Work performed in the frame of WP6 in FZJ Cadarache – 7th December 2009 | Romaric Voinchet

Plan Overview on my courses (skipped): - EFTS/EODI training week in the Culham Research Center (UKAEA); - Summer School on fusion technologies in FZK; - Vacuum training in FZJ. CXRS design. Overview on my activities: - Impact of the radiation on the thermal condition of the shutter; - First estimation of the distortions of the mirrors under the combined thermal and mechanical loads (in collaboration with Andreas Krimmer); - On going tasks: investigations to reduce the temperature at the first mirror. Focus on the mirror adjustment: admissible pressure and stresses at a point contact. Additionnal slide: previous activities.

CXRS design Overview of the core CXRS:

CXRS design Upper port n°3: core CXRS*: Shutter* (protects M1 from the plasma when appropriated): *FZJ Pictures

Overview on my activities Impact of the radiation on the thermal condition of the shutter The flaps are sheets of steel aiming to protect the first mirror against the radiations from the plasma during no-diagnostic time: Aim: analyze the impact of the heat transfer by radiation on the cooling of the flaps. The flaps have been replaced by one unique plate of stainless steel (called “flap”); The environment, the retractable tube, has been modeled by a simple cylinder: The calculation method: « AUX12 matrix »: definition of the matrix of the radiative case and creation of « superelements » from this matrix.

Overview on my activities Impact of the radiation on the thermal condition of the shutter Inputs The radiation from the plasma is estimated at 0.02W/cm²; The temperature of the inner surface of the tube is 100°C; The emissivity of the tube is varied from 0.1 to 1; The emissivity of the flap is varied from 0.3 to 1; The cooling is modeled by a constant temperature of 150°C of the surface representing the wall of the cooling channel. Cooling by radiation to the tube Cooling by radiation to the tube Cooling from the coolant Heat flux from the plasma

Overview on my activities Impact of the radiation on the thermal condition of the shutter Results The temperature at flap stabilizes from a tube emissivity of 0.55 for any flap emissivity; The highest impact of the convection cooling is obtained for low flap emissivity: up to 125°C reduction for a tube emissivity of 0.1. Calculations to be followed in detail

Overview on my activities First estimation of the distortion of mirrors with the combination of thermal and mechanical loads Comparison of different concepts for the mirror cooling: Passive (metallic mesh) cooling on the back side (concept A): Material, heat load, substrate thickness and contact pressure influence investigated. Active (with cooling channel) (concept B): Influence of material, distance of cooling channels from mirror surface and coolant pressure investigated. Output: curvature radius (to be maximized), deflection and temperature (to be minimized). Metallic mesh Mirror Frame First estimation of the distribution

Overview on my activities First estimation of the distortion of mirrors with the combination of thermal and mechanical loads Curvature radius and maximal deflection for stainless steel (concept A): Results Concept A for stainless steel: With small contact pressure With design contact pressure No contact force 4MPa contact pressure   Minimal local radius (m) Maximal deflection (µm) maximum temperature T (°C) ΔT (°C) SS 23 119 14 184 415 75 Mo 563 5 53 45 350 10 W 431 7 64 38 355 The maximum temperature and deflection were obtained for stainless steel; Molybdenum and tungsten satisfying: high curvature radius, low deflection and temperature, but tungsten has high neutron heating (not preferable in principle).

Overview on my activities First estimation of the distortion of mirrors with the combination of thermal and mechanical loads Curvature radius and maximal deflection for stainless steel (concept B): d=12mm d=25mm Higher temperature at the sides (larger amount of material at the side)  convex shape at the edges Increase of d until the middle plane leads to a less concave shape (heating above the cooling channels becomes important); Maximum curvature radius for a distance d between 12 and 25mm; Overall curvature radius is influenced by positioning of the cooling channels; For molybdenum the pressure on the cooling has negligible impact, not the case for cooper (higher thermal conductivity and low Young modulus).

Overview on my activities On-going task based on the work of the “D. V Overview on my activities On-going task based on the work of the “D.V. Efremov Scientific Research Institute of Electrophysical Apparatus” Aim: reduction of the temperature at M1 (directly facing the plasma) Heated by neutrons and by short wave radiation on its surfaces facing the plasma; Cooled by the cooling channel wall of the substrate. Cooper felt Mirror Cooling channel Frame Substrate The investigations have to be performed considering: The heat transfer coefficient (HTC); The substrate material; The substrate length; The cooling channel design.

Focus on the mirror adjustment: high contact pressure on a point Definition of the contact between the mirror adjustment ball and tube/holder Approach: Mirror holder analysis with Ansys: determination of the reaction loads at the balls; Definition of the design criteria; Calculation of the critical contact stresses of our model; Compromise solutions.

Focus on the mirror adjustment: high contact pressure on a point Reaction loads at the balls: - B1: 31,8kN - B2: 12,4kN Definition of the admissibility criteria (in validation process): Equivalent Young modulus defined by (point contact) [1]: Contact radius (point contact) [2]: Hertz pressure point contact [2]: Ellipsoid contact [2]: Von Mises (elasticity criterion) = 0,27*p0 [3] (b: big contact ellipsoid radius) Von Mises ≤ Rp0.2 Rp0.2: Elasticity limit considering 0.2% elongation [1]: U. Persson, H. Chandrasekaran, A. Merstallinger, Adhesion between some tool and work materials in fretting and relation to metal cutting, article Elsevier, 2001. [2]: ENS Cachan, CONTACT : THEORIE DE HERTZ, internet page [3]: ASM International Handbook Committee, ASM Handbook, 1996 (“Contact Fatigue of Hardened Steel”, p. 692) [4]: AFCEN, RCC-MR 2007, A10.3000

Focus on the mirror adjustment: high contact pressure on a point To avoid over constrained condition: point contact B1 (critical case): F o y R z x Inputs: R=17,5mm, E(ball, plan)=196GPa, F=32kN Material: inconel 718 - Syd=785MPa at 400°C under 0,01dpa (Syd=0,85*Sy [4]) Main results At O: Hertz pressure p0=6170MPa contact surface radius a=1,6mm Von Mises = 1670MPa No suitable solution yet for the current ball dimension: the design shall be modified. [4]: ITER MATERIAL PROPERTIES HANDBOOK, ALLOY 718, ITER document.

Focus on the mirror adjustment: high contact pressure on a point B1 alternative approach: spherical roller o R2 R Inputs: the same as previous slide + l=40mm y z l Main results at O: Von Mises ≤ 785MPa; Spherical profile radius: R2 ≥ 170mm; Hertz pressure p0 = 2890MPa; Radius of the contact ellipsoid: a=1,6mm; b=3,4mm. x Could be acceptable, but the attachment of the roller to the tube could be problematic: to study. The mirror adjustment is still an issue: alternatives have to be explored: - replacement of one ball by a spherical roller, - change of the concept to dedicate the whole force from the preload to one ball and let the force from the EM moment to an additional ball (considerably less loaded).

Additionnal slide: previous activities Analytical mechanical analysis of the shutter: « Shutter optimization », Mechanical analysis of the mirror holder: « Mirror holder numerical analysis », Primary + secondary stress P+Q = 463MPa (< 1,5*Sm = 465MPa for inconel 718) Presentation of the previous activities: « Activities of Romaric Voinchet »