ECRIS 2002
Simulation of the Extraction from an ECRIS
The model describing the phenomena taking place in the extraction system of an ECR ion source has been extended. Electrons with arbitrary energy can now be used in the simulation to compensate the positive space charge of the ions close to the plasma boundary. The thickness of the resulting plasma boundary will increase if electrons with energies in the order of several 10 eV to several 100 eV are present. This effect seems to decrease the emittance slightly.
If the plasma density distribution is not homogeneous in the plane of the extraction system because the plasma is guided by the superposition of the hexapole and the solenoid the azimuthal electric field component together with the solenoidal magnetic field will increase the emittance. In azimuthal direction the potential drops within 30 degree in both azimuthal directions. Depending on the space charge this drop can be as high as several 100 Volts. This is a multiple of the ion energy within the plasma. That is why the plasma electrode should be placed at a location with a homogeneous plasma density distribution. On the other side the required ions should be able to reach that extraction electrode and not be trapped by any potential wall. To simulate these effects a 3D computer code is absolutely necessary.
Author: P. Spädtke
Development of the new High Temperature Oven for ECRIS
The evaporation from non gaseous materials with the miniature oven that was developed at GSI for temperatures between 600°C and 1500°C has become an elaborated and routinely used technique. The upper temperature limit of the GSI standard oven prevents the evaporation of materials with low vapor pressure. Therefore a new type of high temperature oven (HTO) is being developed for an operating temperature of up to 2000°C. After the first tests with a prototype outside the source some technical modifications were necessary for the tests in the ECR source to solve the problems with the high heating current and the lateral deformation of the heating wire. These modifications lead also to an increase of the heater lifetime and an easier and cheaper machining procedure. The upgraded HTO was successfully tested under real operation conditions inside the ion source with titanium at 1700°C. To increase the operating temperature step by step the next test was made with vanadium at 1800°C. A spectrum was obtained with 60 μA of V8+ at 16kV extraction voltage. By slightly increasing the oven temperature without retuning the source the V8+ level also increased up to 160μA. The next test with boron at a temperature near to 2000°C will be made in the future.
Author: R. Lang et al.
Experimental investigation of the afterglow operation
Besides the cw operation of the CAPRICE type ECRIS installed at the High Charge State Injector (HLI) of GSI the afterglow operating mode is favorable when providing beam for the Heavy Ion Synchrotron (SIS). The synchrotron requests high intensities in short pulses of several hundred microseconds but at a low repetition rate of typically 1 pulse per second. The major demands of accelerator injection are good long time stability and good pulse to pulse reproducibility of the ion beam. Following these boundary conditions experiments with different ion species were performed at the ECR injector test setup (EIS) which is copy of the HLI injection beam line. In order to find the best operating conditions for optimized afterglow performance systematic studies were performed with 136Xe, the heaviest stable rare gas isotope. Different rf pulse conditions (pulse length, repetition rate, pulse shape) were compared. The influence of the ion source parameters on the afterglow mode were studied in comparison to the cw mode.
Author: K.Tinschert et al.