RFQ Linac Research Articles

Engineering design of the RF input coupler for the IFMIF prototype RFQ linac

For the IFMIF/EVEDA RFQ linac, engineering design of the RF input coupler is carried out. The RF input coupler with a cooling port (L=λ/4), based on a 6 1/8in. co-axial waveguide, is designed for the CW operation. Three cooling channels are installed into the inside of loop antenna, the outer-conductor and the inner-conductor around RF window. For the loop size, RF coupling factors on beam loading are evaluated with based on the measured S11 parameter and Q value on aluminum RFQ module. In order to fulfill the acceptance Q0 value of 9000 for the RFQ, the insertion depth of L=45mm is chosen. For this loop antenna size, magnetic field strength around the loop and surface loss density on the loop are evaluated, it is found to satisfy with the RF coupler acceptance values. Coupling cavity with ridge-type structure is also designed for the RF transmitted power test. It is evaluated to be 7.2kW and 0.5W/cm2 for RF power dissipation and RF surface loss density on the RF transmitted power of 200kW.

An adjustable focusing system for a 2 MeV H− ion beam line based on permanent magnet quadrupoles

A compact adjustable focusing system for a 2 MeV H− RFQ Linac is designed, constructed and tested based on four permanent magnet quadrupoles (PMQ). A PMQ model is realised using finite element simulations, providing an integrated field gradient of 2.35 T with a maximal field gradient of 57 T m−1. A prototype is constructed and the magnetic field is measured, demonstrating good agreement with the simulation. Particle track simulations provide initial values for the quadrupole positions. Accordingly, four PMQs are constructed and assembled on the beam line, their positions are then tuned to obtain a minimal beam spot size of (1.2 × 2.2) mm2 on target. This paper describes an adjustable PMQ beam line for an external ion beam. The novel compact design based on commercially available NdFeB magnets allows high flexibility for ion beam applications.

RHIC EBIS: basics of design and status of commissioning11This work is performed under the auspices of the U.S. Department of Energy and the National Aeronautics andSpace Administration.

RHIC EBIS will be used for producing multicharged ions from helium to uranium using primary ions from various external ion sources. The EBIS is followed by an RFQ and short linac, forming the new preinjector which will produce beams used for physics at RHIC and the NASA Space Radiation Laboratory, The design of RHIC EBIS is based on the BNL Test EBIS, which was a successful 10A electron current prototype. Improvements have been made in the RHIC EBIS design to increase the capacity of the ion trap, repetition frequency of operation, electron current, acceptance for injected ions, and improve vacuum conditions in the ionization region. RHIC EBIS has been assembled and installed in its final position. Commissioning is now underway to reach its project parameters. The results of this commissioning stage are presented.

Essay of Accelerator R&D in a Small Laboratory of a University <Study of three POP accelerators using heavy ion RFQ linac of Tokyo Institute of Technology ―1992–2008―>

Essay of Accelerator R&D in a Small Laboratory of a University <Study of three POP accelerators using heavy ion RFQ linac of Tokyo Institute of Technology ―1992–2008―>

Multibeam cavity for low energy beam acceleration

In order to accelerate high intensity ion beams, it is necessary to suppress a defocusing force by the space charge effect. The function of the defocusing force is extremely strong in the low energy region. One of the solutions is the relaxation of the defocusing force by dividing the high intensity beam into several beams. We then propose a high intensity injector system with a multibeam IH type radio frequency quadrupole (IH–RFQ) linac, and simulated the resonance frequency and the electromagnetic field distributions in the multibeam type IH–RFQ linac. We report the design of the multibeam type IH–RFQ linac.

First operation of the rf-focused interdigital linac structure

The new rf-focused interdigital (RFI) linac structure came into operation at the Linac Systems laboratory in May of 2006, after a multi-year development program supported by the US Department of Energy. The RFI linac structure is basically an interdigital (or Wideröe) linac structure with rf quadrupole focusing incorporated into each drift tube. The RFI prototype operates at 200-MHz and consists of an ECR ion source, an Einzel lens LEBT, a radial-strut, four-bar RFQ linac section to 0.75MeV and an RFI linac section to a final energy of 2.5MeV. The total length of the prototype is 2.2m. The RFQ and RFI linac sections are resonantly coupled and require a total of 120kW of rf power for cavity excitation. The energy of the accelerated beam was confirmed by requiring it to pass through a 2.25-MeV energy-degrading foil. The specifications for the RFI linac prototype were chosen to address the demanding Boron Neutron Capture Therapy medical application. There are, however, many other potential applications for the structure as it has efficiency and size advantages for both protons and heavy ions at a variety of energies and currents. To date, we have achieved a beam current of approximately 1mA peak at a relatively low duty factor. We continue to improve the performance of the prototype structure on a daily basis as we better understand the optimal operational settings for the prototype system. Now that the first operational milestone for the RFI linac structure has been achieved, Linac Systems will vigorously pursue projects and partnerships for multiple applications such as compact and intense neutron sources, proton and carbon injector linacs for synchrotrons and PET isotope production.

The design of a four-rod RFQ LINAC for VEC-RIB facility

The design of a four-rod RFQ LINAC for VEC-RIB facility

Facilities and Methods: KEK-Jaeri Joint RNB Facility, TRIAC

Research and development on an isotope separator on-line (ISOL)-based radioactive nuclear beam (RNB) facility in Japan had mainly been carried out at the Institute for Nuclear Study (INS), University of Tokyo [1]. The first RNB acceleration was realized with the split-coaxial RFQ (SCRFQ) and interdigital-H (IH) type linacs in March 1997. A joint RNB facility, TRIAC (Tokai Radioactive Ion Accelerator Complex) facility, is partly based on the re-installation of the above INS-facility in Tokai site of the Japan Atomic Energy Research Institute (JAERI). It will open up the RNB science with 1.1 MeV/u RNBs from FY2005. The higher energetic (5-8 MeV/u) RNBs will be available in the near future.

Emittance measurement for intense beam of heavy ions from RIKEN 18 GHz ECRIS

In order to investigate the ion-optical parameters of the RIKEN 18 GHz electron cyclotron resonance ion source injection line into the RIKEN RFQ linac, we measured the beam emittance for a wide mass range of the ions. First results indicate a strong extraction current dependence of the normalized emittance. When using the insertion method to produce metallic ions from solid rod with high melting point, we observed that the beam emittance of metallic ions was very large compared to the beam emittance of ions from gaseous element. It may be due to the plasma instability caused by inserting the rod into the plasma deeply.

Recent investigations and applications of thin diamond-like carbon (DLC) foils

In previous experiments, diamond-like carbon (DLC) foils which are being produced at Kurchatov Institute, have proven well suited as long-lived stripper foils for high-energy heavy-ion tandem accelerators and ultra-thin secondary-electron (SE) emitting foils for TOF spectrometers. This paper presents the recent advances in DLC targetry with main emphasis given to development and applications of ultra thin foils (maximum diameter up to 70 mm) with high uniformity and minimal possible effective thickness, the latter has been evaluated by measurements of both energy loss and angular scattering of heavy ions transmitting through the foils. Comparative lifetimes of DLC stripper foils irradiated with high intensity (150 μA) He + beams at 2 MeV are reported, which demonstrate the favorable use of DLC foils as supplemental strippers at RFQ linacs. In conclusion, the attractive results of application of ultra-thin DLC foils to TOF detectors for heavy ion AMS as well as to compact tandem accelerators are presented.

Enhancement of ion beam charge states by adding a second anode to the metal-vapor vacuum-arc ion source

We report detailed investigations of ion charge state enhancement in an alternative metal-vapor-vacuum arc ion source configuration, consisting of two anodes with staggered (but partially overlapping) high current discharges in axial high magnetic field gradients. The experiments demonstrated that driving an additional current in a vacuum arc in a magnetic mirror configuration resulted in substantial ion charge state enhancement. Maximum ion charge states of Pb 6+ and U 8+ were extracted. Results are presented for high charge state uranium beam generation and acceleration in the 27 MHz heavy-ion RFQ LINAC TIPr-1.

Nano-beam production by RFQ with ion-trap injector

Nano-beam production by RFQ with ion-trap injector

Measurement of the laser plasma properties of the direct plasma injection method to the RFQ LINAC on the RIKEN laser ion source

The laser plasma properties of the RIKEN laser ion source on the direct plasma injection system (DPIS) were measured for analysis of the DPIS beam dynamics. From the installed electrostatic analyzer and the measured calibration value from Ceratron to Faraday Cup, the current values and pulse time structure for each carbon charge state in the laser plasma were obtained.

Simulation of direct injection scheme for RFQ linac

A new efficient injection method from a laser ion source to a RFQ was proposed and is being tested in RIKEN (The Institute of Physical and Chemical Research, Japan). Laser plasma is induced just before the entrance of the RFQ and is injected directly into the RFQ channel. In order to understand this new scheme, a particle tracking simulation study, which focused on the entrance of the RFQ, has been started with three-dimensional (3D) space charge effect in a realistic 3D electric field map. According to the beam tracking calculation, the predicted currents are smaller than experimentally obtained values. To obtain better accuracy of the simulation, motion of electrons should be described adequately.

Carbon beam acceleration using a simple injection method into an RFQ

For medium-heavy ions, a new injection method into a RFQ linac is proposed. Laser plasma is created by an intense pulsed laser system and directly injected into the RFQ without any focusing devices. This method may eliminate complex difficulties due to space-charge effects in the low-energy transport system. Using the TITech RFQ, a verification test has been performed. From the laser ablated carbon plasma, C 4+ and C 3+ beams were captured successfully and were accelerated to the designed energy of the RFQ. The observed total current of carbon beam reached 8 mA, which exceeded the designed current of the RFQ. This method can be easily applied to existing RFQs which are used in medical and industrial accelerator systems.

A plan for on-line production and acceleration of radioactive isotope beams by use of electron cyclotron resonance ion source NANOGAN

For the precise low background experiments on β decay and material sciences, we are planning to build a new ISOL-type facility to accelerate various β-radioactive nuclei utilizing the existing 5 MV Van de Graaff accelerator and an RFQ linac. Present status of the designing work is reported. In the present work, optical elements of the 41-m-long beam transport line to connect Van de Graaff accelerator and an RFQ linac were designed. Using two dipole magnets, two electric quadrupole doublets and six electric quadrupole triplets, low energy radioactive nuclear beams can be transported with sufficient efficiency.

Numerical simulation and optimization of multicomponent ion beam from RIKEN electron cyclotron resonance ion sources

A new version of a program library for numerical simulation of ion beam transportation is presented. The library is aimed at high current and low energy multicomponent beams from ion sources and based on the macroparticle method. It has been used to simulate and optimize the transport line between the 18 GHz ECR ion source and RFQ linac at RIKEN. It is shown that it is possible to improve the ion transportation efficiency to a factor of 2 or 3 using the solenoid instead of the present einzel lens as a first element of the line.

A 25.5 MHz double-coaxial λ/4-resonator as a rebuncher in heavy ion linac system

A 25.5 MHz double-coaxial λ/4-resonator has been constructed to be used as a rebuncher between a 25.5 MHz RFQ linac and a 51 MHz interdigital-H linac for the acceleration of short-lived nuclei. By employing a double coaxial structure, the resonator length is only 130 cm; the length of the natural λ/4-resonator is 294 cm. The resonator, 69 cm in inner diameter, has six acceleration gaps. The bare shunt impedance is 40.6 MΩ/m. The ions with a charge-to-mass ratio 1/10 can be rebunched by feeding an rf power of 1.4 kW.

Intense ion beam produced plasmas on TIT-RFQ linac

Intense ion beams from an RFQ linac can be used to investigate the plasma experiments. At present, a 4He + beam with the mean current of 2 mA in a macropulse is focused to about 1.1 mm 2 on the target surface. The output-beam is switched from a beam dump to the target within 50 ns by using a fast electrostatic beam kicker. This kicker synchronizes to the RF-pulse, and it is used to control the timing between the beam-target interaction and the diagnostic equipment. The experiments were performed with a gas target. The behavior of the ion beam-produced plasma was observed.

Acceleration test of heavy-ion in RFQ linac for HIF basic experiments

A new heavy-ion acceleration system has been developed for basic research on heavy-ion inertial fusion and ion-pumped laser at Tokyo Institute of Technology. This system consists of the TIT-RFQ linac, a hexapole cusp-field type ion source, a solenoid lens, magnetic quadrupole lenses and an analyzing magnet. By using the new system, acceleration of N + beam by the TIT-RFQ was first possible. We could obtain N + beam with an energy of 3.066 MeV and a maximum intensity of 0.4 nA as the results of acceleration test. The outline of this system and the acceleration test are presented.