temperature measurement and real-time validation · • surface temperature measurement is part of...
TRANSCRIPT
Temperature measurement and real-time
validation
A. Herrmann, B. Sieglin, M. Faitsch,
P. de Marné, ASDEX Upgrade team
1st IAEA Technical Meeting on
Fusion Data Processing, Validation and Analysis
ITER- diagnostics categories
The ITER plasma diagnostics are required to provide accurate measurements of
plasma behaviour and performance. They are typically classified in different
categories from operations point of view:
Group 1a1 machine protection
Group 1a2 basic machine control
Group 1b advanced plasma control
Group 2 measurements required for evaluation and physics studies.
The machine is unable to operate without a working diagnostic providing
every Group 1a parameter (CIS & PCS).
Thermography is part
of the machine protection
(surface temperature)
1st IAEA TMFDPVA, Nice, 1-3 June 2015 A. Herrmann 2
Tore Supra: D. Guilhem, G. Martin, R. Reichle, H. Roche, M. Jouve, L. Ducobu, P. Messina, Infrared surface temperature measurement for
long pulse; real-time feedback control in an actively cooled machine, Review of Scientific Instruments 70 (1) (1999) 427–430.
ASDEX Upgrade: Herrmann, A., R. Drube, T. Lunt, et al., Real-time protection of in-vessel components in ASDEX Upgrade. Fusion Engineering
and Design, 2011. 86(6-8): p. 530-534
Talk by Sven Martinov
(optical) temperature measurement and
machine protection
3
• Stationary temperature profiles on short
time scales (τeq << ΔtDischarge)
• Typical heat fluxes q = 10-20 MW/m2.
• Where are the critical temperatures?
– Surface temperature
(local melting, cracks, recrystallization)
– Interface temperatures, cooling
channel
• The sensitive component is inside the
target …
• But the surface temperature is measured.
• Correlation to the temperature inside the
bulk.
• The machine protection is as good as
– the temperature measurement and
– the thermal model of the target.
W7-X target tile (cross section)
2
1
/100
mMW
K
q
T
Heat resistance:
1st IAEA TMFDPVA, Nice, 1-3 June 2015 A. Herrmann 3
Actively cooled targets
Critical Ts is time dependent
steady state:
• Ts given by the interface
transient (short vs. transition time):
• Ts limit due to surface temperature
• -> Energy impact
dq
TTT scoolss
)(
c
tqTTT t
sss
2)( 0
sm
MJ
Graphite
220
:
sm
MJ
Tungsten
240
:
1st IAEA TMFDPVA, Nice, 1-3 June 2015 A. Herrmann 4
mmad 4.0~ 1 ms, W
Temperature calculation
1)exp(
1),(
24
1
T
c
cTM e
1st IAEA TMFDPVA, Nice, 1-3 June 2015 A. Herrmann 5
Temperature calculation
1)exp(
1),(
24
1
T
c
cTM p
1st IAEA TMFDPVA, Nice, 1-3 June 2015 A. Herrmann 6
• Planck radiation
– Surface morphology
– Layers/deposits
– Reflections
• ‚Parasitic radiation‘
– Bremsstrahlung
– Marfes (impurity radiation)
– Arcs
– Dust
+
• Overestimation of the bulk temperature due to:
– Surface morphology - Deposits/layers.
7
Additional contributions - Examples
1st IAEA TMFDPVA, Nice, 1-3 June 2015 A. Herrmann 7
Additional contributions – Examples (II)
1st IAEA TMFDPVA, Nice, 1-3 June 2015 A. Herrmann 8
Arcs Bremsstrahlung/Reflections
Dust
Problems - summary
• The measured surface temperature is biased by
– Additional Planck radiation
– Other sources of radiation
• Both contributions result in a too high temperature (Tmeasured > Tsurface)!
• Inherent safe
• … but might reduce the operation range significantly
• Are there parameters that are applicable for real time data validation?
• YES
– Time behaviour
– Spectral dependence
1st IAEA TMFDPVA, Nice, 1-3 June 2015 A. Herrmann 9
Layers and temperature
• Tokamak experiments (JET)
• Layers at the inner target.
• Verified by spectroscopic
measurements (background)
• About 150 K / MW/m2
P. Andrew et al.
Journal of Nuclear Materials 337–339 (2005) 99–103
1st IAEA TMFDPVA, Nice, 1-3 June 2015 A. Herrmann 10
Layer effects (I)
Bulk material: thermal data known
s
l
lbslayer q
dTTT
1.
(Nearly) no effect on the measured
surface temperature
2.
The surface temperature is
increased
The derived heat flux is too
large if the surface effect is not
considered.
bl
bl
Temperature gradient in top of the bulk
blbKm
Wmd 10/110050
The additional ΔT is 45 K/MWm-2
sa
d
50
2
The time constant for such a thin region is
short.
Ts
Tb
Tc
sq
Numerical:
After this time the time behaviour of the
surface temperature follows the heating
of the bulk.
1st IAEA TMFDPVA, Nice, 1-3 June 2015 A. Herrmann 11
Layer effects (II)
+
1st IAEA TMFDPVA, Nice, 1-3 June 2015 A. Herrmann 12
Hot spots result in an artificial temperature
increase
• The measured temperature is
calculated from the photons
belonging to two (ore more)
temperatures.
• The microscopic temperature
patterns are fixed over many
heating cycles. R_T – temperature ratio hot spot/bulk
R_a – area ratio hot_spot/total area
EK 98 Tl Th
Tl Th Tl Th
1st IAEA TMFDPVA, Nice, 1-3 June 2015 A. Herrmann 13
Wavelength selection (I)
• Planck’s law
– Unique relation between
radiation/photon emission of a
body and temperature.
– Depends on the wavelength
(broad band radiation).
• Select an optimum wavelength:
– Temperature range.
– Environment (vacuum, air).
– Available detectors (costs).
Planck’s formulae for radiation from a
black body into the half space
1)exp(
1),(
25
1
T
c
cTM e
2162
1 10741,32 Wmhcc
mm
WM e
2][
mKk
chc 4
2 10438.1
mKT 3
max 10898.2
1 1050.5
1000
3000
2000
300
500
tem
pe
ratu
re [
K]
wavelength [m]100
101
102
103
104
105
106
710
sp
ectr
al
rad
ian
t e
xit
an
ce
[W/(
m^
2
m)]
Vis/NIR MWIR LWIR
1st IAEA TMFDPVA, Nice, 1-3 June 2015 A. Herrmann 14
Wavelength selection (II)
• Typical wavelengths regions for T
measurement:
– Vis/near infrared (vis/NIR, ~ 1μm)
– Mid wave infrared (MWIR, ~ 5μm)
– Long wave infrared (LWIR, ~ 10
μm)
• MWIR and LWIR cover temperature
range from 500 to 3500 K.
• Vis/NIR covers a ‘small’ T-range.
• T measurement error:
• Strong error mitigation in the vis/NIR
wavelength region:
– Comparator like behaviour.
– robustness against change of
system parameters (emissivity).
)(arg2 Bck
Bck
ett
Bck
S
S
S
S
K
K
c
T
T
T +
+
+
;argdet Bckett SSS + )1)/(exp( 2arg
T
cKS ett
1)exp(
1),(
25
1
T
c
cTM e
0 500 1000 1500 2000 2500 3000103
104
105
106
107
108
3500
vis/NIR
MWIR
LWIR
10 % cal. error
mitigation
amplific.
1st IAEA TMFDPVA, Nice, 1-3 June 2015 A. Herrmann 15
Bremsstrahlung
• Strong decrease of
Bremsstrahlung contribution
between 1 and 5 μm (1/λ2).
• Optimum wavelength – 5 μm
• Cold and dense plasmas
contribute to Bremsstrahlung.
• Reduced target load due to
divertor detachment.
Tbrems
< 500 K
Tbrems
>2500 K
Temperature equivalent for Bremsstrahlung.
A constant pressure of neTe = 1x1022 eVm-3 is assumed.
e
ff
e
eeffB
T
hcExpG
T
nZconst
dVd
dW
2/1
2
2
1
1st IAEA TMFDPVA, Nice, 1-3 June 2015 A. Herrmann 16
Reflections
• Target acts as a mirror in the
optical system.
• Time behaviour of reflections can‘t
be used to discriminate between
reflections and target.
• Reduce reflections as much as
possible.
• Simulation of reflections for an
ideal 3D geometry.
• Identification of ‚critical regions‘ –
dominated by reflections.
IR images (radiometric units), simulated by SPEOS CAA V5
Based, looking at the outer divertor with W monoblock.
(Left) Image in direct radiance when the flux coming on the sensor
is only the thermal emission of hot targets.
(Right) Real image of the camera when the flux picked up by the
camera includes also the reflection effects.
1st IAEA TMFDPVA, Nice, 1-3 June 2015 A. Herrmann 17
Reduction of reflections
• Sand blasted compared to ‚as
manufactured‘
– ‚as manufactured‘ – dominant
direct reflection (mirror)
– sand blasted – dominant diffusive
reflection, suppression of direct
reflections
• Moderate increase of the emissivity
(0.2 -0.3) @ about 4 μm
sand blasted as manufactured
BB 1/5
0 500 1000 1500 2000 2500
20
40
60
80
100
Reflectivity of both parts, %
Wavelength, nm
Rtot, shiny part
Rdiff, shiny part
Rtot, shiny, 90o!
Rdiff, shiny, 90o
Rtot=Rdiff, matt
1st IAEA TMFDPVA, Nice, 1-3 June 2015 A. Herrmann 18
2 wavelength (ratio) measurement
Assumptions for the ratio measurement:
• Tobj >> TBck
• λ < λmax (Wien), i.e NIR range
• Grey body
1st IAEA TMFDPVA, Nice, 1-3 June 2015 A. Herrmann 19
),(1),()( 111111 BckBBobjBB TMTMM +
1)exp(
1),(
25
1
T
c
cTM
),(21),(
),(1),(
)(
)(
222
1111
22
11
BckBBobjBB
BckBBobjBB
TMTM
TMTM
M
M
+
+
object reflected
background radiation
+
1
2
11
22
12
21
2
ln5)(
)(ln
)(
11
W
W
obj M
M
cT 0
0,2
0,4
0,6
0,8
1
1,2
1,4
1,6
1,8
2
0,8 0,9 1 1,1 1,2
f_e
epsi_ratio
2 color vs. single color
ε1/ε2
usedobj f
Single band vs. ratio measurement
ratio
ratio
single single
Machine protection – add. information
Optical diagnostic to
measure surface
temperature evolution
• high spatial resolution
(millimetres)
• high time resolution
(microseconds)
• detection wavelength
selectable
• measured temperature is
sensitive to surface
modifications
qs(t,x) – target heat load
Cooling media channel -
Calorimetry for
measurement of global
energy removal.
Thermocouples at
different positions. • Localised
• Limited time
response
• Not affected by
surface effects
• 2 TCs for direct
heat flux recording
Tb1
Tb2
Ts (t,x)
Δx
x
TTq bb
21
1st IAEA TMFDPVA, Nice, 1-3 June 2015 A. Herrmann 20
Summary
• Surface temperature measurement is part of machine protection.
• The cooling structure has to be ‘protected’ against overheating
– The tolerable surface temperature is time dependent
• Short term events (ELMs)
• Degeneration of thermal parameters.
• The measured photon flux is falsified by additional photon sources and
reflections.
• The resulting (measured) surface temperature is too high – reduction of the
operational space.
• Real time validation is possible by:
– Considering the temporal evolution – dT/dt or heat flux calculations.
– Typical time constants are ms.
– Measuring @ 2 (or more) wavelengths to eliminate Bremsstrahlung
contribution.
– Using vis/NIR data points for 1 point calibration (comparator like behaviour).
1st IAEA TMFDPVA, Nice, 1-3 June 2015 A. Herrmann 21
alt. Summary
• The measured temperature is
usually not the bulk temperature.
• Machine safety (inherent safe,
restrictions for the operation range)
• Verify the measured temperature,
deduce the true bulk temperature.
• Keep the diagnostic as simple as
possible!
1st IAEA TMFDPVA, Nice, 1-3 June 2015 A. Herrmann 22
Temperature
Temperature evolution and power
calculation (transient like ELMs, TCs)
Characterize the surface of the
material (hot spot fraction) for on-line
T correction.
In situ surface characterization.
Multi-wave, multi-band
measurement, single detector chip
(hot spots, Layer, reflections, ε, τ).
Spectral measurements
(1D profile -> 2D chip).
Photothermal methods
Multi-color pyroreflectrometry
com
ple
xity