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Delayline Detector DLD6060-8S Manual
Delayline Detector DLD6060-8S Manual | Surface Concept GmbH
5.3 Data Acquisition
Each readout line of the detector anode is connected to a fast amplifier followed by a constant fraction
discriminator (CFD) for pulse shaping. They are encapsulated inside the pulse processing electronics (ACU
= Amplifier-CFD-Unit or AU = Amplifier-Unit). The main function of the CFD is digital pulse discrimination,
ideally without any time-walk even at varying pulse heights. A Time-to-Digital Converter (TDC) behind
these chains serves as stop-watch for arrival time measurements.
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 4-fold 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 4-fold coincidence
condition of an incoming event and a fitting 4-fold 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.
