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NASA NTRS1986

A position sensitive microchannel photomultiplier for ultraviolet space astronomy

The 25-mm microchannel-plate, position-sensitive UV astronomy photomultiplier tube presented is intended for the EOM-1 Spacelab Mission's FAUST payload and conducts wide-field imaging surveys in the VUV over the 1400-1800-A range. The sealed detector encompasses a CsI photocathode deposited on the inner surface of a MgF2 window, a stack of microchannel plates, and a wedge-and-strip two-dimensional position-sensing anode. Since the wedge-and-strip principle requires only three anode signals, flight electronics can be reduced to three charge amplifiers and three analog-to-digital converters.

Lampton, M.↗

NASA NTRS1986

Hybrid analog/digital, large format, photon counting detectors for astronomy

The development of a new microchannel plate photon-counting detector with an analog readout method based on a resistive anode is reported. This detector exhibits extremely high, stable electron gains of 10 to the 8th. At this gain, the spatial resolution is no longer primarily limited by the noise of the resistive anode, so that digital methods of readout, such as discrete conductors, lose their advantage. These detectors can be readily scaled to 40 mm and 70 mm formats to match plate scales of 2-m (and larger) telescopes. New, high speed digital electronics fully exploit the high spatial and time resolution made possible by gains of this level. Analysis of the theoretical performance of this detector shows that the major limitation to the spatial resolution is the proximity focus of the photocathode and the first microchannel plate. The detector has been mated to an echelle spectrograph developed.

Crocker, J.↗

NASA NTRS1992

Receiver performance of laser ranging measurements between the Lunar Observer and a subsatellite for lunar gravity studies

The optimal receiver for a direct detection laser ranging system for slow Doppler frequency shift measurement is shown to consist of a phase tracking loop which can be implemented approximately as a phase lock loop with a 2nd or 3rd order loop filter. The laser transmitter consists of an AlGaAs laser diode at a wavelength of about 800 nm and is intensity modulated by a sinewave. The receiver performance is shown to be limited mainly by the preamplifier thermal noise when a silicon avalanche photodiode is used. A high speed microchannel plate photomultiplier tube is shown to outperform a silicon APD despite its relatively low quantum efficiency at wavelengths near 800 nm. The maximum range between the Lunar Observer and the subsatellite for lunar gravity studies is shown to be about 620 km when using a state-of-the-art silicon APD and about 1000 km when using a microchannel plate photomultiplier tube in order to achieve a relative velocity measurement accuracy of 1 millimeter per second. Other parameters such as the receiver time base jitter and drift also limit performance and have to be considered in the design of an actual system.

Davidson, Frederic M.↗

NASA NTRS1976

High-resolution imaging X-ray detector

The paper describes an X-ray detector using microchannel plates as a photocathode surface and imaging photoelectron multiplier, and a crossed wire grid as a two-dimensional position-sensitive detector. The position resolution is 10 microns. The crossed wire grid consists of 100-micron-diam wires on 200-micron centers. Position sensing is accomplished by electronic interpolation to 1/20 of the wire spacing. The quantum efficiency of the microchannel plates varies from 29% at 0.28 keV to 5% at 3 keV. This detector will provide second-of-arc X-ray imaging in the focal plane of the 342.9-cm focal length grazing-incidence telescope being prepared for the HEAO-B observatory. By addition of suitable photocathodes, it can be used for single-photon imaging light detection in the UV, visible, and near-IR-ranges. In all cases, it gives a very low dark counting rate, allows timing of individual events to 1 microsec or less, and can handle counting rates up to 10,000 per sec.

Kellogg, E.↗

NASA NTRS1977

High resolution imaging X-ray detector for astronomical measurements

The article describes the X-ray detector which will provide second-of-arc images for the HEAO-B X-ray observatory. The instrument uses microchannel plates as a photocathode surface and imaging photoelectron multiplier, and a crossed wire grid as a two-dimensional position-sensitive detector. Position determination is accomplished by electronic interpolation between the coarse grid wires. The detector provides the arrival time and position of each event which occurs within its field of view. Measurements of the spatial resolution (15 microns), temporal resolution (7.8 microsec), image distortion (less than 10 microns), uniformity of efficiency (less than plus or minus 10%), dark counting rate (0.2 cts/sq cm/s), and quantum efficiency (10% at 1.54 keV) of this detector are described. A summary of the procedure which was found useful during the initial turn-on of microchannel plates is given.

Henry, J. P.↗

NASA NTRS2003

Results From Cs Activated GaN Photocathode Development for MCP Detector Systems at GSFC

We describe the development of high quantum efficiency W photocathodes for use in large area two dimensional microchannel plate based detector arrays to enable new W space astronomy missions. Future W missions will require improvements in detector sensitivity, which has the most leverage for cost-effective improvements in overall telescope/instrument sensitivity. We use new materials such as p-doped GaN, AIGaN, ZnMgO, Sic and diamond. We have currently obtained QE values > 40 % at 185 nm with Cesiated GaN, and hope to demonstrate higher values in the future. By using controlled internal fields and nano-structuring of the surfaces, we plan to provide field emission assistance for photoelectrons while maintaining their energy distinction from dark noise electrons. We will transfer these methods from GaN to ZnMgO, a new family of wide band-gap materials more compatible with microchannel plates. We also are exploring technical parameters such as doping profiles, internal and external field strengths, angle of incidence, field emission assistance, surface preparation, etc.

Norton, Tim↗

NASA NTRS1990

A probe for real-time images of particle beams and their analyses in a merged-beams apparatus

A real-time charged particle beam probe was developed, which can be used both as a beam diagnostic (beam tuning) and to quantitatively determine the three-dimensional density distribution of a beam. The probe consists of a microchannel plate, an aluminized phosphor screen deposited on a fiber-optic faceplate, a flexible fiber-optic bundle, and a charge injection device (CID) in tandem. Digital or analog video output of the CID is fed into a computer or oscilloscope, respectively, for analysis or observation. The probe can be moved continuously along the beams' paths to obtain 'pictures' of the beam at any desired interval, thus giving three-dimensional form factors. The beams, singly or simultaneously, may be observed on the monitor facilitating the task of beam adjustment for optimum overlap. The digital output is used for quantitative computation of the beam overlaps. The device is linear with beam intensity, but the performance degrades with time due to beam damage of the microchannel plate.

Forand, J. L.↗

NASA NTRS1994

Delay Line Detectors for the UVCS and Sumer Instruments on the SOHO Satellite

Microchannel plate based detectors with cross delay line image readout have been rapidly implemented for the SUMER and UVCS instruments aboard the Solar Orbiting Heliospheric Observatory (SOHO) mission to be launched in July 1995. In October 1993 a fast track program to build and characterize detectors and detector control electronics was initiated. We present the detector system design for the SOHO UVCS and SUMER detector programs, and results from the detector test program. Two deliverable detectors have been built at this point, a demonstration model for UVCS, and the flight Ly alpha detector for UVCS, both of which are to be delivered in the next few weeks. Test results have also been obtained with one other demonstration detector system. The detector format is 26mm x 9mm, with 1024 x 360 digitized pixels, using a low resistance Z stack of microchannel plates (MCP's) and a multilayer cross delay line anode (XDL). This configuration provides gains of approximately 2 x 10(exp 7) with good pulse height distributions (less than 50% FWHM) under uniform flood illumination, and background levels typical for this configuration (approximately 0.6 event cm (exp -2)sec(exp -1)). Local counting rates up to about 400 events/pixel/sec have been achieved with no degradation of the MCP gain. The detector and event encoding electronics achieves about 25 millimeter FVHM with good linearity (plus or minus approximately 1 pixel) and is stable to high global counting rates (greater than 4 x 10(exp 5) events sec(exp -1)). Flat field images are dominated by MCP fixed pattern noise and are stable, but the MCP multifiber modulation usually expected is uncharacteristically absent. The detector and electronics have also successfully passed both thermal vacuum and vibration tests.

Seigmund, O. H. W.↗

NASA NTRS1984

The development and test of ultra-large-format multi-anode microchannel array detector systems

The specific tasks that were accomplished with each of the key elements of the multi-anode microchannel array detector system are described. The modes of operation of position-sensitive electronic readout systems for use with high-gain microchannel plates are described and their performance characteristics compared and contrasted. Multi-anode microchannel array detector systems with formats as large as 256 x 1024 pixels are currently under evaluation. Preliminary performance data for sealed ultraviolet and visible-light detector tubes show that the detector systems have unique characteristics which make them complementary to photoconductive array detectors, such as CCDs, and superior to alternative pulse-counting detector systems employing high-gain MCPs.

Timothy, J. G.↗

NASA NTRS1980

Instrumentation development for the EUVE

The prototype mirror was successfully replated with a thick layer of nickel and diamond turned again. Optimization of the sensitivity of the instruments was studied with emphasis on the filter material, and on the available telemetry. The JHU Preliminary Project Definition Document was critically analyzed. Further studies of the electron cloud distribution produced by a channel plate were performed, and a wedge and strip anode with 17 quartets per inch was shown to image with better than 0.5% linearity. Half the microchannel plates being used in the lifetest completed initial processing and are in the lifetest vacuum chamber.

Finley, D.↗

NASA NTRS1980

Circular Scan Streak Tube Development

A streak tube having circular scan was designed, built and tested. Continuous circular scan, easily derived from out of phase sine waves applied to the conventional deflection plates, permits the timing of pulses traveling long baselines. At the tube's output a circular array of 720 elements is scanned to provide 30 to 40 picosecond resolution. Initial difficulties with electron bombarded silicon arrays were circumvented by using microchannel plates within the streak tube to provide the needed electronic amplification and digital sensitivity and coupling the 720 element arrays to the electron beam by means of a phosphor on a fiber optics. Two ceramic body tubes with S-20 photocathodes were tested and delivered.

Nevin, S.↗

NASA NTRS2003

The Deflection Plate Analyzer: A Technique for Space Plasma Measurements Under Highly Disturbed Conditions

A technique has been developed to measure the characteristics of space plasmas under highly disturbed conditions; e.g., non-Maxwellian plasmas with strong drifting populations and plasmas contaminated by spacecraft outgassing. The present method is an extension of the capabilities of the Differential Ion Flux Probe (DIFP) to include a mass measurement that does not include either high voltage or contamination sensitive devices such as channeltron electron multipliers or microchannel plates. This reduces the complexity and expense of instrument fabrication, testing, and integration of flight hardware as compared to classical mass analyzers. The new instrument design is called the Deflection Plate Analyzer (DPA) and can deconvolve multiple ion streams and analyze each stream for ion flux intensity (density), velocity (including direction of motion), mass, and temperature (or energy distribution). The basic functionality of the DPA is discussed. The performance characteristics of a flight instrument as built for an electrodynamic tether mission, the Propulsive Small Expendable Deployer System (ProSEDS), and the instrument s role in measuring key experimental conditions are also discussed.

Wright, Kenneth H., Jr.↗

NASA NTRS2004

The Deflection Plate Analyzer: A Technique for Space Plasma Measurements Under Highly Disturbed Conditions

Wright, Kenneth H., Jr.↗

NASA NTRS1991

Fundamental and practical limitations of FUV/EUV photon-counting image detectors

In EUV and FUV space-astronomy applications, the best contemporary detector designs are based on the use of microchannel plates due to their ability to deliver photon-counting performance with high efficiency. The major unresolved issue is the choice of position-readout system for the individual photoevents. Electrical event-readout systems are divided into two classes: the discrete wire anodes that perform coordinate digitization by wire-group selection, and the continuous centroid-position encoders for which coordinates are digitized in the associated electronics. The centroid-position encoder techniques are discussed in terms of how they overcome the four chief limitations of the discrete-wire readouts - their limited format size, their flat focal surface, their fundamental hex-channel vs squared-pixel moire pattern, and their image undersampling. With these limitations overcome, microchannel based image systems can deliver the performance demanded by the forthcoming generation of applications in space astronomy.

Lampton, M.↗

NASA NTRS1974

Negative affinity X-ray photocathodes

A new X-ray image intensifier is described. The device should eventually have a quantum efficiency which is an order of magnitude greater than that of presently available high spatial resolution X-ray detectors, such as microchannel plates. The new intesifier is based upon a GaAs crystal photocathode which is activated to achieve negative electron affinity. Details concerning the detector concept are discussed together with the theoretical relations involved, X-ray data, and optical data.

Vanspeybroeck, L.↗

NASA NTRS1976

Spectroscopic survey of the far-ultraviolet /1160-1700 A/ emissions of Capella

A far-ultraviolet spectral survey of Capella (Alpha Aur, G5 III + G0 III) has been obtained using a highly sensitive rocketborne spectrograph with a microchannel plate detector. The spectral distribution is very similar to that of the sun; however, if the line surface fluxes are due to the primary (G5 III), then, except for Ly-alpha, they are about an order of magnitude greater than those of the quiet sun

Vitz, R. C.↗

NASA NTRS1977

The Photicon

The Photicon is a novel imaging optical detector utilizing a conventional semitransparent photocathode, imaging electrostatic optics, microchannel plates, and a crossed-wire-grid position-sensitive charge detector. Its sensitivity to single optical photons over a two-dimensional area, high-resolution imaging, and timing capability render it useful for recording scintillations from X-ray image converters in X-ray astronomy. A digital word indicating the position of a single photon event is produced; the image can be stored in an array or serially. Spatial resolution to 20 microns in a 25 mm diam active area detector is reported, and modifications to achieve a spectral range of 120-730 nm are mentioned.

Kellogg, E.↗

NASA NTRS1978

The High Resolution Imaging Instrument for HEAO-B

The High Resolution Imaging Instrument for the HEAO-B X-ray Telescope satellite is designed to reproduce images of celestial X-ray sources in the range of 0.2 to 4.0 keV. It provides both imaging and temporal data. The basic detector is a two-stage microchannel plate with a crossed-grid charge detector. Preamplifiers, detector bias supplies, and some processing circuits are colocated with the detector. The remaining electronic circuits are located in a remote central electronic assembly. The processing system is designed for single-photon processing. The imaging data rate is limited to 100 data points per second. Non-imaging total-field count rate is acquired with a maximum dead time of 14 microseconds per event.

Kubierschky, K.↗