GSI, Darmstadt
ITEP, Moscow
IAP, Frankfurt am Main
To provide for the high beam currents as required of the FAIR project, the GSI Unilac High Current Injector (HSI) must deliver 18 mA of U4+ ions at the end of the prestripper section. With the design existing up to 2008, the RFQ could not reach the necessary beam currents at the RFQ output, as simulations had shown. Furthermore, parts of the existing LEBT must be modified, and a new straight source branch must be added to provide for the full required beam current. As a first step of an HSI frontend upgrade, the RFQ has been modernized in summer 2009 with a completely new electrode design. Commissioning of the HSI has shown that the transmission of the RFQ increased significantly (from 55% to 85% in high current Uranium operation, 95% in medium current operation). As expected, further bottlenecks for the transmission of the complete HSI (matching LEBT-to-RFQ, matching to the Superlens) have been detected. An upgrade of LEBT magnets is foreseen for 2010, the additional linear source branch will follow.
GSI, Darmstadt
IKP, Mainz
IAP, Frankfurt am Main
HIM, Mainz
GSI applied for a new superconducting (sc) cw-LINAC in parallel to the existing UNILAC. Such a machine is highly desirable with respect to the progress in the field of Superheavy Elements (SHE) for example. The UNILAC at GSI is limited in providing a proper beam for SHE and in fulfilling the requirements for FAIR simultaneously. A sc CH-structure is the key component of the proposed efficient and compact linac. In first vertical rf-tests at the Institute of Applied Physics (IAP) maximum gradients up to 7 MV/m were achieved. The cavities for the cw-LINAC should be operated at 217 MHz providing gradients of about 5.1 MV/m at a total length of minimum 0.6 m . In a first step a prototype of such a sc cw-LINAC as a demonstrator is financed by the Helmholtz Institute Mainz (HIM). The demonstrator is the first section of the proposed cw-LINAC consisting of a sc CH-cavity embedded by two sc solenoids. The aim is a full performance test of the demonstrator with beam at the GSI high charge injector (HLI) in 2013. Presently the tendering of the solenoids, the cavity, the cryostat and the rf-amplifier is in preparation.
IAP, Frankfurt am Main
GSI, Darmstadt
The search for Super-Heavy Elements (SHE) is one of the frontiers in nuclear physics. By trend the production cross sections decrease significantly for larger proton numbers and heavier nuclei, respectively. To limit the required beam time it is necessary to use the highest available intensity. This prefers cw operation and the use of superconducting cavities. A cw operated superconducting linac using CH-cavities at GSI has been designed. As front end the existing 108 MHz High Charge Injector (HLI) will be used which is presently being upgraded for cw operation. The superconducting part of the linac covers the energy between 1.4 AMeV and 7.5 AMeV. It consists of 9 multi-cell CH-cavities operated at 217 MHz. Each cavity is optimized for a specific particle velocity but without beta profile. Above 3.5 AMeV the linac is fully energy variable. The first superconducting CH-cavity is already under construction and will be tested with beam delivered by the HLI. The talk covers the development of the prototypes and the overall design including beam dynamics issues.
IAP, Frankfurt am Main
The Frankfurt Neutron source FRANZ is under construction*. The ARMADILLO bunch compressor** as a part of it is composed of a 5MHz electric kicker, a magnetic dipole chicane and rf-rebunching cavities. The design phase of the bunch compressor has reached the final stage. A 175MHz 2MeV proton linac forms 100ns long beam pulses consisting of nineμbunches with 150mA. Deflected by the 5MHz kicker theμbunches are guided on different paths to arrive within 1ns at a n-production target. Due to high space charge forces rebuncher cavities are included***. The peak current at the target is expected to be in the range of 10A in a 1ns proton pulse, which is equivalent to a longitudinal pulse compression ratio of 45. A new code specific for complex magnetic multi aperture system and for high current applications has been developed. Hardware designs according to the beam dynamics results are in progress. Improved 3D magnetic and electric fields will be applied in the future beam dynamics studies including high space charge forces. The preliminary designs and the beam dynamics studies will be presented in this contribution.
* O. Meusel, et al.: LINAC06, Knoxville, Tennessee USA, 2006, pp. 159-161.
** L. P. Chau, et al.: EPAC08, Genoa, Italy, 2008, pp. 3578-3580.
*** D. Noll, another contribution at this conference.
IAP, Frankfurt am Main
The Frankfurt Neutron Source (FRANZ) currently under construction at IAP (Goethe University of Frankfurt) is designed to produce short neutron pulses at high intensity and repetition rates up to 250 kHz [*]. To achieve a bunch length of one nanosecond despite the high space charge forces, a bunch compressor of the Mobley type [**] using four dipole magnets and two rebunchers has been developed [***] to merge 9 linac bunches into the final focus. The first rebuncher cavity, a λ/4 resonator operating at 87.5 MHz, has to feature nine beam paths due to the multi-trajectory system. Additionally the gaps have to be displaced relatively to each other in a way that all bunches arrive at the correct rf phase. The second rebunching cavity will provide final focusing as well as an energy variation of ±0.2 MeV in front of the target and will be operating at 175 MHz. This paper presents the design of these novel cavities as well as the simulated beam dynamic properties.
* Meusel et al., LINAC 2006
** Mobley, Phys. Rev. 88(2), 360-361 (1951)
*** Chau et al, LINAC 2010
IAP, Frankfurt am Main
Space charge lenses use a confined electron cloud for the focusing of ion beams. Due to the electric space charge field, focusing is independent of the particle mass. For this reason the application of the space charge lens especially in the field of heavy ion beams is advantageous. Moreover, the trapped non neutral plasma cloud compensates the space charge forces of the ion beam. The focusing strength is given by the confined electron density whereas the density distribution influences the mapping quality of the space charge lens. An important parameter for the focusing capability of the space charge lens is besides the homogeneous electron distribution a high electron density. In ongoing theoretical and experimental work methods have been developed to determine the most important parameters like electron temperature and electron density distribution for an optimized lens design. Based on the experimental results a new space charge lens has been designed to focus low energy heavy ion beams like 2,4 AkeV U4+ at the low energy transport section into the GSI High Current Injector. Experimental results will be presented and compared with numerical simulations.
*W. Barth, "THE INJECTOR SYSTEMS OF THE FAIR PROJECT", LINAC08, Victoria, BC, Canada
GSI, Darmstadt
NSCL, East Lansing, Michigan
IAP, Frankfurt am Main
Heavy, highly-charged ions (HCI) with only one or few electrons are interesting systems for precision experiments as for instance tests of the theory of quantum electrodynamics (QED). To achieve high precision, kinetic energy and spatial position of the ions have to be well controlled. This is in contradiction to the production process that employs stripping of electrons at high energies by sending relativistic highly-charged ions with still many electrons through matter. In order to match the production at 400 MeV/u with the requirements of the experiments - stored and cooled HCI at low energy - the linear decelerator facility HITRAP has been built at the experimental storage ring (ESR) at GSI in Darmstadt. The ions are first decelerated in the ESR from 400 to 4 MeV/u, cooled and extracted. The ion beam phase spaces are then matched to an IH-structure, decelerated from 4 to 0.5 MeV/u before a 4-rod RFQ reduces the energy to 6 keV/u. Finally, the HCI are cooled in a Penning trap to 4 K. Extensive ion optical calculations were performed and in recent tests up to one million highly-charged ions have been decelerated from 400 MeV/u to 0.5 MeV/u.
IAP, Frankfurt am Main
Recent international cw operated high-current applications with ambitious requirements regarding beam power and quality ask for new linear accelerator developments. In this context the CH-structure (Crossbar-H-mode) has been developed at the Institute for Applied Physics (IAP) of Frankfurt University. It is a multi-cell drift tube cavity for the low and medium energy range operated in the H21-mode and can be used for superconducting as well as for room temperature applications. Because of the large energy gain per cavity, which leads to high real estate gradients, the CH-cavity is an excellent candidate for the efficient acceleration in high power proton and ion accelerators with fixed velocity profiles. One possible application for this kind of cavity is the EUROpean research programme for the TRANSmutation (EUROTRANS) of high level nuclear waste in an accelerator driven system (ADS), which requires an efficient high-current cw-linac (600 MeV, 4 mA, protons, 352 MHz). The paper describes the status of the CH-cavity development and the actual beam dynamics results for the reference design of the 17 MeV EUROTRANS injector.
IAP, Frankfurt am Main
The Frankfurt Neutron source FRANZ is under construction*. The ARMADILLO bunch compressor** as a part of it is composed of a 5MHz electric kicker, a magnetic dipole chicane and rf-rebunching cavities. The design phase of the bunch compressor has reached the final stage. A 175MHz 2MeV proton linac forms 100ns long beam pulses consisting of nineμbunches with 150mA. Deflected by the 5MHz kicker theμbunches are guided on different paths to arrive within 1ns at a n-production target. Due to high space charge forces rebuncher cavities are included***. The peak current at the target is expected to be in the range of 10A in a 1ns proton pulse, which is equivalent to a longitudinal pulse compression ratio of 45. A new code specific for complex magnetic multi aperture system and for high current applications has been developed. Hardware designs according to the beam dynamics results are in progress. Improved 3D magnetic and electric fields will be applied in the future beam dynamics studies including high space charge forces. The preliminary designs and the beam dynamics studies will be presented in this contribution.
IAP, Frankfurt am Main
High intensity beams which are increasingly needed for a variety of applications pose new challenges for beam chopping. An ExB chopper system for proton beams of up to 200 mA and repetition rates of up to 250 kHz is under development at IAP. It will be tested and installed in the low energy section of the Frankfurt Neutron Source FRANZ at beam energies of 120 keV. The chopper consists of a static magnetic dipole field and a pulsed electric field in a Wien filter-type ExB configuration. The electric field temporarily compensates the magnetic deflection thus creating a proton pulse in forward direction, while the duty cycle of the electric field is minimized in order to reduce the risk of voltage breakdowns. Downstream of the chopper a septum will be used to separate the beams ensuring dumping outside the transport line in order to avoid uncontrolled power deposition and the resultant production of secondary particles. Numeric field optimizations and beam simulations including secondary electron effects are presented. Measurements of the high voltage pulse generator based on MOSFET technology and capable of generating 12 kV at 250 kHz as well as beam deflection experiments are shown.
BNL, Upton, Long Island, New York
IAP, Frankfurt am Main
Kyushu University, Hakozaki
The EBIS based preinjector for RHIC is now being commissioned. The Linac was delivered in April 2010 and commissioning started in May, 2010. It accelerates ions from 0.3 MeV/u to 2 MeV/u with 27 accelerating gaps, one internal quadrupole triplet, and operates at 100.625 MHz. The Linac is followed by a beam transport line to Booster which includes seven quadrupoles, two bunchers, and an achromatic bend system with resolution of 500 at 2 MeV/u to select the required charge state. Diagnostics include a pepperpot emittance probe, phase probes , fast Faraday cup, adjustable slits, three sets of multiwire profile monitors, three current transformers, two Faraday cups, and two beam stops. This contribution will report results of linac tuning and cold measurements, and commissioning of the Linac and high energy transport line with helium and gold beams.
BNL, Upton, Long Island, New York
Kyushu University, Hakozaki
IAP, Frankfurt am Main
This talk will present commissioning of a new heavy ion pre-injector at Brookhaven National Laboratory. This preinjector uses an Electron Beam Ion Source (EBIS), and an RFQ and IH Linac, both operating at 100.625 MHz, to produce 2 MeV/u ions of any species for use, after further acceleration, at the Relativistic Heavy Ion Collider, and the NASA Space Radiation Laboratory. Among the increased capabilities provided by this preinjector are the ability to produce ions of any species, and the ability to switch between multiple species in 1 second, to simultaneously meet the needs of both physics programs.