Engineering topics

Gaines, G. A.

Publications and source records attributed to Gaines, G. A..

3 records

NASA NTRS1995

Microchannel Plates for the UVCS and SUMER Instruments on the SOHO Satellite

The microchannel plates for the detectors in the SUMER (Solar Ultraviolet Measurements of Emitted Radiation) and UVCS (Ultraviolet Coronograph Spectrometer) instruments aboard the Solar Orbiting Heliospheric Observatory (SOHO) mission to be launched in late 1995 are described. A low resistance Z stack of microchannel plates (MCP's) is employed in a detector format of 27 mm x 10 mm using a multilayer cross delay line anode (XDL) with 1024 x 360 digitized pixels. The MCP stacks provide gains of greater than 2 x 10(exp 7) with good pulse height distributions (as low as 25% FWHM) under uniform flood illumination. Background rates of approx. 0.6 event cm(exp -2) sec(exp -1) are obtained for this configuration. Local counting rates up to about 800 events/pixel/sec have been achieved with little drop of the MCP gain. MCP preconditioning results are discussed, showing that some MCP stacks fail to have gain decreases when subjected to a high flux UV scrub. Also, although the bare MCP quantum efficiencies are close to those expected (10%), we found that the long wavelength response of KBr photocathodes could be substantially enhanced by the MCP scrubbing process. Flat field images are characterized by a low level of MCP fixed pattern noise and are stable. Preliminary calibration results for the instruments are shown.

Siegmund, O. H. W.↗

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 NTRS1990

Highly curved microchannel plates

Several spherically curved microchannel plate (MCP) stack configurations were studied as part of an ongoing astrophysical detector development program, and as part of the development of the ALEXIS satellite payload. MCP pairs with surface radii of curvature as small as 7 cm, and diameters up to 46 mm have been evaluated. The experiments show that the gain (greater than 1.5 x 10 exp 7) and background characteristics (about 0.5 events/sq cm per sec) of highly curved MCP stacks are in general equivalent to the performance achieved with flat MCP stacks of similar configuration. However, gain variations across the curved MCP's due to variations in the channel length to diameter ratio are observed. The overall pulse height distribution of a highly curved surface MCP stack (greater than 50 percent FWHM) is thus broader than its flat counterpart (less than 30 percent). Preconditioning of curved MCP stacks gives comparable results to flat MCP stacks, but it also decreases the overall gain variations. Flat fields of curved MCP stacks have the same general characteristics as flat MCP stacks.

Siegmund, O. H. W.↗