Development of a vacuum arc ion source for injection of high current uranium ion beam into the unilac at GSI

To fill up the GSI heavy ion synchrotron (US) to its space charge limit with uranium ions, a new vacuum arc ion source (VARIS), based on the MEVVA IV ion source has been developed and implemented into operation. The ion source has proven its capability in several long period beam times at the high current injector at GSI. With the new ion source it was possible to exceed the space charge limit of 15 mA U⁴⁺ ions at the entrance of the linear accelerator (UN1LAC)for the very first time. The reliability as well as the noise behaviour has been improved to such a degree, that this ion source can be used for injection info an accelerator without objection. In this article we present the improvements of the ion Source with the most important operational data. The emission current density of the new ion source has been increased from 60 mA/cm² for the common used GSI-MEVVA to 170 mA/cm². This results in a full beam ion current of 156 mA at 35 kV with a fraction of four fold charged uranium ions of 67%. The analysed U⁴⁺ ion beam after dc post acceleration amounts to 25 mA at 131 kV which is 1.7 times higher than the requested ion beam current at the entrance of the RFQ. The reduced power density of the vacuum arc results in a higher efficiency and longer life time. Solenoids which are creating magnetic fields to enhance the charge state of the ions are no more placed inside the vacuum system. This ion source design results in a higher availability after ion source replacement at the injector, and longer life time.