mode to above 2.6 MHz. We also found a simplified tuning method for the field unflatness, involving changing the inserted length of a few plug tuners. For achieving CW-beam commissioning, two full-size RFQs were constructed successively. The commissioning results indicate that the beam transmission rate decreased by approximately 3% as the normalized field unflatness decreased by 1%. A 10-MeV CW proton beam with an average beam current of 2.1 mA was achieved at the target of Injector-I, and the output beam energy of the RFQ was 3.18 MeV.

CW RFQ design and investigation for multi-charge-state acceleration of radioactive beams from BISOL

A continuous-wave (CW) heavy-ion radio frequency quadrupole (RFQ) has been designed to accelerate radioactive beams from the Beijing Isotope Separation On-Line (BISOL) facility. This RFQ will accelerate high-charge-state ions such as 132Sn21+ from 3 keV/u to 300 keV/u with a vane length of 3.77 m at a frequency of 81.25 MHz. The transmission efficiency reached 98.1% in simulation. The output longitudinal normalized rms emittance is 0.31 keV/u⋅ns. Tolerance analysis shows that this RFQ can handle a wide range of non-ideal beams while retaining a relatively high transmission efficiency and low longitudinal emittance. In order to increase the intensity of the radioactive ion beams (RIB), this RFQ will accelerate multi-charge-state beams simultaneously. In the case of the tin beam (Sn), we have studied the transmission of adjacent charge state beams and multi-charge-state beams in this RFQ. The transmission efficiency and output transverse beam quality of the multi-charge-state beams are close to the results of the single-charge-state beam, but the output longitudinal emittance is larger. For the radio frequency (RF) structural design, we have compared different types of RFQ, including an IH RFQ, a 4-rod RFQ and a 4-vane RFQ. We have selected a 4-vane RFQ design with dipole stablizer rods, due to the considerations of power consumption, the flatness of electric field, cooling convenience and machining efficiency. We have performed full 3D simulations with multi-physics analysis.

RF structure design of the China Material Irradiation Facility RFQ

The radio frequency structure design of the radio frequency quadrupole (RFQ) for the front end of China Material Irradiation Facility (CMIF), which is an accelerator based neutron irradiation facility for fusion reactor material qualification, has been completed. The RFQ is specified to accelerate 10 mA continuous deuteron beams from the energies of 20 keV/u to 1.5 MeV/u within the vane length of 5250 mm. The working frequency of the RFQ is selected to 162.5 MHz and the inter-vane voltage is set to 65 kV. Four-vane cavity type is selected and the cavity structure is designed drawing on the experience of China Initiative Accelerator Driven System (CIADS) Injector II RFQ. In order to reduce the azimuthal asymmetry of the field caused from errors in fabrication and assembly, a frequency separation between the working mode and its nearest dipole mode is reached to 17.66 MHz by utilizing 20 pairs of π-mode stabilizing loops (PISLs) distributed along the longitudinal direction with equal intervals. For the purpose of tuning, 100 slug tuners were introduced to compensate the errors caused by machining and assembly. In order to obtain a homogeneous electrical field distribution along cavity, vane cutbacks are introduced and output endplate is modified. Multi-physics study of the cavity with radio frequency power and water cooling is performed to obtain the water temperature tuning coefficients. Through comparing to the worldwide CW RFQs, it is indicated that the power density of the designed structure is moderate for operation under continuous wave (CW) mode.

Design, fabrication, and beam commissioning of a continuous-wave four-rod rf quadrupole

A new heavy-ion linac within a continuous-wave (CW) 4-rod radio-frequency quadrupole (RFQ) was designed and constructed as the injector for the separated-sector cyclotron (SSC) at the Heavy Ion Research Facility at Lanzhou (HIRFL). In this paper, we present the development of and the beam commissioning results for the 53.667 MHz CW RFQ. In the beam dynamics design, the transverse phase advance at zero current, σ0⊥, is maintained at a relatively high level compared with the longitudinal phase advance (σ0∥) to avoid parametric resonance. A quasi-equipartitioning design strategy was applied to control the emittance growth and beam loss. The installation error of the electrodes was checked using a FARO 3D measurement arm during the manufacturing procedure. This method represents a new approach to measuring the position shifts of electrodes in a laboratory environment and provides information regarding the manufacturing quality. The experimental results of rf measurements exhibited general agreement with the simulation results obtained using CST code. During on-line beam testing of the RFQ, two kinds of ion beams (Ar408+ and O165+) were transported and accelerated to 142.8 keV/u, respectively. These results demonstrate that the SSC-Linac has made a significant progress. And the design scheme and technology experiences developed in this work can be applied to other future CW RFQs.20 MoreReceived 22 May 2015DOI:https://doi.org/10.1103/PhysRevAccelBeams.19.010402This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Physical SystemsAccelerator applicationsPulsed-power acceleratorsAccelerators & Beams

Beam characterization of a new continuous wave radio frequency quadrupole accelerator

A new Continuous Wave (CW) Radio Frequency Quadrupole (RFQ) for the ATLAS (Argonne Tandem Linac Accelerator System) Intensity Upgrade was developed, built and tested at Argonne National Laboratory. We present here a characterization of the RFQ output beam in the longitudinal phase space, as well as a measurement of the transverse beam halo. Measurement results are compared to simulations performed using the beam dynamics code TRACK.

Development and beam test of a continuous wave radio frequency quadrupole accelerator

The front end of any modern ion accelerator includes a radio frequency quadrupole (RFQ). While many pulsed ion linacs successfully operate RFQs, several ion accelerators worldwide have significant difficulties operating continuous wave (CW) RFQs to design specifications. In this paper we describe the development and results of the beam commissioning of a CW RFQ designed and built for the National User Facility: Argonne Tandem Linac Accelerator System (ATLAS). Several innovative ideas were implemented in this CW RFQ. By selecting a multisegment split-coaxial structure, we reached moderate transverse dimensions for a 60.625-MHz resonator and provided a highly stabilized electromagnetic field distribution. The accelerating section of the RFQ occupies approximately 50% of the total length and is based on a trapezoidal vane tip modulation that increased the resonator shunt impedance by 60% in this section as compared to conventional sinusoidal modulation. To form an axially symmetric beam exiting the RFQ, a very short output radial matcher with a length of $0.75\ensuremath{\beta}\ensuremath{\lambda}$ was developed. The RFQ is designed as a 100% oxygen-free electronic (OFE) copper structure and fabricated with a two-step furnace brazing process. The radio frequency (rf) measurements show excellent rf properties for the resonator, with a measured intrinsic $Q$ equal to 94% of the simulated value for OFE copper. An ${\mathrm{O}}^{5+}$ ion beam extracted from an electron cyclotron resonance ion source was used for the RFQ commissioning. In off-line beam testing, we found excellent coincidence of the measured beam parameters with the results of beam dynamics simulations performed using the beam dynamics code TRACK, which was developed at Argonne. These results demonstrate the great success of the RFQ design and fabrication technology developed here, which can be applied to future CW RFQs.

High intensity electron cyclotron resonance proton source for low energy high intensity proton accelerator

Electron cyclotron resonance (ECR) proton source at 50 keV, 50 mA has been designed, developed, and commissioned for the low energy high intensity proton accelerator (LEHIPA). Plasma characterization of this source has been performed. ECR plasma was generated with 400-1100 W of microwave power at 2.45 GHz, with hydrogen as working gas. Microwave was fed in the plasma chamber through quartz window. Plasma density and temperature was studied under various operating conditions, such as microwave power and gas pressure. Langmuir probe was used for plasma characterization using current voltage variation. The typical hydrogen plasma density and electron temperature measured were 7x10(11) cm(-3) and 6 eV, respectively. The total ion beam current of 42 mA was extracted, with three-electrode extraction geometry, at 40 keV of beam energy. The extracted ion current was studied as a function of microwave power and gas pressure. Depending on source pressure and discharge power, more than 30% total gas efficiency was achieved. The optimization of the source is under progress to meet the requirement of long time operation. The source will be used as an injector for continuous wave radio frequency quadrupole, a part of 20 MeV LEHIPA. The required rms normalized emittance of this source is less than 0.2 pi mm mrad. The simulated value of normalized emittance is well within this limit and will be measured shortly. This paper presents the study of plasma parameters, first beam results, and the status of ECR proton source.

Characterization of plasma parameters, first beam results, and status of electron cyclotron resonance source

Electron cyclotron resonance (ECR) plasma source at 50 keV, 30 mA proton current has been designed, fabricated, and assembled. Its plasma study has been done. Plasma chamber was excited with 350 W of microwave power at 2450 MHz, along with nitrogen and hydrogen gases. Microwave power was fed to the plasma chamber through waveguide. Plasma density and electron temperature were studied under various operating conditions, such as magnetic field, gas pressure, and transversal distance. Langmuir probe was used for plasma characterization using current-voltage variation. The nitrogen plasma density calculated was approximately 4.5 x 10(11) cm(-3), and electron temperatures of 3-10 eV (cold) and 45-85 eV (hot) were obtained. The total ion beam current of 2.5 mA was extracted, with two-electrode extraction geometry, at 15 keV beam energy. The optimization of the source is under progress to extract 30 mA proton beam current at 50 keV beam energy, using three-electrode extraction geometry. This source will be used as an injector to continuous wave radio frequency quadrupole, a part of 100 MeV proton linac. The required root-mean-square normalized beam emittance is less than 0.2pi mm mrad. This article presents the study of plasma parameters, first beam results, and status of ECR proton source.