A. Staebler

Computer Simulation of the Reionization Effects for the ASDEX-Upgrade Neutral Beam Injector

Powerful neutral beams used in many present-day magnetic fusion devices to heat the plasma to high temperatures must pass a region of finite background pressure where the magnetic stray field is rather high. Reionization of neutral beam particles and their subsequent deflection onto walls may lead to serious power loadings if no proper protection is provided. The simulation of this problem for the neutral beam injection system of the ASDEX-Upgrade tokamak is examined. The magnetic field distribution and the particle trajectories are calculated in full three-dimensional geometry. The statistical methods applied to simulate the {approximately} 10{sup 6} beam particles necessary to obtain a reliable power density distribution on the various surfaces of the duct region are described in some detail. Results are given for different magnetic field configurations of the tokamak. Because of the focusing effect of the strongly varying magnetic field, power densities in excess of 2 MW/m{sup 2} are found in extreme cases. Additional large area shieldings are installed to protect the most exposed regions of the entrance port of the vessel. 12 refs., 9 figs.

Large Scale Titanium Getter Pumps for the ASDEX-Upgrade Neutral Beam Injectors

For the ASDEX-Upgrade neutral beam injectors, each of which will deliver 6 MW of hydrogen, titanium getter pumps will be used as the fast pumping system. Each injector has a pumping speed of 2.800.000 l/s installed. The design of the pumps is based on the experience made with the smaller systems for ASDEX and Wendelstein 7-AS. Titanium is evaporated from compound wires onto cast aluminum surfaces, which are corrugated to enhance the pumping speed. The pumping speed measured at the testbed for two pumps confirms the design value. The capacity is enough for 1000 beam pulses at full power.

Initial Operation and Performance of the ASDEX Long-Pulse Injection System

The modified ASDEX neutral injection system started operation with long pulses (±2.5s) in spring 1987. The complete system has been operational since December 1987. Meanwhile more than 3000 ASDEX discharges have used neutral beam heating with a beam power of up to 80 % of the design value (3.2 MW). This paper reports the performance of the system in the first year of injection experiments with emphasis on the behaviour of the duct and the ion removal system.

PERFORMANCE OF THE FIRST ASDEX UPGRADE NEUTRAL BEAM INJECTOR

Plasmas of the ASDEX Upgrade tokamak have been heated with H 0 beams of up to 7 MW and D 0 beams of up to 10 MW. Beam modulation allows to inject at any power level between zero and full power. Measurements characterizing the NBI system performance, the power accountability, and the operational experience obtained so far are discussed.

DESIGN OF ION REMOVAL SYSTEM AND MAGNETIC SHIELDING FOR THE ASDEX-UPGRADE NEUTRAL INJECTION BEAM LINE

The ion removal system of the ASDEX Upgrade injection is presented. A careful shielding of high magnetic stray fields requires threedimensional computer analysis for a detailed solution.