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DLD4040 R2.55 & R3.54 Manual | Surface Concept GmbH
Note
It is easy to mistake an overload for no signal at all. To distinguish between these two,
check the pressure. A pressure increase indicates an overload.
The DLD has been calibrated for an optimized MCP voltage and it is strongly advised to use this optimized
voltage value for operation. It is given in the specification sheet. A change of the MCP voltage can lead
to artifacts within the images (see
). The MCP voltage should only be increased to compensate a
decrease in amplification of the MCP stack do to degradation. MCPs degradation is recognizable by a slow
permanent decrease of the count rate and happens either due to overloads or due to the normal behavior
in the burn-in phase. In such a case a new detector working voltage should be determined by making a
detector voltage scan or in the worst case: the MCPs must be replaced. For further detailed information on
MCP degradation and detector working voltages see
Figure 8: Example of an overvoltage on the MCPs (left) and an under voltage at high count rates (right).
5.5 MCP Outgasing during Operation
It is an intrinsic feature of the MCPs that they outgas during operation for quite a while due to desorption
of gas molecules which are still available inside the MCP pores. This effect becomes mainly visible at low
pressure which is reached after bake out and scales significantly with the size and the load of the MCPs.
The increase can easily reach more than one decade starting from the 10-10mbar range for new MCPs
being operated with a load of a couple of million counts per second. The effect of outgasing reduces with
operation time of the detector in-vacuum. The reduction of the outgasing can also be enforced by running
a degas procedure, which consists in the end of the operation of the detector under high load from a
homogeneously distributed intensity for a long time period. The degas procedure must be repeated to
some extend after each venting. For further information on the degas procedure for MCPs see
.
