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

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

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  1. 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

  2. Motivation/outline 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

  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: 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

  4. Reminder: 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)

  5. Changes of the interplanar 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:

  6. Crystal temperature affect 2d interplanar spacing Experiments at Alcator C-Mod (MIT-PSFC)

  7. 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).

  8. Use of ultra-high purity beryllium is a MUST 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.

  9. Use of ultra-high purity beryllium is a MUST 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.

  10. 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

  11. 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

  12. Water and Peltier-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.

  13. New sensors in MIT-PPPL spectrometer 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

  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: 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.

  15. EXTRA

  16. 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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