RFX-mod thermal measurement system: a possible diagnostic for plasma-wall interaction

1. RFX-mod thermal measurement system:a possible diagnostic for plasma-wall interaction M. Dalla Palma1, E. Sartori2 and the RFX-mod Team 1 Consorzio RFX, EURATOM-ENEA Association, corso Stati Uniti 4, I-35127 Padova, Italy 2 Università degli Studi di Padova, Italy Padova, April 28th 2010

2. Outline • Description of the RFX-mod thermal measurement system • Purpose of the activity:correlation of plasma-wall interaction with thermal measurements • Approach: • development of models for thermal characterization of tiles, vacuum vessel and toroidal support structure • development of an integrated thermal model • inference of plasma parametersfrom thermal experimental measurements, by using the integrated model • comparison of the deduced plasma parameters with that ones obtained from other measurements • RFX past analyses

3. Thermal measurements on RFX-mod • Plasma-Wall Interaction (PWI) diagnostic by correlating thermal fluxes to the thermocouple (TC) measurements The thermal measurement system is important for: • Machine diagnostic to control: • the achievement of the operational limits due to high heat fluxes on the graphite tiles • irregular temperature due to localized plasma-wall interaction • temperature increase due to Joule effect in the coils

4. Thermocouples set on RFX-mod 8 TCs on the first wall - Integrated System of Internal Sensors(ISIS) [20÷400°C] 228 total TCs on the vacuum vessel rings [20÷200°C] 16 TCs on vacuum vessel sheet[20÷200°C] 16 TCs on the copper shell[20÷180°C] 16 TCs on the copper shell clamping bands[20÷180°C] 16 TCs on the toroidal support structure[20÷60°C] 8 TCs on 4 saddle coils [20÷100°C] 19 TCs on 3 magnetizing coils[20÷200°C] Plasma

5. TCs layout on the external surface of the vacuum vessel θ = 0° 337.5° 292.5° 247.5° 202.5° 157.5° 112.5° 67.5° 22.5° θ = 0° φ = 0° ring 1 φ = 355° ring 72 25° 40° 65° 100° 125° 180° 270° 320° GAP on copper shell (112.5°) GAP on copper shell (292.5°) TCs on dense sectors TCs for comparison with other sensors or diagnostics TCs on vacuum vessel sheet TCs on vacuum vessel rings θ = 0°  External equator, θ = 90°  Top

6. Planned activity • Correlation of plasma wall interaction (PWI) with thermal measurements, in particular: • quantification of power density and energy of the uniform distributed and localized PWI • localization of the un-uniform and/or wall-locked PWI • Approach: • development of models for thermal characterization of tiles, vacuum vessel and toroidal support structureby numerical analyses and validation with experimental measurements • development of an integrated thermal modelsimulating heat fluxes from the first wall to the whole toroidal support structure • inference of plasma parametersfrom thermal experimental measurements, by using the integrated model • comparison of the deduced plasma parameters with that ones obtained from magnetic measurements and possibly with IR camera measurements of the tile surface temperature.

7. 1. Thermal characterization Plasma Tiles

8. 1. Thermal characterization Plasma Tiles Rings

9. 1. Thermal characterization Plasma Tiles Rings Toroidal structure Vessel sheet Copper shell Shell clamping bands

10. 1. Thermal characterization The model parameters are optimized considering: • Effective shape and dimensions of tiles, vacuum vessel and toroidal support structure • Thermo-physics parameters of materials • Thermal contact resistance at the interfaces • Heat transfer mechanisms among interfaced structures Plasma Tiles Rings Toroidal structure

11. 1. Thermal characterization PWI: radiation and convection Plasma Tiles Rings Toroidal structure

12. 1. Thermal characterization Thermal conduction through fixing keys Plasma Tiles Rings Toroidal structure

13. 1. Thermal characterization Th. Conduction through vessel supports+Convection (chimney effect) and radiation Thermal conduction through fixing keys PWI: radiation and convection Plasma Tiles Rings Toroidal structure

14. 2. Development of an integrated thermal model Thermal results Th. Conduction through vessel supports+Convection (chimney effect) and radiation Th. conduction through fixing keys PWI: radiation and convection Model validation: comparison with experimental measurements Plasma Tiles Rings Toroidal structure

15. 3. Inference of plasma parameters Integrated model Thermal measurements Th. Conduction through vessel supports+Convection (chimney effect) and radiation Th. conduction through fixing keys PWI: radiation and convection Plasma Tiles Rings Toroidal structure

16. 3. Inference of plasma parameters mode locking region • quantification of the power density and energy of uniform distributed and localized PWI • localization of the un-uniform and/or wall-locked PWI Integrated Model Plasma Thermal measurements 4. Validation with magnetic and IR camera measurements

17. Past thermal analyses Thermal analyses were carried out with the old RFX finite element model simulating experimental sessions of old RFX First wall temperatures [°C] Vacuum vessel temperatures [°C] New thermal analyses are ongoing with finite element models simulating the thermal behaviour of the RFX-mod. The thermal results are compared with the RFX-mod thermal measurements.

18. RFX-mod thermal measurement system:a possible diagnostic for plasma-wall interaction M. Dalla Palma1, E. Sartori2 and the RFX-mod Team Thank you for your attention! 1 Consorzio RFX, EURATOM-ENEA Association, corso Stati Uniti 4, I-35127 Padova, Italy 2 Università degli Studi di Padova, Italy Padova, April 28th 2010