ANL, Argonne
ANL Physics Division is pursuing a major upgrade of the ATLAS National User Facility. The overall project will dramatically increase the beam current available for the stable ion beam research program, increase the beam intensity for neutron-rich beams from Californium Rare Isotope Breeder Upgrade (CARIBU) and improve the intensity and purity of the existing in-flight rare isotope beam (RIB) program. The project will take place in two phases. The first phase is fully funded and focused on increasing the intensity of stable beams by a factor of 10. This will be done using a new normal conducting, CW RFQ accelerator and replacing three cryostats of split-ring resonators with a single new cryostat of high-performance quarter-wave resonators. To further increase the intensity for neutron-rich beams, we have started development of a high-efficiency charge breeder for CARIBU based on an Electron Beam Ion Source. The goal of the proposed second phase will be to increase the energies and intensities of stable beams, as well as, increase the efficiency and beam current for CARIBU and in-flight RIB beams. The focus of this paper is on innovative developments for Phase I of the project.
ANL, Argonne
A new cryomodule is being designed for the ongoing ATLAS efficiency and intensity upgrade. The cryomodule consists of 7 Quarter-Wave Resonators (QWR) with β-G=0.075 and 4 SC solenoids to replace the existing split-ring cavities. To reduce the resonator frequency jitter due to micro-phonics we choose a frequency of 72.75 MHz instead of 60.625 MHz. At 72.75 MHz, the cavity is shorter by about 20 cm. The choice of the design β was optimized based on the beam dynamics and the actual performance of ATLAS cavities. To reach a record high accelerating voltage of 2.5 MV per cavity or higher, the EM design was carefully optimized. The main goal of the optimization was to minimize the peak magnetic and electric fields while still keeping good values for the stored energy, the shunt impedance (R/Q) and the geometric factor (Rs/Q). The cavity height was also another important parameter. The optimization has lead to a final shape which is cylindrical in the bottom and conic on the top keeping a high real-estate gradient. The optimization also included the internal drift tube face angle required for beam steering correction.
ANL, Argonne
An integral part of the ongoing ATLAS efficiency and intensity upgrade is an RFQ to replace the first section of the existing injector. The proposed RFQ is 3.8 m long made of 106 cells with 30 keV/u input energy and 260 keV/u output energy. The RFQ was designed using the DesRFQ code which produces a file consisting of the length, modulation and the 8 coefficients of the 8-term potential for every cell. To independently check the design we created full 3D models of the RFQ including cell modulation in both Micro-Wave Studio (MWS) and Electro-Magnetic Studio (EMS). The MWS model was used to verify the phasing and energy gain along the RFQ using particle tracking and the EMS model was used to extract the electric field cell by cell assuming the electrostatic approximation. A very good agreement was obtained between the full 3D model and the 8-term potential description in TRACK. In addition to the standard sinusoidal vane profile we studied the option of converting the cells with maximum modulation (~ 40 cells) into trapezoidal cells. The output energy was increased from 260 keV/u to ~ 300 keV/u with minimal change to beam dynamics. This option is the final RFQ design.
ANL, Argonne
An emittance meter based on a pepper-pot coupled to a CsI (Tl) scintillator has been developed over the last several years [1] at Argonne National Laboratory. A compact version of such a probe for on-line emittance measurements has been designed, built and installed into the low energy beam transport (LEBT) line of the Argonne Tandem Linac Accelerator System (ATLAS) and also downstream of the gas catcher of the recently commissioned Californium Rare Isotope Breeder Upgrade (CARIBU). The probe has demonstrated the capability to measure emittance of ion beams with a current density as low as 10 nA/cm2. Systematic emittance measurements in the ATLAS LEBT for different ion species have been done and results will be presented. The probe, based on a pepper-pot coupled to an MCP viewing system, has been designed and built to measure the emittance of low intensity (102-106 ions/s) radioactive CARIBU ion beams.
[1] S. Kondrashev et al. Development of a pepper-pot emittance probe and its application for ECR ion beam studies. Nuclear Instruments and Methods in Physics Research A 606, 2009, pp. 296-304.
Fermilab, Batavia
ANL, Argonne
Significant advances were demonstrated in the design and computer simulations of multi-GeV proton and H-minus linacs. Several codes were applied for the simulation of 8 GeV linac and resulted to extremely good coincidence of all beam parameters. New procedures such as stripping of H-minus ions due to various mechanisms were implemented into the tracking code. The author of this presentation has several publications in PRSTAB and Nuclear Instruments on various aspects of beam dynamics for 8 GeV linac.
ANL, Argonne
An upgrade project is underway at the ATLAS superconducting RF (SRF) heavy-ion linac at Argonne National Laboratory to dramatically increase the intensity of both stable beams and short-lived isotopes from the CARIBU fission source. The upgrade includes a new normal conducting RFQ injector and an SRF cryomodule consisting of seven high-performance 72.75 MHz quarter-wave cavities optimized for ions with velocity of 0.077c. The module will deliver more than 17.5 MV of accelerating potential over 5 meters and replace three existing split-ring cryomodules. Key to this performance will be a new cavity fast tuning system that replaces the voltage-controlled-reactance (VCX) fast tuner. The recently completed ATLAS upgrade cryomodule installed in June 2009 has a real estate gradient of 14.5 MV over 4.6 meters, the highest for any low-beta cryomodule, however, performance is 40% less than could be achieved without the VCX. As such, the VCX is being replaced with a high-power rf coupler and a fast piezoelectric-based tuner to be used together to control the cavity phase. Cold test results of a prototype power coupler and piezo-tuner are presented here.