Thermal control of x-ray crystals and detectors for ITER CXIS
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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

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Thermal control of x-ray crystals and detectors for ITER CXIS

L. Delgado-Aparicio1 and P. Beiersdorfer2

1Princeton Plasma Physics Laboratory (PPPL)

2Lawrence Livermore National Laboratory (LLNL)

Conceptual design review of

ITER CORE X-RAY CRYSTAL IMAGING SPECTROMETER

June 4-5th, 2013


Motivation outline
Motivation/outline CXIS

Reliable measurements of plasma emissivity, ion temperature and toroidal flow velocity profiles, requires:

In-situ uniformity calibration of detectorsNeeded for calibrated measurements of the local plasma emissivity and estimates of impurity density and its gradients.

In-situ wavelength calibrationNeeded for calibrated measurements of the plasma rotation velocity and spectrometer instrumental function.

Crystal/detector temperature monitoring & control

Ambient temperature excursions can affect interplanar spacing introducing apparent velocity offsets


Temperature monitoring control of crystal and detector is crucial for their proper functioning
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: 22±3oC during bakeout & 22±0.1oC during operation

Detector: 22±3oC during bakeout & 22±0.5oC 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


Reminder c mod spectrometer uses an atmosphere of he for x ray energies of 3 4 kev
Reminder crucial for their proper functioning: C-Mod spectrometer uses an atmosphere of He for x-ray energies of 3-4 keV

Ne-like Mo32+ line falls into H-like Ar spectrum

He-like Ar

detectors

He-like Ar

Crystal

H-like Ar

Detector

H-like Ar Crystal

(Similar imaging systems in NSTX, KSTAR, EAST and LHD operate in vacuum)


Changes of the interplanar 2d spacing could be misinterpreted as doppler shifts
Changes of the crucial for their proper functioninginterplanar 2d-spacing could be misinterpreted as Doppler shifts

The relationship between the Doppler shift (DS) and the vi:

Bragg diffraction:

Assuming a constant “d”, the observed relative wavelength shift is given by:

For a constant “l”, a change “Dd” leads to a change “Dq”.

For small changes:


Crystal temperature affect 2d interplanar spacing
Crystal temperature affect 2d interplanar spacing crucial for their proper functioning

Experiments at Alcator C-Mod

(MIT-PSFC)


External heat loads can be mitigated using a dewar concept for crystal and detector housings
External heat-loads can be mitigated using a Dewar concept for crystal and detector housings

Not only double-walled but each wall is coated with a highly reflected material (typically Ag).

Vacuum of at least 10-3Torr to keep the conduction below acceptable values.

Estimates also assumed a Dewar-type Be window arrangement (+coatings 100-200 Å).


Use of ultra high purity beryllium is a must
Use of ultra-high purity beryllium is a MUST for crystal and detector housings

Kr

The margin of error in Be window transmissivity is considerable when overall transmission is small to begin with.

T(Fe24+, 6mm)=14%; T(W64+, 6mm)=40%.

Thinner windows are of course, desirable.


Use of ultra high purity beryllium is a must1
Use of ultra-high purity beryllium is a MUST for crystal and detector housings

STANDARD

ULTRA-HIGH

Effects of larger absorption due to the presence of impurities with high-atomic numbers is significant when compared standardvsultra-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.


Internal heat loads can be mitigated using a he flow entering through bottom walls
Internal heat-loads can be mitigated using a He-flow entering through bottom walls

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-20oC


Internal heat loads can be mitigated using a he flow entering through bottom walls1
Internal heat-loads can be mitigated using a He-flow entering through bottom walls

Gas flow (THe-gas is 20oC lower than the desired enclosure temperature):

Crystal enclosure: 11.8m3/hr and 5.8m3/hr during bakeout & operation.

Detector enclosure: 27m3/hr and 12m3/hr during bakeout & operation.

Flow rate can be cut in half if temperature difference were doubled to 40oC (30oC for the enclosure with THe-gas=-10oC).

Crystals should be tested for being able to withstand thermal cycling.

He cooling with gas @ T-20oC


Water and peltier cooling are options for dissipating internal heat loads
Water and entering through bottom wallsPeltier-cooling are options for dissipating internal heat-loads

Inner wall with embedded water pipes

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.

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.


New sensors in mit pppl spectrometer could enable real time monitoring feedback
New sensors in MIT-PPPL spectrometer entering through bottom walls could enable real-time monitoring & feedback

RTDs installed on

the crystal mounts

IR temperature sensor

Be

window

Gas RTDs next to He-inlet

19-pin KF50 adapter carrying 5 RTD channels

Four RTDs on the optical table


Summary
Summary entering through bottom walls

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: 22±3oC during bakeout & 22±0.1oC during operation

Detector: 22±3oC during bakeout & 22±0.5oC 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.


Extra
EXTRA entering through bottom walls


Spectrometer temperature excursions have been correlated with test cell temperature swings
Spectrometer temperature excursions have been correlated with test cell temperature swings

  • Worked at 30-32oC for nearly week.

  • Cell cooled down to ~26oC in a day after AC was fixed, and even

  • further to ~22 oC after LN2

  • cooled the TF magnets.

  • Spectrometer and crystal temperature experience temperature swings/drifts ~ 1℃.

  • Gradients between the front and back of spectrometer ~ 4-5℃


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