• H. Vormann, W.A. Barth, L.A. Dahl, W. Vinzenz, S.G. Yaramyshev
  GSI, Darmstadt
• A. Kolomiets, S. Minaev
  ITEP, Moscow
• U. Ratzinger, R. Tiede
  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.

• L. Groening, W.A. Barth, W.B. Bayer, G. Clemente, L.A. Dahl, P. Forck, P. Gerhard, I. Hofmann, M. Kaiser, M.T. Maier, S. Mickat, T. Milosic, H. Vormann, S.G. Yaramyshev
  GSI, Darmstadt
• D. Jeon
  ORNL, Oak Ridge, Tennessee
• D. Uriot
  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.

Slides