Thermal control of x-ray crystals and detectors for ITER CXIS L. Delgado-Aparicio 1 and P....
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Thermal control of x-ray crystals and detectors for ITER CXIS L. Delgado-Aparicio 1 and P. Beiersdorfer 2 1 Princeton Plasma Physics Laboratory (PPPL) 2 Lawrence Livermore National Laboratory (LLNL) Conceptual design review of ITER CORE X-RAY CRYSTAL IMAGING SPECTROMETER June 4-5 th , 2013
Thermal control of x-ray crystals and detectors for ITER CXIS L. Delgado-Aparicio 1 and P. Beiersdorfer 2 1 Princeton Plasma Physics Laboratory (PPPL)
Thermal control of x-ray crystals and detectors for ITER CXIS
L. Delgado-Aparicio 1 and P. Beiersdorfer 2 1 Princeton Plasma
Physics Laboratory (PPPL) 2 Lawrence Livermore National Laboratory
(LLNL) Conceptual design review of ITER CORE X-RAY CRYSTAL IMAGING
SPECTROMETER June 4-5 th, 2013
Slide 2
Motivation/outline In-situ wavelength calibration Needed for
calibrated measurements of the plasma rotation velocity and
spectrometer instrumental function. Reliable measurements of plasma
emissivity, ion temperature and toroidal flow velocity profiles,
requires: In-situ uniformity calibration of detectors Needed for
calibrated measurements of the local plasma emissivity and
estimates of impurity density and its gradients. 2 Crystal/detector
temperature monitoring & control Ambient temperature excursions
can affect interplanar spacing introducing apparent velocity
offsets
Slide 3
Temperature monitoring & control of crystal and detector is
crucial for their proper functioning ITER specifications indicate
that the crystal should be kept at a constant temperature within a
fraction of a degree. Temperature excursions would likely arise
from the changes in the ambient temperature and possibly also from
neutron/gamma/x-ray flux. Need to quantify temperature gradients
within the spectrometer housing. Baseline scenarios considered for
ITER CXIS components: Crystal: 223 o C during bakeout & 220.1 o
C during operation Detector: 223 o C during bakeout & 220.5 o C
during operation Cooling may be accomplished by flowing helium
throughout the enclosures, water through the walls of the
enclosures, or by electrical cooling (e.g. Peltier coolers).
Combinations of these techniques can be conceived if its desired to
reduced the amount of gas cooling 3
Slide 4
Reminder: C-Mod spectrometer uses an atmosphere of He for x-ray
energies of 3-4 keV H-like Ar Crystal H-like Ar Detector He-like Ar
Crystal He-like Ar detectors Ne-like Mo 32+ line falls into H-like
Ar spectrum (Similar imaging systems in NSTX, KSTAR, EAST and LHD
operate in vacuum) 4
Slide 5
Changes of the interplanar 2d-spacing could be misinterpreted
as Doppler shifts The relationship between the Doppler shift (DS)
and the v i : Assuming a constant d, the observed relative
wavelength shift is given by: For a constant , a change d leads to
a change . 5 Bragg diffraction: For small changes:
Slide 6
Crystal temperature affect 2d interplanar spacing 6 Experiments
at Alcator C-Mod (MIT-PSFC)
Slide 7
External heat-loads can be mitigated using a Dewar concept for
crystal and detector housings 7 Not only double-walled but each
wall is coated with a highly reflected material (typically Ag).
Vacuum of at least 10 -3 Torr to keep the conduction below
acceptable values. Estimates also assumed a Dewar-type Be window
arrangement (+coatings 100-200 ).
Slide 8
Use of ultra-high purity beryllium is a MUST 8 The margin of
error in Be window transmissivity is considerable when overall
transmission is small to begin with. T(Fe 24+, 6mm)=14%; T(W 64+,
6mm)=40%. Thinner windows are of course, desirable. Kr
Slide 9
9 Effects of larger absorption due to the presence of
impurities with high- atomic numbers is significant when compared
standard vs ultra-high purity grades of beryllium. Reduction can be
as high as 60%. Be window thickness at C-Mod is 0.1 mm. Add ribs
for thinner windows. STANDARDULTRA-HIGH Use of ultra-high purity
beryllium is a MUST
Slide 10
Internal heat-loads can be mitigated using a He- flow entering
through bottom walls 10 Crystal and detectors are mounted on two
translation and one rotation stages. 20 W in the 2-crystal
enclosure (10 W per arrangement of three stages) while 140 W in the
2-detector housing (15 W per Pilatus detector). Enclosure cooling
by He-gas represents a baseline concept for thermal control. He
cooling with gas @ T-20 o C
Slide 11
Internal heat-loads can be mitigated using a He- flow entering
through bottom walls 11 Gas flow (T He-gas is 20 o C lower than the
desired enclosure temperature): Crystal enclosure: 11.8m 3 /hr and
5.8m 3 /hr during bakeout & operation. Detector enclosure: 27m
3 /hr and 12m 3 /hr during bakeout & operation. Flow rate can
be cut in half if temperature difference were doubled to 40 o C (30
o C for the enclosure with T He-gas =-10 o C). Crystals should be
tested for being able to withstand thermal cycling. He cooling with
gas @ T-20 o C
Slide 12
Water and Peltier-cooling are options for dissipating internal
heat-loads 12 Considered cooling the enclosures by cooling the
inner wall by water and equilibrating by means of a fan that stirs
the He-atm. Calculations show that this approach is viable, but He
convection coefficients are still required. Pelier-cooling on the
crystal mount may provide additional temperature control. Inner
wall with embedded water pipes Pilatus-II manufacturers deliver now
water cooled detectors (experience at LHD). Sensors placed on the
crystal mount and other locations throughout the enclosures will
provide input for adjusting the flow rates and coolant
temperature.
Slide 13
New sensors in MIT-PPPL spectrometer could enable real-time
monitoring & feedback RTDs installed on the crystal mounts Four
RTDs on the optical table Gas RTDs next to He-inlet 19-pin KF50
adapter carrying 5 RTD channels Be window IR temperature sensor
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Slide 14
Summary Our calculations and simulations show that the goal of
maintaining the appropriate temperature within a tightly controlled
range can be achieved. Baseline scenarios considered for ITER CXIS
components: Crystal: 223 o C during bakeout & 220.1 o C during
operation Detector: 223 o C during bakeout & 220.5 o C during
operation The helium flow serves two roles: in the first role it is
a coolant, and in the second role it is a medium that equilibrates
the temperature. We also recommend employing water cooling of the
inner wall to remove some of its heat load as well as Peltier
coolers added to the detectors, crystals and motional stages to
remove their waste heat. Pilatus-II manufacturer is supplying
detectors which are water cooled. Sensors (thermocouples and/or
RTDs) placed on the crystal mount and other locations throughout
the enclosure will provide input for adjusting the flow rate and
coolant temperature. 14
Slide 15
EXTRA 15
Slide 16
Spectrometer temperature excursions have been correlated with
test cell temperature swings Worked at 30-32 o C for nearly week.
Cell cooled down to ~26 o C in a day after AC was fixed, and even
further to ~22 o C after LN 2 cooled the TF magnets. Spectrometer
and crystal temperature experience temperature swings/drifts ~ 1 .
Gradients between the front and back of spectrometer ~ 4-5 16