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）

Outline1. 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

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

Specialists Working Groups on Diagnostics

First Mirrors (FM) also as five High Priority Topics in SWG

ASIPP

HT-7 & EAST

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.

ASIPP

HT-7 & EAST

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

Reflectivity

Resistance to CXAConsideration

Sputtering by CXA HT-7 & EAST

Neutron irradiation does not result in the direct degradation of reflectivity,

but accelerate the CXA sputtering.

Different sputtering yield in different orientation

Appearance of Step structure (microrelief)

Degradation of Reflectivity

CXA

Al mirror has the lowest resistance, lost a large portion of reflectivity ~0.2m, fully degraded h>0.4m. 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)

ASIPP

HT-7 & EAST

Ag,Au,Cu higher reflectivity but lower resistance to sputtering.

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.

ASIPP

HT-7 & EAST

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)

ASIPP

HT-7 & EAST

Reflectance of mirror samples before (dotted) and after (solid) exposure

to one year of Tore Supra plasma (B. Schunke, V. Voitsenya)

ASIPP

HT-7 & EAST

SEM photo of polycrystalline Cu mirror after layer of 2.5 m was eroded by ions of deuterium plasma

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)2970nm.

ASIPP

HT-7 & EAST

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.

Degradation of reflectivity of candidate first mirrors materials under energetic ion bombardment. After V Voitsenya, et al, RSI, 2001

40

45

50

55

60

65

0 1 2 3 4 5 6 7

600 nm

Thickness of sputtered layer, m

Mo poly

W poly

W (111) block

W (111)

Mo (111)

SS (111 )

Single crystal Polycrystal

Molybdenum

Deposition of contaminants HT-7 & EAST

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).

ASIPP

HT-7 & EAST

• Mo mc 110

• Acier 316L

• Cu OFHC

Actual situation: Multiple effects occurring simultaneously

ASIPP

HT-7 & EAST

Results

ASIPP

HT-7 & EAST

ASIPP

HT-7 & EAST

Direct comparative test of single crystal andpolycrystalline mirrors under erosion conditions

ASIPP

HT-7 & EAST

Investigations of diagnostic mirrors in TEXTOROutlook 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 mirror system.

ASIPP

HT-7 & EAST

Exposition of SS mirror samples in Large HelicalDevice (LHD) during 3rd experimental campaign (A.Sagara)

ASIPP

HT-7 & EAST

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;• 2nd exposure: mirrors at 1400C→800C.

ASIPP

HT-7 & EAST

Preparation of the First Mirror Test in JET:locations of cassettes with mirror samples.

ASIPP

HT-7 & EAST

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.

Research on mirror Cleaning

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

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.

ASIPP

HT-7 & EAST

2 Coated in magnetron plasma 2 Coated in the T-10 discharges1 original,3 after the removal of coating

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.

ASIPP

HT-7 & EAST

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

ASIPP

HT-7 & EAST

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

ASIPP

HT-7 & EAST

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 theselection and use of resistant materials has really been covered adequately so far. The development of models is especially weak.

ASIPP

HT-7 & EAST

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.

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.

What can we do?

ASIPP

HT-7 & EAST

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

ASIPP

HT-7 & EAST

Exposure on test limiter inclined at 200 with respect to totoidal direction.

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 )

Parameter

ASIPP

HT-7 & EAST

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.

ASIPP

HT-7 & EAST

Facility Experiment Aim of experiment

Description ResultsWavelengt

h range

Implications for future

studies

HT-7

Planned 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 personsJunling Chen

jlch@ipp.ac.cn 

To make the clear

the correlation between

environment

conditions and

behavior of optical properties

of in-vessel

mirrors of different

materials.

Mirror samples will be exposed on the midplane manipulator and exposed during the same discha

rges.

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 experimenta

l campaign.

An extensive analysis of exposed mirrors and modeling of mirror exposures is foresee

n.

Detailed surface analyses by different techniq

ues;2-D profilo

metry;reflectivity:250-2500 n

m,

Polarization:

300-20.000nm

     

Competitive concept

with Rh film mirrors should be addr

essed 

Presently under consideration for next experi

mentalcampaign

        

ASIPP

HT-7 & EAST

谢谢大家！ Thanks for your attention!

ASIPP

HT-7 & EAST