Heavy-ion Radio Frequency Quadrupole Research Articles

Development of the heavy ion RFQ for CAFE2

A radio frequency quadrupole (RFQ) accelerator which accelerates particles with a mass-to-charge ratio up to 3 to over 1.33 MeV/u was developed. This RFQ was designed based on the existing 162.5 MHz solid-state power sources of the Chinese Accelerator Driven System (C-ADS) injector II. The frequency is relatively high to a heavy ion RFQ which means a weak transverse focusing strength and brings challenges to the beam loss and quality control. The average radius r0 of the RFQ was appropriately chosen to make a compromise between the transverse focusing strength and the maximum surface field. The beam dynamics parameters were carefully optimized to improve the quality of the RFQ output beam so that the beam could be well transported in the following superconducting structure. Beam dynamics simulations and an error study have been performed to evaluate the RFQ and a method which is more suitable for the analyses of small acceptance RFQs has been adopted. And the results of the beam commissioning have been proved to agree well with the simulations.

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.

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.

Project of electro-cyclotron resonance ion source test-bench for material investigation

Development of new materials for future energy facilities with higher operating efficiency is a challenging and crucial task. However, full-scale testing of radiation hardness for reactor materials is quite sophisticated and difficult as it requires long session of reactor irradiation; moreover, induced radioactivity considerably complicates further investigation. Ion beam irradiation does not have such a drawback; on the contrary, it has certain advantages. One of them is high speed of defect formation. Therefore, it provides a useful tool for modeling of different radiation damages. Improved understanding of material behavior under high dose irradiation will probably allow to simulate reactor irradiation close to real conditions and to make an adequate estimation of material radiation hardness. Since 2008 in Institute for Theoretical and Experimental Physics, the ion beam irradiation experiments are under development at the heavy ion radio frequency quadrupole linac and very important results are obtained already [T. V. Kulevoy et al., in Proceedings of the International Topical Meeting on Nuclear Research Applications and Utilization of Accelerators, IAEA Vienna, Austria, 2009, http://www.pub.iaea.org/MTCD/publications/PDF/P1433_CD/darasets/papers/ap_p5_07.pdf]. Nevertheless, the new test bench based on electro-cyclotron resonance ion source and high voltage platform is developed. The project of the test bench is presented and discussed.

Design of a CW high charge state heavy ion RFQ for SSC-LINAC

The new linac injector SSC-LINAC has been proposed to replace the existing Separator Sector Cyclotron (SSC). This effort is to improve the beam efficiency of the Heavy Ion Research Facility of Lanzhou (HIRFL). As a key component of the linac, a continuous-wave (CW) mode high charge state heavy ion radio-frequency quadrupole (RFQ) accelerator has been designed. It accelerates ions with the ratio of mass to charge up to 7 from 3.728keV/u to 143keV/u. The requirements of CW mode operation and the transportation of intense beam have been considered as the greatest challenges. The design is based on 238U34+ beams, whose current is 0.5pmA (0.5 particle mili-ampere, which is the measured 17 emA electric current divided by charge state of heavy ions). It achieves the transmission efficiency of 94% with 2508.46mm long vanes in simulation. To improve the transmission efficiency and quality of the beams, the phase advance has been taken into account to analyze the reasons of beam loss and emittance growth. Parametric resonance and beam mismatch have been carefully avoided by adjusting the structure parameters. The parameter-sensitivity of the design is checked by transportation simulations of various input beams. To verify the applicability of machining, the effects of different vane manufacturing methods on beam dynamics are presented in this paper.

Design and development of a radio frequency quadrupole linac postaccelerator for the Variable Energy Cyclotron Center rare ion beam project

A four-rod type heavy-ion radio frequency quadrupole (RFQ) linac has been designed, constructed, and tested for the rare ion beam (RIB) facility project at VECC. Designed for cw operation, this RFQ is the first postaccelerator in the RIB beam line. It will accelerate A/q < or = 14 heavy ions coming from the ion source to the energy of around 100 keV/u for subsequent acceleration in a number of Interdigital H-Linac. Operating at a resonance frequency of 37.83 MHz, maximum intervane voltage of around 54 kV will be needed to achieve the final energy over a vane length of 3.12 m for a power loss of 35 kW. In the first beam tests, transmission efficiency of about 90% was measured at the QQ focus after the RFQ for O(5+) beam. In this article the design of the RFQ including the effect of vane modulation on the rf characteristics and results of beam tests will be presented.

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.

Design of the RFQ and the LINAC postaccelerator for the VEC-RIB facility

The Variable Energy Cyclotron Centre, Calcutta is presently developing an ISOL postaccelerator-type radioactive ion beam (RIB) facility. In this method, the primary reaction products will be ionized in an on-line ECR ion source, isotopically separated to single out the product of interest and then accelerated up to an energy of . For the postacceleration we plan to use a low- heavy-ion radio frequency quadrupole (RFQ) followed by a heavy-ion IH LINAC. The RF structure and beam dynamics design of the RFQ and LINAC will be presented.

Vacuum arc ion source for the ITEP RFQ accelerator

A version of vacuum arc ion source has been developed and constructed at the Institute for Theoretical and Experimental Physics, Moscow, for use with a heavy ion radio frequency quadrupole linac. The source is operated in a pulsed mode with a pulse length from 5 to 120 μs and a repetition rate of from 1/8 to 1 pps. The injection voltage is up to 90 kV depending on the kind of ions being used, and the beam current at the injector output is up to 500 mA. The results described in this article were made at a beam current of from 10 to 100 mA. In order to obtain ions having a charge-to-mass ratio of about 1/60, metals such as Cu, Mo, Ta, W, and Pb were used as the cathode material. Volt-ampere characteristics and charge state distributions were measured. The charge state spectral variation was investigated throughout the arc current pulse duration as well as the dependence of the mean charge state of the beam ions on the melting point of the cathode material.

Superconducting RFQ's in the 100 MeV Range

Superconducting technology may open the door on the radio frequency quadrupole (RFQ) parameter space to yield interesting proton RFQ's to energies as high as 100 MeV and heavy-ion RFQ's to energies as high as 10 MeV/nucleon. This technology would relax a severe power-based constraint on RFQ design, allowing the use of ''larger-than-normal'' modulations in the electrode geometry, resulting in increased electrode spacing, allowing higher voltage excitations, which, in turn, would result in improved acceleration rates at higher velocities. This technology would also offer a sizeable reduction in the required rf power for many designs and would facilitate the possibility of CW operation. Design considerations for superconducting proton and heavyion RFQ systems will be discussed. Several proton and heavy-ion RFQ designs are presented together with an analysis of their performance and suggestions for practical fabrication in a superconducting format.

RFQ Development at LBL

The radio frequency quadrupole (RFQ) is a structure which can efficiently focus, bunch and accelerate low velocity ion beams. It has many features which make it particularly attractive for applications in the biomedical and nuclear sciences. There are two projects in progress at LBL where the incorporation of heavy ion RFQ technology offers substantial benefits: in the upgrade of the Bevatron local injector, and in the design of a dedicated heavy ion medical accelerator. In order to meet the requirements of these two important applications, a 200 MHz RFQ structure has been designed for ions with charge to mass ratios as low as 0.14, and a low RF power scale model has been built and tested. Construction of the high power model has begun. The status of this project is reviewed and a summary of technical specifications given.