Ady James

Large thin adaptive x-ray mirrors

This paper describes the progress made in a proof of concept study and recent results of a research program into large active x-ray mirrors that is part of the UK Smart X-ray Optics project. The ultimate aim is to apply the techniques of active/adaptive optics to the next generation of nested shell astronomical X-ray space telescopes. A variety of deformable mirror technologies are currently available, the most promising of which for active X-ray mirrors are probably unimorph and bimorph piezoelectric mirrors. In this type of mirror one or more sheets of piezoelectric material are bonded to or coated with a passive reflective layer. On the back or between the piezoceramic layer/layers are series of electrodes. Application of an electric field causes the piezoelectric material to undergo local deformation thus changing the mirror shape. Starting in 2005 a proof of concept active mirror research program has been undertaken. This work included modelling and development of actively controlled thin shell mirrors. Finite element models of piezo-electric actuated mirrors have been developed and verified against experimental test systems. This has included the modelling and test of piezo-electric hexagonal unimorph segments. Various actuator types and low shrinkage conductive bonding methods have been investigated and laboratory tests of the use of piezo-electric actuators to adjust the form of an XMM-Newton space telescope engineering model mirror shell have been conducted and show that movement of the optics at the required level is achievable. Promising technological approaches have been identified including moulded piezo-ceramics and piezo-electrics fibre bundles.

Active X-ray optics for the next generation of X-ray telescopes

The immediate future for X-ray astronomy is the need for high sensitivity, requiring large apertures and collecting areas, the newly combined NASA, ESA and JAXA mission IXO (International X-ray Observatory) is specifically designed to meet this need. However, looking beyond the next decade, there have been calls for an X-ray space telescope that can not only achieve this high sensitivity, but could also boast an angular resolution of 0.1 arc-seconds, a factor of five improvement on the Chandra X-ray Observatory. NASAs proposed Generation-X mission is designed to meet this demand; it has been suggested that the X-ray optics must be active in nature in order to achieve this desired resolution. The Smart X-ray Optics (SXO) project is a UK based consortium looking at the application of active/adaptive optics to both large and small scale devices, intended for astronomical and medical purposes respectively. With Generation-X in mind, an active elliptical prototype has been designed by the SXO consortium to perform point-to-point X-ray focussing, while simultaneously manipulating its optical surface to improve its initial resolution. Following the completion of the large scale SXO prototype, presented is an overview of the production and operation of the prototype, with emphasis on the X-ray environment and preliminary results.

Advances in active X-ray telescope technologies

The next generation of X-ray telescopes will require both high resolution and high sensitivity to target the earliest astronomical objects, to this end the UK based Smart X-ray Optics (SXO) project has been investigating the application of active/adaptive optics to traditional grazing incidence X-ray optics and this has resulted in the fabrication and testing of our first active X-ray prototype in November 2008. Results from these initial tests have proved very encouraging for this advancing technology and have highlighted the prototypes ability to deform its optical surface through piezoelectric actuation. We present a critical analysis of the first prototype system, discussing metrology of the mandrel, the nickel replicated ellipsoidal optics and the prototype. The measured actuator influence functions of the prototype are compared against finite element analysis simulations and the observed characteristics are then described. The advances required in the current technology are then outlined in relation to a second generation of active X-ray prototype, which is scheduled for X-ray testing in 2010.

Progress on the development of active micro-structured optical arrays for x-ray optics

The Smart X-Ray Optics (SXO) project comprises a U.K.-based consortium developing active/adaptive micro-structured optical arrays (MOAs). These devices are designed to focus X-rays using grazing incidence reflection through consecutive aligned arrays of microscopic channels etched in silicon. The silicon channels have been produced both by dry and wet etching, the latter providing smoother channel walls. Adaptability is achieved using piezoelectric actuators, which bend the device and therefore change its focal distance. We aim to achieve a 5 cm radius of curvature which can provide a suitable focal length using a tandem pair MOA configuration. Finite Element Analysis (FEA) modelling has been carried out for the optimization of the MOA device design, consider different types of actuators (unimorph, bimorph and active fibre composites), and different Si/piezoelectric absolute and relative thicknesses. Prototype devices have been manufactured using a Viscous Plastic Processing Process for the piezoelectric actuators and dry etched silicon channels, bonded together using a low shrinkage adhesive. Characterisation techniques have been developed in order to evaluate the device performance in terms of the bending of the MOA channels produced by the actuators. This paper evaluates the progress to date on the actuation of the MOAs, comparing FEA modelling with the results obtained for different prototype structures.

The extreme UV imaging spectrometer for the JAXA Solar-B mission

The ISAS/JAXA Solar-B mission includes an Extreme-UV Imaging Spectrometer (EIS). It detects photons in the wavelength ranges 17 - 21 nm and 25 - 29 nm which include emission lines from several highly ionised species that exist at temperatures log T = 4.7, 5.6, 5.8, 5.9 and 6.0 - 7.3 K. Instrument throughput is increased substantially by the use of multilayer coatings optimized for maximum reflectance in the two selected wavelength bands. The use of back-illuminated CCDs provides significantly enhanced quantum efficiency over that previously available from microchannel plate systems. In this paper we will describe the design and operation of the instrument and present its performance parameters e.g. spectral and spatial resolution and sensitivity. Preliminary results of recent calibration measurements will be described. The role of EIS in the Solar-B mission will be illustrated with reference to the anticipated observing strategy for the first three months of the mission which will be outlined.

Development of net-shape piezoelectric actuators for large x-ray optics

The design of current X-ray telescope systems needs to reach a compromise between the resolution and sensitivity. A new area of interest of adaptive optics is the development of actively controlled thin X-ray mirrors, where aberrations would be corrected. Their assembly on an X-ray telescope would provide an instrument with both high resolution and sensitivity. The Smart X-Ray Optics (SXO) project comprises a U.K.-based consortium developing prototypes for the next generation of X-ray telescopes. The overall aim is to produce X-ray mirrors using thin, below 1mm, structures, comprising Ni mirror shells with bonded piezoelectric unimorph actuators, and with a target resolution of ~0.1 arcs. Such an optic would enable the design of an X-ray telescope with both a greater resolution and collective area than the best currently available by Chandra (0.5arcs) and XMM Newton (1650cm2) respectively. Lead zirconate titanate, PZT-based piezoelectric actuators are being developed in this programme to fit precisely the curved Ni mirror shell prototypes (100×300×0.4mm, radius of curvature 167mm). Viscous plastic processing has been chosen for the fabrication of net-shaped piezoelectric unimorph actuators 75×32×0.18mm, with radius of curvature conforming to those of the X-ray optic. Laser machining has been used for precisely controlling the actuator shape and for the definition of the multi-segment electrodes. Accurate control of the thickness, surface finish and curvature are the key factors to delivering satisfactory actuators. Results are presented concerning the fabrication and characterisation of the piezoelectric actuators, and the integration procedure on the nickel optic.

The Command and Data processing Unit of the Euclid Visible Imager: impact of the data compression needs on the unit design

The Command and Data Processing Unit (CDPU) of the Euclid Visible Imager is one of the two warm electronics units of the instrument. It implements on one side the digital interface to the satellite, for telecommands acquisition and telemetry downloading, and on the other side the interface to the focal plane CCDs readout electronics, for science data acquisition and compression. The CDPU main functionalities include the instrument commanding, control and health monitoring. The baseline unit architecture is presented, reporting the results of the phase B1 study and of the trade-off activity carried out to check the performances of the SW implementation of two different lossless compression algorithms on the baseline target processor (LEON3-FT) and on a HW compressor.

Micromachining optical arrays

This paper describes two fabrication techniques-dry and wet etching- for microstructured optical arrays (MOAs). The MOAs consist of arrays of channels deep etched in silicon. They use grazing incidence reflection to focus the X-rays through the consecutive aligned arrays of channels, ideally reflecting once off a vertical and smooth channel wall in each array. The MOAs were proposed by the Smart X-ray Optics (SXO) programme as small scale optics for micro-probing of biological cells and tissues. The first fabrication method requires inductively coupled plasma (ICP) using Bosch processes. The second one involves etching <110> silicon wafers in alkaline solutions.

Development of spider micro-structured optical arrays for x-ray optics

The Smart X-Ray Optics (SXO) project comprises a U.K.-based consortium developing active/adaptive micro-structured optical arrays (MOAs). These devices are designed to focus X-rays using grazing incidence reflection through consecutive aligned arrays of microscopic channels etched in silicon. Adaptability is achieved using a combination of piezoelectric actuators, which bend the edges of the silicon chip, and a spider structure, which forms a series of levers connecting the edges of the chip with the active area at the centre, effectively amplifying the bend radius. Test spider structures, have been bent to a radius of curvature smaller than 5 cm, indicating that in complete devices a suitable focal length using a tandem pair configuration could be achieved. Finite Element Analysis (FEA) modelling has been carried out for the optimization of the spider MOA device design. Prototype devices have been manufactured using a Viscous Plastic Processing technique for the PZT piezoelectric actuators, and a single wet etch step using {111} planes in a (110) silicon wafer for both the silicon channels and the spider structure. A surface roughness of 1.2 nm was achieved on the silicon channel walls. Characterisation techniques have been developed in order to evaluate the device performance in terms of the bending of the MOA channels produced by the actuators. This paper evaluates the progress to date on the development of spider MOAs comparing FEA modelling with the results obtained for prototype structures.

Active x-ray optics for high resolution space telescopes

The Smart X-ray Optics (SXO) Basic Technology project started in April 2006 and will end in October 2010. The aim is to develop new technologies in the field of X-ray focusing, in particular the application of active and adaptive optics. While very major advances have been made in active/adaptive astronomical optics for visible light, little was previously achieved for X-ray optics where the technological challenges differ because of the much shorter wavelengths involved. The field of X-ray astronomy has been characterized by the development and launch of ever larger observatories with the culmination in the European Space Agency’s XMM-Newton and NASAs Chandra missions which are currently operational. XMM-Newton uses a multi-nested structure to provide modest angular resolution (∼10 arcsec) but large effective area, while Chandra sacrifices effective area to achieve the optical stability necessary to provide sub-arc second resolution. Currently the European Space Agency (ESA) is engaged in studies of the next generation of X-ray space observatories, with the aim of producing telescopes with increased sensitivity and resolution. To achieve these aims several telescopes have been proposed, for example ESA and NASA’s combined International X-ray Observatory (IXO), aimed at spectroscopy, and NASA’s Generation-X. In the field of X-ray astronomy sub 0.2 arcsecond resolution with high efficiency would be very exciting. Such resolution is unlikely to be achieved by anything other than an active system. The benefits of a such a high resolution would be important for a range of astrophysics subjects, for example the potential angular resolution offered by active X-ray optics could provide unprecedented structural imaging detail of the Solar Wind bowshock interaction of comets, planets and similar objects and auroral phenomena throughout the Solar system using an observing platform in low Earth orbit. A major aim of the SXO project was to investigate the production of thin actively controlled grazing incident optics for the next generation of X-ray space telescopes. Currently telescope systems are limited in the resolution and sensitivity by the optical quality of the thin shell optics used. As part of its research programme an actively controlled prototype X-ray thin shell telescope optic of dimensions 30x10cm has been developed to bench test the technology. The design is based on thin nickel shells bonded to shaped piezo-electric unimorph actuators made from lead zirconate titanate (PZT).