1.1 General Description
The RoentDek MCP detector with delay-line anode is a high resolution 2D-imaging and timing device for charged particle
or photon detection at high rates with limited multi-hit capability. The linear active diameter is at least 40mm for the detectors
with the DL40 anode (e.g. DLD40 and DLD40EP), 75mm for the DL80 anode (e.g. DLD80 and DLD75eT), and about
120mm for the DLD120. The
RoentDek Hexanode has a third delay-line layer that gives redundant detection opportunities
either to improve the multi-hit performance, linearity or to allow the use of a MCP setup with central hole and minimized blind
detection area. In its usual version (HEX80) it has about 75mm redundant detection area (HEX120: 100mm redundant, up to
115mm linear with at least two layers, total up to 120mm, HEX100: 100mm redundant detection area, HEX40about 40mm
redundant detection area)
*
. For detectors with central hole (e.g. HEX40/o and HEX80/o) the descriptions in this manual are
also relevant unless otherwise stated. A DLD150 version is available on demand with 150mm active detection diameter.
The detector consists of a pair of selected MCPs in chevron configuration or of a triple stack (Z-stack) and a helical wire delay-
line anode for two-dimensional position readout. The MCPs are either supported by a pair of partially metalized ceramic rings
(1.5/2mm thick, 65/105mm outer diameter for DLD40/DLD80 and HEX80 with metal contacts on the ceramic rings are
suitable for soldering, clamping or spot welding) or the MCP stack is mounted between a metal front ring and a (usually square-
shaped) rear side holder plate, e.g. for the DLD120 and HEX120(100) or custom MCP stack designs.
Operation requires two DC voltages for a (resistance matched) MCP stack on front and back contacts and three voltages for
the anode’s support plate (“holder”) and the anode wire array. All voltages can be supplied by separate HV-supplies or voltage
dividers. The baking limit is specified as 150°C for the detectors and for optionally provided in-vacuum cables and feedthroughs.
The wire array consists of two or three helical wire propagation double (delay) lines. For each dimension a differential wire pair
is formed by a collection (signal) wire and a reference wire. A potential difference of 20V to 50V between signal and reference
wire ensures that the electron cloud emerging from the MCP is mainly collected on the signal wires, shared between the wire
layers for different position encoding directions. The anode holder has to be biased with an intermediate potential with respect
to the anode wires and the MCP back potential to ensure proper charge cloud propagation and spatial broadening in the drift
zone between MCP and anode wires. The optimal voltage depends on the distance between the MCP holder plate and the
anode wires.
Typically the wires should have about 300V more positive potential than MCP back side and the holder about +100V with
respect to the MCP back potential.
Avoid penetration of strong external electrical and magnetic fields into the electron cloud drift region (between MCP and wire
anode). Electrical fringing fields can produce image distortions, magnetic fields (> 50Gauss) disturb the proper charge cloud
broadening and will lead to malfunction of the anode.
The position of the detected particle/photon is encoded by the signal arrival time difference at both ends of each parallel-pair
delay-line, for each layer independently. While the signal speed along the delay line is close to speed of light, one can define a
perpendicular signal speed v
⊥
given by the pitch of one wire loop (typically 1mm) and the time, which a signal needs to propagate
though this loop. This defines the single pitch propagation time per 1mm which is equal to 1/v
⊥
(in units mm/ns).
The corresponding ends of the delay-lines for each dimension are located on the opposite corners of the wire array terminals
on the rear side. The electrical resistance of each wire is between 5 and 100Ω end-to-end, depending on the size of the delay-
line and the wire type used. Corresponding ends of wires can such be identified. The four (or six) terminal pairs have to be
connected to vacuum feedthroughs by a twisted-pair cable configuration (both cables of a pair must have equal lengths, within
5mm). From the feedthroughs the signals must be transmitted (after DC-decoupling) to a differential amplifier or signal
transformer with equally adequate transmission cables.
The difference between the signal arrival times at the adjacent ends of each delay-line is proportional to the position on the
MCP in the respective dimension. The sum of these arrival times is fairly constant with few ns for each event (see below). The
time sequence of the signals can be measured by time-to-amplitude converters (TAC) or an n-fold time-to-digital converter
(TDC), n is at least 4 or up to 7 (Hexanode with separate timing channel). As time reference the signal on the MCP back or
front side can be used for correlating each particle to others or to an external trigger (TOF-measurement).
For the DLD detectors, the digital encoding for obtaining a 2d digital image (X/Y) is
*
In the following we will refer to those detectors using the same anode only by nominating one detector version, e.g. for
DLD40 and DLS40eT as DLD40 unless otherwise noted. Additional remarks, if any, will refer to the different MCP types.
Page 8 of 83 MCP Delay Line Detector Manual (11.0.1304.1)
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