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Description
Microchannel plates (MCP) are a kind of electron multiplier widely used for intensifiers, sensitive detection and time gated 2D imaging apparatus. With coating strips used as a photocathode, they become a powerful tool for X-ray detection [1]. In the Laser Megajoule Facility, they are key components to notably X-ray framing cameras embed in several plasma diagnostics (imagers of spectrometers DP1, DP3, DP9, DP10, and DP19).
For these time-resolved imaging systems to be reliable, we need to extensively characterize the time-response, spatial resolution and flux before saturation of the MCPs. Indeed, when used above nominal use MCPs can generate artifacts.
We will focus on three effects. A first effect concerns the intrinsic limitation of the time-resolution in the design: with a finite pulse duration, the electron multiplication gain continually drops while electrons transit in the channel, thus reducing the gain at short pulses. The second effect concerns cross talks between neighbouring channels which can lead to transverse artifacts up to nanoseconds after the signal [2]. Third, local saturation effects due to channel depletion can arise at high incident flux [3].
Most of these effects have possible parades [4]. We support our study with measurements made on MCPs from different manufacturers, either with picosecond pulsed UV light or continuous Xray irradiation.
[1] E. Kellogg et al, Rev.Sci Instr 47 (1976) 282
[2] L.R. Benedetti et al., Rev.Sci.Instr. 83,10E135 (2012)
[3] O.L. Landen et al., SPIE 0-8194-1251-1/93 (2002)
[4] L.R. Benedetti et al., Rev.Sci.Instr. 87,023511 (2016)