XQC Payload

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The XQC experiment is composed of a 36 pixel microcalorimeter x-ray detector. The entire array is micromachined from a single piece of silicon with each pixel measuring 0.5 x 2.0 mm. A HgTe x-ray aborber is epoxied onto the front surface of each pixel. A schematic diagram of a pixel and the arraying scheme is shown below. You can also look at our brief detector description here.

Here is a pixture of the completed flight array mounted on an alumina circuit board and installed in the flight detector box:

The detector system has to be maintained at a temperture of 60mK above absolute zero during operation. This is achieved using a liquid helium dewar and an adiabatic demagnetization refrigerator (ADR). A cross section of the flight dewar is shown below:

(click to enlarge)

The dewar is composed of nested G10 fiberglass shells to give it good thermal isolation (using vapor cooled shields) and excellent axial stiffness to withstand launch vibration. Here is a view of the unassembled dewar shells:

A top view showing the nested shells with the 130K and 30K vapor cooled shields is shown below:

Here is the completed dewar with electronics boxes on the top surface and the base of its rocket skin section at the bottom. The blue cylinder is the outer vacuum shell of the dewar:

The adiabatic demagnetization refrigerator is the ultra low temperture refrigerator for the microcalorimeter detectors. It uses the pumped liquid helium bath at 1.8K as a heat sink and cools the detectors to 60 mK. The refrigerator works by using a 40 kG superconducting magnet to align the spins of a paramagnetic salt dumping the heat of magnetization to the helium bath. A heat switch is then opened and the field ramped down. The salt then cools adiabatically to the base temperature. The magnetic field is then controlled (slowly ramped down) to keep the detectors at constant temperature. The next picture is the central refrigerant of the ADR which is an enclosed cylinder of Ferric Amonium Alum (FAA):

The salt pill is then suspended on kevlar fibers inside the bore of the superconducting magnet:

Here is a bottom view of the dewar with the vacuum cover removed showing the detector system mounted to the end of the ADR:

The readout electronics and magnet controller for the experiment are housed in a seperate section of the rocket placed just forward of the dewar. The dewar and electronics sections without the outer rocket skin are shown below. The detector readout electronics consists of analog triggers, quick look pulse height analyzers, and digitizers. Each x-ray photon generates a fully digitized waveform which is then telemetered to the ground.

The payload with its aluminum outer rocket skins installed is 18" in diameter. The person in the red shirt in the following picture is standing in front of the experiment electronics section and the dewar section is immediately to his right. The open access panel allows us to transfer liquid helium into the dewar during tests and before launch:

The final experiment is mated to the guidance system, recover system (parachute) and motors to form the full rocket experiment:

This page written and maintained by F. Scott Porter (email: Frederick.S.Porter@gsfc.nasa.gov)
Responsible NASA official: F. Scott Porter (email: Frederick.S.Porter@gsfc.nasa.gov)
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