1. Improvement of divertor probe array for heat flux measurement of
ITC25
Nov.4,2015
Toki(Japan)
Improvement of divertor probe array for heat flux measurement of
Heliotron J divertor leg plasma
H. Matsuuraa,b, Y. Umedab, D. Odac, T. Mizuuchic, Y. Suzukid
aRadiation Research Center, Osaka Prefecture University
bGrad. Sch. of Eng., Osaka Prefecture University
cInstitute of Advanced Energy, Kyoto University
dNational Institute for Fusion Science
This work is partially performed with the support and under the auspices of the NIFS Collaborative Research Program. (NIFS14KUHL061)

2. Background
Innovative divertor design for vast heat load handling is an urgent task for both tokamak and helical system.
Intrisic field lines in helical system make it possible to build a “natural” divertor. Among them, island divertor concept is similar with recently proposed snow-flake divertor, since both has many foot points of field lines.
In Heliotron J, island divertor configuration has already been produced, but heat flux measurement is limited yet.

3. Heliotron-J　(Kyoto University)

4. Island divertor Island divertor (W7-X)
T. Mizuuchi et al. / Journal of Nuclear Materials (2001)

5. Divertor probe array in H-J
#3.5 array was removed.

6. Divertor probe array setting
Angle:40 degree

7. Current probe channels

8. Improvement of divertor probe array (#5.5)
Install calorimeters to measure heat flux.
Used calorimeters are thin film type, which was used in Heliotron E.(Japan SEED Ltd)
Film area should be large and channel number is small in order to monitor total heat load instead of it profile.
Considering pitch angle of field lines, some channel would be necessary on the side area of probe array body.

9. Why thin film calorimeter is desirable?
It has already used successfully in Heliotorn E.
Its size can be reduced to set inside probe array case.
Its time response could be improved by proper manufacturing.
TC signal analysis might be simpler, if thermal isolation is good.

10. Heliotron E calorimeter array
日本シード
CM-001

11. Magnetic field lines
Heat load on probe array might come through side surface. Detail data with HINT2 will be available soon.

12. Calorimeter tip

13. Reduction of contact thermal resistance
chromel – alumel
Thin film
Law of intermediate metal ensures direct measurement of film surface even with separately welded two wires, if no temperature gradient along film surface exists.
Twisted two wire measure the temperature far from film surface. Time response will also becomes slow.

14. Choice of tip material
plasma discharge pulse[s], interval of shots, shot number
( t_pulse=0.2d0, t_shot=600.0d0, N_shot=40 )
pulse-averaged heat flux density, effective thickness[m]
( qave=1.0d6, aleff=1.0d-3 ) Cu Mo

15. Thin tip temperature response
# t_0[s], temp_0[deg.C], t_pulse[s], q_inf[W/m2]
0.050d0, 0.0d0, 0.450d0, 0.5d6
# al1[m], al2[m], al_end[m], eta_t
0.0012d0, d0, 0.002d0, 0.0
# x_st[m], x_end[m], x_step[m], x_1, x_2, x_3
0.0d0, d0, 2.0d-5, d0, d0, d0

16. qsink=0
GAMMA 10 Calorimeter tip

17. Comparison of boundary condition
Red: perfect sink boundary, Blue: perfect isolation boundary,Magenta: infinite boundary
probe tip
Plasma pulse

18. Conclusion
Thin film type calorimeter is chosen to be add divertor probe array in Heliotron J.
To determine its size, channel number and position, more detail magnetic field line study is necessary, including plasma current and finite beta effect.
Its temperature response is well expected with simple analytic equation. So heat flux estimation should be easy and reliable.

19. Future work Magnetic field line calculation with HINT2 code.
Construction, open air test, and installation to Heliotron J before next year campaign.
Combine heat flux estimation process and Heliotron J data acquisition system to use as daily monitoring system.

21. Heliotron J divertor probe array(P2-14, Matsuura)
Addition of thin film calorimeter channel to divertor probe array makes it possible to study island divertor function.
Expected temperature response

22. Heat flux measurement of divertor plasma
Device
Probe
Results
Reference
LHD
HDLP
Heat flux evalution is evaluated with TC data of long pulse without mag. noise.
ITC21
GAMMA 10 CM
Heat load per shot is estimated.
TC respnse is improved but signal jump due to RF noise(?) exists.
FEC2010
OS2012
Heliotron J
HDP(#7.5)
GTP(#8.5)
Hybrid Probe
New probes suffers TC noise problem.
ITC18, ITC19
AESJ/JSPF meeting

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

24. #7.5 Hybrid directional probe
Pin3-5　Cu
diameter
4.5[mm]
Type-K TC Cu
157.5 deg.
section view

25. Fitting to TC data
Heat flux evolution is approximated with the sum of step-like heat pulse.

26. Temperature response to step-like heat influx
Response time is given by thermal diffusion time.
Response amplitude is proportional to the square of the heat flux multifid by sensor size.
If the sensor is cooled, response becomes difficult to detect.( In GAMMA 10, sensors are designed to be thermally isolated. )

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

29. Heat sink boundary
Heat
sink
Kurihara, Kado (OS2006)

30. Heat conduction property of thermal probe tip
material
Heat cond.
[W/mK]
T.Diffus.
[mm^2/s]
Time const. [s] *
plasma Cu
398
117
1.0
H-J edge
Kyoto Mo
138
54.3
1.8
MAP-Ⅱ
Tokyo
SUS 16
4.07
ICP
Nagasaki
Pylex
Glass
1.089
0.686
146
glow
OPU
* response time of TC below L=1[cm] from surface
If the first TC is set 2mm, its time response is estimated
to become smaller by factor of 0.04.

31. TC signal response improvement
use high thermal diffusivity materials such as Cu, Ag, and so on for probe tip
reduce the size of probe tip
set TC connection point as close as posible to plasma irradiation surface
Of course, need fast data logger