Improvement of heat conduction analysis of a small

ITC22
Nov.19,2012
Toki(Japan)
Improvement of heat conduction
analysis of a small thermal probe
H. Matsuuraa, S. Ohshimab, S. Hashimotob, T. Mizuuchib, K.
Nagaokac, H. Takedad, Y. Nakashimad
aRadiation
Research Center, Osaka Prefecture University
bInstitute of Advanced Energy, Kyoto University
cNational Institute for Fusion Science
dPlasma Research Center, University of Tsukuba
This work is partially performed with the support and under the auspices of the
NIFS Collaborative Research Program. (NIFS12KUGM071/NIFS12KUHL047)
Background
Accurate estimate and
control of divertor heat
flux are one of most
urgent issue in fusion
reactor design.
Heat flux change due to Hmode, detachment, and so
on is more interesting than
steady state heat flux or
total heat load per a whole
discharge shot.
Thermal probe (Calorimetric)
method left the space for
improvement to do it.
Diamag.(arb.)
Nucl.Fusion 45 (2005) 1557-1570
Principle of thermal probe
What is necessary for determination of
heat flux q(t) with thermal probe?
• 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
Fitting method must be robust to
TC signal fluctuation
Fitting to TC data
Heat flux evolution is approximated with the sum of step-like heat pulse.
Effect smoothing parameter MTP
MTP＝2
MTP＝5
MTP＝4
MTP＝１０
Temperature response to step-like
heat influx
• Response time is given by thermal
diffusion time.
• Response amplitude is proportional to the
squar 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. )
Here we assume the infinite slab model
with only plasma irradiation boundary.
Heat sink boundary
Heat
sink
Kurihara, Kado (OS2006)
qsink=0
GAMMA 10 Calorimeter tip
Comparison of boundary condition
Red: perfect sink boundary, Blue: perfect isolation boundary,Magenta: infinite boundary
probe tip
Plasma pulse
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
Heat conduction property of thermal probe tip
material
Heat cond.
T.Diffus.
[W/mK]
[mm^2/s]
Time const.
[s] *
Cu
398
117
1.0
Mo
138
54.3
1.8
MAP-Ⅱ
Tokyo
SUS
16
4.07
4.07
ICP
Nagasaki
Pylex
1.089
0.686
146
glow
OPU
plasma
H-J edge
Kyoto
Glass
* response time of TC below L=1[cm] from surface
L2
~
a
If the first TC is set 2mm, its time response is estimated
to become smaller by factor of 0.04.
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. FEC2010
TC respnse is improved but
signal jump due to RF noise(?)
exists.
Heliotron J
HDP(#7.5)
GTP(#8.5)
Hybrid Probe
OS2012
Heat load per shot is estimated. ITC18, ITC19
New probes suffers TC noise
problem.
AESJ/JSPF
meeting
Plasma irradiation data(13th campaign)
(ITC21)
Estimeted plasma heat flux(#78548)
Heat flux[W/m 2]
Co(zp=520)
110
Temp.inc.[deg.]
2000
105
1000
Ctr(zp=520)
100
0
0
2
4
6
time[s]
HDLP was set just outside of LCFS. Magnetic
configuration and NBI direction is chosen so that
fast ion's heat flux reach probe tip.
95
HDLP for Large Helical Device
Thermal diffusion time is of the same order as discharge duration.
Probe temperature data is directly affected by the heat flux change.
New channel is equipped for divertor leg measurement.
divertor "leg"
Spatial resolution: 1~6mm
Particle flux: from Iis
Electron temp.: from V-I data
Heat flux: this work
ch4(0.5)
ch3(1)
ch2(3)
ch1(3)
Comparison of the response for box heat
pulse with two model
2MW/m2, 100ms
heat sink boundary model
1MW/m2, 150ms
thermal isolation boundary model
Temperature at x=2,6,12[mm] is estimeted with two boundary model.
Present (isolation boundary) model reproduces well the TC data. (OS2012)
GAMMA10 Calorimeter system
The west end-mirror region, together with the location of the diagnostic equipment
installed for this experiment.
New hybride probe(#8.5)
Distance betweeen TC and surface is about 1.5mm,
so response time of 10ms is expected.
Cu tip is isolated thermally and electrically. Later
may be cause the signal fluctuation.
Other carbon pins are used for IS fluctuation
measurement with other (#11.5 and #14.5) probes.
B
driving
B-line
Flux
TC signal noise
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
HeliotronJ/GAMMA10.
• We construct a new small sensor and test
it in FY2012 experiment. Both in
HeliotronJ/GAMMA10, TC noise problem
is left.
What is left for future work?
• Improvement of relibility on evaluated
heat flux value or heat conduction
model. Cross check of heat flux
estimation
• Comparison of Q-V characteristic of
divertor plasma with those of low
temperature discharge plasma
• Design and construction of new
sensors for Helioron J/GAMMA 10 to
reduce or remove TC signal noise
Heat flux evalution of LHD
plasma
presented at 21st ITC
Anual. Report of NIFS(2011)
Heliotron-J (Kyoto University)
HDP analysis(H-J)
(Presented at ITC18/ITC19)
#7.5 Hybrid directional probe
Pin3-5 Cu
diameter
4.5[mm]
Type-K TC
Cu
157.5 deg.
section view
Long pulse discharge measurement
Confinement transition
due to biasing
Delay of
TC signal
Thermal
diffusion
time of Cu
0.7[s] delay
1-D const.
Q model
2
q


t150
kJ
/
m
#8.5 Hybride probe (FY2011)
#11.5 probe (old)
New probe
C
BN
Pin3
Pin2,4 double probe
Pin1,5 floating potential
Pin3 not work
Pin3-->Temperature gradient type
thermal probe
H-J用銅GTPのテスト
・約1センチのサイズで熱伝導率の良
い銅を用いてGTPを試作し、４ピンの
ラングミュアプローブと組み合わせて
複合プローブを構成した。
８．５ポート上側よりLCFSのX点近傍
に挿入した。
熱電対信号には放電時のノ
イズが大きく、また放電後の
温度上昇が見られない。
GTPが遮蔽されている？
H-J用銅GTP（#8.5port）の問題
・プローブ駆動装置はプローブの軸方
向に平行にLFCSに接近させる。その
ため、磁力線は側面のBN部にあたり、
GTPはイオンセンシティブプローブの
様にイオンしか受け取ることが出来な
い。
Fig.1, Top view of Heliotron J and the
probe location, and cross sectional
H-Jでは側面にセンサーが必要
view of # 8.5 and # 11.5 sections.
Response of the old sensor
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.
In FY 2010 experiment, time
response of calorimeter sensor
was slow, and data recorder
also worked slowly.
Calorimetric estimation
qave S c
m
V
T t pulse
One division is 16[min], nearly
equal shot interval
• Was Temperature evolution of TC data sufficiently traced?
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 noise
During 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.

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