Susan Breon

ASTRO-E high-resolution x-ray spectrometer

The Astro-E High Resolution X-ray Spectrometer (XRS) was developed jointly by the NASA/Goddard Space Flight Center and the Institute of Space and Astronomical Science in Japan. The instrument is based on a new approach to spectroscopy, the x-ray microcalorimeter. This device senses the energies of individual x-ray photons as heat with extreme precision. A 32 channel array of microcalorimeters is being employed, each with an energy resolution of about 12 eV at 6 keV. This will provide spectral resolving power 10 times higher than any other non-dispersive x-ray spectrometer. The instrument incorporates a three stage cooling system capable of operating the array at 60 mK for about two years in orbit. The array sits at the focus of a grazing incidence conical mirror. The quantum efficiency of the microcalorimeters and the reflectivity of the x-ray mirror system combine to give high throughput over the 0.3- 12 keV energy band. This new capability will enable the study of a wide range of high-energy astrophysical sources with unprecedented spectral sensitivity. This paper presents the basic design requirements and implementation of the XRS, and also describes the instrument parameters and performance.

Thermal design of the XRS helium cryostat

Abstract The required lifetime for the Astro-E X-Ray Spectrometer (XRS) is 2 years, with a goal of 2.5 years. To meet this requirement, significant advances in state-of-the-art longlife cryogenic systems are required. The XRS system is a hybrid neon/helium system with a final stage of cooling provided by an adiabatic demagnetization refrigerator. The thermal design of the helium cryostat is described in this paper. To achieve a lifetime of 2.5 years with a helium volume of approximately 20 litres, the heat load on the helium must be of the order of 800 μW or less. The expected lifetime and sensitivity of the lifetime to changes in the design or external heat loads is modelled. Results of preliminary thermal conductivity measurements are presented and future tests are identified. A study of heat loads that were small enough to be neglected in previous designs of long-life cryogenic systems was undertaken. A summary of the findings is presented.

A High Tc Superconducting Current Lead Assembly for the XDS Helium Cryostat

The X-ray Spectrometer Detector System (XDS) helium cryostat consists of a tank of pumped liquid helium at about 1.3 kelvin suspended inside a seventeen kelvin cylindrical support structure. The tank is a heat sink for an adiabatic demagnetization refrigerator (ADR) and its superconducting magnet. The cryostat’s small initial helium volume and mission lifetime goal of 2.5 years require that the average total heat load to the helium be less than about 800 microwatts. During the mission the superconducting magnet requires a current of 2 amps with a three percent duty cycle. In addition, wires capable of carrying up to 1 amp are needed for cryogenic valve operations during the cryostat’s ground servicing. The best optimized conventional current leads between the 17 kelvin stage and the magnet and valves would contribute an average heat load to the helium of about 3 milliwatts. An assembly of superconducting YBaCuO fibers bonded to a fiberglass tube and suspended by a Kevlar* braid was developed to conduct the current from the 17 kelvin support structure to a vapor-cooled 4 kelvin stage. NbTi wires provide a superconducting path from the 4 kelvin stage to the magnet and valves on the 1.3 kelvin helium tank. This paper describes the assembly’s fabrication and suspension and presents the results of its performance and vibration tests.

The XRS low temperature cryogenic system: Ground performance tests results

Abstract The X-Ray Spectrometer (XRS) instrument is part of the Astro-E mission scheduled to launch early in 2000. Its cryogenic system is required to cool a 32-element array of X-ray microcalorimeters to 60–65 mK over a mission lifetime of at least 2 years. This is accomplished using an adiabatic demagnetization refrigerator (ADR) contained within a two-stage superfluid helium/solid neon cooler. Goddard Space Flight Center is providing the ADR and helium dewar. The flight helium dewar was assembled in Sept. 1997 and subjected to extensive thermal performance tests. This paper presents test results at both the subsystem and component levels. In addition, results of the low temperature topoff performed in Japan with the engineering unit neon and helium dewars are discussed.

Design of the XRS helium insert

The X-Ray Spectrometer (XRS) instrument has gone through numerous iterations, first as an instrument on NASA’s Advanced X-Ray Astrophysics Facility (AXAF), then on AXAF-S, and now scheduled to fly on the Japanese Astro-E satellite. The Astro-E XRS is a high precision x-ray spectrometer with better than 20 eV resolution for x-ray energies from 0.3 to 10 keV. The requirement to obtain a lifetime greater than two years within the weight constraints of Astro-E has presented quite a challenge in the design of the cryogenic system. The design of the superfluid helium insert is described, with emphasis on innovative approaches taken to meet the requirements.

The X-ray Spectrometer - A cryogenic instrument on the Advanced X-ray Astrophysics Facility

The X-ray Spectrometer (XRS) is an instrument on the Advanced X-ray Astrophysics Facility (AXAF), the third of NASA’s Great Observatories scheduled for launch in 1998. The XRS detectors have a resolution of approximately 10 eV over the range 0.3 – 10 keV. To achieve this resolution, the detectors are maintained at or below 0.1 Kelvin using an adiabatic demagnetization refrigerator inside a superfluid helium dewar. In addition, split-Stirling-cycle mechanical coolers are used to extend the anticipated on-orbit helium lifetime to a minimum of 4 years. This paper describes the challenges of developing this hybrid cryogenic system and presents an overview of the current design of the system.

Operation of a Sunpower M87 Cryocooler in a Magnetic Field

The Alpha Magnetic Spectrometer-02 (AMS-02) is an experiment that will be flown as an attached payload on the International Space Station to detect dark matter and antimatter. It uses large superconducting magnets cooled with superfluid helium to bend the path of cosmic particles through a series of detectors, which then measure the mass, speed, charge, and direction of the particles. Four Sunpower M87N Stirling-cycle cryocoolers are used to extend the mission life by cooling the outer vapor-cooled shield of the dewar. The main magnet coils are separated by a distance of approximately 1 m and the coolers are located approximately 1.5 m from the center line of the magnet, where the field is nearly 1000 gauss at the cryocooler cold tip. Interactions between the applied magnetic field and the linear motor may result in additional forces and torques on the compressor piston. Motion of the compressor and displacer pistons through the magnetic field spatial gradients will generate eddy currents. Additional eddy currents are created during magnet charge, discharge, and quench by the time-varying magnetic field. The results of tests to demonstrate the performance of the cryocoolers in an external magnetic field, with and without magnetic shielding, are presented.

5-Year Lifetime Hybrid Superfluid Helium Dewar for the AXAF X-Ray Spectrometer (XRS)

The focal plane of the AXAF X-Ray Spectrometer requires an operating temperature of 0.1 K with a mission lifetime of 5 years. This demanding task is accomplished with a hybrid cryogenic subsystem consisting of mechanical coolers, a superfluid helium dewar and an adiabatic demagnetization refrigerator. By using mechanical coolers to remove heat from the dewar outer vapor-cooled shield, a 5-year lifetime is achievable with only a 483-liter tank. This approach takes advantage of flight-proven, high-performance dewar technology and recent success in the development of split, Stirling-cycle mechanical coolers. Although the dewar design principles are similar to those used previously, parasitic heat flow is reduced to a new level by an optimized tension strap support system and careful attention to insulation system details. The benefit of the mechanical coolers is maximized by dewar interface design features that minimize parasitic heating and thermal impedance of the coupling. The dewar design and thermal performance analysis are discussed. Helium lifetime sensitivities and the effects of mechanical cooler failures are predicted.

Thermal performance of the XRS helium cryostat

The Astro-E/X-Ray Spectrometer (XRS) is required to operate for 2 years on-orbit with approximately 20 liters of superfluid helium. The total heat load on the helium must be less than 1 mW, which is significantly smaller than any previous spaceborne helium system. Consequently, the XRS cryostat incorporates several new techniques that have not been used before in spaceborne cryogenic systems, including high temperature superconducting leads, a film flow suppressor in the vent line, and kevlar suspension systems. The thermal design of the cryostat is described and results of the ground tests of both an engineering model cryostat and the flight cryostat are presented. Tests of the flight cryostat are incomplete at the writing of this paper, so only preliminary results are given.

Space Flight Qualification Program for the AMS-02 Commercial Cryocoolers

The Alpha Magnetic Spectrometer-02 (AMS-02) experiment is a state-of-the-art particle physics detector containing a large superfluid helium-cooled superconducting magnet. Highly sensitive detector plates inside the magnet measure a particle’s speed, momentum, charge, and path. The AMS-02 experiment will study the properties and origin of cosmic particles and nuclei including antimatter and dark matter. AMS-02 will be installed on the International Space Station on Utilization Flight-4. The experiment will be run for at least three years.