Progress of the development of the IPP RF negative ion source for the ITER neutral beam system

Abstract

Abstract. IPP Garching has successfully developed a RF driven negative ion source for the ITER neutral beam injection system. The RF source is now an interesting alternative to the reference design with filamented sources due to its in principle maintenance-free operation. Current densities of 330 A/m 2 and 230 A/m 2 have been achieved for hydrogen and deuterium, respectively, at a pressure of 0.3 Pa and an electron/ion ratio of 1 for a small extraction area (7.0x10 -3 m 2 ) and short pulses (< 4 s). Reliable deuterium operation with more than 150 pulses in the required parameter range was obtained by an improved cesium operation utilizing a control of all source temperatures (grid as well as source body) and monitoring the amount of cesium in the source. The development concentrates now on extending the pulse length to up to 1 hour and extending the size of the source. The long pulse test bed went into operation last year; pulses of up to some 100 seconds with more or less stable conditions in terms of extracted currents and Cs dynamics have been achieved with current densities in the range of 150 -200 A/m 2 in hydrogen operation. The pulse length, however, is still limited by non-sufficient cooling of some parts of the source and the RF circuit. The commissioning of the so-called "half-size" source test facility started recently with the first plasma pulses; this large RF source with the width and half the height of the ITER NNBI source is dedicated to the demonstration of the homogeneity of a large RF plasma -extraction is foreseen in a latter phase -and the tests of an ITER-relevant RF circuit.

Vibrationally resolved ionization cross sections for the ground state and electronically excited states of the hydrogen molecule

“…A volume recombination channel is Molecular Assisted Recombination (MAR) [3,4] which is based on ionization of hydrogen molecules, followed by dissociative recombination of the molecular ions. It has been shown in [5] that the contribution of MAR to the total plasma recombination in the divertor can be in the order of several 10 % Low-temperature low-pressure hydrogen plasmas, for example in ion sources for neutral beam heating (NBI) of fusion experiments [6], linear plasma generators [7] or small laboratory experiments, can be in the socalled recombining plasma regime, characterized by low electron density and temperature. In such recombining plasmas the recombination of atomic and molecular hydrogen ions is of high relevance for populating excited states in the hydrogen atom.…”

Design of the “half-size” ITER neutral beam source for the test facility ELISE

“…It is planned to manufacture and assemble the test facility within two years from the start of the project. (3) Grounded grid 60 kW (4) ( …”

“…The installation of a bias plate enhanced the extracted negative ion current significantly on the test facility BATMAN [3,5] and was essential for deuterium experiments. For ELISE a cooled bias plate is foreseen as an option with no individual apertures but "window frame" like openings around the beamlet groups (figure 9).…”

“…The rf source development for negative hydrogen ions at IPP has achieved the ITER targets with respect to current density (33 mA/cm 2 H -and 23 mA/cm 2 D -at the calorimeter) and pulse length (1h) at the IPP testbeds BATMAN and MANITU, but still with small extraction areas of 70 cm 2 and 200 cm 2 , respectively [1,2,3]. In addition a nearly half-size ITER plasma source has been constructed and operated since 2006 at the test facility RADI but only allowing plasma operation without extraction.…”

Magnetic filter field for ELISE––Concepts and design

“…In small test facilities at IPP Garching these current densities at the required parameters have been reached simultaneously [4][5][6][7]. An important step to support the development of the full size ion source and injector test beds at RFX Padua, is the IPP experiment ELISE, which is currently in the commissioning phase in Garching [8].…”