Transcript ASIPP HT-7 & EAST

ASIPP
HT-7 & EAST
Research status of First Mirror and proposals
for the HT-7 experiment
J.L Chen (陈俊凌），M.Q Tan (谭模强）
Outline
1. Introduction
2. Sputtering by CXA (Mirror materials selection production, test)
3. Deposition of contaminants (In-vessel mirror tests)
4. Cleaning of mirrors Laser ablation and GD cleaning of deposits
5. What can we do?
6. Proposals for the HT-7 experiment
Introduction
HT-7 & EAST
Specialists Working Groups on Diagnostics
Neutron Working Group
Thomson scattering Working Group
Spectroscopy Working Group
Working Group on Beam-Aided Spectroscopy and NPA
Reflectometry Working Group
First Mirror Working Group
Radiation Effects Working Group
International Diagnostic Database Working Group
First Mirrors (FM) also as five High Priority Topics in SWG
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All diagnostics in
ITER which uses
radiation in the
ultraviolet, visible and
infrared wavelength
range will have to
view the plasma via a
mirror. These first
mirrors must survive
in an extremely
hostile environment
and maintain an
acceptable optical
performance.
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First mirror be exposed to neutron ,  particle, CXA, -ray, ray….
The wavelength range of interest is from 5 nm in vacuum UV region up to 100 mm in the
far infrared range. The requirement is to maintain a mean surface roughness which does
not exceed 0.1 of the operating wavelength. Mirrors used for diagnostics in present
magnetic confinement experiments would not maintain the required performance for
more than a few tens of seconds under these conditions.
UV and X-ray radiation ~up to 500 kW/m2, surface heating;
Neutron flux up to 8 W/cm3 , mainly volumetric modifications of the material;
Charge exchange atoms - up to 23*1019 particles/(m2*s) with energies0.1-several keV;
Deposition of material eroded from the divertor and first wall.
Particle flux: Neutron and CXA is the most important
Resistance to CXA
Consideration
Reflectivity
Sputtering by CXA
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Neutron irradiation does not result in the direct degradation of reflectivity,
but accelerate the CXA sputtering.
Different
sputtering yield
in different
orientation
CXA
Appearance of
Step structure
(microrelief)
Degradation of
Reflectivity
Al mirror has the lowest resistance, lost a large portion of reflectivity
~0.2m, fully degraded h>0.4m. Cu lost 70%, ~0.8 m. The rate of
R(h) dependence for W and Ta (after maximum) mirrors looks rather
similar to R(h) dependence for the later stage of sputtering of a Cu mirror.
Rh film on Cu substrare maintained its initial R after ~7 m sputtered.
No any noticeable degradation of reflectance ~5(for mono W) and ~7(Mo)
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Ag,Au,Cu higher reflectivity but
lower resistance to sputtering.
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W,Mo,SS lower reflectivity but
higher resistance to sputtering.
Mirrors must be fabricated either of monocrystalline metal (Mo or W), or as a
metal film on metal substrate (Rh is probably the best candidate) with the film
thickness depending on the mirror location relatively to the core plasma, i.e.,
depending on the degree of attenuation of the CXA flux to the mirror surface.
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Materials selection of FM
•Development of the technology of mirror preparation (bulk mirrors
and metal film on metal substrate mirrors)
•
Simulation experiments the long-term sputtering tests are being
conducted for mirrors of different metals with different structure:
(i) Polycrystalline (Be, Al, SS, Cu, Mo, Ta, W);
(ii) Monocrystalline (SS, Mo, W) ;
(iii) Metal film on metal substrate (Be/Cu, Cu/Cu, Rh/Cu, Rh/SS,
Mo/SS, Mo/Mo). The energy distribution of ions of deuterium
plasma is wide (0.1-1.5 keV)
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Reflectance of mirror samples before (dotted) and after (solid) exposure
to one year of Tore Supra plasma (B. Schunke, V. Voitsenya)
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SEM photo of polycrystalline Cu
mirror after layer of 2.5  m was
eroded by ions of deuterium
plasma
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Scanning electron micrographs of the
surfaces of W(a,b) and Ta(c,d) mirrors
after sputtering layers with thickness:
(a)870nm;(b)2710nm;(c)960nm;(d)297
0nm.
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An extensive R&D program is on going in which candidate mirror
materials are subject to energetic particle bombardment with ion sources
and plasma simulators, and to environmental tests in tokamaks. The
degradation of the performance of the mirrors is measured.
600 nm
Molybdenum
65
SS (111)
60
Mo (111)
55
W (111)
50
W (111) block
Mo poly
45
W poly
40
Single crystal
Polycrystal
0
1
2
3
4
5
6
Thickness of sputtered layer, m
Degradation of reflectivity of candidate first mirrors materials under energetic ion
bombardment. After V Voitsenya, et al, RSI, 2001
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Deposition of contaminants
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The scheme of deposit appearing on the diagnostic window due to physical
sputtering of the surface materials of the wall and the possible way to
decrease the rate of deposit growing.
1 - periphery plasma, 2 - flux of CX atoms, 3 – diagnostic duct, 4 - sputtered atoms of a duct
material, 5 – diagnostic window, 6 - deposit on the window surface, 7 – sputtered atoms of a
deposit material, 8 - diaphragms made of material with low sputtering yield (e.g., Ta, W).
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Actual situation: Multiple effects occurring simultaneously
• Mo mc 110
• Acier 316L
• Cu OFHC
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Results
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Direct comparative test of single crystal and
polycrystalline mirrors under erosion conditions
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Investigations of diagnostic mirrors in TEXTOR
Outlook for 2005
► Mirrors in the erosion conditions
● Direct comparative test of candidate mirrors.
● Impact of surface finishing on the optical performance of single crystal
mirrors
in the erosion conditions (collaboration with Kurchatov institute,
Russia).
► Mirrors in the deposition conditions
● Modeling of plasma-gas interaction in the periscope mirror system
with UEDGE code (collaboration with LLNL, USA).
● Modeling of impurity transport and deposition in the periscope
mirror system with ERO code.
● Experiment on deposition mitigation in the Periscope-Upgrade
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Exposition of SS mirror samples in Large Helical
Device (LHD) during 3rd experimental campaign (A.Sagara)
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Retractable heatable mirror system
• Single crystal and polycrystalline molybdenum mirrors were
exposed;
• Exposure in the Private Flux Region (PFR);
• Series of identical ELMy H-Mode discharges;
• Partially detached plasma in the divertor;
• 1st exposure: mirrors at room temperature;
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Preparation of the First Mirror Test in JET:
locations of cassettes with mirror samples.
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Research on mirror Cleaning
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This could be laser cleaning (this possibility is under investigation in PPPL and in
Kurchatov Institute).
Flashlamp cleaning (Counsell UKAEA) - a Xe flashlamp close to the mirror but not
blocking its view (the first pulse may be needed to clean the flashlamp itself!).
Local discharge cleaning.
Cleaning rate magnitudes around 1nm/min are relevant to what is
known about chemical erosion in ECR plasmas. The rate of cleaning
increases when the magnetic flux crosses the polluted area at the
angle of incidence exceeding 30Deg. There is strong incentive to
address the other types of discharge which show a promise as
cleaning tool.
Sizable efforts were made to improve the cleaning ability of low
temperature plasmas . Mirror in-situ cleaning shows a promise as a
potential technique for ITER
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Deposition of contamination onto first mirror is another important
degradation of reflectance. deposits not only decrease the reflectance
of mirrors, but also distort the spectrum of reflected radiation because
of interference. However the role of deposition of contaminants is still
not clear for the FMs of the core plasma.
2 Coated in magnetron plasma
2 Coated in the T-10 discharges
1 original,3 after the removal of coating
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For the FMs of laser diagnostics , high repetition frequency of laser
shots the thin surface layer of mirror is subjected to short-term
thermal impacts with a resulting effect very much similar to a fatigue
deformation.
Laser tests were performed
on first mirror prototypes to
find the single shot damage
threshold and multipulse
laser damage threshold.
Diffusion scattering coefficients via number of laser shots for sc Mo
mirror under different laser fluence-0.78, 0.84, 1.25 J/cm2
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Scan-electron
microscope photos of
mirror surface,
horizontal line gives a
scale: (a)molybdenum
single crystal,
(b)molybdenum
polycrystal.
Electron microscope
photo of single crystal Mo
mirror surface after
influence of multiple laser
irradiation. Magnification:
(a)100,(b)1000 times
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First Mirror Programme
• Selection and use of materials that are resistant to erosion
due to sputtering.
• Measurement on existing tokamaks under ITER like edge
conditions.
• Development of models of the process.
• Development of mitigating methods (baffles, shutters etc)
• Development of cleaning techniques
All are being pursued but not aggressively enough. Only the
selection and use of resistant materials has really been
covered adequately so far. The development of models is
especially weak.
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Actual situation:
Multiple effects occurring simultaneously
Time averaged measurements
Poorly known edge plasma conditions
Models at a very early stage of development
Many experiments are ‘interpreted’ without the use
of models.
What can we do?
HT-7 & EAST
Research proposals in HT-7 experiment
The fabrication of high quality mirrors:
Material selection and the fabrication process.(polishing and cleaning)
Thick films on metallic substrate. (Rh films or)
Pre-characterization of mirrors should be made:
Optical properties;
Elemental composition of the mirror surface;
Surface topography;
Surface roughness curvature were investigated.
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Experiment:
Erosion-deposition rate depend on position and material of mirrors,
plasma parameters, VV conditioning modes and using mitigation
measures. So the “history” of reflectivity deterioration of each
mirror will be unique.
1. Mirrors were exposed for series of identical shots at the same
plasma conditions in the SOL of HT-7.
2. Mirrors on sample rack of the removable midplane manipulator.
Key: position and orientation.
The position erosion equal to deposition.
Study of composition and morphology of the deposits.
Estimation of deposition rates on the mirrors.
Investigation of mirror reflectivity degradation
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Parameter
Exposure on test limiter inclined at 200 with respect to totoidal directio
Averaged density;
The number of shots, duration of exposure;
average temperature of the leading edge.
The temperature excursions up to.
Numerical modeling.(ERO code , uedge code , EIRENE, BBQ )
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Polarimetry: characterization of retro-reflector exposed to plasma.
Pre and post exposure mirror analyses
• Surface topography(roughness,flatness, profilometry-erosion)
• Surface analysis (EDS,XPS,SIMS,SEM), deposition measurements
Deposition layer thickness measurements.
Optical measurements( ellipsometry, reflectivity UV->FIR).
Analysis methods
Contaminants analysis:ERDA (Elactic Recoil Detection Analyses), RBS
(Rutherford Back Scattering), SIMS, SEM, Profilometer, X-ray
diffraction, film annealing.
The relative reflectance was measured by means of a specular reflectance
accessory of the Lambda 35 spectrophotometer.
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Facility
Experiment
Planned
HT-7
Comparative test of
PC molybdenum,
PC Tungsten and
fine grain Tungsten
and stainless steel
mirrors under
erosion-dominated
(r=28.5-30cm)
conditions in the
SOL of HT-7.
Contact persons
Junling Chen
[email protected]
Aim of
experiment
To make
the clear
the
correlation
between
environme
nt
conditions
and
behavior
of optical
properties
of invessel
mirrors of
different
materials.
Description
Mirror
samples will
be exposed
on the
midplane
manipulator
and exposed
during the
same
discharges.
SS Mirror
installed at the
inner wall, a
little over the
central plane
of the device,
~5cm from the
plasma and
without any
protection.
Exposure time
next whole
experimental
campaign.
Results
An
extensive
analysis of
exposed
mirrors and
modeling of
mirror
exposures is
foreseen.
Wavelengt
h range
Detailed
surface
analyses by
different
techniques;
2-D
profilometry
;
reflectivity:
250-2500
nm,
Polarization
:
30020.000nm
Implicatio
ns for
future
studies
Competitiv
e concept
with Rh film
mirrors
should be
addressed
Presently
under
considerati
on for next
experiment
al
campaign
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HT-7 & EAST
谢谢大家！
Thanks for your attention!
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