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
IAP, Frankfurt am Main
The GSI linear accelerator UNILAC provides heavy ion beams at Coulomb barrier energies for search and study of super heavy elements. Typical cross-sections of 55 fb require beam doses of 1.4·1019 according to a beam time of 117 days. Several upgrades will reduce the beam time to only 16 days. A second injection branch with a 28GHz-MS-ECRIS anticipates a factor of 10 in particle intensity. By a new cw rfq-structure all accelerator tanks are suitable for a duty cycle of at least 50% instead of 25% presently. Due to this, thermal power increase of 19 rf-amplifiers eased by higher ion charge states of the ECRIS is necessary. Finally the UNILAC timing system controlling 50Hz pulse-to-pulse operation of up to six beams differing in ion species and energy has to be modified considering beam diagnostics electronics and pulsable magnets. The front end comprising ECRIS, rfq- and IH-structure is cw suitable and will serve as injector for a new future sc-cw-linac.
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.
GSI, Darmstadt
A low current high duty factor U10+-beam from the Penning Ion Source as well as a high current low duty factor U4+-beam from a MeVVa source were used for machine investigations in the GSI-UNILAC and synchrotron (SIS18). Carbon stripper foils (20, 40 and 50 ug/cm2) were mounted in the gas stripper section at 1.4 MeV/u to provide for highly charged uranium ions (40+) to be delivered to the SIS18 for life time beam measurements. High current tests were performed to check the durability of the carbon foils. No measurable variation of the stripped low and high current beam in the poststripper DTL could be detected during the life time of the foils. An U40+-beam current of up to 1.0·10+11 particles per 100mues could be reached in the transfer line to the SIS18. This paper will report on the investigations of stripper foils with different thickness. Additionally long time observation of all relevant beam parameters (transverse emittance, energy spread and energy loss, bunch shape, beam transmission up to the SIS-injection) are presented.
GSI, Darmstadt
ORNL, Oak Ridge, Tennessee
CEA, Gif-sur-Yvette
Recent experiments at the Universal Linear Accelerator (UNILAC) at GSI provided evidence for space charge driven resonances along a periodic DTL. A transverse fourth order resonance has been detected by recording the four fold symmetry in phase space. As predicted in [D. Jeon et al., Phys. Rev. ST Accel. Beams 12, 054204 (2009)], the resonance dominates over the envelope instability. Additionally, evidence for resonant emittance transfer from the longitudinal to the transverse plane has been found for settings providing equal depressed tunes of the involved planes.
