The X-ray Astronomy group at the University of Leicester is responsible for the development of two out of three of the focal plane cameras for the EPIC instrument on ESA's cornerstone mission XMM. CCDs are being developed in collaboration with EEV Ltd. of Chelmsford, UK, to perform the imaging spectroscopy at the prime focus of the telescope. The detectors require Fano-limited energy resolution and high detection efficiency over the 0.1 - 15 keV band. Devices are being constructed using high resistivity bulk silicon (> 8000 (Omega) cm) producing deep depletion, with an efficiency at the iron line (6.4 keV) of 85%. The low energy (< 1 keV) X-ray performance is being maximized in the front-illumination devices by using novel `open electrode' structures resulting in an efficiency of 23% at carbon- k (277 eV). The test results of devices manufactured are presented for a range of X-ray lines and the data are compared to modelled results based on the device parameters.

The Objective Crystal Spectrometer on the SPECTRUM-X-GAMMA satellite will use three types of natural crystals LiF(220), Si(111), RAP(001), and a multilayer structure providing high-resolution X-ray spectroscopy of Fe, S, O, and C line regions of bright cosmic X-ray sources. 330 - 360 LiF(220) crystals of dimensions approximately 23 X 63 mm² are required to cover one side of a large (1000 X 600 mm²) panel, which is to be mounted in front of one of two high throughput X-ray telescopes. Rocking curves of 441 LiF(220) crystals measured by using an expanded Cu - K(alpha) ₂ beam were analyzed to select the best ones for the flight model. An important parameter is the non-parallelity of the crystal lattice planes with respect to the rear side of the crystals, since it is of the same order of magnitude as the rocking curve width. By lapping the rear side to diminish the non- parallelity and selection the main parameters of the rocking curve averaged over all crystals can be improved at least by a factor of 1.6 both in full width half maximum and peak reflectivity.

CUBIC, the Cosmic Unresolved x-ray Background Instrument using CCDs, is instrumented to make non-dispersive spectral observations, with moderate energy resolution over the energy range 200 eV - 10 keV. The CUBIC filter set is designed to attenuate optical and UV photons, with special emphasis on blocking geocoronal lines. To still allow useful soft x-ray transmission, a single thin (1200 angstroms) Al/Ti filter has been designed as the Optical/UV blocking filter. Since the detectors are mechanically collimated, the CUBIC filters are susceptible to pin hole punctures from micrometeoroids. We review some of the LDEF micrometeoroid measurements, and find that while there is good probability that micrometeoroids will transit our filter, the holes will be small enough and few enough in number to have no significant impact on our stray light counting rate.

Theoretically, gallium arsenide detectors offer an attractive alternative to silicon for the high energy x-ray astronomer, due to the greater absorption power of the material. However, in practice, GaAs detectors made from bulk-grown crystals have a spectral resolution which falls well short of both expectation and that achieved by silicon detectors of comparable thickness. In contrast, a detector fabricated from GaAs grown by the liquid phase epitaxial (LPE) process displays full charge collection with a resolution in agreement with that expected from measurements of leakage current and device capacitance. Experimental results are presented showing the level of spectral resolution possible in a variety of GaAs detectors, including Liquid Enhancement Czochralski material from various manufacturers, Vertical Bridgeman and LPE material. Both the detector performance and the electrical characteristics (voltage- current, noise, etc) have been explored for each device.

We have designed, built, and tested the first successful imaging microchannel-plate (MCP) detector that uses two orthogonal, printed circuit, serpentine delay lines in a three-dimensional architecture. Laser-ablation machining is used to cut slots that allow delay lines in two layers parallel to the MCP to sample and read out x and y image positions. Previous anodes that use delay-line timing to read out both dimensions of an image employ a wire-would anode. The goal of this readout is to provide as many picture elements (pixels) as possible in two dimensions, with high temporal resolution, high throughput, high dynamic range, and good spatial linearity. This detector achieves this goal with off-the-shelf electronics and is robust for space flight. The full width half maximum spatial resolution is 32 micrometers at the center of the detector and is typically < 35 micrometers throughout the detector. The rms linearity is 40 micrometers in each readout dimension, after applying only radial corrections for fringe field effects near the perimeter, and < 20 micrometers after applying additional simple (1- dimensional) corrections. We discuss fabrication techniques.

Developments in high resolution double delay line (DDL) and cross delay line image readouts for applications in UV and soft X-ray imaging and spectroscopy are described. Our current DDL's achieve approximately equals 15 micrometers X 25 micrometers FWHM over 65 X 15 mm (> 4000 X 500 resolution elements) with counting rates of > 10⁵ (10% dead time), good linearity (+/- approximately equals 1 resolution element) and high stability. We have also developed 65 mm X 15 mm multilayer cross delay line anodes with external serpentine delay lines which currently give approximately equals 20 micrometers FWHM resolution in both axes, with good linearity (approximately equals 30 micrometers ) and flat field performance. State of the art analog to digital converter and digital signal processor technology have been employed to develop novel event position encoding electronics with high count rate capability (2 X 10⁵ events sec^-1).

A crossed delay line (CDL) readout for use in conjunction with a z-stack of 40 mm diameter microchannel plates (MCPs) has been designed using standard transmission line theory. The CDL readout was subsequently wound and tested in various configurations to determine if the electrical characteristics followed predicted trends. The agreement was good. The optimized CDL and MCPs were then designed into a sealed tube format which could be manufactured with either a visible or ultraviolet photocathode. The components were assembled into a vacuum system version and tested. The prototype detector displayed 15 micrometers resolution and a maximum deviation from linearity of 180 micrometers over the 40 mm format.

The fourth Japanese X-ray astronomy satellite, ASTRO-D, was launched successfully by the Institute of Space and Astronautical Science on February 20, 1993 and was named ASCA. Two of the focal plane detectors are imaging gas scintillation proportional counters (Gas Imaging Spectrometer:GIS). The GIS sensors performed the energy resolution of 8% FWHM at 6 keV, and position resolution of 0.5 mm FWHM on-board, which confirmed their ultimate capability as gas counters. The non-Xray background counting rate was approximately 6 X 10^-4 c/s/cm²/keV in the energy range of 2 - 10 keV, which was as low as that achieved by the Ginga instrument. The scientific results obtained by the GIS sensors are also presented.

A hybrid detector, which combines an optical avalanche chamber with a phoswich, is currently under development. The optical avalanche chamber--a proportional counter designed to give large quantities of light photons during charge multiplication, mounts on the front of the scintillator and gives response at low energies, while the solid scintillator takes over at energies where the gas becomes transparent (> 90 keV). Both sections of the hybrid will be read out by a common set of photomultipliers under the phoswich. The addition of the gas section to the phoswich improves the energy resolution of the instrument by a factor of 2.5 at 25 keV and the spatial resolution by a factor of 10 at the same energy. The net result is an instrument with broad band coverage and high sensitivity which will be used for coded aperture imaging on long duration balloon flights.

The MIXE includes a state-of-the-art imaging proportional counter which utilizes fluorescence gating in order to achieve high sensitivity in the bandwidth from the xenon k-edge (35 keV) to 100 keV. The current detector system includes a parallel amplification stage to allow for improved energy resolution without sacrificing spatial resolution. Another novel feature is the molybdenum/stainless steel pressure vessel, which is an important factor in achieving low background rates. In this paper we compare the results of Monte Carlo simulations with laboratory experiments and present data obtained during a recent balloon flight from Palestine, Texas.

Microstrips offer significant advantages over traditional wire grids in gas-filled proportional counters in the areas of energy resolution, durability, and spatial uniformity. The objective of microstrip work at Marshall Space Flight Center is to produce a large area (30 cm square) microstrip with optimized parameters for use in hard x-ray astronomy balloon-borne detectors. MSFC facilities for producing microstrips are used to investigate effects on performance of various parameters such as anode width, anode uniformity, cathode-anode spacing, and substrate conductivity. Mechanical production limitations of 10 cm squares have spawned efforts to piece together several small microstrips to form a `mosaic' pattern which will be large enough for use in an imaging flight detector. In addition, the relative merits of thin film dielectric coatings vs. glass plate separation of orthogonal readout layers for 2D imaging microstrips are being investigated. Selected results of this work and progress toward a large area flight detector will be reported.

The high pressure xenon ionisation chamber was designed for measurements gamma-ray lines from cosmic sources in the energy range 0.1 - 10 MeV. This chamber was installed on board of the orbital station "MIR" and the measurements are carried out. The 3 litter's chamber was filled with 0.6 'ifcm3 density xenon mixed with hydrogen for increasing the drift velocity of electrons. The energy resolution is 1.3% FWHM at photon energy I MeV without electronics noise (2.00/o total). This experiment has been lasting for about three years without any degradation although the detector is strongly irradiated traversing the South-Atlantic anomaly four times a day. The high energy resolution of xenon ionisation chamber made it possible to register lines in gamma-ray bursts energy spectra. Up to this time we have observed events with ~Fe* deexitation and red-shifted 511 keV annihilation lines. This experiment is carried out on board of the heavy orbital station. The distortion of measured data by the induced in vessel mass radioactivity is measured. Also we discuss the influence of vil<ration and acoustic noise.

We report the launch and rescue of the ALEXIS small satellite. ALEXIS is a 113-kg satellite that carries an ultrasoft x-ray telescope array and a high-speed VHF receiver/digitizer (BLACKBEARD), supported by a miniature spacecraft bus. It was launched by a Pegasus booster on 1993 April 25, but a solar paddle was damaged during powered flight. Initial attempts to contact ALEXIS were unsuccessful. The satellite finally responded in June, and was soon brought under control. Because the magnetometer had failed, the rescue required the development of new attitude control techniques. The telemetry system has performed nominally. The BLACKBEARD experiment was turned on shortly after contact, and has returned its first data. We discuss preliminary lessons learned from ALEXIS.

We have developed detectors design for high resolution spectroscopic imaging for the EUV spectrometer on the ORFEUS-SPAS mission. The detectors employ spherically curved microchannel plates and a delay line read out system. We present results from the testing and calibration of the detectors prior to their integration into the spectrometer. The design, MCP preconditioning, and imaging characteristics are discussed for 2 rectangular spectral detectors and for the fine guidance detector. Each spectral detector achieves a 30 X 100 micrometers FWHM resolution element size over a 95 mm X 25 mm anode format with good linearity (< 30 micrometers ) in the spectral direction. The fine guidance detector, used for drift corrections, achieves good resolution and will meet the necessary centroiding requirements.

In this paper we describe the design of the Spatial Heterodyne Spectrometer that we are developing for velocity-resolved observations of the diffuse interstellar C IV emission, and we describe a new implementation of the Spatial Heterodyne Spectroscopy (SHS) concept that reduces contamination due to grating scattering and unwanted orders in wide field applications. Laboratory tests of this concept at visible and ultraviolet wavelengths demonstrate that this SHS technique is suitable for the study of faint, diffuse emission lines at any wavelength, particularly in the ultraviolet, where the full advantages of interference spectroscopy have not been realized. Specifically, the development of SHS will provide the opportunity to map both the distribution and radial velocities of the hot (10⁵ K) component of the interstellar medium. An SHS spectrometer capable of obtaining the first velocity-resolved (20 km s^-1) line profiles of the C IV (lambda) 1548 emission line in the Cygnus loop and in the hot component of the interstellar medium at high Galactic latitude is currently being developed for suborbital observations. Our long term goal is the development of SHS for a radial-velocity-resolved sky survey of the 104+5) K `coronal gas' component of the interstellar medium using a small satellite with an approximately one year operational lifetime.

We are developing a rocket-borne, imaging, wide-field, survey experiment to study global interactions in the multiphase interstellar medium. The experiment will map diffuse C IV (C³⁺) (lambda) 1549, H₂ (lambda) (lambda) 1575 - 1645 Lyman band fluorescence, and dust-scattered starlight continuum ((lambda) (lambda) 1400 - 1900) emission over one quarter of the sky in a single rocket flight. Good imaging is maintained in two dimensions, permitting the direct exclusion of stars entering the field of view. The payload consists of four independent, co-aligned telescopes of identical optical construction. Three telescopes are made sensitive in a narrow band by depositing tuned all-dielectric multilayers on the mirror surfaces to achieve a so-called `self-filtering' camera. Each telescope incorporates a large-format imaging microchannel plate detector that is read out using a two- dimensional, crossed, serpentine delay line anode which we have developed. The rocket flight, scheduled for launch in 1994, will be the first flight of a two-dimensional, crossed, serpentine delay line anode.

We report on progress in the development of high quantum detection efficiency photocathodes for microchannel plate based photon detectors to increase soft X-ray, EUV and FUV response. Initial investigations of NaBr, KI and CsBr opaque photocathodes are discussed. All show QDE's of approximately 40% in the 300 - 1000 angstroms regime, and QDE > 60% at approximately 100 angstroms. KI also shows high QDE, approximately 60%, for soft X-rays (approximately 11 angstroms). Photoelectron energy and number distributions are also presented. Lifetest measurements on KBr and CsBr photocathodes show good long term stability for storage in dry nitrogen. A co-evaporated photocathode is also evaluated.

We present and compared two different approaches for modelling microchannel plate (MCP) devices in regime of gain saturation. In our numerical model an MCP is described as a ladder network of interacting R and C lumped elements. The Kirchhoff equations of the network are coupled to a gain equation describing the amplification of input pulses as they progress into the microchannels. This non-linear system can be solved numerically and can be included into a best-fit algorithm capable of determining the model parameters from experimental data. An alternative analytical model was developed assuming a simplified network and describing pulse amplification and wall charge replenishment with a pair of differential equations. In this way, simpler analytical equations are found that describe an MCP in a broad range of operating conditions. Measurements on a Z-stack MCP photomultiplier showed that the numerical model provides a fairly accurate description of the MCP in pulse mode. The analytical model, although less accurate, is more suited to best-fit algorithms, allowing a remarkable reduction of computer time and of convergence problems.

We have designed and fabricated a high-vacuum facility for the detailed characterization of the Multi-Anode Microchannel Array (MAMA) detector systems at Extreme Ultraviolet and Far Ultraviolet wavelengths between about 300 angstroms and 3000 angstroms. The first task for this facility is the characterization of the MAMA detectors for the European Space Agency/NASA Solar and Heliosphere Observatory (SOHO) mission. This paper describes the different configurations of the characterization facility and outlines the SOHO MAMA characterization procedures.

We have initiated the characterizations of the Multi-Anode Microchannel Array (MAMA) detector systems for the European Space Agency/NASA Solar and Heliospheric Observatory (SOHO) mission. In this paper we briefly review the configurations of the SOHO MAMA detectors and describe their expected performance characteristics based on the results of characterizations of the curved-channel microchannel plates and of the initial characterization of the first engineering model detector system for the Solar Ultraviolet Measurements of Emitted Radiation instrument.

We review design considerations and present preliminary details of the performance of a new imaging system for hard X-ray astronomy in the 20 - 600 keV energy range. The detector is a 40 cm X 40 cm NaI(Tl)/CsI(Na) phoswich module, read out by a 7 X 7 array of square PMTs. The detector comprises the main part of the next generation Energetic X-ray Imaging Telescope Experiment (EXITE2), which had its first flight on 13 June 1993 from Palestine, Texas. Imaging is accomplished via the coded-aperture mask technique. The mask consists of 16 mm square lead/tin/copper pixels arranged in a cyclically repeated 13 X 11 uniformly redundant array pattern at a focal length of 2.5 m, giving 22 arcmin resolution. The field of view, determined by the lead/brass collimator (16 mm pitch) is 4.65 degrees FWHM. We anticipate a 3 sigma sensitivity of 1 X 10^-5 photons cm^-2 s^-1 keV^-1 at 100 keV in a 10⁴ sec balloon observation. The electronics incorporate two on-board computers, providing a future capability to record the full data stream and telemeter compressed data. The design of the current detector and electronics allows an upgrade to EXITE3, which adds a proportional counter front-end to achieve lower background and better spatial and spectral resolution below approximately 100 keV.

Presently, a Fourier telescope design is flying on the Japanese Solar-A satellite providing hard x-ray images of the Sun. Fourier designs are presently being considered for the next generation of high energy observing instruments (e.g., HESP). Hard x-rays (10-500 ke V) are produced by solar flares and cosmic sources such as the Crab nebula. Imaging these x-rays will allow insight to be gained as to processes at work in these energetic sources. Hard xrays, while not imageable by conventional means, may be imaged by Fourier telescopes. In this paper, an advanced rotating modulation collimator (RMC) design using several spatial frequencies is numerically modeled and examined using an end-to-end photon counting simulation. It is then compared to two basic Fourier telescopes measuring only two spatial frequencies, a spatial modulation collimator (SMC) and a RMC. While the more advanced telescope provided better images, diminishing improvement with more spatial frequencies for simple sources is clearly indicated. In addition, a tradeoff was identified for low flux sources in that for simple sources the basic telescope required fewer photons to achieve a stable image than did the more advanced version.

Superconducting tunnel junctions as sensitive elements in detectors intended for application to X-ray astronomy provide the possibility to improve the energy resolution by more than one order of magnitude compared to standard semiconductor detectors. We present our results with a detector system consisting of a separate absorber film and superconducting aluminum tunnel junctions attached to its edges. The arrangement of our detector, exploiting `quasiparticle trapping', provides position resolution in addition to very high energy resolution. Progress in resolving power is expected as a result of the implementation of our epitaxially grown vanadium absorber films, exhibiting a long mean free path for electrons. Details of the absorber film fabrication are discussed and several methods of characterizing the quality of our absorber films are presented. In addition to the experimental results with our detectors, we report on our model of electronic noise in tunnel junctions.

The quantum efficiency (QE) and flat field characteristics of back-illuminated 1024 X 1024 Tektronix CCDs have been measured in the extreme ultraviolet (EUV) between 44 and 1216 angstroms. These CCDs have been fabricated for the focal plane detector of the Extreme-ultraviolet Imaging Telescope (EIT) on the Solar and Heliospheric Observing spacecraft. The back-side surface of the EIT CCDs have been specially processed to enhance and stabilize the EUV QE. All requirements for QE are met by these devices, although a poorly understood variation of QE with temperature will complicate data analysis.

CUBIC, the Cosmic Unresolved X-ray Background Instrument Using CCDs, is designed to make moderate resolution X-ray spectral measurements at spatial scales of a few degrees. While the energy range is nominally 200 eV - 10 keV, the CCDs have been designed to maximize the soft X-ray performance by using novel structures. The CUBIC CCDs, fabricated by Loral Fairchild, are 1024 X 1024 pixels in size, with 18 micrometers X 18 micrometers pixels. The CCDs use a new `thin poly' gate structure designed to maximize low energy quantum efficiency, while still retaining the advantages of front-side illumination and the high Charge Transfer Efficiency of a three-phase device. Being front-side illuminated, the design avoids the surface stability problems of backside illuminated devices. Fabrication of the first lot of CCDs and test structures has been completed, and we report laboratory camera testing of the CCDs at Penn State.

The recent restructuring of the AXAF program has necessitated a review of the design of the ACIS instrument. In this paper we report on the current status of these design activities. We concentrate on changes to the baseline CCD and its impact on aspects such as the operating modes. Also we review changes to the mechanical design with respect to the passive cooling scheme facilitated by the change to a highly eccentric deep earth orbit.

We describe the development at Lincoln Laboratory of large-area CCD imager arrays for soft x-ray astronomy. One such array consists of four, closely abutted, 420 X 420-pixel CCDs for the ASCA (formerly Astro-D) satellite that was launched on February 20, 1993. The CCDs were fabricated on p-type 6500-(Omega) -cm material in order to attain the deep depletion depths needed for the higher-energy (> 4 keV) photons. The use of high- resistivity material and the effects of space-radiation are among the principal technical issues which will be discussed. We are also developing the next-generation CCD sensors for the Advanced X-ray Astrophysics Facility which is currently scheduled for launch in 1998. This mission will use two multichip focal planes comprising ten chips, each of a larger format (approximately 1000 X 1000 pixels). In addition to a new CCD, this program will require other technology developments such as an innovative packaging method for the nonplanar focal planes.

We present a compilation of CCD quantum efficiency measurements made at soft x-ray and extreme ultraviolet wavelengths. The measurements include CCDs of varying architecture and have been obtained from a number of projects over the last several years.

We report quantum efficiency measurements of back-illuminated, ion-implanted, laser- annealed charge coupled devices (CCDs) in the wavelength range 13 - 10,000 angstroms. The equivalent quantum efficiency (EQE equals equivalent photons detected per incident photon) range from a minimum of 5% at 1216 angstroms to a maximum of 87% at 135 angstroms. Using a simple relationship for the charge collection efficiency of the CCD pixels as a function of depth, we present a semi-empirical model with few parameters which reproduces our measurements with a fair degree of accuracy. The advantage of this model is that it can be used to predict CCD QE performance for shallow backside implanted devices without detailed solution of a system of differential equations, as in conventional approaches, and yields a simple analytic form for the charge collection efficiency which is adequate for detector calibration purposes.

Monte Carlo simulations of charged particle events in CCDs are described. Efficient background rejection can be obtained by a combination of energy veto and event morphology censoring. The data are compared with in-flight measurements taken during a sounding rocket flight of a prototype detector. Implications for future missions are discussed. It is shown that the external charged particle background may be small enough that other effects such as locally induced radioactivity and soft electron contamination become important factors.

An experimental analysis of Niobium based superconducting tunnel junctions is presented, evaluating their performance as photon counting detectors. Several mechanism are found to be responsible for the degradation of the energy resolution. In particular, the high magnetic fields necessary to suppress the Josephson current in square junctions are shown to smear the energy bandgap. It is experimentally verified that in junctions with special geometries the Josephson current can be sufficiently suppressed by much lower fields. Several loss and contamination mechanisms are also discussed. Experimental results on new developments, such as quasiparticle trapping blocks, source collimation and substrate buffering, are presented, with a view to demonstrating significant improvements in energy resolution.

In this paper we briefly describe the design and initial laboratory performance of the Proportional Counter Array (PCA) for the X-ray Timing Explorer (XTE). The PCA consists of 5 identical, sealed and collimated (1 degree(s) FWHM), xenon/methane multi-anode proportional counters sensitive to x-rays with energies between 2 and 60 keV. Each detector has an effective area of approximately 1,500 cm². The data system can tag the relative time of arrival of each event with an accuracy of 1 microsecond(s) . The overall absolute time accuracy will be maintained by the spacecraft to better than 1 ms. Following the design principles of the HEAO-1 A2 HED detectors, the PCA adopts the interleaved anode connection scheme with an active propane anti-coincidence layer in the front and a similar anti-coincidence xe/methane layer on three other sides of the detector. The interleaved anode connection scheme and the anti-coincidence layers reject background events caused by charged particles with high efficiency, thus significantly reducing the background event rate at lower energies. As of June, 1993, the fabrication and assembly of all the five detectors had been completed. Their performance evaluation and characterization are currently under way. XTE is scheduled to be launched with a Delta-II rocket in the summer of 1995.

The Diffuse X-Ray Spectrometer (DXS) experiment was flown as an attached Shuttle payload in January 1993 aboard the STS-54 mission of the Space Shuttle Endeavor. DXS consists of two large-area Bragg crystal X-ray spectrometers that cover the 44 - 83 angstroms wavelength range, and are designed to measure the spectrum of the low energy (0.15 < E < 0.28 keV) diffuse X-ray background with roughly 10 eV energy resolution and 15 degree(s) angular resolution. These diffuse X-rays are thought to be generated by a very hot (10⁶ K) component of the interstellar medium that occupies a large fraction of the interstellar volume near the Sun. Astrophysical plasmas near 10⁶ K are rich in emission lines, and the relative strengths of these lines, besides providing information about the physical conditions of the emitting gas, also provide information about its composition, history and heating mechanisms. We present preliminary spectra of the soft X-ray background in the energy range 0.15 < E < 0.28 keV. Spectra were obtained from along a great circle that lies 0 degree(s) - 10 degree(s) north of the galactic plane between galactic longitudes 150 degree(s) and 300 degree(s). The spectra show emission lines, the first direct evidence that the soft X-ray background arises in hot interstellar gas. The spectra seen along the great circle in different resolution elements are different from one another. We fitted a range of models to these spectra, and present preliminary results of these fits.

The evaluation of the performances of a toroidal grating for the high-resolution EUV spectroheliometer (HiRES) has been realized. This is a holographically ruled grating operating in a normal incidence Rowland configuration at the 510 - 630 angstroms spectral range. An analysis of the grating resolution performances has been realized by means of a scintillator- intensifier-CCD detector showing very good results. Also a measurement of the grating diffraction efficiency has been performed, showing on the contrary a value lower than the predicted one.