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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Background events in microchannel plates

Measurements have been made to assess the characteristics and origins of background events in microchannel plates (MCPs). An overall background rate of about 0.4 events/sq cm persec has been achieved consistently for MCPs that have been baked and scrubbed. The temperature and gain of the MCPs are found to have no significant effect on the background rate. Detection of 1.46-MeV gamma rays from the MCP glass confirms the presence of K-40, with a concentration of 0.0007 percent, in MCP glass. It is shown that beta decay from K-40 is sufficient to cause the background rate and spectrum observed. Anticoincidence measurements indicate the the background rate caused by cosmic ray interactions is small (less than 0.016 events/sq cm per sec).

Siegmund, O. H. W.↗
NASA NTRS1989

A high resolution delay line readout for microchannel plates

Investigations are reported of delay line configurations used to encode photon event locations in microchannel plate (MCP) detectors. Several delay line schemes of planar and multilayer structure are discussed. The importance of the delay line substrate material is examined, and it is shown that the raw signals from delay lines are narrow (about 3-4 ns FWHM). The factors determining the delay line resolution are evaluated, and it is demonstrated that these are in agreement with measurements. Resolutions of about 18-micron FWHM have been achieved. Measurements of the linearity of the delay line readout show that event centroid locations deviate from perfect linearity by less than 50 microns, even with the very simple anode fabrication methods employed. The image stability has also been evaluated and it is shown that image shifts are less than one resolution element over a period of two months.

Siegmund, O. S. W.↗
NASA NTRS1992

X-ray focusing using microchannel plates

We present measurements of the X-ray focusing properties of square-pore microchannel plates (MCP's). Square-pore MCP's contain large numbers of closely packed optical surfaces, as required for grazing incidence X-ray optics. The surface of individual MCP channels has been measured and found to have high microroughness transverse to the channel axis and low microroughness parallel to the axis. The high frequency transverse roughness, on length scales greater than 400 nm, has a rms value of 5.9 nm and a Gaussian autocorrelation function with correlation length of 1.41 micron. We find that the geometric misalignments of the surfaces of different channels limit the angular resolution obtainable with current samples of MCP's to 7.1 arcmin.

Kaaret, P.↗
NASA NTRS1985

Electronic readout systems for microchannel plates

The modes of operation of position-sensitive electronic readout systems which use high-gain microchannel plate (MCP) electron multipliers are described, and their performance characteristics, along with those of the MCP, are compared. Among the structures presented are the wedge-and-strip, Codacon, and multilayer coincidence-anode MAMA (Multimode Microchannel Array) arrays. Spatial resolution of 25 x 25 sq microns (coincidence anode arrays) is achieved with an array format of 256 x 1024 pixels. On the basis of the performance data it is concluded that the readout systems using only conducting electrodes offer the best performance characteristics.

Timothy, J. G.↗
NASA NTRS1988

Charge coupled devices vs. microchannel plates in the extreme and far ultraviolet - A comparison based on the latest laboratory measurements

While microchannel plates (MCPs) have been established as imaging photon counters in the EUV and FUV for some years, CCDs are associated with low light level sensing at visible and near-IR wavelengths. Attention is presently given to recent proposals for CCDs' use as EUV and FUV detectors with quantum efficiencies sometimes exceeding those of MCPs; quantum resolution, format size, dynamic range, and long-term stability are also used as bases of comparison, for the cases of both space-based astronomical and spectroscopic applications.

Vallerga, J.↗
NASA NTRS1984

Microchannel plate EUV detectors for the Extreme Ultraviolet Explorer

The design and operating characteristics of the prototype imaging microchannel plate (MCP) detector for the Extreme Ultraviolet Explorer (EUVE) Satellite are discussed. It is shown that this detector has achieved high position resolution performance (greater than 512 x 512 pixels) and has low (less than one percent) image distortion. In addition, the channel plate scheme used has tight pulse height distributions (less than 40 percent FWHM) for UV radiation and displays low (less than 0.2 cnt/sq cm-s) dark background counting rates. Work that has been done on EUV filters in relation to the envisaged filter and photocathode complement is also described.

Siegmund, O. H. W.↗
NASA NTRS1986

Microchannel plates and image detection at soft X-ray wavelengths

Detector systems based on the high-gain microchannel plate (MCP) electron multiplier have been used extensively for imaging at soft X-ray wavelengths both on the ground and in space. The latest pulse-counting electronic readout systems provide zero readout-noise, spatial resolutions (FWM) of 25 microns or better and can determine the arrival times of detected photons to an accuracy of the order of 100 ns. These systems can br developed to produce detectors with active areas of 100 mm in diameter or greater. The use of CsI photocathodes produces very high detective quantum efficiencies to wavelengths between about 100 and 1A (0.1 to 10 keV) with moderate energy resolution. The operating characteristics of the different types of soft X-ray MCP detector systems are described, and the prospects for future developments are discussed.

Timothy, J. G.↗
NASA NTRS1990

Low-Noise, Long-Life, High-Gain Microchannel-Plate Glass

Dark noise reduced substantially without degrading other properties. Glass suitable for use as active material for microchannel plates (MCP's) free of constituents including significant amounts of radioactive isotopes.

Feller, W. Bruce↗
NASA NTRS1974

Preliminary results with saturable microchannel array plates

Microchannel array plates with a performance comparable to that of a conventional channel electron multiplier have been obtained for the first time. These array plates employ an angled electrostatic field to inhibit the feedback of positive ions within the microchannels. Saturated output pulse height distributions with modal gain values in excess of 10 million have been obtained and stable operation demonstrated over a range of ambient pressures from 0.0000001 to 0.00008 torr. However, a time-dependent reduction in the gain has been observed with these experimental plates because of the accumulation of charge on the insulating strips which are inserted in the wall of the microchannel to establish the angled electrostatic field.

Timothy, J. G.↗
NASA NTRS1987

Ultraviolet quantum detection efficiency of potassium bromide as an opaque photocathode applied to microchannel plates

The quantum detection efficiency (QDE) of potassium bromide as a photocathode applied directly to the surface of a microchannel plate over the 250-1600 A wavelength range has been measured. The contributions of the photocathode material in the channels and on the interchannel web to the QDE have been determined. Two broad peaks in the QDE centered at about 450 and about 1050 A are apparent, the former with about 50 percent peak QDE and the latter with about 40 percent peak QDE. The photoelectric threshold is observed at about 1600 A, and there is a narrow QDE minimum at about 750 A which correlates with 2X the band gap energy for KBr. The angular variation of the QDE from 0 to 40 deg to the channnel axis has also been examined. The stability of Kbr with time is shown to be good with no significant degradation of QDE at wavelengths below 1216 A over a 15-day period in air.

Siegmund, Oswald H. W.↗
NASA NTRS1993

Microchannel plate modal gain variations with temperature

Measurements of the modal gain of two high-gain curved-channel microchannel plates (MCPs) at various operating temperatures are presented. Both MCPs were fabricated from the Long Life glass with 12-micron diam channels on 15-micron centers. The modal gain was found to decrease with increasing temperature at a rate of -0.1 percent C. This reduction of gain with temperature is attributed primarily to an axial temperature gradient along each MCP channel creating a nonuniform electric field within the channel that lowers the effective output gain. A lowering of the secondary electron yield resulting from increased phonon scattering of secondary electrons released within the walls of the MCP channels was assessed, but was found to have a negligible contribution to the drop in gain with temperature.

Slater, David C.↗
NASA NTRS1989

Flat field response of the microchannel plate detectors used on the Extreme Ultraviolet Explorer

The results of the extreme ultraviolet (EUV) flat field calibrations of two of the flight detectors to be flown on the Extreme Ultraviolet Explorer Satellite (EUVE) are presented. Images of about 40 million detected events binned 512 by 512 are sufficient to show microchannel plate fixed pattern noise such as hexagonal microchannel multifiber bundle interfaces, 'dead' spots, edge distortion, and differential nonlinearity. Differences due to photocathode material and dependencies on EUV wavelength are also described. Over large spatial scales, the detector response is flat to better than 10 percent of the mean response, but, at spatial scales less than 1 mm, the variations from the mean can be as large as 20 percent.

Vallerga, J. V.↗
NASA NTRS1982

Characteristics of a microchannel plate intensifier

A telephoto optical system has been designed for imaging applications involving a use of the spectral region from 2000 to 7500 A. The optics images onto the photocathode of a multichannel plate photomultiplier (PMT). Interference filters are employed to provide spectral selectivity. The PMT consists of three microchannel plate intensifiers (MCP), arranged in a 'Z' configuration. MCP photomultiplier pulse height distributions are discussed along with aspects of spatial distribution, the electron gain pulse height distribution, and the charge loss due to edge effects. Attention is given to the electron gain pulse height distribution obtained from four anodes connected in parallel, taking into account a uniform illumination of the photocathode.

Sandie, W. G.↗
NASA NTRS1982

Optimization of the performance of a tandem microchannel plate detector as a function of interplate spacing and voltage

The effect of varying the size of the gap voltage and spacing on the performance of a tandem pair of microchannel plates (MCP) is investigated. Results show that increasing the voltage in the gap increases the gain of the pair and also produces a narrower Gaussian pulse-height distribution, although beyond a critical voltage the gain of the channel plate pair is found to plateau. A model is developed which explains the nonlinear gain behavior of individual microchannels and the behavior of the electron cloud emitted from the first MCP as it spreads out between the two MCPs and hits the surface of the second. The model calculates the plateau voltage as a function of the gap size, the gain of each MCP, and the diameter of the channels, and is found to show good agreement with the observed results. It is concluded that interplate gaps of up to several millimeters can be accommodated without a significant degradation in pulse-height distribution.

Rogers, D.↗
NASA NTRS1989

Performance characteristics of a curved-channel microchannel plate with a curved input face and a plane output face

The presently performance-evaluated format, in which a high-gain curved-channel microchannel plate (M2MCP) has a spherical concave input face and a plane output face, allows the input face of the MCP (1) to match such curved focal surfaces as that of a Rowland-circle spectrometer mounting, while (2) having a high-resolution plane readout array in proximity focus with the output face. This MCP has been evaluated in a discrete-anode multicathode microchannel array detector system. The saturated modal gain was found to be inversely proportional to the length/diameter ratio of the channels and directly proportional to the applied MCP voltage.

Slater, David C.↗
NASA NTRS1983

Maximizing the quantum efficiency of microchannel plate detectors - The collection of photoelectrons from the interchannel web using an electric field

High quantum efficiency and two-dimensional imaging capabilities make the microchannel plate (MCP) a suitable detector for a sky survey instrument. The Extreme Ultraviolet Explorer satellite, to be launched in 1987, will use MCP detectors. A feature which limits MCP efficiency is related to the walls of individual channels. The walls are of finite thickness and thus form an interchannel web. Under normal circumstances, this web does not contribute to the detector's quantum efficiency. Panitz and Foesch (1976) have found that in the case of a bombardment with ions, electrons were ejected from the electrode material coating the web. By applying a small electric field, the electrons were returned to the MCP surface where they were detected. The present investigation is concerned with the enhancement of quantum efficiencies in the case of extreme UV wavelengths. Attention is given to a model and a computer simulation which quantitatively reproduce the experimental results.

Taylor, R. C.↗
NASA NTRS1977

Self-scanned anode array with a microchannel plate electron multiplier - The SSANACON

A photoelectron counting detector utilizing a 128-element linear self-scanned anode array to collect the output of a dual microchannel plate electron multiplier is described. The operation of the detector, its spatial resolution and detection efficiency, and radiation behavior are discussed. The low-noise detector was developed for the Mariner Jupiter/Saturn mission UV spectrometer, and offers a large dynamic range and count rate of 0.003 per anode-sec. It can measure simultaneously two spatially separated signals differing by more than six orders of magnitude in count rate.

Broadfoot, A. L.↗
NASA NTRS1984

Absolute and angular efficiencies of a microchannel-plate position-sensitive detector

This paper presents a characterization of a commercially available position-sensitive detector of energetic ions and neutrals. The detector consists of two microchannel plates followed by a resistive position-encoding anode. The work includes measurement of absolute efficiencies of H(+), He(+), and O(+) ions in the energy range between 250 and 5000 eV, measurement of relative detection efficiencies as a function of particle impact angle, and a simple method for accurate measurement of the time at which a particle strikes the detector.

Gao, R. S.↗