Publication archive

Publication archive

Asymmetric NbN-Nb-Al-AlOx-Al-Nb superconducting tunnel junctions have been investigated as photon counting detectors at x-ray and ultraviolet (UV)-visible wavelengths. The inclusion of a thin NbN passivation layer on the top electrode of the devices in place of the natural niobium oxides has reduced the quasiparticle loss rates, thereby enhancing the probability of multiple tunnel processes. As a consequence, the detector responsivity has increased from 900e-/eV, up to values in excess of 2000e-/eV in the temperature range 0.30-0.8 K. Such a responsivity level has allowed single photon counting performance at wavelengths as long as 700 nm and at operating temperatures as high as 830 mK. The devices show a linear response in the UV-visible range, while at 6 keV the expected nonlinearities in the energy response and moderate energy resolution similar to that found in Nb-Al junctions are observed.
Published: 16 May 1998
It is now over 40 years since the gaseous disc of our galaxy was discovered to be warped from radio observations of neutral hydrogen [1]. Subsequently the warp has been detected in the distribution of galactic dust [2], molecular clouds [3], and luminous stars [4,5]. Roughly half of all spiral galaxies have similarly warped discs, which suggests that warps are common and long-lived phenomenon. However, there is still no consensus as to what induces galactic discs to become warped: intergalactic winds, tidal interactions with satellites, magnetic pressure and massive dark halos have all been proposed as causative agents. Here we use data from the Hipparcos satllite [6] to probe the Milky Way's warp.
Published: 03 April 1998
Published: 02 March 1998
We use absolute trigonometric parallaxes from the Hipparcos Catalogue to determine individual distances to members of the Hyades cluster, from which the 3-dimensional structure of the cluster can be derived. Inertially-referenced proper motions are used to rediscuss distance determinations based on convergent-point analyses. A combination of parallaxes and proper motions from Hipparcos, and radial velocities from ground-based observations, are used to determine the position and velocity components of candidate members with respect to the cluster centre, providing new information on cluster membership: 13 new candidate members within 20 pc of the cluster centre have been identified. Farther from the cluster centre there is a gradual merging between certain cluster members and field stars, both spatially and kinematically.
Published: 01 March 1998
We present the COS B/EGRET 1997 ephemeris for the rotation of the Geminga pulsar. This ephemeris is derived from high-energy gamma -ray observations that span 24 yr. The recently obtained accurate position and proper motion are assumed. A cubic ephemeris predicts the rotational phase of Geminga with errors smaller than 50 milliperiods for all existing high-energy gamma -ray observations that span a 24.2 yr timing baseline. The braking index obtained is 17 +/- 1. Further observation is required to ascertain whether this high value truly reflects the rotational energy loss mechanism, or whether it is a manifestation of timing noise. The ephemeris parameters are sufficiently constrained so that timing noise will be the limitation on forward extrapolation. If Geminga continues to rotate without a glitch, as it has for at least 23 yr, we expect this ephemeris to continue to describe the phase, with an error of less than 100 milliperiods, until 2008. Statistically significant timing residuals are detected in the EGRET data that depart from the cubic ephemeris at a level of 30 milliperiods. Although this could simply be an additional manifestation of timing noise, the EGRET timing residuals appear to have a sinusoidal modulation that is consistent with a planet of mass 1.7/sin i MSun orbiting Geminga at a radius of 3.3 AU.
Published: 01 February 1998
Some recent results associated with the development of tantalum based photon counting superconducting tunnel junctions (STJ) suitable for use as broad-band low resolution spectrometers for optical and ultraviolet astronomy are presented. A 20x20 micron square tantalum based STJ, operated at a temperature of 0.3 K, has demonstrated a limiting resolution of ~ 8 nm at 200 nm and ~ 80 nm at 1000 nm. The device is extremely linear in response with photon energy, and covers the waveband from 200 nm to 2 micron while measuring the individual photon wavelength and arrival time. The short wavelength limit is currently constrained by the current experimental configuration (a fibre optic) as well as to some extent the sapphire substrate. The estimated quantum efficiency for single photons is over ~ 50% between 200 and 700 nm with a maximum of ~ 75% at 550 nm. Such an STJ when packaged into an array could contribute significantly to many fields of near infrared, optical and ultraviolet astronomy being able to provide efficiently and simultaneously the broad band spectrum and photon arrival time history of every single object in the field over a very wide dynamic range.
Published: 01 February 1998
Accuracy in the absolute position in the sky is one of the limiting factors for pulsar timing, and timing parameters have a direct impact on the understanding of the physics of Isolated Neutron Stars (INS). We report here on a high-accuracy measurement of the optical position of Geminga (mv=25.5), the only known radio-quiet INS. The procedure combines the Hipparcos and Tycho catalogues, ground-based astrometric data,and Hubble Space Telescope (HST) Wide Field Planetary Camera (WFPC2) images, to yield Geminga's absolute position to within ~ 40 mas (per coordinate). Such a positional accuracy, unprecedented for the optical position of a pulsar or an object this faint, is needed to combine in phase gamma -ray photons collected over more than 20 years, i.e. over 2.5 billions of star' revolutions. Although quite a difficult task, this is the only way to improve our knowledge of the timing parameters of this radio silent INS. Based on Observation with the ESA Hipparcos satellite.
Published: 05 January 1998

Reference: ESA/SPC(97)40

Made available online in October 2015.

Table of contents:

  1. Summary and scope
  2. Mission overview
  3. Programme participation
  4. Science and project management
  5. Operations and scientific data
  6. References
  7. Acronyms
  8. Appendices
Published: 31 October 1997
The present document describes the mission operations associated with the International Ultraviolet Explorer (IUE) spacecraft in the context of the 18.5 years of orbital operations in the IUE Project which was a collaboration between NASA, ESA and PPARC. In chapter 1 the objectives of the IUE mission, the goals and capabilities of the spacecraft, the payload and the ground segment are described, as well as some examples of the scientific capabilities of the project. The characteristics of the spacecraft, the spacecraft subsystems and the ground observatory control systems are detailed in chapter 2. Chapter 3 lists the main spacecraft events in the course of the 18 years of the duration of the orbital operations. In chapter 4, the IUE orbit and its evolution is described. The most important problems in the spacecraft subsystems are described in Chapter 5 together with the solutions. Special emphasis is given to the different Attitude Control systems associated with the progressive Gyro failures culminating in the One-Gyro control system used during the last six months of orbital operations. In chapter 6, the spacecraft thermal design is described. The three appendixes contain important dates in the area of spacecraft operations:
  • Appendix A: Earth shadow seasons
  • Appendix B: Orbital corrections (Delta-V's)
  • Appendix C: On-Board-Computer malfunctions
Published: 16 September 1997
We discuss the capabilities of superconducting tunnel junctions as detectors for ultraviolet, optical, and near-infrared astronomy. Such junctions have recently been shown to allow the detection of individual optical and ultraviolet photons with an inherent spectral resolution related to the critical temperature of the absorbing superconductor. Limiting resolutions at 500 nm ranging from 5 - 40 nm (for materials with critical temperatures between 0.1 to 10 K) should be achievable. These detectors should have a high quantum efficiency (50 per cent) over a very broad wavelength range from the ultraviolet to the near infrared (100 - 2000 nm). The overall efficiency is limited by reflection from the superconducting film, and should be improved significantly by appropriate anti-reflection coatings. The devices function at very high incident photon rates - with count rates of order 10 kHz or higher being feasible, and photon arrival time datation possible to microsec-level accuracy. It is realistic in the future to envisage that these devices, of a size typically 20-50 micron², could be packaged into imaging arrays. These key characteristics imply that many areas of optical and ultraviolet astronomy could benefit significantly from their further development.
Published: 12 June 1997
We report the detection of individual optical and ultraviolet photons using a different approach to photon detection based on a superconducting tunnel junction. A 20 × 20 micron² junction, employing a 100 nm niobium film and operated at a temperature of ~ 0.4 K, has been used to detect individual photons with inherently high quantum efficiency (> 45%) over a broad wavelength range (between 200 and 500 nm), yielding high temporal (sub-ms) resolution, spatial resolution determined by the junction size, under conditions of minimal dark current, and in the absence of read noise. The quantum efficiency is limited by surface reflection, and could be improved by the deposition of antireflection coatings. The theoretical wavelength response range continues into the far UV and soft x-ray region, and is presently limited beyond 500 nm largely by the available signal processing electronics. The device intrinsically functions at very high incident photon rates - with count rates of order ~ 10 kHz or higher being feasible and again currently limited primarily by the signal processing electronics - thus providing a correspondingly enhanced dynamic range by several orders of magnitude compared with previous panoramic photon counting detectors. The measured charge output from the device is highly linear with photon energy resulting in an optical photon detection system with intrinsic spectral resolution, related to the critical temperature of the junction material and, in the current device, providing a limiting spectral resolution of about 50 nm. It is realistic in the future to envisage that these devices could be packaged into arrays, with the resulting system characteristics offering advantages over detectors based on semiconductors
Published: 02 May 1997
The electric-field and wave experiment (EFW) on Cluster is designed to measure the electric-field and density fluctuations with sampling rates up to 36000 samples s-1. Langmuir probe sweeps can also be made to determine the electron density and temperature. The instrument has several important capabilities. These include (1) measurements of quasi-static electric fields of amplitudes up to 700 mV m-1 with high amplitude and time resolution, (2) measurements over short periods of time of up to five simualtaneous waveforms (two electric signals and three magnetic signals from the seach coil magnetometer sensors) of a bandwidth of 4 kHz with high time resolution, (3) measurements of density fluctuations in four points with high time resolution. Among the more interesting scientific objectives of the experiment are studies of nonlinear wave phenomena that result in acceleration of plasma as well as large- and small-scale interferometric measurements. By using four spacecraft for large-scale differential measurements and several Langmuir probes on one spacecraft for small-scale interferometry, it will be possible to study motion and shape of plasma structures on a wide range of spatial and temporal scales. This paper describes the primary scientific objectives of the EFW experiment and the technical capabilities of the instrument.
Published: 15 January 1997
The Mini-STEP concept was conceived from a desire by NASA to reduce the cost of the satellite test of the equivalence principle (STEP) experiment below that of the already downsized Quick STEP concept. The goal was for the total cost, including payload, spacecraft, launch vehicle, reserves and operations, to be in the 50 million US dollar range. Stanford University and the Jet Propulsion Laboratory studied this simplified STEP concept between March and June 1995. A similar concept was developed in parallel by the European Space Agency (ESA) as an alternative to the M3 STEP mission.
Published: 15 November 1996
On 4 June 1996, the maiden flight of the Ariane 5 launcher ended in failure. Only about 40 seconds after initiation of the flight sequence, at an altitude of about 3700m, the laucher veered off its flight path, broke up and exploded. Engineers from the Ariane 5 project teams of CNES and Industry immediately started to investigate the failure.

This is a report detailing their findings and suggested courses of action.

Published: 20 July 1996
The x-ray performance of Nb-Al-AlOx-Al-Nb superconducting tunnel junctions deposited on sapphire has been studied for phonon mediated detection of x rays absorbed in the substrate in the energy range 750 to 6000 eV. Two separate channels of phonon propagation can be identified. One produces a discrete signal peak, due to high frequency phonons originating from the x-ray absorption sites in a shallow layer below the junction. The other contributes to a monotonic signal tail, due to low frequency phonons, reaching the junction after diffusive or multiple scattering at surfaces.
Published: 02 April 1996
An investigation into the phonon contamination of x-ray sensitive superconducting tunnel junctions arising from the x-ray photoabsorption in various substrates has been conducted. Results are presented on the design of a superconducting tunnel junction (STJ) which substantially reduces or even eliminates phonon induced noise from the substrate. Such noise is the predominant feature in x-ray spectra from junctions due to the bulk of the photons being absorbed in the substrate rather than in the thin superconducting film. The design involves the choice of a suitable buffer sandwich between the substrate and the STJ. Such a buffer would appear not only to attenuate the phonons created in the x-ray photoabsorption in the substrate but also to scatter the phonons inelastically, introducing a frequency down-conversion. Such a process ensures that few phonons of energy sufficient to break Cooper pairs in the superconducting film of the STJ enter the junction.
Published: 01 March 1996

Editor: Bruce Battrick

This report presents the proposed update of ESA's long-term programme in Space Science, known as 'Horizon 2000 Plus'. It covers the period 1995-2016 and represents the forward roll-over of the twenty-year Horizon 2000 programme developed in 1984 and due to terminate in 2006.

Contents:

  • Foreword – R.-M. Bonnet, Director of the ESA Science Programme
  • Introduction – L. Woltjer, Chairman of the Survey Committee
  • Why Space Science
  • I. Coherence, Balance and Continuity with Horizon 2000
  • II. The Pillars of Horizon 2000 Plus
  • III. Horizon 2000 Plus in Outline
  • IV. Relationship with Other Programmes
  • V. Financial Aspects and Schedule
  • VI. Summary of Recommendations
  • VII. Topical Team Reports
  • Annex 1. Responses to the Call for Mission Concepts for Horizon 2000 Plus
  • Annex 2. Contributors
Published: 02 July 1995
The performance of photon detectors based on superconducting tunnel junctions are related to their current - voltage (I-V) curve characteristics and, ultimately, to the quality of the thin tunnel barriers (of order 1 nm) which separate the two superconducting thin films. Both the optimization of the spectroscopic performance of these detectors and the development of a reproducible and high yield fabrication route, require a better understanding of barrier quality and growth techniques. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) provide valuable tools for the investigation of the barrier region and for the control of the quality of the different thin films and related interfaces. In this paper, the results of a TEM and AFM evaluation of Nb-Al-AlOx-Nb tunnel junctions are reported, together with their interpretation on the basis of the I-V curve performance at low temperature (T >= 0.3 K). Thickness disuniformities of the Al plus AlOx overlayer and evidence of barrier defects have been found, which may place constraints on the spectroscopic performance of such devices. Through the use of TEM it has also been possible to confirm the epitaxial nature of the Nb base electrode. The junction counter electrode however appears to be polycrystalline, with a columnar morphology and an average grain width of 40 nm. The overall structure of the various layers may well place constraints on the tunneling characteristics of the device.
Published: 16 April 1995
Using a common methodology to analyze data from the Active Magnetospheric Particle Tracer Explorer/Ion Release Module (AMPTE/IRM) and International Sun-Earth Explorer 2 (ISEE 2) satellites we report on the statistical properties of bursty bulk flow events (BBFs) in the inner plasma sheet (IPS). A positive correlation between BBFs and the AE index suggests that BBFs are predominantly geomagnetically active time phenomena. Earthward BBFs are more frequent close to midnight and away from Earth, up to a distance of approximately 19 RE. Tailward BBFs are very infrequent in the IRM data set and somewhat less infrequent in the ISEE 2 data set in the region of the satellites' spatial overlap, possibly due to the more active conditions prevailing during the ISEE 2 mission in that region. However, in both data sets the ratio of tailward to earthward BBFs increases with distance from Earth; more than 20% of all BBFs are anti-sunward tailward of X = -19 RE in the ISEE 2 data set. BBFs are responsible for 60-100% of the measured earthward transport of mass, energy and magnetic flux past the satellite in the regions of maximum occurrence rate, even though they last approximately 10-15% of the IPS observation time there. Thus BBFs represent the primary transport mechanism at those regions. The one-to-one correspondence between BBFs and substorm phase, as well as the relative contribution of BBFs to the total transport observed during substorms are questions that await further investigation based on multi instrument studies of individual events.
Published: 15 November 1994
Recent experimental results show a linear energy response in high quality Nb-Al-AlOx-Nb superconducting tunnel junction detectors for photon energies between 1.5 and 6.4 keV. The experimental data are based on both direct x-ray illumination and on the escape and re-absorption of fluorescent photons created in the junction electrodes and in the silicon substrate. The observed linearity of the energy response raises questions on the validity of some theoretical models which describe the relaxation process occurring in a superconducting thin film after x-ray photoabsorption. Such models generally predict nonlinear effects due to large quasiparticle number densities and short recombination times.
Published: 16 August 1994
31-May-2020 08:29 UT

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