I. Hepburn

The x-ray microcalorimeter spectrometer onboard Athena

One of the instruments on the Advanced Telescope for High-Energy Astrophysics (Athena) which was one of the three missions under study as one of the L-class missions of ESA, is the X-ray Microcalorimeter Spectrometer (XMS). This instrument, which will provide high-spectral resolution images, is based on X-ray micro-calorimeters with Transition Edge Sensor (TES) and absorbers that consist of metal and semi-metal layers and a multiplexed SQUID readout. The array (32 x 32 pixels) provides an energy resolution of < 3 eV. Due to the large collection area of the Athena optics, the XMS instrument must be capable of processing high counting rates, while maintaining the spectral resolution and a low deadtime. In addition, an anti-coincidence detector is required to suppress the particle-induced background. Compared to the requirements for the same instrument on IXO, the performance requirements have been relaxed to fit into the much more restricted boundary conditions of Athena. In this paper we illustrate some of the science achievable with the instrument. We describe the results of design studies for the focal plane assembly and the cooling systems. Also, the system and its required spacecraft resources will be given.

Structural analysis of a cryogen-free refrigerator for space

Abstract Future X-ray observatories in space, such as European Space Agencys (ESA) X-ray evolving universe spectroscopy (XEUS) mission, will require cooling to the region 10–100 mK to enable the utilisation of advanced cryogenic photon detectors in cryogenic spectrometer instruments. Such missions are envisaged to be completely cryogen-free, replacing the traditional superfluid liquid helium cryostat with a space worthy mechanically cooled system. As part of the Mullard Space Science Laboratorys (MSSL) adiabatic demagnetisation refrigerator (ADR) development programme, we have investigated the construction of a flight cryostat containing a 10 mK ADR (the MSSL double ADR (dADR)) that can be cooled by a single Astrium (formally Matra Marconi Space (MMS)) 4 K mechanical cooler. A proto-type dADR has been constructed and will be flight proven as part of a sounding rocket payload, where the dADR system will be used to cool an array of superconducting tunnel junction (STJ) detectors at the focus of an X-ray telescope.

Millikelvin cryocooler for space- and ground-based detector systems

This paper describes the design of a continuously operating millikelvin cryocooler (mKCC) and its origins. It takes heritage from the double adiabatic demagnetization refrigerator (dADR) which was built for the European Space Agency (ESA). The compact design is based on a tandem configuration continuous ADR which alternately cycles two dADRs. The mKCC is a single module (dimensions 355 x 56 x120 mm) which operates from a 4 K bath (liquid or cryocooler) and provides an interface to the user which is settable from < 100 mK to 4 K. Predicted maximum cooling power at 100 mK is 7μW. It will use only single crystal tungsten magnetoresistive heat switches (the first ADR cooler to do so) and the measured thermal performance of these heat switches is presented. The mKCC uses ten shielded 2 Tesla superconducting magnets capable of ramping to full field in 20 – 30 seconds. This has been demonstrated in the lab and the results are given for the successful performance of a prototype Chromium Potassium Alum (CPA) pill using one of these magnets. The mKCC has been designed to be fully automated and user friendly with the aim of expanding the use of millikelvin cryogenics and providing a good testing and operating platform for detector systems.

Cooling system for ultralow-temperature cryogenic detector cameras

A prototype ultra low temperature cryogen free refrigerator has been developed at the Mullard Space Science Laboratory that may be coupled to ground based cryo-coolers or space cryo-coolers. Enabling such detectors to be used, in which the fact that the detector is at very low temperature is of little concern. A development system has ben constructed as proof of consent for two space based refrigeration systems, one of which is under construction. The developed system and subsequent systems provide a compete turnkey refrigeration system for cryogenic detector cameras. The refrigeration system may be utilized in either static or in moving environments, for example vehicles, aircraft or satellites, since the power consumption is low between 24 and 224 Watts and masses are in the region of 50-90 Kg, depending on the system.

High-speed spectro-photo-polarimeter for the Subaru Telescope

A conceptual design study of a high-speed spectro-photo- polarimeter for the Subaru Telescope is presented. Use of Superconducting Tunneling Junction detectors was compared with the use of Hybrid Photodiode or Photomos arrays with dispersive optics. Expected performances using at the Subaru Telescope were evaluated. This instrument will be extremely useful for a large variety of astronomical studies, especially for the field of mass accretion onto compact objects: white dwarfs, neutron stars and black holes, and low amplitude photospheric pulsation studies of stars.