The Adiabatic Demagnetization Refrigerator for the Micro-X Sounding Rocket Telescope

Abstract

The Micro-X Imaging X-ray Spectrometer is a sounding rocket payload slated for launch in 2011. An array of Transition Edge Sensors, which is operated at a bath temperature of 50 mK, will be used to obtain a high resolution spectrum of the Puppis-A supernova remnant. An Adiabatic Demagnetization Refrigerator (ADR) with a 75 gram Ferric Ammonium Alum (FAA) salt pill in the bore of a 4 T superconducting magnet provides a stable heat sink for the detector array only a few seconds after burnout of the rocket motors. This requires a cold stage design with very short thermal time constants. A suspension made from Kevlar strings holds the 255 gram cold stage in place. It is capable of withstanding loads in excess of 200 g. Stable operation of the TES array in proximity to the ADR magnet is ensured by a three-stage magnetic shielding system which consists of a superconducting can, a high-permeability shield and a bucking coil. The development and testing of the Micro-X payload is well underway.

Update on the Micro-X Sounding Rocket payload

“…In addition, the Kevlar suspension is part of a three-stage vibration suppression system which keeps mechanical energy from being transmitted from the rocket skin to the detector system during powered flight. 12,13 Mechanical tests showed the current design can withstand 20 times the expected launch loads. The magnet, part of the suspension system and the salt pill can be seen in Figure 4e.…”

Vibration Isolation Design for the Micro-X Rocket Payload

“…In order to maintain high energy resolution, the detectors are cooled to 50 mK by an adiabatic demagnetization refrigerator (ADR) to limit thermal noise 1 . The duration of the sounding rocket flight will be approximately 15 minutes, with the observation taking about 5 minutes, so recycling of the ADR in flight is not possible 3 . Therefore, the ADR must be cycled before flight and the detectors kept cold during launch.…”

“…The vibration isolation system for the Micro-X payload has several stages: damping suspension pieces between the skin and the dewar, a system of G10 tubes inside the dewar supporting the helium can and a kevlar suspension to isolate the detector stage from the liquid helium stage 3 . Isolating the inner stages from the vibration at the outer stages is achieved by staggering the resonant frequencies of the stages in such a way that the resonant frequency of the stages increase closer to the detector.…”

“…Isolating the inner stages from the vibration at the outer stages is achieved by staggering the resonant frequencies of the stages in such a way that the resonant frequency of the stages increase closer to the detector. This means that the coldest stages are the stiffest, and have resonant frequencies that sit in regions that are damped by each of the stages acting between the cold stage and the skin 4 . In June, 2012, we travelled to Wallops flight facility to submit the payload to launch-level vibration testing.…”

Thermal Design for the Micro-X Rocket Payload

“…Micro-X is a sounding rocket experiment which acts as an X-ray imaging spectrometer [1] [2]. Its detectors are Transition Edge Sensors (TESs) which provide projected 3 eV resolution in the soft X-ray band from 0.3 to 2.5 keV.…”