SIS Detector

The imaging spectrograph includes two, redundant detectors. Either one can be used since the pop-up mirror, which enters the optical path when the second detector is to be used, is retractable. Only one detector is operated at a time. The detector characteristics are listed in the following table. The use of the secondary detector will lower the sensitivity of the imaging spectrograph due to the extra reflection of the pop-up mirror. The sensitivity with the secondary detector in place will be approximately 75% of the sensitivity with the primary detector since the pop-mirror has the ARC #1200 MgF2 overcoat. The sensitivities listed in the table are for the original SAIC detector in the primary position.  The newer Photek detectors are less responsive in the UV but have a more stable, band-limited response that is desirable for these observations.

The detector consists of a microchannel plate intensifier with a wedge and strip anode. Since maintanence of performance specifications over the mission lifetime is a design driver, the HVPS is commandable so that the detector gain can be maintained at 4x10**6 even at a charge extraction rate as high as 10 Coulomb/yr.

UV Detector Characteristics
Minimum Frame period 0.112 seconds
Maximum Count Rate 200 K counts/sec
Photocathode Cesium Iodide deposited on MCP front surface
Input Window Magnesium Fluoride
Detector size 25 mm diameter
MCP Arrangement Z stack (3 plates)
Anode Wedge and Strip, 3 electrode
Quantum efficiency 10% at 135 nm
Supplier SAIC/EVSD Model T221-001
Position resolution spatial dimension 16 elements across 16.5 mm
spectral dimension 160 elements across 15.6 mm
Output 4 bit by 8 bit photon position
High Voltage Power Supply adjustable for variable gain
Mean Gain 4x10**6 electrons/photon
Power 3 Watts
Weight 4 lbs
Qualification Temperature -29° C to +50° C

Page Last Modified: July 2, 2014