Advanced Unilac Upgrade for Fair

To provide for the high beam currents as required from the FAIR project, the GSI Unilac High Current Injector (HSI) must deliver 18 mA of U 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 shown by simulations. As a first upgrade step, the RFQ has been modernized successfully in summer 2009 with a new electrode design. Furthermore the existing LEBT must be modified, and a new straight source branch will provide for the full beam performance. Commissioning of the HSI has shown that the transmission of the RFQ increased significantly (from 55% to 85% for high current uranium operation, 95% for medium current operation). Further upgrades aim to improved HSI-transmission by optimizing the matching to the RFQ, and to the IH-DTL. The upgrade of the LEBT starts in 2010. INTRODUCTION The GSI Universal Linear Accelerator UNILAC comprises the High Current Injector HSI, the High Charge State Injector HLI and the poststripper section (Alvarez and Single Resonators). The HSI comprises two ion source terminals (2.2 keV/u), a low energy beam transport system LEBT, an RFQ (120 keV/u), a short adapter RFQ (Superlens) and an IH-DTL (two tanks, 1.4 MeV/u). The UNILAC serves for the synchrotron SIS18 by a transfer channel. Figure 1: GSI UNILAC schematic overview.