Test Facility Extraction From A Large Ion Source Experiment Research Articles

ITER-relevant 600 s steady-state extraction of negative hydrogen ions at the test facility ELISE

Abstract The neutral beam heating system for the future international fusion experiment ITER will be based on RF driven ion sources delivering a large (≈1×2 m2) and homogeneous negative hydrogen or deuterium ion beam of several ten Amperes over up to several hundred seconds. The size scaling experiment ELISE (Extraction from a Large Ion Source Experiment) is an integral part of the R&D road-map towards the ITER neutral beam heating system. Recently, 90 % of the ITER target for the extracted current density was achieved in hydrogen for 600 s, increasing the pulse length over that such current densities are possible by a factor of more than ten. For ten second beam pulses the ITER target current density was achieved. These breakthrough results are made possible by a steady-state capable HV power supply together with an improved version of internal potential rods and a modified topology of the magnetic filter field.

Preparation of the ELISE test facility for long-pulse extraction of negative ion beams

The test facility ELISE (Extraction from a Large Ion Source Experiment) at IPP Garching, Germany, aims to demonstrate ITER-relevant negative ion beam parameters which are required for the NBI system of ITER. ELISE is equipped with a Radio Frequency driven source and an ITER‐like extraction system with half the ITER size. An H− or D− beam can be extracted for 10s every 3min from the continuously operating plasma source. The duration of the beam pulses is currently limited by the power supplies available at IPP. Although up to now record-setting 1h plasmas have been produced in H− as well as in D−, long plasma pulse operation with multiple beam blips showed a key issue: the co-extracted electron current during the extraction phase is strongly dynamic and temporally instable, particularly in D−. These instabilities are likely caused by back-streaming positive ions and Cs dynamics in the source. In order to investigate the source physics in long beam pulses, an upgrade of ELISE using a steady state high voltage power supply is envisaged. This upgrade requires a new steady state diagnostic calorimeter for which a few concepts are being investigated, which make use of several thermocouples, IR thermography and water calorimetry to measure beam intensity, divergence, profile and homogeneity. In addition the suitability of a tungsten wire calorimeter to characterize the steady state beam is being examined. Shielding of delicate components in the beam line, e.g. a large DN 1250mm gate valve, by means of suitable protection scrapers, is being considered. A selection of these technical solutions is presented and discussed in the paper.