The IPP RF Source: A High Power, Low Pressure Negative Ion Source For The Neutral Beam Injection System Of ITER

Abstract

Abstract. IPP Garching has successfully developed a RF driven negative ion source for the ITER neutral beam injection system. The RF source was chosen recently as the reference source for ITER 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 less than 1 for a small extraction area (7.0x10 -3 m 2 ) and short pulses (< 4 s). The development concentrates now on extending the pulse length and extending the size of the source on two dedicated test facilities. The pulse length can be extended up to one hour at the long pulse test facility having an extraction area of 0.02 m 2 . The large source test facility is equipped a large RF source with the width and half the height of the ITER beam source in order to demonstrate the homogeneity of a large RF plasma. The paper will give a short overview on the results achieved at the three test facilities of IPP; the underlying physical mechanisms are discussed with an emphasis on electron suppression.

Status of the ITER heating neutral beam system

“…This is an important consideration for ITER as the ion source will become highly activated during operation and all such operations must be carried out remotely. The RF driven source has achieved the extracted D and H current densities and coextracted electron fractions required for the ITER system at the required filling pressure, 0.3 Pa [1,2,3], and t -he consumption of caesium during operation of the RF driven source is found to be acceptable, unlike that of the filamented source. An initial assessment of the consumption is 3.5 x 10 g/s/aperture [4], which, if extrapolated to ITER gives 0.16 g/h of operation.…”

“…The only types of ion sources capable of meeting the extracted D − current densities required for neutral beam injectors are the arc driven or radio frequency (RF) driven caesiated ion sources [8][9][10]. The RF driven ion source of the type being developed at IPP, Garching, Germany has been chosen for ITER because no filaments are used during the operation and hence there is no need to regularly replace filaments.…”

“…The highest acceptable source filling pressure (the pressure measured prior to plasma formation in the source) has been calculated to be 0.3 Pa. The RF driven source has achieved the extracted D − and H − current densities and co-extracted electron fractions required for the ITER system at the filling pressure of 0.3 Pa [8][9][10].…”

Progress of the ELISE test facility: results of caesium operation with low RF power

“…For almost all the pulses, the bias current instead of the bias voltage was kept constant during the RF pulse. By keeping the currents constant the particle fluxes onto the plasma grid are kept constant which is beneficial for stable operation as demonstrated at the prototype sources at BATMAN and MANITU [14,48]. The dependence of the extracted ion current density and the electron/ion ratio on the filter field current is given in figure 20 for two different values of the extraction voltage at a well caesiated ELISE source.…”

Three-dimensional simulation of electron extraction process and optimization of magnetic field based on multi-aperture structure of negative hydrogen ion source

“…In the research of RF negative hydrogen ion source devices, the Max-Planck-Institute für Plasma Physik (IPP) in Germany, as an advanced research institution, has developed BATMAN, BATMAN upgrade, MANITU, ELISE and RADI experimental devices over the years [2][3][4]. These devices are characterized by different ion source size, pulse length, extraction area and RF power [1,[5][6][7][8]. RF ion sources can be divided into driver region, expansion region and extraction region.…”