Micro-channel plate (MCP) detectors have long been a workhorse for space-based x-ray research and are advantageous over other imaging detectors because of their low size, weight and power. The Lunar Environment heliospheric x-ray Imager (LEXI), will utilize a MCP to image Earth’s magnetosphere in soft x-rays from the lunar surface. A critical element for interpreting on-orbit data is to understand the quantum detection efficiency (QDE) of the MCP. LEXI’s MCP is coated with potassium bromide (KBr) to increase the soft x-ray QDE. Historically, few measurements of QDE exist in the soft x-ray band for KBr detectors. This paper reviews the performance of LEXI’s detector, and the QDE experiment procedure conducted at and results from the Advanced Light Source synchrotron soft x-ray beam line (6.3.2) over the energy range 70eV-1300eV. A unique beam line setup was required to limit the photon flux as to not saturate the pores of the MCP or detector signal chain. The experimental results are similar to previous literature, with some caveats unique to this MCP and experimental setup.
The lunar environment heliospheric x-ray imager (LEXI) is a wide field-of-view soft x-ray imager built to monitor the shape and motion of Earth’s magnetopause over multiple days. Set to land on the lunar surface as part of NASA’s commercial lunar payload services (CLPS) program, LEXI will measure soft x-rays (0.1-2 keV) produced by the charge exchange between the solar wind and neutral atoms in the near-earth environment. LEXI focuses x-rays in its 9.1° by 9.1° field of view using a tiled 3 by 3 array of “lobster-eye” micropore optics (MPOs). LEXI’s MPOs were first tested individually with a short range x-ray source to characterize the optics and select the best MPOs for flight. Once assembled into a flight array, the MPOs were tested in the PANTER x-ray beamline facility at multiple energies to determine the array’s point spread function and effective area as a function of off-axis angle. We present preliminary calibration results of LEXI’s individual MPO elements and assembled MPO array to qualify the instrument optics for flight.
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