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Beam extraction at the large ELISE test facility is currently possible only pulsed, with short extraction phases, so-called extraction blips, of up to 10 s each ≈150 s. Over the past years, a good insight into the physics of this operational mode has been gained for both hydrogen and deuterium operation. The uniformity of the co-extracted electrons was identified as a key issue and it was possible to achieve 1000 s plasma pulses in hydrogen with repetitive extraction blips and an extracted current density of over 90 % of the ITER target value by improving the co-extracted electron symmetry. In deuterium roughly 67 % of the ITER target for the extracted current density has been achieved for long pulses. During such pulses an overall increase of the co-extracted electron current is typically observed between one blip and the next one, even though the electron current is observed to actually decrease during each blip. These opposing effects are explained by different caesium dynamics during the source plasma phase when compared to the beam phase and they were one motivation behind the currently ongoing upgrade of ELISE to a CW extraction system. This update consists of two main hardware changes: i) installation of a new CW high voltage power supply and ii) installation of a CW beam calorimeter. Being able to achieve beam pulses of up to 1 hour will allow knowledge to be gained on the physics of caesium redistribution and conditioning over the long timescales needed for ITER operation. [ABSTRACT FROM AUTHOR]

The ion sources used in the ITER NBI beam lines will deliver over one hour a current density of 200 A/m² negative deuterium ions, accelerated to 1 MeV or over 1000 s a current density of 230 A/m² negative hydrogen ions, accelerated to 870 keV. The ELISE ion source (0.9×1.0 m² with an extraction area of 0.1 m²) has half the size of the ion source foreseen for ITER. Aim of the ELISE test facility is to demonstrate that such large RF driven negative ion sources can achieve the following parameters at a filling pressure of 0.3 Pa: extracted current densities of 286 A/m² in deuterium and 329 A/m² in hydrogen, a ratio of co-extracted electrons to extracted ions below one and a beam homogeneity better than 90 %. The pulse length should be one hour in deuterium and 1000 s in hydrogen. Reliable and reproducible long pulse operation (up to one hour) with high RF power (up to 75 kW/driver) is possible after technical issues have been resolved stepwise. Experiments are now focused on the physics of approaching the requirements for the ITER NBI ion source. The most crucial factor limiting the source performance during long pulses with high RF power is a steady increase and a strong top-bottom asymmetry in the co-extracted electron current. Measures for partially counteracting this increase and asymmetry are external permanent magnets strengthening the standard magnetic filter field, internal potential rods and a new caesium conditioning technique, the so-called caesium overconditioning. Combining these measures enabled performing reproducible high-performance 1200 s pulses in hydrogen. During such pulses, about 90 % of the ITER requirement for the extracted negative ion current density were achieved while exceeding the requirement for the accelerated current density. [ABSTRACT FROM AUTHOR]

The goal of the ELISE test facility is to demonstrate that large RF-driven negative ion sources (l x l m 2 source area with 360 kW installed RF power) can achieve the parameters required for the ITER beam sources in terms of current densities and beam homogeneity at a filling pressure of 0.3 Pa for pulse lengths of up to one hour. With the experience in operation of the test facility, the beam source inspection and maintenance as well as with the results of the achieved source performance so far, conclusions are drawn for commissioning and operation of the ITER beam sources. Addressed are critical technical RF issues, extrapolations to the required RF power, Cs consumption and Cs ovens, the need of adjusting the magnetic filter field strength as well as the temporal dynamic and spatial asymmetry of the co-extracted electron current. It is proposed to relax the low pressure limit to 0.4 Pa and to replace the fixed electron-to-ion ratio by a power density limit for the extraction grid. This would be highly beneficial for controlling the co-extracted electrons. [ABSTRACT FROM AUTHOR]

The ion source of the ELISE test facility (0.9×1.0 m² with an extraction area of 0.1 m²) has half the size of the ion source foreseen for the ITER NBI beam lines. Aim of ELISE is to demonstrate that such large RF driven negative ion sources can achieve the following parameters at a filling pressure of 0.3 Pa and for pulse lengths of up to one hour: extracted current densities of 28.5 mA/cm² in deuterium and 33.0 mA/cm² in hydrogen, a ratio of co-extracted electrons to extracted ions below one and deviations in the uniformity of the extracted beam of less than 10 %. From the results obtained at ELISE so far it can be deduced that for demonstrating the ITER parameters, an RF power of 80 kW/driver will be necessary, i.e. final aim is to demonstrate long pulses (up to one hour) at this power level and a stable source performance. The most crucial factor limiting the source performance during such pulses - in particular in deuterium - is a steady increase in the co-extracted electron current. This paper reports measures that counteract this steady increase, namely applying a dedicated long pulse caesium conditioning technique and modifying the filter field topology by adding strengthening external permanent magnets. Additionally, RF issues are discussed that prevented increasing the RF power towards the target value. Although it was not possible up to now to perform long pulses at 80 kW/driver, a significant improvement of the source performance and its stability are demonstrated. The latter allowed performing the very first 1 h deuterium pulse in ELISE. [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 ITER neutral beam heating systems are based on the production and acceleration of negative ions (H/D) up to 1 MV. The requirements for the beam properties are strict: a low core beam divergence (< 0.4 °) together with a low source pressure (≤ 0.3Pa) would permit to reduce the ion losses along the beamline, keeping the stripping particle losses below 30%. However, the attainment of such beam properties is not straightforward. At IPP, the negative ion source testbed BATMAN (BAvarian Test MAchine for Negative ions) allows for deepening the knowledge of the determination of the beam properties. One of the diagnostics routinely used to this purpose is the Beam Emission Spectroscopy (BES): the Hα light emitted in the beam is detected and the corresponding spectra are evaluated to estimate the beam divergence and the stripping losses. The BES number of lines of sight in BATMAN has been recently increased: five horizontal lines of sight providing a vertical profile of the beam permit to characterize the negative ion beam properties in relation to the source parameters. Different methods of Hα spectra analysis are here taken into account and compared for the estimation of the beam divergence and the amount of stripping. In particular, to thoroughly study the effect of the space charge compensation on the beam divergence, an additional hydrogen injection line has been added in the tank, which allows for setting different background pressure values (one order of magnitude, from about 0.04Pa up to the source pressure) in the beam drift region. [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]

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 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 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]

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]

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]

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]