50 Jahre GSI

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Basic plasma investigations on the Frankfurt high intensity proton source with an electrostatic 127° cylinder spectrometer

For the International Fusion Materials Irradiation Facility, a new volume source has been developed and tested in 1999. The plasma generation is performed by means of a filament-driven arc discharge. Besides, a solenoid for the plasma confinement, the ion source is equipped with a filter magnet to control the electron energy in the plasma. Using a 127° cylinder spectrometer, the energy distributions of H+, H2+, H3+ and electrons as a function of different discharge parameters were measured. Based on these investigations, fundamental plasma parameters are derived, such as plasma-wall potential, electron and ion temperatures. Furthermore, with the knowledge of the electron-energy distributions, it is possible to verify the mechanism of the proton generation in the hydrogen plasma. This paper summarizes the results of basic plasma investigations. The goal of these investigations was to get a better understanding of the plasma physics within the proton source. In addition, it was an aim to gain insight into the trend of experimental results and to be able to improve the ion source performance.  more...

Author: R. Hollinger et al.

Status of vacuum arc ion source development for injection of high current uranium ion beams into the GSI accelerator facil

To fill up the GSI heavy ion synchrotron (SIS) 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 (UNILAC) 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 into an accelerator without objection.

In this article we present the improvements of the ion source with the most important operational data.

As part of the ion source development the ion and electron energy distributions were measured with an electrostatic cylinder spectrometer device. The energy spectrometer discriminates charged particles with different energy to charge ratio which – in case of different ion species within an extracted beam – allows a charge sensitive evaluation of ion energy distributions. Energy distributions are measured for various discharge parameters, i.e. arc current, magnetic flux densities close to the discharge region, and cathode materials. Different plasma parameters can be derived from these measurements: the anode drop, charge resolved mean energy and the energy spread of ions, mean electron energy and electron temperature. The electron energy may support the development of a plasma model of a vacuum arc plasma consisting of high charge states.

Observations of the vacuum arc with a digital video camera have been carried out as well as three-dimensional computer simulations for the multi-aperture accel–decel extraction system.   more...

Author: R. Hollinger et al.