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ITER & dust Dust = major issue in term of ITER safety In vessel dust quantities: extrapolation from current experiments In vessel dust diagnostics & removal.

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Presentation on theme: "ITER & dust Dust = major issue in term of ITER safety In vessel dust quantities: extrapolation from current experiments In vessel dust diagnostics & removal."— Presentation transcript:

1 ITER & dust Dust = major issue in term of ITER safety In vessel dust quantities: extrapolation from current experiments In vessel dust diagnostics & removal tools Dust reactivity

2 In vessel dust quantity: ITER prediction Dust production : Material erosion = redeposition dust Cd Normal operation Disruption ELMs Conditioning Unipolar arcs (?) Safety people: Erosion measurements with Speckle interferometry or plasma impurities calculation and Cd=1 Operation people: To Reduce Cd value in order to constraint the intervention (removal) period Need of reliable dust diagnostics

3 In vessel dust quantity: ITER prediction Cd Tore Supra evaluation: dust recovery after a known operation period. Assume homogeneity = 31g ( 5 months, 1438 shots) erosion processes: normal operation: incident plasma flux + C sputtering yield = quantity of C eroded = upper value of C redeposited = 27gr (however, much lower quantity since 50-80% redeposited locally!) conditioning (HeGD mainly): 1day of HeGD = 3g of C sputtered. for 5 months of operation: 50gr of C eroded and then redeposited. by the way, no dust formation from C Arnas evaluation. disruption: every disruption = 300kJ (mean value) from plasma gun results, eroded quantity/disruption could be approximated simply by the following expression: Mc (g) = [(Ethermal*0.1) /Esublimation] * 12 (g) = 0.6 g/disruption 80-120 gr eroded by disruption in Tore Supra (15% of frequency) Balance and Cd estimation Cd=30/200=15% (in JT60U = 7%)

4 In vessel dust quantity: ITER prediction Cd Best estimate ~ 10%, TO BE CONFIRMED by a comprehensive study (AUG, JET ILW and Alacotor C) For present ITER material choice and C D =10 %, dust production = 0.5 g carbon and 0.6 g for Be per 400 s, full power discharge. Negligible for W erosion is small. For all material, dominating processes will be: melting and droplet formation during disruption and ELMs, unipolar arcing (no estimation in current tokamak), He and H embrittlement and blistering (inducing surface inhomogeneity and arcing?) More work needed: especially on modelisation and crosscheck with experiments on plasma gun.

5 In vessel dust diagnostics & removal tools EFDA task TW6-TSS-SEA5.1 Dust measurements and removal techniques (Chair by S Rosanvallon) dust diagnostics for ITER: limit = 6x3 kg of dust on hot surfaces (divertor) due to H 2 production and explosion in case of 0 2 (Air) ingress possible mitigation: injection of neutral gas: not working limit the Air possible leaks (DCR under study) (could remove this safety limit) possible consequence of explosion: dust in suspension and explosion limit of dust explosion not known yet (under study) almost impossible to measure (to be studied) limit ~ 400kg in vessel quantity: 100kg (Be)/ 200kg (C) / 100kg (W) 160µm / 4000µm / 100µm (homogeneous erosion, if not higher erosion) due to release activated material to the environment size of dust to measure: between 100nm to 100µm complex structure (fractal, fibers,…) and composition

6 In vessel dust diagnostics & removal tools EFDA task TW6-TSS-SEA5.1 Dust measurements and removal techniques (Chair by S Rosanvallon) diagnostics for knowledge CCD & transport, laser extinction, embarked laser diffractometry, collection of dust (removal) diagnostics for safety: monitor the dust quantities in the VV Upper limit (>100kgs): erosion speckle interferometry (10-40µm), laser metrology (>100µm) erosion assessment from plasma measurements Lower limit (18kg in divertor): IR measurements (layers and dust identical) + LIBS evaluation (very risky, things could change if oxygen control) link to operation issues: conversion factor evaluation: from feedback experiments, from surface diagnostics, … removal: use of existing or under development techniques set of system must be used (as usual) integration very difficult (ask for support from out of fusion people, meeting in Nice end of this year)

7 In vessel dust diagnostics & removal tools Diagnostics & Removal R&D: –Technical feasibility considering divertor design, optical accesses, reference surfaces, etc

8 In vessel dust diagnostics & removal tools Diagnostics & Removal R&D: –Dust collection under the divertor cassette? (washing with gas?) Evacuation

9 In vessel dust diagnostics & removal tools Removal strategy: Removal of dust, flakes and deposited films from the vessel is a three stage process: –Material mobilization: material must be detached from the surface on which it is attached including gaps/castellations –Collection of the mobilized materials (Vacuum cleaner, electrostatic transport) –Transport within/outside the vessel Main issues –Lack of solution for transport outside the VV (design impact), –Need of robotised arm

10 In vessel dust diagnostics & removal tools Diagnostics & Removal open question: Quantity to be measured (ITER input, ITER TF created) Link between local measurements and global inventory? link between dust in suspension measurements and global inventory? (inject gases and measure the mobilised dusts) What are the set of systems to be used for dust removal? What are the studies needed before Tokamak demonstration? …………… Need to have a dedicated mock up For dust diagnotics & removal For dust mobilization and explosion studies For detritiation studies (test of accessibility) Mock up = divertor sector + vacuum vessel and port(s), with possibilities to work under vacuum or inert gas ITER Task Force launched 20 days ago. Goal : Draft the effort and relevant plan of ITER Designers to provide studies and design activity necessary to bring the DCR to the TCM approval

11 Dust sampling and reactivity studies Dust sampling in current machine: Goal: correlation of dust and operation process, maintenance etc…

12 Dust sampling and reactivity studies Dust sampling in current machine: Goal: correlation of dust and operation process, maintenance etc… Surface morphology of melt zone: W Droplets or Dust Melt zone

13 Dust sampling and reactivity studies Dust sampling in current machine: Goal: correlation of dust and operation process, maintenance etc…

14 Dust sampling and reactivity studies Dust sampling in current machine: Goal: correlation of dust and operation process, maintenance etc… BET measurements done on plasma layers recovered in TS and in TEXTOR: On going comparison between TEXTOR and TS samples Studies to be done in order to link SSA and chemical reactivity with Oxygen, steam,….


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