High intensity heavy ion beam emittance measurements at the GSI UNILAC

The GSI UNILAC, a heavy ion linac originally dedicated for low current beam operation, together with the synchrotron SIS 18 will serve as a high current injector for FAIR (international facility for antiproton and ion research). The UNILAC post stripper accelerator consists of five Alvarez tanks with a final energy of 11.4 MeV/u. In order to meet the requirements of FAIR 15 emA ²³⁸U²⁸⁺, transverse normalised emittances of 0.8 m mrad and 2.5 mm mrad an UNILAC upgrade program is foreseen to increase the primary beam intensity as well as the beam brilliance. A detailed understanding of the beam dynamics during acceleration and the transport of space charge dominated beams is necessary. For this purpose the beam brilliance dependency on the phase advances in the Alvarez DTL was studied. Machine investigations were performed with various beam diagnostics devices established in the UNILAC. Measurements done in 2006 using a high intensity heavy ion beam coincide with the beam dynamics work package of the European JRA "high intensity pulsed proton injector" (HIPPI). Results of these measurements are presented as well as corresponding beam dynamics simulations.

INTRODUCTION

The GSI heavy ion accelerator complex consists presently of the UNIversal LInear ACcelerator UNILAC (Figure 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 2.2keV/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.