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Delayline Detector DLD4040 Manual
DLD4040 R2.55 & R3.54 Manual | Surface Concept GmbH
The measurement results, in terms of differences and sums are fed into the PC via an USB interface
and are completed to 2D images (with or without time stamps) by the histogram module of the data
acquisition DLL. Data processing and presentation on the PC is realized by the end-user software (see the
corresponding software manuals for detailed information on the software package).
5.4 Working with the DLD - Important Details
The DLD is a counting system that works in a laterally resolving sense by detecting four pulses from the
four ends of the delayline meanders in fourfold coincidence. It only works correctly within a certain range
of the supply voltage. The MCP voltage has to exceed an operation threshold for the detector otherwise
the pulse detection is not possible. This is due to the induced pulses on the delayline which have to reach
a certain amplitude to be detected by the electronics, independent on the intensity of the electron source
(e.g. mercury lamp). On the other hand, if the MCP voltage and/or the intensity of the electron source are
too high, the detector overloads and again pulse detection is not possible. Saturation effects of the MCPs
limit the amount of electrons provided by single pulses. An intensity increase of the electron source leads
to an increased number of hits on the MCP. The current per bunch and therefore the amplitude of the
pulses decreases.
There are two kinds of overloads: local and global ones. A local overload (locally high intensity on the MCP)
leads to no count rate within this local area and to an absolute “black spot” in the images. An intensity too
high and homogeneously distributed over the whole MCP first leads to diffuse images and with further
increasing intensity to randomly distributed artificial structures up to no count rate at all (global overload).
The explanation for the effects for a local overload is a pulse amplitude that is too low to be detected by the
electronics. The explanation for the global overload effects is mainly the loss of the fourfold coincidence
condition of an incoming event and a fitting fourfold coincidence of random pulses, respectively. High
intensity on the MCPs always leads to a significant pressure increase. Therefore an observed pressure
increase can always be taken as an indicator for an overload of the detector, when problems with the
functionality of the DLD occur.
Figure 7: Example of a partial overload (left) and a heavy (global) overload (right).
