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SUMMARY:Caesiated H- source operation with helium
DTSTART;VALUE=DATE-TIME:20180903T051000Z
DTEND;VALUE=DATE-TIME:20180903T053500Z
DTSTAMP;VALUE=DATE-TIME:20260909T093845Z
UID:indico-contribution-48-322@indico.inp.nsk.su
DESCRIPTION:Speakers: Katsuyoshi Tsumori (National Institute for Fusion Sc
 ience)\nThe consumption rate of caesium (Cs) for negative hydrogen (H-) io
 n source increases when the source operation gas is changed from hydrogen 
 to deuterium.  A clear indication that a deuterium discharge erodes Cs ato
 ms on the surface to increase work function\, and thus\, co-extracted elec
 tron current.  We have proposed a model that the enhanced sputtering yield
  of Cs from the plasma grid (PG) due to deuterium ions\, which carries mor
 e kinetic energy to Cs adsorbed on the surface directly or indirectly\, is
  the main reason for this fast dissipation of Cs.\nIntroduction of helium 
 (He) into discharge can verify the enhanced sputtering effect due to heavi
 er ions in ion source discharge.  Comparing the effect due to seeded Cs be
 fore and after the He injection into discharge through Cs OES signals as w
 ell as the H- density measured with cavity ring-down method\, the sputteri
 ng/evaporation enhancement due to He is estimated.  Neutral atoms and posi
 tive ions in the He discharge should cause enhanced sputtering like deuter
 ium\, while the system does not generate neutron under the induction of ac
 celeration voltage to diagnose the extracted negative ion beam.  Plasma pa
 rameters of the H2 and He plasmas will be investigated by diagnostics tool
 s installed on NIFS-RNIS (National Institute for Fusion Science\, Research
  and development Negative Ion Source) together with cavity ring down.  Enh
 anced consumption rate of Cs will be compared with proposed sputtering yie
 ld data to predict the rate for deuterium operation of negative ion source
 s.\n\nhttps://indico.inp.nsk.su/event/11/contributions/322/
LOCATION:
URL:https://indico.inp.nsk.su/event/11/contributions/322/
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BEGIN:VEVENT
SUMMARY:Influence of External Magnets and the Potential Rods on the Plasma
  Symmetry in the ELISE Ion Source
DTSTART;VALUE=DATE-TIME:20180903T044000Z
DTEND;VALUE=DATE-TIME:20180903T050500Z
DTSTAMP;VALUE=DATE-TIME:20260909T093845Z
UID:indico-contribution-48-367@indico.inp.nsk.su
DESCRIPTION:Speakers: Christian Wimmer (Max-Planck-Institut für Plasmaphy
 sik)\nThe Neutral Beam Injection (NBI) system for ITER requires large scal
 e sources for negative hydrogen ions. The ELISE test facility at IPP Garch
 ing uses a ½ scale ITER-source (extraction area of 0.1 m$^2$ at ELISE) an
 d shall demonstrate the feasibility of the ITER parameters (extracted $j_\
 \mathrm{H^-} = 329~ \\mathrm{A/m^2}$ for 1000 s\, $j_\\mathrm{D^-} = 286~\
 \mathrm{A/m^2}$ for 3600 s\, with a co-extracted electron current below th
 e ion current at a source filling pressure of below 0.3 Pa). In long pulse
 s the co-extracted electron current density $j_\\mathrm{e}$ is strongly in
 creasing and usually limits the source performance. Two measures for stabi
 lizing and lowering $j_\\mathrm{e}$ have been applied at ELISE in the past
 : on the one hand adding bars of permanent magnets outside of the source s
 trengthening the magnetic filter field and on the other hand the installat
 ion of potential rods perpendicular to the magnetic field lines close to t
 he extraction system. Since $\\mathbf{F} \\times \\mathbf{B}$ drifts lead 
 to a vertically asymmetric plasma\, an influence of both measures on the p
 lasma symmetry is expected by modifying the magnetic field or electric pot
 ential topology in the source. The plasma asymmetry is a crucial parameter
 \, since it may lead to an inhomogeneous beam under certain conditions. Th
 e change of the plasma symmetry close to the extraction system\, determine
 d by two double probes\, is presented.\n\nhttps://indico.inp.nsk.su/event/
 11/contributions/367/
LOCATION:
URL:https://indico.inp.nsk.su/event/11/contributions/367/
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SUMMARY:Long Pulse Operation at ELISE: Approaching the ITER Parameters
DTSTART;VALUE=DATE-TIME:20180903T041000Z
DTEND;VALUE=DATE-TIME:20180903T043500Z
DTSTAMP;VALUE=DATE-TIME:20260909T093845Z
UID:indico-contribution-48-369@indico.inp.nsk.su
DESCRIPTION:Speakers: Dirk Wünderlich (Max-Planck-Institut für Plasmaphy
 sik)\nThe ion source of the ELISE test facility ($0.9×1.0 \\\,\\mathrm{m}
 ^2$ with an extraction area of $0.1 \\\,\\mathrm{m}^2$) has half the size 
 of the ion source foreseen for the ITER NBI beam lines. Main aim of ELISE 
 is to demonstrate that such large RF driven negative ion sources can achie
 ve the following parameters at a filling pressure of $0.3 \\\,\\mathrm{Pa}
 $: extracted current densities of $28.5 \\\, \\mathrm{mA}/\\mathrm{cm}^2$ 
 in deuterium for a pulse length of $3600 \\\,\\mathrm{s}$ and $33.0 \\\, \
 \mathrm{mA}/\\mathrm{cm}^2$ in hydrogen for $1000 \\\, \\mathrm{s}$\, a ra
 tio of co-extracted electrons to extracted ions below one and deviations i
 n the uniformity of the extracted beam of less than $10 \\\, \\%$.\n\nThis
  presentation describes results of the recent ELISE experimental campaigns
  in hydrogen and deuterium. Focus is laid on long pulse operation (up to t
 he pulse length required for ITER) with high RF power (possible are up to 
 75 kW/driver). The performance obtained during such pulses is restricted m
 ainly by a strong temporal increase of the co-extracted electrons. Additio
 nally\, the co-extracted electron current can show a pronounced top-bottom
  asymmetry. For SPIDER and MITICA as well as for the ITER NBI system the l
 atter can pose a risk to the extraction grid (EG)\, acting as a dump for t
 hese electrons: even when the measured global amount of co-extracted elect
 rons is below the limit\, a strong asymmetry can result in local overheati
 ng of the EG.\n\nSeveral measures for reducing\, stabilizing and symmetriz
 ing the co-extracted electron current while not reducing significantly the
  extracted negative ion current have been investigated systematically. Exa
 mples are modifying the electrostatic potentials close to the extraction s
 ystem by means of elements additionally introduced into the source and mod
 ifying the temperatures of different ion source components. \n\nPresented 
 and discussed are extracted negative ions and co-extracted electron curren
 t densities obtained during these investigations as well as results of pla
 sma and beam diagnostics (indicating the plasma parameters and their homog
 eneity and the beam homogeneity\, respectively).\n\nhttps://indico.inp.nsk
 .su/event/11/contributions/369/
LOCATION:
URL:https://indico.inp.nsk.su/event/11/contributions/369/
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