Radio Frequency Quadrupole Research Articles

Radio Frequency Quadrupole for Bunching Electron Beam: Electromagnetic Field, Particle Velocity Range, and Accuracy at 10 GHz

The Radio Frequency Quadrupole (RFQ) accelerator invented by Kapchinskii and Tepliakov can focus, bunch, and accelerate charged-particle beams simultaneously. Typically, it operates at frequencies up to 500 MHz, for low particle velocities ( β ). The first attempt to design cylindrical RFQ for electrons in the GHz region was done using 3 GHz at Frascati in 1990. In this paper, an analytical approximation of the electromagnetic field is given, and linearized in the beam region for a rectangular Electron Radio Frequency Quadrupole (ERFQ). The differences between the proton-RFQ and the electron-RFQ are discussed. Then, it will be shown that contrary to the quadrupoles for protons or heavy-ions, the ERFQ is suited for electron velocities in the range 0.5 - 0.7 c, and possible applications are given. Finally, it is illustrated, with numerical field computations that this approach gives sufficient accuracy at 10 GHz.

Ion source and LEBT of KAHVELab proton beamline

The KAHVE Laboratory, at Boğaziçi University, Istanbul, Turkey is home to an educational proton linac project. The proton beam will originate from a 20 keV H+ source and will be delivered to a two module Radio Frequency Quadrupole (RFQ) operating at 800 MHz via a low energy beam transport (LEBT) line. Currently, the design phase being over, commissioning and stability tests are ongoing for the proton beamline which is already produced and installed except the RFQ which is being manufactured. This work summarizes the design, production and test phases of the ion source and LEBT line components.

The parameters of radio frequency quadrupole linear accelerator for DARIA project

The new proton linear accelerator (linac) with output energy 13 MeV and 100 mA current is under development at NRC “Kurchatov Institute” - ITEP for DARIA project. The linac consists of Radio-Frequency Quadrupole (RFQ) and Drift Tube Linac (DTL) with operating frequency 162.5 MHz. The RFQ is based on 4-vanes structure with shifted coupling windows. DTL has a modular structure and consists of separated individually phased cavities with focusing magnetic quadrupoles located between the cavities. The DTL is based on interdigital H-mode (IHDTL) 5-gaps cavities. The 6D beam matching between RFQ and DTL is provided by magnetic quadrupole lenses and RF-bunchers. The paper presents results of the radio-frequency (RF) design, thermal analyses and RF tuning of RFQ linac accelerating structure.

Ion guide simulation for GALS setup

A new setup is under construction at the Flerov Laboratory of Nuclear Reactions (FLNR), JINR, Dubna, to study heavy neutron-rich nuclei along a closed neutron shell N=126. One of the important parts of the setup is the ion guide system. From several ion guide options, a Radio Frequency Quadrupole (RFQ) ion guiding system was chosen. This special ion guiding system was developed and optimized using SIMION simulation software. Also, precise comparison with the alternative Sextupole ion guide (SPIG) system was performed. Along with ion guide simulation, modernization of reference cell was completed and it is ready for offline experiments to find optimal laser ionization scheme.

Multivariant spatial and geometric interpolation of field maps through model order reduction

Complex three-dimensional field maps can be efficiently denoised and compressed in data volume by high order single value decomposition. Extension of the method to inter/extrapolation and determination of basis function representation is reported here. Inter/extrapolation of denoised and compressed maps is applied to spatial coordinates and especially to the parameters defining the geometry of devices creating such maps. It significantly increases the efficiency of the provision of compact and noise-free maps combined with high resolution. The method is illustrated by creating corresponding maps for rf cells of radio-frequency quadrupoles.

Improved bunching and longitudinal emittance control in an RFQ

A new application of vane modulation variation in a Radio Frequency Quadrupole (RFQ) cell has been applied that significantly improves beam bunching and longitudinal emittance control to achieve lower longitudinal rms emittance at the RFQ output. This procedure occurs in the individual cells, is independent of the overall design, and therefore is general, affording an extra parameter for beam manipulation. It can be applied besides the usual goals of vane modulation variation, e.g., to achieve higher acceleration efficiency. Examples of the cumulative effects on the overall design are provided to point out further exploration avenues for the designer.

The General Purpose Ion Buncher: A radiofrequency quadrupole cooler-buncher for DESIR at SPIRAL2

We report on the conception and first tests of the General Purpose Ion Buncher (GPIB), the radio-frequency beam-cooler and buncher that will supply the DESIR (Decay, Excitation and Storage of Radioactive Ions) experimental hall to be constructed to complement the SPIRAL1 and SPIRAL2 facilities in GANIL. Its goals are both to reduce the emittance and if necessary to bunch the radioactive ion beam from the GANIL production facilities to adapt it to the needs of the different experimental setups in the DESIR hall. The mechanical design is similar to the existing ISCOOL quadrupole at ISOLDE but the new radio-frequency system enables a much stronger radial confinement. The GPIB is developed at LP2i Bordeaux11LP2i Bordeaux was known as Centre d’Études Nucléaires de Bordeaux-Gradignan (CENBG) before the name was changed in 2022. in parallel with the PIPERADE double Penning trap and a beamline has been constructed there to characterize both. The cooling of a 30keV beam to an emittance of 3 π mm mrad and a transmission above 80% in continuous mode is demonstrated for currents up to a few nA. Some first results concerning the bunching mode are also shown though this mode is still under development.

Commissioning of the St. Benedict RF carpet

The Superallowed Transition BEta NEutrino Decay Ion Coincidence Trap (St. Benedict) aims to measure the beta-neutrino angular correlation parameter for superallowed mixed beta decay transitions between mirror nuclei in order to conduct precision tests of the Standard Model. St. Benedict will include a gas catcher, a differentially pumped extraction system, a radio-frequency quadrupole (RFQ) cooler and buncher, and a Paul trap to utilize radioactive ion beams produced at the Nuclear Science Laboratory of the University of Notre Dame. The two-part differentially pumped extraction system contains a RF carpet at a helium gas pressure of around 3 mbar, and a radio-frequency quadrupole (RFQ) ion guide at a pressure of around 2×10−3 mbar. Transport efficiency of potassium ions in the first part of the extraction system using the RF carpet in the presence of gas flow was determined to be near 100% in the 0.75 to 5 mbar pressure range using the ion surfing transport method.

An advanced radio-frequency quadrupole ion cooler for accelerator mass spectrometry

An advanced radio-frequency quadrupole (RFQ) ion cooler was developed for accelerator mass spectrometry to use element-selective laser photodetachment and ion-molecule reactions for isobar suppression. The system will be installed as a central part of the new Anion Laser Isobar Separator (ALIS) at the 6 MV AMS system of CologneAMS.The new RFQ design intends to solve the technical challenge of the deceleration and trapping of heavy molecular ion beams with high emittance. Therefore, an elliptical injection electrode was developed to slow down the ions far away from the central entrance aperture. A new and easy-to-manufacture guide-field assembly was developed. For this purpose, diagonally-split cylindrical surface electrodes are capacitively coupled to a core rod that is carrying the RF signal. Consequently, only low DC voltages are needed to create a gradually changing potential in the longitudinal direction. The RFQ and the acceleration electrodes are installed in a self-aligned structure.

Characterization of the isobar separator for anions integrated into the A. E. Lalonde laboratory’s 3 MV AMS system

Accelerator Mass Spectrometry (AMS) of isotopes with abundant negative ion-forming isobars often requires the use of large accelerators to achieve high sensitivity measurements. The Isobar Separator for Anions (ISA) is a radio frequency quadrupole (RFQ) reaction cell system that can provide selective isobar suppression in the low energy system, prior to injection into an accelerator. A commercial version from Isobarex Corp. has been installed in a second injection line of the 3 MV tandem accelerator system at the A. E. Lalonde AMS Laboratory, University of Ottawa. Here, we present the characterization of the ISA for its optimization of S– suppression and Cl– transmission. He gas was selected as a cooling buffer gas, as it provided the best Cl– transmission of ∼50 % through the ISA column. These tests use NO2 as a reaction gas due to its well-known exothermic reaction with S– but endothermic reaction with Cl–. More than six orders of magnitude reduction of S to Cl has been observed.

Demonstration of an intense lithium beam for forward-directed pulsed neutron generation

As an alternative to research nuclear reactors, a compact accelerator-driven neutron generator that uses a lithium beam driver could be a promising candidate since it produces almost no undesired radiation. However, providing an intense lithium-ion beam has been difficult, and it has been thought that the practical application of such a device would be impossible. The most critical problem of insufficient ion fluxes has been solved by applying a direct plasma injection scheme. In this scheme, a pulsed high-density plasma from a metallic lithium foil generated by laser ablation is efficiently injected and accelerated by a radio-frequency quadrupole linear accelerator (RFQ linac). We have obtained a peak beam current of 35 mA accelerated to 1.43 MeV, which is two orders of magnitude higher than a conventional injector and accelerator system can deliver.

Design of a radio frequency quadrupole for a high intensity heavy-ion accelerator facility

We report a design work of a continuous-wave (cw) radio frequency quadrupole (RFQ) for the injector linac of the High Intensity heavy-ion Accelerator Facility project. The rf design and multiphysics analysis were conducted to enhance the long-term stability and reliability of the cavity. To minimize the peak modified Poynting vector and peak surface electric field associated with the rf breakdown rate, the cross section and the vanes segmentation of the RFQ cavity were optimized. Pi-mode stabilizing loops (PISLs) were adopted for the cavity to increase the mode separation between the quadrupole and the neighboring dipole modes, intending to reduce the emittance growth and beam loss caused by the field asymmetry of the quadrupole mode. Due to the lack of a universal criterion of acceptable mode separation, the field asymmetry of the quadrupole mode was directly used as the design criterion for the PISL. Tuners were designed to tune the cavity frequency and longitudinal field flatness. Thermal distributions on tuners with and without rf sealing were investigated, and we found that rf sealing was indispensable in decreasing the tuner's temperature. A multiphysics analysis was carried out to maintain the cavity frequency while running with different rf power, in an attempt to avoid frequently adjusting the cooling water temperature when accelerating different ions. The analysis also verified that a large wall thickness could make the cavity possess a low stress and a minor deformation.

APFRFQ – A SIMULATION ENVIRONMENT FOR THE DEVELOPMENT OF HIGH-CURRENT LINEAR ION ACCELERATORS WITH RF FOCUSING

Presented is an interactive environment, APFRFQ, for calculating linear accelerators based on rf field focusing of different types, namely, alternating phase focusing (APF), rf quadrupole focusing (RFQ) and a combination of previous two methods (APF&RFQ). The APFRFQ environment is capable of performing the following tasks in the interactive mode: setting the parameters of the accelerating gaps, calculating the accelerating-focusing channels of linear accelerators taking into account the real geometry of the electrodes, performing numerical simulation of particle dynamics in the calculated channels with the space charge forces taking into account, matching the input parameters of the beam with the given six-dimensional phase distribution and the accelerating structure.

Design of a CW BISOL RFQ for Three Kinds of High-Charge-State Ions Simultaneous Acceleration

Based on the latest design requirements proposed by the Beijing On-Line Isotope Separation (BISOL) project, a new Sn22+-based, 81.25 MHz CW radio frequency quadrupole (RFQ) with external bunching has been designed. This RFQ can accelerate Sn22+ to 0.5 MeV/u with an output longitudinal-normalized rms emittance of 0.20 keV/u·ns over a length of 5.6 m. The tolerance and error analysis results indicate that this RFQ can handle a wide range of non-ideal beams while maintaining relatively lower longitudinal emittance growth and higher transmission efficiency. To maintain the beam intensity, the RFQ will simultaneously accelerate three kinds of high-charge-state mixed ions (132Sn21+, 132Sn22+ and 132Sn23+), the simulation results given by Impact-T show that the RFQ can achieve high transmission of the mixed beam. Compared with the previous Sn21+-based internal bunching RFQ scheme, this RFQ has a shorter length and smaller output emittance, which is beneficial to the designs of subsequent Medium-energy Beam Transport (MEBT) and Drift Tube Linac (DTL). In electromagnetic design, a four-vane structure with 48 tuners and 16 π-mode stabilizers (PSLs) were chosen. The results of the multi-physics analysis show that the maximum temperature rise and the maximum deformation of the cavity are 13.6 K and 40.3 µm, respectively. The results simulated with CST Microwave Studio (CST) and HFSS software were consistent.

Design of a compact RFQ linac for the transportable neutron source

A transportable accelerator-driven neutron source based on the Radio Frequency Quadrupole (RFQ) linac is developing at Xi’an Jiaotong University (X-TANS). It will be a promising tool for the non-destructive inspection of immovable objects. The neutron yield above 10 11n/s can be obtained via 7Li(p,n)7Be reaction with a proton beam energy of 2.5 MeV. To exactly guarantee the transportability of the neutron source, it is essential to achieve the light, compact and low-power consumption of RFQ linac. The operation frequency of 325 MHz is chosen considering the balance among cavity size, cavity consumption, and electrode aperture. In addition, compact dynamics scheme is adopted to achieve short RFQ by sacrificing a beam bunching efficiency. The beam dynamics design and optimization have been performed based on Parmteqm. Beam tracking results show that RFQ can accelerate the proton beam to 2.5 MeV with an electrode length of 2.6 m and an effective transmission efficiency of 93.8%. To enlarge the redundancy of the input beam mismatch and make the beam match easier from LEBT to RFQ, the electrode aperture is designed to shrink gradually in the RFQ entrance. In addition, we also performed the RF electromagnetic design and optimization based on the full-length 3D RFQ model. Multiphysics simulations of the cavity in different working conditions are investigated at last.

Upgrade of the 4-rod radio frequency quadrupole for SARAF Phase II Linac

The 176 MHz 4-rod radiofrequency quadrupole (RFQ) is the crucial part of the Soreq Applied Research Accelerator Facility (SARAF) injector and must be able to operate at RF powers up to 190 kW continuous wave and transport 5 mA proton and deuteron beams. The SARAF Phase I RFQ is planned for use in Phase II. The period between the termination of Phase I and the installation of Phase II provided an opportunity to introduce RFQ improvements to fully meet the Phase II requirements. These upgrades and improvements are presented in this report together with the results of the recent conditioning campaigns.

Theoretical and experimental studies of multi-port RF power feeding in rod-type radio frequency quadrupole (RFQ) linac

An analytical and experimental study of multi-port RF power feeding in a four rod-type radio frequency quadrupole (RFQ) has been discussed. First, we have derived generalized relations for multi-coupler power feeding based on S-parameters for n balanced couplers. Using simulation and measurements on a prototype, the optimum position and orientation of two and four couplers in an 80 MHz extended vane rod type RFQ have been determined. A low power RF test has been carried out to show the phase and power balancing using S parameter analysis for two and four mock-up couplers for the RFQ. As a corroborative study, the vane tip voltage measured with a vector voltmeter showed that voltage corresponding to power fed through a single coupler (β = 1) agrees with the value when the same power is fed using two or four couplers.

High-power inductive coupler with a high-voltage DC blocker

The authors of this study developed a high-power inductive coupler with a high-voltage DC blocker that is capable of delivering up to 100 kW of CW RF power at 176 MHz and 4 kV DC. The high-power indictive coupler was developed at the Soreq Nuclear Research Center for the radio-frequency quadrupole of the Soreq Applied Research Accelerator Facility. The purpose of the DC blocker is to enable the application of high-voltage DC bias to the inner conductors of the couplers in order to prevent the multipacting phenomena. A new, mechanically and thermally improved, version of the RF coupler is designed and implemented in conjunction with the DC blocker. The underlying design principles, indigenous development, and results of tests of the coupler are presented here.

Commissioning of the 7 MeV H[formula omitted] linac injector for a 200 MeV proton synchrotron

This paper describes the beam commissioning progress of the 7 MeV H− linac injector for the proton synchrotron of Xi’an 200 MeV Proton Application Facility (XiPAF). To fulfill a flux of 105∼108p/cm2/s with a uniformity better than 90% on a 3 cm × 3 cm sample size at the experimental station, the number of the accumulated protons in each cycle in the synchrotron is designed to be larger than 2 × 1011. The protons are acquired from the H− beam stripped by the carbon foil, which enables transverse space painting during injection. The maximum pulse length of the injected beam is 40μs. With an estimation of 40 for the intensity gain factor, the injected beam is required to have a peak current of higher than 1 mA, with the normalized transverse emittance of 90% particles less than 6 and 4 πmm mrad for the horizontal and vertical planes, respectively, and the momentum spread of 90% particles within ±0.45%. The injector mainly consists of an H− ion source, a low energy beam transport line (LEBT), a 3 MeV radio frequency quadrupole (RFQ) accelerator, a 7 MeV interdigital H-mode drift tube linac (IH-DTL), and an injection beam transport line. After several stages of beam commissioning, the linac injector has reached a pulsed peak current of 2.5 mA, with normalized emittance (90% particles) less than 4.4 and 2.2 πmm mrad, 90% momentum spread less than ±0.55%, which lays a good foundation for the beam commissioning of the synchrotron.

Development of a beam energy adjustment system after a Radio-Frequency-Quadrupole

The Low Energy heavy-ion Accelerator Facility (LEAF) is a low-energy, high-intensity, heavy ion accelerator for multidisciplinary research developed at the Institute of Modern Physics (IMP). Beam commissioning of the facility began in 2018, but until recently, only a fixed beam energy of 0.5 MeV/u was available because the main accelerator structure is a Radio-Frequency Quadrupole (RFQ), which hinders LEAF to meet the requirements of the experimental terminals, for example, 12C+12C fusion reaction investigation at astrophysical energies requires beam energies adjustable from 0.3 MeV/u to 0.7 MeV/u. To expand the beam energy range, a “constant-beta” structure Drift Tube Linac (DTL) was developed providing an adjustable beam energy from 0.3 to 0.7 MeV/u. To control the beam quality, specifically the energy spread, two re-bunchers are employed, one upstream and one downstream of the DTL. Here we present the development of the key device: an Interdigital H-mode DTL (IH-DTL). First, we discuss the beam dynamics design for the beam energy adjustment system, then we present details of the test bench, and finally, we report measurements performed with the finished hardware. The measurements of energy adjustment and energy spread agree well with the simulations, demonstrating the feasibility of this design.