October 1, 2009 Janos Marki: IR measurements at TCV 1/14

IR measurements during ELM experiments on TCV

(collaboration with MAST)

J. Marki, R. A. Pitts, B.P. Duval and TCV Team

2009 Joint Annual Meeting of the Special Expert Working Groups: Transient Loads and High-Z Materials,

IST, Ljubljana

October 1, 2009 Janos Marki: IR measurements at TCV 2/14

History

• Original idea: EPS 2007• Discussions, emails, etc• EU Priority support received end spring 2008• PSI 2008: discussion of details• Trigger unit + support structure built by end summer

2008 (thanks to MAST workshop in great part)• Original date for start – mid-August, nearly shipped but

got stuck – postponed until end IAEA (October)• TCV: beginning of November - flywheel generator breaks

down, reparation by April• TCV: Wait until summer for ECRH operation• July 2009 Camera arrives!!!!• September 2009 Camera leaves

October 1, 2009 Janos Marki: IR measurements at TCV 3/14

Experimental Setup

Detector type CMT 256 M HS

(TCV)

CMT 256 L HS

(MAST)

FPA size 256 x 256 256 x 256

Spectral range 1.5 - 5.1 μm 7.6 - 8.9 μm

Frame rate 880 Hz 880 Hz

Subframe mode 25 kHz @ 16 x 8 25 kHz @ 16 x 8

Integration time 1 μs -2 ms 1 μs -2 ms

• Measure IR photon flux digital signal• Apply blackbody calibration apparent

temperature• Assuming real surface temperature T• Spatio-temporal evolution of T + simple

model of deposited surface layer power

flux PIR (THEODOR 2D code = inverse

solution of heat conduction equation)

ThermosensorikCMT256 M HS1.5 – 5.1 μm

FOVVIR

FOVHIR ThermosensorikCMT256 L HS (MAST)

7.6-8.9 μm

October 1, 2009 Janos Marki: IR measurements at TCV 4/14

Full frame chamber views

October 1, 2009 Janos Marki: IR measurements at TCV 5/14

Experimental Programme

• Main goal: characterise FWD- & REV-B ELMs (target temperatures, power fluxes, divertor wetted areas, temporal shape of heat deposition, statistics, power balance, in-out assymetries) in ohmic and X3 ECRH-heated scenarios

• Secondary objective: measure ITER-relevant filamentary losses at the top of the machine by making use of TCV’s flexibility in terms of plasma geometry

Shot parameters

A-scenario REV-B FWD-B scenario B-scenario REV-B

October 1, 2009 Janos Marki: IR measurements at TCV 7/14

Shot parameters

FWD-B

#37513

REV-B “A”

#37649

REV-B “B”

#37638

ne 5 – 6e19 5.8 – 6e19 6.4 – 7.4e19

Ip -370 kA 410 kA 420 kA

fELM 70 Hz 140 Hz 200 Hz

dWELM 1.2 ± 0.2 kJ 0.85 ± 0.25 kJ 0.43 ± 0.13 kJ

WPlasma 18-19 kJ 24 kJ 30.5 – 32 kJ

dW/WELM ~6% ~3.5% ~1.25%

October 1, 2009 Janos Marki: IR measurements at TCV 8/14

IR data• VERY preliminary analysis suggests

similar in-out ELM heat deposition ratios

REV-B outer REV-B inner

FWD-B innerFWD-B outer

October 1, 2009 Janos Marki: IR measurements at TCV 9/14

Diagnostics

• Langmuir probes (colum, floor, outer wall) in Isat mode of operation (particle flux)

• Fast visible camera (information on filament propagation)

• Thomson scattering with denser edge channels (pedestal density & temperature)

• BOLO and AXUX N/A – full power balance needs to be done using earlier discharges

October 1, 2009 Janos Marki: IR measurements at TCV 10/14

Second separatrix exp.

•ITER worry: ELM energy fluxes arriving at the upper dump plates in far SOL. •If substantial, would require blanket modules in upper dump area to become high heat flux components needs verification• By using TCV versatility, turning the plasma upside down moves interesting deposition region into the vertical system’s field of view

• in REV-B, corresponds to FWD-B upper deposition

October 1, 2009 Janos Marki: IR measurements at TCV 11/14

First results•Inter – ELM, a bit of a dim flash visible from time to time, otherwise, no sign of heat deposition

•In every ELM, a number of filaments make it to the top (usually at least 7-10)

•Many more filaments visible than for the outer divertor (remark – not so pretty on TCV in general on outer, but still, some even visible on inner divertor

•The existence of filaments is easy to observe, with some luck, even the mode number, however, calculating their energy content, even with a large number of assumptions, is not easy (possibly not feasible with a restricted view like this

October 1, 2009 Janos Marki: IR measurements at TCV 12/14

Last planned experiments (1)

• Goal is to have a better understanding of surface layer temperature response

• 3 LP tiles left uncleaned, larger temperature response than cleaned tiles, seems to grow over time (larger for 1.5 kJ ohmic ELMs in 2008 than for 7.5 kJ X3 ELMs in 2007)

October 1, 2009 Janos Marki: IR measurements at TCV 13/14

Last planned experiments (2)

• attempt L-mode X2 ECRH power steps (worry: shot (<2s) not long enough for near-asymptotic behaviour at target + low-density strike point splitting)

• 1 session to characterise detector behaviour with various filters (transients needed, most easily done by repetition of ohmic L-mode) – hoping to understand layer behaviour better from this

October 1, 2009 Janos Marki: IR measurements at TCV 14/14

Layers: regrowth after cleaning

During TCV shutdown, all tiles have been removed from TCV and grit-blasted, with the exception of 3 LP tiles

Photographs taken after 112 2s discharges (start-up, most disrupted early)

regions of co-deposition can clearly be seen as a blue tinge on the cleaned tiles

interference colour method by Wienhold and Littmark [1]:

TCV: bluish hue = carbon co-deposited layer thicknesses 60 – 100 nm or 180 – 200 nm (first two interference bands, assuming C and Si layer behaviour similar)