Emittance Measurements at GSI UNILAC

At GSI heavy ion beams are accelerated by the UNIversal Linear ACcelerator UNILAC (see Fig. 1) and the heavy ion synchrotron SIS 18. Heavy ion beams are delivered to the High Current Injector (HSI) from two different ion source terminals: Penning type (PIG) sources for low and MUCIS/ MEVVA type sources for high beam intensities. An RFQ and two IH structures accelerate the ions from 2.2 keV/u up to 1.4 MeV/u. Afterwards the charge state is increased by a gas stripper and a subsequent magnetic charge separator system. Additionally an ECR source and the High Charge Injector (HLI) provide for directly high charged particle beams. The beam is matched to the Alvarez Drift Tube Linac (DTL) by two rebunchers and five quadrupoles and then accelerated up to 11.4 MeV/u. In the transfer channel (TK) to SIS 18 a stripper foil optionally provides for beams of higher charge states. The UNILAC was originally designed for low current operation. To fill SIS 18 up to the space charge limit the high current injector HSI was mounted in 1999 and upgraded in 2004 [1, 2]. Presently the highest achieved number of U ions at SIS injection amounts to 1 · 10 per 100μs (4.5 emA). For the future accelerator complex of FAIR the UNILAC has to deliver up to 3.3 · 10 particles of U per 100μs (15 emA) to SIS 18 with normalised transverse emittances of βγ x = 0.8 mmmrad and βγ y = 2.5 mmmrad [2]. As the Alvarez quadrupoles do not provide for adequate zero current phase advances σ0 for highly space charge dominated beams, it can be assumed, based on calculations with the multiparticle simulation code PARMILA, that just about 1.9 · 10 particles of U per 100μs (8.4 emA) are contained within these emittances. In order to meet the FAIR requirements a dedicated upgrade of the UNILAC is essential [3], one aim is to improve the high current beam brilliance by increasing σ0 of the Alvarez DTL.