Measurement of divertor heat flux at the end-cell of the GAMMA 10

H. Matsuuraa, H. Takedab, K. Ichimurab, K. Hosoib, Y. Nakashimab, M. Sakamotob, M. Shojic, K. Nagaokac, T. Imaib

aRadiation Research Center, Osaka Prefecture University bPlasma Research Center, University of Tsukuba

cNational Institute for Fusion Science

OS2012/PMIF2012Aug.28,2012Tsukuba(Japan)

Contents of my presentation

• Why is plasma heat flux(energy flux) important?

• What is thermal probe and how is it used ?

• What is necessary for GAMMA 10 (or ITER) plasma heat flux measurement?

• What did we do?What have we obtained?

• What is left for future work?

PSI and heat(Energy) flux

• Plasma medicine and biomaterial treatment

• Plasma CVD and etching

• Space vehicles, such as Hayabusa

• Divertor design and ELM control

Plasma heat flux is important in wide PSI field.

New J. Phys. 11 (2009) 115012

Classical thermal probe

Concept of thermal probe ( or solid calorimeter)

q(t)

Heat flux

tTD

=L2/ t

pulse

TC

T(t)

Measurement data

Inverse heat conduction model

tTD

=L2

/ tpulse

Long pulse plasma

Short pulse plasma

L

q(t)

T(t)

T(t)

q(t)

tip material Heat conductivity

Thermal diffusivity

time constant[s] for L=10[mm]

example

[W/mK] [mm2/s]

Cu 400 100 1.0 H-J

Mo 138 54.3 1.8 MAP-II

SUS 16.0 4.07 4.07 ICP/Magnetron

Pylex Glass 1.089 0.686 146 glow

Measurement of heat flux changeHeat flux change due to H-mode, detachment, plug ECH, and so on is more interesting than steady state heat flux or total heat load per a discharge shot.

LHD results( presented at ITC21)

How about heat flux?

What is necessary for determination of q(t) as like in LHD experiment?

• Fitting procedure of measured TC data with response function model with physical causality

• Response function of probe/calorimeter sensor with appropriate modeling

• A small sensor with fast response (small thermal diffusion time) and good SN ratio

Here we assume the infinite slab model with only plasma irradiation boundary.

Heat sink boundary

Heatsink

Kurihara, Kado (OS2006)

qsink=0

GAMMA 10 Calorimeter tip

Comparison of boundary condition

Plasma pulseprobe tip

Red: perfect sink boundary, Blue: perfect isolation boundary,Magenta: infinite boundary

GAMMA10 Calorimeter system

The west end-mirror region, together with the location of the diagnostic equipment installed for this experiment.

Response of the old sensor

• Was Temperature evolution of TC data sufficiently traced?

In FY 2010 experiment, time response of calorimeter sensor was slow, and data recorder also worked slowly.

q ave S c m V T t pulse

Calorimetric estimation

The heat-flux density is evaluated from the difference between the temperature of the calorimeter tip measured just before the discharge and that measured immediately after the discharge.

One division is 16[min], nearly equal shot interval

Improvement of sensor

Old calorimeter New calorimeter

Material copper copper

TC connection from irradiation surface

about 10mm about 2mm

thermal diffusion time about 1[s] about 40[ms]

Thermocouple Type T with sheath Type T without sheath

Response of TC signal

TC signal noiseDuring and just after discharge, there exist large noises in TC signal.They come from RF power, magnetic field induction, ....

Noise at t=400-2000ms is well compensated with no plasma shot data.

Comparison of the response for box heat pulse with two model

Temperature at x=2,6,12[mm] is estimeted with two boundary model.Present (isolation boundary) model reproduces well the TC data.

heat sink boundary model

2MW/m2, 100ms

thermal isolation boundary model

1MW/m2, 150ms

Conclusion(What we did.)

• We develop a new fitting procedure of measured TC data, and demonstrate with LHD probe data.

• We expand response function model to be applicable to small sensors in GAMMA10.

• We construct a new calorimeter sensor and test it in FY2012 experiment.

What is left for future work?

• Determination of the TC noise origin and reduction of it. ( Isolation Amplifier used in Heliotron J experiment may be effective.)

• Cross check of heat flux estimation

• Determination of heat flux evolution with plug ECH or ICRF additional heating

• Diagnostic as a thermal probe (for example, divertor Ti measurement)

This work is partially performed with the support and under the auspices of the NIFS Collaborative Research Program. (NIFS12KUGM071/NIFS12KUHL047)

Thank you for kind attention.

Any questions and comments are welcome.

Sheath heat transmission factor

HDP analysis(H-J)(Presented at ITC18/ITC19)