C. Martens

Overview of the RF source development programme at IPP Garching

The development of a large-area RF source for negative hydrogen ions, an official EFDA task agreement, is aiming at demonstrating ITER-relevant ion source parameters. This implies a current density of 200?A?m?2 accelerated D? ions at a source filling pressure of ?0.3?Pa and an electron-to-ion ratio of ?1 from an extraction area similar to the positive-ion based sources at JET and ASDEX Upgrade and for pulse lengths of up to 1?h. The work is progressing along three lines in parallel: (i) optimization of current densities at low pressure and electron/ion ratio, utilizing small extraction areas (<0.01?m2) and short pulses (<6?s), in this parameter range the ITER requirements are met or even exceeded; (ii) investigation on extended extraction areas (<0.03?m2) and pulse lengths of up to 3600?s and (iii) investigation of a size-scaling on a half-size ITER plasma source. Three different test beds are being used to carry out these investigations in parallel. An extensive diagnostic and modelling programme accompanies the activities. The paper discusses the recent achievements and the status in these three areas of development.

Physical performance analysis and progress of the development of the negative ion RF source for the ITER NBI system

For heating and current drive the neutral beam injection (NBI) system for ITER requires a 1 MeV deuterium beam for up to 1 h pulse length. In order to inject the required 17 MW the large area source (1.9 m × 0.9 m) has to deliver 40 A of negative ion current at the specified source pressure of 0.3 Pa. In 2007, the IPP RF driven negative hydrogen ion source was chosen by the ITER board as the new reference source for the ITER NBI system due to, in principle, its maintenance free operation and the progress in the RF source development. The performance analysis of the IPP RF sources is strongly supported by an extensive diagnostic program and modelling of the source and beam extraction. The control of the plasma chemistry and the processes in the plasma region near the extraction system are the most critical topics for source optimization both for long pulse operation as well as for the source homogeneity. The long pulse stability has been demonstrated at the test facility MANITU which is now operating routinely at stable pulses of up to 10 min with parameters near the ITER requirements. A quite uniform plasma illumination of a large area source (0.8 m × 0.8 m) has been demonstrated at the ion source test facility RADI. The new test facility ELISE presently planned at IPP is being designed for long pulse plasma operation and short pulse, but large-scale extraction from a half-size ITER source which is an important intermediate step towards ITER NBI.

Low Pressure and High Power RF Sources for Negative Hydrogen Ions for Fusion Applications (ITER neutral beam injection) (invited)

The international fusion experiment ITER requires for the plasma heating and current drive a neutral beam injection system based on negative hydrogen ion sources at 0.3 Pa. The ion source must deliver a current of 40 A D(-) for up to 1 h with an accelerated current density of 200 Am/(2) and a ratio of coextracted electrons to ions below 1. The extraction area is 0.2 m(2) from an aperture array with an envelope of 1.5 x 0.6 m(2). A high power rf-driven negative ion source has been successfully developed at the Max-Planck Institute for Plasma Physics (IPP) at three test facilities in parallel. Current densities of 330 and 230 Am/(2) have been achieved for hydrogen and deuterium, respectively, at a pressure of 0.3 Pa and an electron/ion ratio below 1 for a small extraction area (0.007 m(2)) and short pulses (<4 s). In the long pulse experiment, equipped with an extraction area of 0.02 m(2), the pulse length has been extended to 3600 s. A large rf source, with the width and half the height of the ITER source but without extraction system, is intended to demonstrate the size scaling and plasma homogeneity of rf ion sources. The source operates routinely now. First results on plasma homogeneity obtained from optical emission spectroscopy and Langmuir probes are very promising. Based on the success of the IPP development program, the high power rf-driven negative ion source has been chosen recently for the ITER beam systems in the ITER design review process.

RF-Plasma Source Commissioning in Indian Negative Ion Facility

The Indian program of the RF based negative ion source has started off with the commissioning of ROBIN, the inductively coupled RF based negative ion source facility under establishment at Institute for Plasma research (IPR), India. The facility is being developed under a technology transfer agreement with IPP Garching. It consists of a single RF driver based beam source (BATMAN replica) coupled to a 100 kW, 1 MHz RF generator with a self excited oscillator, through a matching network, for plasma production and ion extraction and acceleration. The delivery of the RF generator and the RF plasma source without the accelerator, has enabled initiation of plasma production experiments. The recent experimental campaign has established the matching circuit parameters that result in plasma production with density in the range of 0.5–1×1018/m3, at operational gas pressures ranging between 0.4–1 Pa. Various configurations of the matching network have been experimented upon to obtain a stable operation of the set up...

Commissioning of the negative ion testbed ELISE

The tests of the large RF driven sources for the ITER neutral beam system will be started on the neutral beam test facility PRIMA in Padua not before 2015. As an important intermediate step a half size ITER source has been designed at Max Planck Institute for Plasma Physics (IPP) and will be operated on the new test facility ELISE (Extraction from a Large Ion Source Experiment) which is presently being commissioned. The target is to generate a negative ion beam of 20 A, accelerated to 60 keV. Up to now all components of the test facility are assembled, the power supply, the cooling and the control system have been commissioned and the first plasma will be initiated in September. In preparatory experiments the mutual inductance of two adjacent drivers has been investigated and the coupling of a total RF power of 280 kW to a similar half size source has been demonstrated.

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

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/m2 and 230 A/m2 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 (7.0×10−3 m2) 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 m2. 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 ph...

Development of a rf negative-ion source for ITER neutral beam injection

The development at IPP of a large-area rf source for negative hydrogen ions, an official EFDA task agreement, aims to demonstrate ITER-relevant source parameters. This implies a current density of 20mAcm−2 accelerated D− at a source-filling pressure of <0.3Pa, an electron to ion ratio of <1, and for pulse lengths of up to 1h. The principle suitability concerning current density, pressure, and electron content has been demonstrated with the test facility Bavarian Test Machine for Negative Ions but with only small extraction area (70cm2) and for pulse length of <6s. The further development concentrates now on long pulse operation at the test stand Multi-Ampere Negative Ion Test Unit (MANITU), which became operational this spring. For source size extension from 70to1000cm2 MANITU and a third test facility, currently under development, called RADI will be used. This article will report on the latest results of the work in progress. A critical issue for ITER is reliable source operation at high current densiti...

Status of the ELISE Test Facility

The test facility ELISE, equipped with a large radio frequency (RF) driven ion source (1×0.9 m2) of half the size of the ion source for the ITER neutral beam injection (NBI) system, is operational since beginning of 2013. The first experimental campaign was dedicated to a thorough qualification of the test facility and its diagnostic tools at low RF power (80 kW in total, i.e. 20 kW per driver) in volume operation, i.e. operation without cesium, where the negative hydrogen ion production is done in the plasma volume only. This paper reports on the main results of the second and third experimental campaigns, where Cs was inserted in the ion source for an enhancement of the negative ion production by the surface process. The second experimental campaign was done still with low RF power, both for hydrogen and deuterium, with pulse lengths of up to 500 s. The results of this campaign are rather encouraging, especially in hydrogen, where large current densities with respect to the low RF power could be achieve...