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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 achieved at a ratio of co-extracted electrons to extracted ions of 0.5-0.6 at the relevant source pressure of 0.3 Pa. Similar large extracted ion currents could be achieved also in deuterium, but with larger amounts of co-extracted electrons. The required ratio of co-extracted electrons to extracted ions of one could be achieved only in short pulses. The third experimental campaign aimed then for approaching the required ITER NBI parameters with respect to the ion and electron extracted currents, both for hydrogen and deuterium, by increasing the RF power with short pulses, i.e. beam-on times of up to 10 s and RF-on time up to 20 s. Current densities near the ITER NBI requirements could be achieved in hydrogen at a ratio of co-extracted electrons to extracted ions of 0.5-0.6 at the relevant source pressure of 0.3 Pa. As it was the case for the low RF operation, the required filter field was significantly lower than expected from the experience with the small prototype RF source. Similar large extracted ion currents could be achieved also in deuterium, but with larger amounts of co-extracted electrons; the main problem in deuterium operation are the non-stable currents of the co-extracted electrons, most probably caused by the high dynamic of the Cs redistribution in the system. The reasons for this larger instability are still under investigation. [ABSTRACT FROM AUTHOR]

The RF-driven negative hydrogen ion source (H, D) for the international fusion experiment ITER has a width of 0.9 m and a height of 1.9 m and is based on a scale prototype source being in operation at the IPP test facilities BATMAN and MANITU for many years. Among the challenges to meet the required parameters in a caesiated source at a source pressure of 0.3 Pa or less is the challenge in size scaling of a factor of eight. As an intermediate step a ¼ scale ITER source went into operation at the IPP test facility ELISE with the first plasma in February 2013. The experience and results gained so far at ELISE allowed a size scaling study from the prototype source towards the ITER relevant size at ELISE, in which operational issues, physical aspects and the source performance is addressed, highlighting differences as well as similarities. The most ITER relevant results are: low pressure operation down to 0.2 Pa is possible without problems; the magnetic filter field created by a current in the plasma grid is sufficient to reduce the electron temperature below the target value of 1 eV and to reduce together with the bias applied between the differently shaped bias plate and the plasma grid the amount of co-extracted electrons. An asymmetry of the co-extracted electron currents in the two grid segments is measured, varying strongly with filter field and bias. Contrary to the prototype source, a dedicated plasma drift in vertical direction is not observed. As in the prototype source, the performance in deuterium is limited by the amount of co-extracted electrons in short as well as in long pulse operation. Caesium conditioning is much harder in deuterium than in hydrogen for which fast and reproducible conditioning is achieved. First estimates reveal a caesium consumption comparable to the one in the prototype source despite the large size. [ABSTRACT FROM AUTHOR]

The ITER project requires additional heating provided by two injectors of neutral beams resulting from the neutralisation of accelerated negative ions. To study and optimise negative ion production, the SPIDER test facility (particle energy 100keV; beam current 50A) is under construction in Padova, with the aim of testing beam characteristics and to verify the source proper operation. The SPIDER beam will be characterised by the instrumented calorimeter STRIKE, whose main components are one-directional carbon fibre carbon composite tiles. Some prototype tiles have been employed in 2012 as a small-scale version (mini-STRIKE) of the entire system to investigate the features of the beam from BATMAN at IPP-Garching. As the BATMAN beamlets are superposed at the measurement position, about 1m from the grounded grid, an actively cooled copper mask is located in front of the tiles; holes in the mask create an artificial beamlet structure. Recently the mini-STRIKE has been updated, taking into account the results obtained in the first campaign. In particular the spatial resolution of the system has been improved by increasing the number of the copper mask holes. Moreover a custom measurement system has been realized for the thermocouple signals and employed in BATMAN in view of its use in SPIDER. The present contribution gives a description of the new design of the system as well as of the thermocouple measurements system and its field test. A new series of measurements has been carried out in BATMAN. The BATMAN beam characterisation in different experimental conditions is presented. [ABSTRACT FROM AUTHOR]

The negative ion source test facility ELISE (Extraction from a Large Ion Source Experiment) is in operation since beginning of 2013 at the Max-Planck-Institut für Plasmaphysik (IPP) in Garching bei München. The large radio frequency driven ion source of ELISE is about 1×1 m² in size (1/2 the ITER source) and can produce a plasma for up to 1h. Negative ions can be extracted and accelerated by an ITER-like extraction system made of 3 grids with an area of 0.1m², for 10 s every 3 minutes. A total accelerating voltage of up to 60kV is available, i.e. a maximum ion beam power of about 1.2 MW can be produced. ELISE is equipped with several beam diagnostic tools for the evaluation of the beam characteristics. In order to evaluate the beam properties with a high level of detail, a sophisticated diagnostic calorimeter has been installed in the test facility at the end of 2013, starting operation in January 2014. The diagnostic calorimeter is split into 4 copper plates with separate water calorimetry for each of the plates. Each calorimeter plate is made of 15×15 copper blocks, which act as many separate inertial calorimeters and are attached to a copper plate with an embedded cooling circuit. The block geometry and the connection with the cooling plate are optimized to accurately measure the time-averaged power of the 10 s ion beam. The surface of the blocks is covered with a black coating that allows infrared (IR) thermography which provides a 2D profile of the beam power density. In order to calibrate the IR thermography, 48 thermocouples are installed in as many blocks, arranged in two vertical and two horizontal rows. The paper describes the beam calorimetry in ELISE, including the methods used for the IR thermography, the water calorimetry and the analytical methods for beam profile evaluation. It is shown how the maximum beam inhomogeneity amounts to 13% in average. The beam divergence derived by IR thermography ranges between 1° and 4° and correlates relatively well with the values measured by beam emission spectroscopy with up to 30% difference. It has also been observed that the beam inhomogeneity decreases with lower beam divergence. [ABSTRACT FROM AUTHOR]

The development of a radio frequency (RF) driven source for negative hydrogen ions for the neutral beam heating devices of fusion experiments has been successfully carried out at IPP since 1996 on the test facility BATMAN. The required ITER parameters have been achieved with the prototype source consisting of a cylindrical driver on the back side of a racetrack like expansion chamber. The extraction system, called "Large Area Grid" (LAG) was derived from a positive ion accelerator from ASDEX Upgrade (AUG) using its aperture size (ø 8 mm) and pattern but replacing the first two electrodes and masking down the extraction area to 70 cm². BATMAN is a well diagnosed and highly flexible test facility which will be kept operational in parallel to the half size ITER source test facility ELISE for further developments to improve the RF efficiency and the beam properties. It is therefore planned to upgrade BATMAN with a new ITER-like grid system (ILG) representing almost one ITER beamlet group, namely 5 x 14 apertures (ø 14 mm). Additionally to the standard three grid extraction system a repeller electrode upstream of the grounded grid can optionally be installed which is positively charged against it by 2 kV. This is designated to affect the onset of the space charge compensation downstream of the grounded grid and to reduce the backstreaming of positive ions from the drift space backwards into the ion source. For magnetic filter field studies a plasma grid current up to 3 kA will be available as well as permanent magnets embedded into a diagnostic flange or in an external magnet frame. Furthermore different source vessels and source configurations are under discussion for BATMAN, e.g. using the AUG type racetrack RF source as driver instead of the circular one or modifying the expansion chamber for a more flexible position of the external magnet frame. [ABSTRACT FROM AUTHOR]

NBI systems based on the generation, acceleration and neutralization of negative hydrogen or deuterium ions are foreseen for heating and current drive in ITER. Since 2007 the RF driven ion source prototype developed at the Max Planck Institut für Plasmaphysik (IPP) is the ITER reference source. Negative hydrogen ions are predominantly produced by conversion of hydrogen atoms or positive ions at the cesiated surface of the plasma grid (PG), the first grid of a three-grid extraction system. In interaction of the charged plasma particles with a magnetic filter field and a bias voltage applied to the PG an extended boundary layer evolves - a several centimeters thick plasma volume close to the PG relevant for the transport and extraction of the negative hydrogen ions. Aim of this work is to investigate the relative relevance of the negative hydrogen ion production by conversion of atoms compared to conversion of positive ions. The ratio of these two conversion channels is connected to the homogeneity of the extracted negative ion beam. Three codes dealing with the relevant physical processes in the boundary layer are introduced and applied. The most recent code results indicate that conversion of atoms is the dominant production channel and that for ensuring a homogeneous negative ion beam production the gas uniformity close to the PG is of greater importance than the plasma uniformity. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The homogeneity of the extracted current density from the large RF driven negative hydrogen ion sources of the ITER neutral beam system is a critical issue for the transmission of the negative ion beam through the accelerator and the beamline components. As a first test, the beam homogeneity at the IPP long pulse test facility MANITU is measured by means of the divergence and the stripping profiles obtained with a spatially resolved Doppler-shift spectroscopy system. Since MANITU is typically operating below the optimum perveance, an increase in the divergence corresponds to a lower local extracted negative ion current density if the extraction voltage is constant. The beam Hα Doppler-shift spectroscopy is a rather simple tool, as no absolute calibration-both for the wavelength and the emission-is necessary. Even no relative calibration of the different used lines of sight is necessary for divergence and stripping profiles as these quantities can be obtained by the line broadening of the Doppler-shifted peak and the ratio of the integral of the stripping peak to the integral of the Doppler-shifted peak, respectively. The paper describes the Hα MANITU Doppler-shift spectroscopy system which is now operating routinely and the evaluation methods of the divergence and the stripping profiles. Beam homogeneity measurements are presented for different extraction areas and magnetic filter field configurations both for Hydrogen and Deuterium operation; the results are compared with homogeneity measurements of the source plasma. The stripping loss measurements are compared with model calculations. [ABSTRACT FROM AUTHOR]

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 for RF powers ranging between 25-85 kW and pulse lengths ranging between 4-20 s. It has been observed that the range of the parameters of the matching circuit, over which the frequency of the power supply is stable, is narrow and further experiments with increased number of turns in the coil are in the pipeline to see if the range can be widened. In this paper, the description of the experimental system and the commissioning data related to the optimisation of the various parameters of the matching network, to obtain stable plasma of required density, are presented and discussed. [ABSTRACT FROM AUTHOR]

The neutral beam injection (NBI) system of ITER is based on a large RF driven negative hydrogen ion source. For good beam transmission ITER requires a beam homogeneity of better than 10%. The plasma uniformity and the correlation with the beam homogeneity are being investigated at the prototype ion sources at IPP. Detailed studies are carried out at the long pulse test facility MANITU with a source of roughly 1/8 of the ITER source size. The plasma homogeneity close to plasma grid is measured by optical emission spectroscopy and by fixed Langmuir probes working in the ion saturation region. The beam homogeneity is measured with a spatially resolved Hα Doppler-shifted beam spectroscopy system. The plasma top-to-bottom symmetry improves with increasing RF power and increasing bias voltage which is applied to suppress the co-extracted electron current. The symmetry is better in deuterium than in hydrogen. The boundary layer near the plasma grid determines the plasma symmetry. At high ion currents with a low amount of co-extracted electrons the plasma is symmetrical and the beam homogeneity is typically 5–10% (RMS). The size scaling and the influence of the magnetic field strength of the filter field created by a plasma grid current is studied at the test facility RADI (roughly a 1/2 size ITER source) at ITER relevant RF power levels. In volume operation in deuterium (non-cesiated source), the plasma illumination of the grid is satisfying. [ABSTRACT FROM AUTHOR]

In 2007 the IPP RF driven negative hydrogen ion source was chosen by the ITER board as the new reference source for the ITER neutral beam system. In order to support the design of the Neutral Beam Test Facility in Padua and its commissioning and operating phases, IPP is presently constructing a new test facility ELISE (Extraction from a Large Ion Source Experiment) for a large-scale extraction from a half-size ITER RF source. Plasma operation of up to one hour is foreseen; but due to the limits of the IPP HV system, pulsed extraction only is possible. The extraction system is designed for acceleration of negative ions of up to 60 kV. The start of the ELISE operation is planned for middle of 2010. The aim of the design of the ELISE source and extraction system was to be as close as possible to the ITER design; it has however some modifications allowing a better diagnostic access as well as more flexibility for exploring open questions. The design was also supported by diagnostics and modeling efforts of the processes leading to negative ion production and extraction in a RF source. [ABSTRACT FROM AUTHOR]

IPP Garching is developing H-/D- RF ion sources for the ITER neutral beam system. On the MANITU testbed the experiments are focussed on long pulse H-/D- beam extraction with a 100 kW prototype source. The negative ion production is based on surface conversion of atoms and positive ions on Caesium layers. In long pulses with H- beam extraction the ion currents were stable but with too high fraction of co-extracted electrons. The electron current could be lowered considerably by avoiding copper impurities from the Faraday screen in the plasma which was achieved by coating of the inner surfaces of the source with Molybdenum. A positive bias potential with respect to the source applied to the plasma grid, the bias plate or to a metal rod installed near the plasma grid enables regulation of the electron current during long pulses. In this way low values consistent with the ITER requirements can be achieved without significant loss of ion current. [ABSTRACT FROM AUTHOR]

The injection of energetic neutral hydrogen atoms plays an important part for plasma heating in fusion experiments. In order to fulfill the requirements of the ITER neutral beam injection (NBI), a RF-driven ion source based on the generation of negative ions prior to neutralization has been successfully developed at IPP Garching. Negative hydrogen ions are generated on a cesiated converter surface (plasma grid) by neutral particles and positive ions and are then transported to the extraction apertures, where the ion beam formation process takes place. Numerical models are necessary to include the relevant physical aspects of these processes. The Monte Carlo transport code CSFLOW is used to describe the dynamical behavior of the cesium distribution on the source walls during vacuum operation. The negative ion transport process is simulated by means of the probabilistic ion transport code TRAJAN, focussing on the effects of aperture diameter variations in mono- and multiaperture extraction systems. A simulation of ion beam formation is carried out with the KOBRA3 ray tracing code, which allows a full 3d potential solution without any symmetry restriction. This is necessary to simulate beam steering effects by a non-axisymmetric magnetic field and electrode configuration for the design of the extraction systems for future negative ion experiments. [ABSTRACT FROM AUTHOR]

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 physical mechanisms are discussed with an emphasis on electron suppression. [ABSTRACT FROM AUTHOR]

IPP Garching is heavily involved in the development of an ion source for Neutral Beam Heating of the ITER Tokamak. RF driven ion sources have been successfully developed and are in operation on the ASDEX-Upgrade Tokamak for positive ion based NBH by the NB Heating group at IPP Garching. Building on this experience a RF driven H- ion source has been under development at IPP Garching as an alternative to the ITER reference design ion source. The number of test beds devoted to source development for ITER has increased from one (BATMAN) by the addition of two test beds (MANITU, RADI). This paper contains descriptions of the three test beds. Results on diagnostic development using laser photodetachment and cavity ringdown spectroscopy are given for BATMAN. The latest results for long pulse development on MANITU are presented including the to date longest pulse (600 s). As well, details of source modifications necessitated for pulses in excess of 100 s are given. The newest test bed RADI is still being commissioned and only technical details of the test bed are included in this paper. The final topic of the paper is an investigation into the effects of biasing the plasma grid. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

The negative ion beam extraction from the multi-hole ion source is considered. Results of numerical simulations (based on PIC method) of the influence of transversal magnetic field aplied near the extraction grid (filter field), and in the plasma chamber volume (confining field) are presented. The application of confinig field results in significantly increased negative ions yield. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

IPP Garching has spent several years developing a RF driven H[sup -] ion source intended to be an alternative to the current ITER (International Thermonuclear Experimental Reactor) reference design ion source. A RF driven source offers a number of advantages to ITER in terms of reduced costs and maintenance requirements. Although the RF driven ion source has shown itself to be competitive with a standard arc filament ion source for positive ions many questions still remain on the physics behind the production of the H[sup -] ion beam extracted from the source. With the improvements that have been implemented to the BATMAN (Bavarian Test Machine for Negative Ions) facility over the last two years it is now possible to study both the extracted ion beam and the plasma in the vicinity of the extraction grid in greater detail. [ABSTRACT FROM AUTHOR]