4
$\begingroup$

Micro-channel plate (MCP) detectors are microscopic holes in a plate. They get put in an electric field and there act like many tiny dynodes, amplifying any electrons that enter. This makes them useful, amongst other things, in sensors that need snappy reaction times and spatial resolution. They get manufactured for instance by etching out the 'soft' center part of fibre optics-bundles or stretching bundles of glass tubes. I read in several documents relating to MCP that their performance degrades with use, and wikipedia states that 'MCPs have a fixed charge that they can amplify in their life'. On the other hand, i saw that they get a 'electron scrubbing' treatment (they get put in a big electric field and basically worked out) that is supposed to bring their amplification down to a sustained level, and MCPs are even used as electron sources in xray sources and there supposedly last longer than the usual filaments.

My question(s):

  • how is the fixed life-time charge justified, what happens?
  • is there different breeds of MCP some of which are not beholden to the lifetime charge, and if so how does that work?

UPDATE: It seems that many papers conflate MCPs with MCP-Photocathode Detectors, and some, 'damage'/'reduced efficiency'-references may actually refer to the Photocathode, not the MCP itself. Also, the 'lifetime-charge' may actually refer to a synthetic definition of 'lifetime' that only counts quantum efficiencies (QE) between 100% and x% (80?)of initial value as 'life' (analogous to some LED 'lifetime' definitions) - thus the MCP-PC QE levelling out at 70% would not be counted as infinite life. - Some MCP 'scrubbing' apparatus' actually use another MCP as electron source...

Can somebody confirm?

$\endgroup$
  • $\begingroup$ Never have worked with MCPs, I am not confident that I can provide accurate detail and hesitate to offer an "answer" as such. Still, one possible source of damage is high-current erosion which can be expected vary over the conducting surface in a way that tracks the field strength. Smoothing rough edges should help. $\endgroup$ – dmckee Dec 7 '18 at 21:13
  • $\begingroup$ Agree with @dmckee. It is likely that the MCP's are degraded in the same way as cold-cathode nanoemitters do: the sharp edges that furnish extremely high field gradients also carry measurable amounts of current and thereby get vaporized and thereby blunted or rounded off. $\endgroup$ – niels nielsen Dec 10 '18 at 7:46
  • $\begingroup$ @dmckee - so are you saying that the effect relies on sharp edges, and the field strengths created by those in turn speeds up their erosion? So the scrubbing treatment would then be a means to whittle the edges down to a level where the field strengths are sufficiently low and the edges sufficiently rounded (=stable) to create a steady state? Or is it one of those things where one party calls it 'stable' because in their short-cycle use-case the erosion never features, and the other party says it's degrading because they only have long-term use cases? $\endgroup$ – bukwyrm Dec 10 '18 at 10:32

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.