Optimization of the three-dimensional electric f ield in IH-DTL

The tuning process of the three-dimensional electric field near the beam axis is very important in the optimization of the Interdigital H-mode Drift Tube Linac (IH-DTL). The tuning of the longitudinal field distribution, the Kilpatrik (Kp) factor, and the transverse dipole field have been discussed in detail, combined with the radio-frequency tuning process of the 53.667 MHz short IH-DTL cavity, which was designed to accelerate ²³⁸U³⁴⁺ from 0.143 MeV/u to 0.289 MeV/u in the SSC-Linac injector project at the Institute of Modern Physics. The flatness criterion and the tube tuning method are discussed in order to meet the beam dynamics requirements. In the tube tuning process, the energy gain error in the cells should be reduced to less than ±2%, and the Kp factor should be reduced to 1.6. The transverse dipole field and the method that uses a "plunger" to dismiss this dipole field are evaluated. The experience gained from the first cavity optimization benefits the tuning process of the three remaining IH-DTL cavities in the SSC-Linac project.     

Particle-in-cell mode beam dynamics simulation of the low energy beam transport for the SSC-linac injector

A new SSC-linac system (injector into separated sector cyclotron) is being designed in the HIRFL (heavy ion research facility of Lanzhou). As part of SSC-Linac, the LEBT (low energy beam transport) consists of seven solenoids, four quadrupoles, a bending magnet and an extra multi-harmonic buncher. The total length of this segment is about 7 meters. The beam dynamics in this LEBT has been studied using three-dimensional PIC (particle-in-cell) code BEAMPATH. The simulation results show that the continuous beam from the ion source is first well analyzed by a charge-to-mass selection system, and the beam of the selected charge-to-mass ratio is then efficiently pre-bunched by a multi-harmonic buncher and optimally matched into the RFQ (radio frequency quadrupole) for further acceleration. The principles and effects of the solenoid collimation channel are discussed, and it could limit the beam emittance by changing the aperture size.     

HIRFL-CSR commissioning in 2006 and 2007

HIRFL-CSR, a new heavy ion cooler-storage-ring system at IMP, had been in commissioning since the beginning of 2006. In the two years of 2006 and 2007 the CSR commissioning was finished, including the stripping injection (STI), electron-cooling with hollow electron beam, C-beam stacking with the combination of STI and e-cooling, the wide energy-range synchrotron ramping from 7 MeV/u to 1000 MeV/u by changing the RF harmonic-number at mid-energy, the multiple multi-turn injection (MMI), the beam accumulation with MMI and e-cooling for heavy-ion beams of Ar, Kr and Xe, the fast extraction from CSRm and single-turn injection to CSRe, beam stacking in CSRe and the RIBs mass-spectrometer test with the isochronous mode in CSRe by using the time-of-flight method.     

A pilot experiment for mass measurement at CSRe

A pilot experiment of mass measurement was performed at CSRe with the method of isochronous mass spectrometry. The secondary fragments produced via RIBLL2 with the primary beam of 400 MeV/u ^36Ar delivered by CSRm were injected into CSRe. The revolution periods of the stored ions,which depend on the mass-to-charge ratios of the stored ions,were measured with a time-of-flight detector system. The results show that the mass resolution around 8×10^-6 for △m/m is achieved.     

Design study of the SSC-LINAC re-buncher

A re-buncher with spiral arms for a heavy ion linear accelerator named as SSC-LINAC at HIRFL (the heavy ion research facility of Lanzhou) has been constructed. The re-buncher, which is used for beam longitudinal modulation and matching between the RFQ and DTL, is designed to be operated in continuous wave (CW) mode at the Medium-Energy Beam-Transport (MEBT) line to maintain the beam intensity and quality. Because of the longitudinal space limitation, the re-buncher has to be very compact and will be built with four gaps. We determined the key parameters of the re-buncher cavity from the simulations using Microwave Studio software, such as the resonant frequency, the quality factor Q and the shunt impedance. The detailed design of a 53.667 MHz spiral cavity and measurement results of its prototype will be presented.     

A particle-in-cell mode beam dynamics simulation of medium energy beam transport for the SSC-Linac

A new linear accelerator system, called the SSC-Linac injector, is being designed at HIRFL (the heavy ion research facility of Lanzhou). As part of the SSC-Linac, the medium energy beam transport (MEBT) consists of seven magnetic quadrupoles, a re-buncher and a diagnose box. The total length of this segment is about 1.75 m. The beam dynamics simulation in MEBT has been studied using the TRACK 3D particle-in-cell code, and the simulation result shows that the beam accelerated from the radio frequency quadrupole (RFQ) matches well with the acceptance of the following drift tube linac (DTL) in both the transverse and longitudinal phase spaces, and that most of the particles can be captured by the final sector focusing cyclotron for further acceleration. The longitudinal emittance of the RFQ and the longitudinal acceptance of the DTL was calculated in detail, and a multi-particle beam dynamics simulation from the ion source to the end of the DTL was done to verify the original design.     

Beam dynamics simulation of HEBT for the SSC-linac injector

The SSC-linac (a new injector for the Separated Sector Cyclotron) is being designed in the HIRFL (Heavy Ion Research Facility in Lanzhou) system to accelerate ²³⁸U³⁴⁺ from 3.72 keV/u to 1.008 MeV/u. As a part of the SSC-linac injector, the HEBT (high energy beam transport) has been designed by using the TRACE-3D code and simulated by the 3D PIC (particle-in-cell) Track code. The total length of the HEBT is about 12 meters and a beam line of about 6 meters are shared with the exiting beam line of the HIRFL system. The simulation results show that the particles can be delivered efficiently in the HEBT and the particles at the exit of the HEBT well match the acceptance of the SSC for further acceleration. The dispersion is eliminated absolutely in the HEBT. The space-charge effect calculated by the Track code is inconspicuous. According to the simulation, more than 60 percent of the particles from the ion source can be transported into the acceptance of the SSC.     

HIRFL-CSR commissioning in 2006 and 2007

HIRFL-CSR, a new heavy ion cooler-storage-ring system at IMP, had been in commissioning since the beginning of 2006. In the two years of 2006 and 2007 the CSR commissioning was finished, including the stripping injection (STI), electron-cooling with hollow electron beam, C-beam stacking with the combination of STI and e-cooling, the wide energy-range synchrotron ramping from 7 MeV/u to 1000 MeV/u by changing the RF harmonic-number at mid-energy, the multiple multi-turn injection (MMI), the beam accumulation with MMI and e-cooling for heavy-ion beams of Ar, Kr and Xe, the fast extraction from CSRm and single-turn injection to CSRe, beam stacking in CSRe and the RIBs mass-spectrometer test with the isochronous mode in CSRe by using the time-of-flight method.     

Numerical optimization and multi-particle dynamics simulation of the radial matching section of the RFQ

The ABC code is an optimization program for the development of matching channels and dynamical matchers in radio frequency quadrupole (RFQ) structures, and a new approach to this code to define the geometry of the radial matching section of the RFQ has been developed. This approach is based on the application of the numerical optimization step by step. This optimization is intended to search for the initial matching condition of a beam, the optimization of parameters of a cell of the channel on given characteristic parameters and traces of a beam in linear channels in both forward and backward directions. To further verify the results of the optimization, multi-particle beam dynamics simulations have been carried out using the BEAMPATH and TRACK codes. The result of the beam dynamics simulation shows that the optimization result of the ABC code is reasonable and this approach provides an opportunity to redesign the structure of the radial matching section of the RFQ.     

PIC mode simulation of solenoid collimation channel

A new SSC （Separated Sector Cyclotron）-Linac is being designed to serve as an injector for the SSC at the HIRFL （Heavy Ion Research Facility Lanzhou）. The beam intensity at the LEBT （Low Energy Beam Transport） for the heavy ions after the selection is typically low and the space charge effects are inconspicuous. The space charge effects become obvious when the beam current increases to a few hundred microamperes. The emittance growth deriving from the space charge effects may be particularly troublesome for the following linac and cyclotron. An optical system containing three solenoids has been designed for the LEBT to limit the beam emittance and to avoid the unnecessary beam loss in the cyclotron, as well as for the purpose of immunizing the LEBT emittance growth due to the space charge effects. The results of the PIC （Particle- In-Cell） mode simulation illustrate that this channel could limit the beam emittance growth and increase the beam brightness.