Activities relevant to PWI in fusion devices of Slovenian Fusion Association SFA Association EURATOM

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Activities relevant to PWI in fusion devices of
Slovenian Fusion Association (SFA) (Association
EURATOM - MHST) Iztok Cade Joef Stefan
Institute, Ljubljana, Slovenia
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1. Introductory information on SFA 2. Physics
projects in the field of PWI 3. Overview of
individual projects 4. Relevance to particular
PWI tasks
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1. Introductory information on SFA

• CoA between EURATOM and MHST signed in March
  2005
• Institutions
• Joef Stefan Institute (JSI), Ljubljana
• / Coop. Nova Gorica Polytechnic and Faculty for
  Electrical Eng. UL /
  
• - University of Ljubljana (UL)/Faculty for
  Mechanical Eng.
• - Institute of Metals and Technology, Ljubljana
  (in prep.)
• Staff 40 (20 FTE)
• Projects 5 (1 1) Physics, 2 Underlying
  Technology,
• 2 Technology

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2. Physics projects in the field of PWI
P2. Interaction of vibrationally excited
hydrogen with fusion relevant materials (VEVOF)
(from June 4th, 2003 continuation of two year
CS project) P3. Heterogeneous catalytic
recombination of neutral hydrogen atoms on
fusion relevant materials (and atomic hydrogen
catalytic probe) (from January 1st, 2005) P5.
Application of ion beam analytical methods to
the studies of plasma wall interaction in
tokamaks (IBAF) (from January 1st, 2005) P6.
Deuterium retention and release from materials
complementary method to tritium methods (new)
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3. Overview of individual projects
P2 Interaction of vibrationally excited
hydrogen (H2, D2) with fusion relevant materials
(VEVOF) Iztok Cade1, Primo Pelicon1, Sabina
Markelj1, Zdravko Rupnik1, Milan Cercek2, Toma
Gyergyek2, and Vida igman3 1 Microanalytical
Centre, Department for Low and Medium Energy
Physics (F2), JSI, Ljubljana 2 Plasma Physics
Laboratory, Department for Reactor Physics (F8),
JSI, Ljubljana 3Nova Gorica Polytechnic, Nova
Gorica
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• Processes of interest
• - Vibrational distribution of molecules released
  from the surfaces due to thermal desorption and
  recombinative desorption for different surface
  temperature and composition.
• - Ratio of atomic to molecular species and its
  variation with the surface parameters.
• 2. Interaction of vibrationally excited molecules
  with plasma-facing materials
• - Change of vibrational distribution caused by
  interaction with surfaces,
• - Transfer of vibrational energy to the wall and
  its effects on erosion yields, and
• - Wall sticking probability for excited
  molecules.
• Isotope effect on above processes is of key
  interest.

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Final goal of experimental set-up

• Test atmosphere partially dissociated neutral
  hydrogen gas or low temperature hydrogen plasma.
• Vibrational spectroscopy of hydrogen molecules
  by detecting negative ions from dissociative
  electron attachment and determination of the rate
  of dissociation.
• In situ and in real time H and D depth profiling
  by ion beam analysis method ERDA (Elastic Recoil
  Detection Analysis).

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Detector of vibrationally excited hydrogen
molecules (DTVE)
Basics Diagnostic technique is based on the
detection of H- ions produced by dissociative
electron attachment (DEA) at and below about 4
eV incident electron energyy H2(X 1Sg,v)
e ? H2-(X 2Su) ? H- H

• Characteristics of 4 eV DEA
• Very strong rise of CS with v,R excitation (CSs
  in 10-16 cm2 range for high v)
• Vertical threshold production of zero - energy
  ions
• Pronounced isotope effect for low v

Same process for HD, D2, T2, Lifetime of H2- is
very short, 10-16 s.
Method first developed in LDMA (DIAM), UPMC, Paris
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New DTVE
B
Electrode material Ti Vacuum chamber and support
elements Al alloy Magnetic field Helmholtz coils
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New DTVE ion extraction principle
Efficient collection and high mass and low
energy selectivity
Ion trajectory simulation by CPO3D program
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Cross sections for DEA to H2 and D2 - 14 eV DEA
process

• The only available absolute measurements in the
  literature are from Rapp (D. Rapp et al., Phys.
  Rev. Lett. 14 (1965), 533-5)
• All other experimental values normalised to the
  peak value of 14 eV process
• Background due to secondary processes -
  metastable molecules c3?u (threshold at 11,76 eV)

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Cross sections for DEA to H2 and D2 - 4 eV process

• Determination of 4 eV cross sections relatively
  to 14 eV
• Important for the theory and also for plasma
  modelling

G. J. Schultz and R. K. Asundi, Phys. Rev. 158
(1967), 25-9
J. Horacek et al., Phys. Rev. A 70 (2004) 052712
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• Some numbers
• Limit of detection of VEHM by DTVE

2.4x1018 m-3 would yield 4x108 ions/s if CS is
1x10-20 cm2 or 100 c/s for 3x1011 m-3 - detection
limit

• Possible collateral benefits
• Volume production of VEHMs from hydrocarbons.
• Cross sections for DEA to VEHM.
• VEHM reactivity on dust particles

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Test atmospheres for exposure of samples to VEHMs
Test atmospheres - Partially dissociated neutral
gas

• hot-filament dissociation of hydrogen produces
  partially dissociated neutral test atmosphere
• vibrationally excited molecules are produced by
  atom recombination on the wall
• diagnostics DTVE coupled to the test chamber

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Source of VEHM

• Recombination of hydrogen atoms on surfaces of
  different fusion relevant materials (W,C,Be)
• Hydrogen molecules dissociate on tungsten
  filament
• Vibrational spectroscopy of molecules produced
  by recombination

P 2.5 10- 5 mbar Twall - 80 to -130oC
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Test atmosphere - Low-temperature plasma

• linear magnetised plasma machine determination
  of hydrogen plasma parameters
• plasma sources hot filament DC discharge,
  capacitive and/or inductive RF discharge
• modelling and PIC simulation boundary layers of
  non-Maxwellian hydrogen plasma
• diagnostics
• - Langmuir probes, emissive probes,
  electrostatic energy analyser
• - mass spectrometer, DTVE analyser - both via
  sniffer probe

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Linear magnetised plasma machine
After C. Liu.Hinz et al., Journal of Nuclear
Materials 220-222 (1995) 1126
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In-situ hydrogen depth profiling in samples
exposed to controlled atmosphere

• Samples exposure to controlled neutral hydrogen
  atmosphere
• rate of dissociation
• vibrational distribution of molecules
• Depth profile of H and D determined by ERDA
• Main interest
• H and D depth profile in W, C and other materials
• interaction of neutral particles (H2, H, D2, D)
  with materials
• Project goal are quantitative data for edge
  plasma modeling

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Pilot study on W

• Heating of sample
• Flow-in of D2 - chemisorbtion
• Dissociation of D2 - adsorbtion of D on the
  surface
• Recombination of D with H, desorbtion of HD, H2
  and D2 molecules
• Dissociation of H2 - exposure to H atoms

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• P2 - Work plan for immediate future
• Modeling of neutral, partially dissociated
  hydrogen gas in vessel made of fusion relevant
  material.
• Development of procedures for quantitative data
  extraction from experimental results for
  non-trivial experiments.
• VEHMs from recombination in afterglow plasma and
  from hydrocarbons.
• Vibrational spectroscopy of desorbed molecules
  TD, permeation.
• Influence of VEHMs on chemical erosion.
• Improvements and measurements on the set-up for
  in situ determination of hydrogen/deuterium depth
  profiles.
• Experiments with magnetized hydrogen plasma.
• Design and construction of a sniffer probe (MS
  and DTVE) for sampling in neutral hot gas (H and
  VHME transport) and in a low temperature
  magnetized hydrogen plasma.
• Active collaboration with IPP FZ Jülich

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P3 Heterogeneous surface recombination of
neutral hydrogen atoms on fusion relevant
materials (and atomic hydrogen catalytic
probe) Miran Mozetic, Alenka Vesel and
Aleksander Drenik Department of Surface
Engineering and Optoelectronics (F4), Joef
Stefan Institute, Ljubljana, Slovenia
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Hydrogen plasma is used for final cleaning and
passivation of electronic components

• Common methods for plasma characterization
• Langmuir probes
• Mass spectroscopy
• Optical emission spectrometry
• Optical absorption spectrometry
• Titration
• Catalytic probes

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Surface effects depend on plasma parameters
Discharge parameters
Surface effects
Plasma parameters

• gas mixture
• pressure
• gas flow
• type of discharge
• voltage
• current
• magnetic field
• reactor

• composition
• structure
• morphology
• wettability
• compatibility

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Catalytic probes operation principles

• There is a flux of H atoms on catalytic surface
• H atoms recombine on the surface H H ? H2
  4.5 eV
• Power dissipated on the surface P ½ g Wd jH
• The catalyst is heating at dT/dt P/mcp (often
  over 10K/s)

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A typical probe temperature in H rich atmosphere
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A catalytic probe
Probe tip
Catalytic probes (FOCP version)
The right choice of catalytic material depends on
particular requirements
Best choice Nickel catalytic probe
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H density versus pressure in 300W RF plasma
reactor
H density depends on pressure
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Effect of surface temperature g(T)
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P3 - Conclusions
Density of neutral hydrogen atoms is often the
most important plasma parameter H atoms are
present in remote parts of plasma
reactor Catalytic probe is an accurate tool for
determination of H density Enables real-time
monitoring of H density Probes will be used soon
at TEXTOR, Jülich
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P5 Application of ion beam analytical methods
to the studies of plasma wall interaction in
tokamaks (IBAF) P. Pelicon, D. Hanel, M.
Kavcic, I. Cade, Z. Rupnik, J. Simcic, S.
Markelj, M. Budnar, Z. Grabnar Microanalytical
Centre, Department for Low and Medium Energy
Physics (F2), Joef Stefan Institute, Ljubljana
http//www.rcp.ijs.si
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2 MV HVEE Tandetron, 4120 medium
current Installed 1997
4 beamlines -External beam (PIXE) -Microbeam
(PIXE/RBS/STIM/SE) -PIXE/RBS and ERDA/TOF-ERDA
-High resolution X-ray spectrometry
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RBS/ERDA measurement setup Beam 4230 keV
7Li2, Sample tilted 75 RBS detector at 160,
ERDA detector at 30 ERDA detector equipped with
11 µm Al foil Dose controlled by mesh charge
integrator (Tungsten mesh, wire diameter 38
micrometers density of 3.2 lines/mm, open area
of 77.4 )
TOF ERDA is also available
ERDA of hydrogen with 7Li ions, P. Pelicon et
al., NIM B 227, 591 (2005)
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Fig 4 Results of the round robin measurements
"Hydrogen in Silicon", organized by Bundesastalt
Für Materialforschung und prüfung (BAM),
Berlin. The result of the IJS, obtained with the
Elastic Recoil Detection Analysis (ERDA) with Li
ions, is marked by red circle, average value by
thick blue line. Result of the laboratory 1 is
the result of BAM. (Source U. Reinholz, H.P.
Weise, BAM Berlin, Round robin test "Hydrogen in
Silicon", Results sent to the participants of the
round-robin).
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ERDA analysis of a sample from graphite limiter
from TEXTOR
A
A
C
B
B
Test limiter used in experiment on TEXTOR.
Samples were cut from a limiter piece. ERDA
spectra measured at several positions on the
outer surface of sample A. Depth concentration
profiles and lateral dependence on total hydrogen
and deuterium concentration in the limiter
surface are determined by SIMNRA M. Mayer, IPP
Garching fit. Deuterium concentration values
are obtained with Rutherford recoil
cross-sections, therefore its absolute
concentrations are not exact.
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Ion microbeam
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• Ion microbeam
• OM triplet lens
• Installed in June 2000
• proton beam size
• High current mode (PIXE, RBS, SE, PBW)
• 100 pA 0.9 x 1 µm
• Low current mode (STIM),
• 104 ions/sec 0.5 x 0.8 µm

• Detectors for
• -PIXE
• -RBS
• -STIM
• -Secondary Electrons
• motorized 5-axis vacuum
• goniometer (VG Omniax)
• 2 optical microscopes
• Chopper for dose normalization

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From Carbon deposition and fuel accumulation in
a castellated limiter exposed under
erosion-dominated conditions in the SOL of
TEXTOR A. Litnovsky, V. Philipps, P. Wienhold, G.
Sergienko, A. Kreter, O. Schmitz, U. Samm,
P.Karduck, M. Blöme, B. Emmoth, and M. Rubel
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Analysis of the front surface Sector 4
X
Y
Sect. 4
Each line consists of rectangular scans
dimension 2.5 x 1 mm2, 2 mm apart.
Sect. 1
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PIXE spectrum
Spectrum analysis is performed by GUPIX J. W.
Maxwell et al.
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P6. Deuterium retention and release from metal
surfaces a complementary method to nuclear
tritium methods (proposal) V. Nemanic, B.
Zajec, M. umer Department of Surface
Engineering and Optoelectronics (F4), Joef
Stefan Institute, Ljubljana, Slovenia
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Prediction of tritium inventory and release from
constructional materials, for example stainless
steel, exposed to gaseous tritium is crucial to
ensure safe handling and decommissioning of
future fusion reactors. So far, only high
sensitivity of tritium experimental methods
enabled getting required data. A.Perevezentsev,e
t al. Fus. Sci. Techn., 48, 208 (2005), UKAEA
group Rosanvallon, Bekris, Braet, Coad, Counsell
et. al, Fus.sci.tech. 48, 268 (2005) The
approach of Joef Stefan Institute group (V.
Nemanic, B. Zajec, M. umer) is simple and
eliminates safety precautions needed in tritium
experiments. It is based on combining of UHV
preparation techniques and precise measurements
by passive vacuum gauges at stable temperature.
The uptake and subsequent spontaneous release
kinetics can be gained by deuterium. By
additional use of quadrupole mass spectrometer,
observation of HD, H2 and D2 becomes possible
what gives precious data about kinetics, isotope
exchange and residual hydrogen release.
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Deuterium exposure in a well outgassed UHV
chamber made of stainless steel AISI 316. (V
0.56dm3, A 500 cm2). The registered pressure
change ? 110-2 mbar in exposure of 1 mbar D2,
(303 K, 84 h) corresponds to absorption of
5.41014 D atoms /cm2. The slope dp/dt ?
3.4x10-8 mbar/s corresponds to sticking
probability ? 1x10?12. Similar low values were
only registered by applying tritium.
A.Perevezentsev,et.al. Fus.Sci.Techn. 41, 746
(2002)), T.Hirabayashi, M.Saeki,
J.Nucl.Mat. 120, 309, (1984)
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A typical 7 day spontaneous gas release after D2
exposure

composed
measured
QMS
QMS
QMS
estim. H2 bckg
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Kinetics of spontaneous release 2 (of 7) days

QMS
H2 bckg
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P6 - Short summary and outlook for future work

• Deuterium uptake kinetics in st. steel at r.t.
  can be followed by the sensitivity that is
  otherwise achieved only by nuclear methods.
• Beside D2, great extent of H2 and HD is always
  released regardless of the former outgassing
  procedure.
• The initial release kinetics D2 is 2 orders of
  magnitude higher than bckg. H2.
• Tritium release of T2 and HT can hardly
  be distinguished as precisely.
• Deuterium diffuses deep into the bulk and does
  not release easily ("non-classical mechanism"
  suggested by A.Perevezentsev).
• Tritium experiments gave HTO as the main T
  bearing compound. In our case, deuterium is only
  released as D2 and HD. Water is removed easily
  when low outgassing rates are needed UHV and XHV.
  
• - V. Nemanic, B. Zajec, J. etina, J Vac. Sci.
  Technol. A, 19, 215 (2001)
• - J.-P. Bacher, C. Benvenuti, P. Chiggiato, M.-P.
  Reinert, S. Sgobba, A.-M. Brass, J. Vac. Sci.
  Technol. A 21, 167 (2003)

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4. Relevance to particular PWI tasks

• SFA involvement on TF topics
• Erosion behaviour and impurity location in
  tokamaks (P5-IBA diagnostics)
• Material transport and redeposition (P5-IBA
  diagnostics)
• Fuel recycling, retention and removal (P3-Atomoic
  hydrogen flow tracing, P6-Deuterium retention and
  release(a.c.))
• Off-normal heat loads
• Edge modelling, erosion and deposition modelling
  (P2-Data on H2(v), D2(v), H and D interaction
  with wall materials for Eirene)
• Edge and SOL physics (P2-Processes with H2(v)
  and D2(v) in edge plasmas)
• Task force relevant diagnostics (P2-Development
  of diagnostics for vibrational spectroscopy of H2
  and D2 molecules, P3Catalytic probe for hydrogen
  atom concentration)