The RoentDek MCP detectors with delay-line anode apply an electronic particle (or photon) counting technique.
The electronic circuits register digitally the information on the position and on the arrival time for each individual
particle. The information is available in real-time and free of any “read-out noise” or blur, as known from
CCD read-out
and can be correlated with other recordings (or other detected particles) in real time. A detector system consists of
several components:
Detector heads,
feedthrough
with signal decoupling,
power supply
assembly,
front-end electronics
(amplifier and timing discriminator) and
time-to-digital converter
(TDC). In order to achieve a performance best-suited for your application, a few choices
have to be made. This guide shall help you in these decisions.
1 Detector heads:
A detector head consists of the micro-channel
plate (MCP) stack and the delay-line anode.
The MCP stack usually contains two
(resistance-matched) micro-channel plates with pore sizes of 12.5 or 25
micron and a channel length-to-diameter ratio (L/D) of 80:1 or 60:1, stacked
in so-called Chevron
configuration. The MCP stack is operated in gain
saturation so that every particle hit creates a distinct electromagnetic
signature and a well defined charge cloud, which is collected on the
delay-line anode. Due to the characteristics of the delay-line anode several
electronic signals on distinct contacts are produced in a time sequence,
which encodes the information on the position and absolute time of the
particle impact. The time sequence is usually registered by a (TDC) after
front-end electronics’ signal shaping.
The standard product choices DLD40, DLD80
and DLD120
use chevron stacks from Photonis (-Burle),
the number denominates the effective MCP diameter. Generally, larger
detector heads will give better performance (even for the absolute position
resolution). The DLD40 can be delivered with two different MCP types (12.5
or 25 micron pore size, please contact
RoentDek for advise on this choice). For some applications it might be beneficial to
implement a triple MCP stack (Z-stack option _/z,
e.g. DLD80/z)
for improving the <
ion-feedback characteristics. This can be relevant in advanced multi-hit applications.
The required open area will usually determine the choice of the detector
size, but the number of desired position pixels in the image (which depends
also on the TDC choice) must also be considered. While the active anode size
customarily matches the MCP size, it is possible to order a
differently-sized anode, e.g. to increase the position resolution or to
account for space restrictions, e.g. DLD40L(XL),
with consists of a 40mm MCP with 80mm
(120mm) active anode.
Detectors for multi-hit analysis
(e.g. fragment imaging):
The HEX
option (HEX80
and HEX120)
is designated for experimental situations when particle bursts
(“multi-hit”) shall be detected,
i.e. more than one particle is likely to arrive about within a 100 ns
period.
Detectors with central hole:
RoentDek
can deliver detector options with central
hole to allow a particle/photon beam pass though the detector (option
_/o). Those
detectors are usually built with
Hexanodes (HEX40/o, HEX80/o,
HEX120/o) and have customarily a 6.4
mm hole. They often require a special (user-defined) shielding tube.
Special MCP
with improved performance characteristics or
coatings (e.g. for efficiency-enhanced
VUV/X-ray
detection) can be
incorporated in our detectors. It is also possible to build
custom-designed, specially-shaped
delay-line anodes (e.g. with an internal
phosphor screen) and also delay-line
anode for one-dimensional read-out
only.
Furthermore, special
encapsulated detector heads
for visible and
near-UV single photon detection
can be ordered: DLD40PMT
and DLD80PMT.
For those there is a choice of
photo-cathodes (please contact
RoentDek).
It is recommended to order a
FT12-TP-type vacuum feedthrough
and signal-decoupling plug with the detector (for HEX-option:
FT16-TP) because the signal
decoupling and biasing of the detector is very critical for the performance.
Furthermore, a mounting gear for the detector head on and with a “Conflat”
vacuum flange can be ordered, options _/100,
_/150 and
_/200, the numbers denominating
the inner flange diameter in mm. Of course, the flange diameter must be
bigger than the outer detector size as given in the product descriptions.
Typically, the mounting gear included in these product options is for the
largest fitting detector size, but it is also possible to order a
feedthrough/mounting-gear on a larger mounting flange (e.g.
FT12-TP/150s for a DLD40 on
a Conflat flange with 150 mm inner diameter). If you need any special
flanges or extra ports in the customarily offered flanges please contact
RoentDek.
It should be
noted that the standard “–TP”
option will transform the intrinsically
differential delay-line signals into single-ended signals with 50Ω
impedance. It is possible to order the decoupling plug without this
–TP option.
The DLD40PMT
and DLD80PMT
already contain a
FT12-TP-type decoupling circuit.
However, they might need an extra cooling housing, please contact RoentDek.
3 High voltage power supply
A
RoentDek DLD
or HEX
detector requires 5 separate potentials
(plus a sixth if a front mesh shall be independently biased) for operation.
In most cases it is sufficient to supply the “MCP back” and “holder” contact
with the same potential; and the BA3 floating battery box reduces the number
of independent power supply channels needed to 3 or 4. Depending on the task
it might be possible to operate the detector even with only 1 or 2
independent power supply channels (please contact
RoentDek
for
details).
In any case, the power supplies should
have enough range, stability and excess-current trip protection. Two
versions can be delivered, the HV2/4
with two independent channels (require a NIM bin
or the
RoentDek
SPS2 for operation) or the
BIASET2. For
applications with MCP front and MCP back on the same polarity, the
High Voltage terminator is
necessary as a voltage stabilizing unit.
RoentDek offers
customarily a set of amplifying/timing electronic circuit boards (DLATR)
inside a 19” case with mains power supply, the
ATR19. The
DLATR board is a constant fraction
discriminator (CFD) circuit with pre-amplifier. The
ATR19 case hosts all
inputs/outputs and controls for operating the boards.
Usually the
ATR19 is equipped with 6 channels (3
DLATR boards) for
DLD-type detectors or 8 channels
(4 DLATR
boards) for HEX-type
detectors; in both versions,
one channel is “spare” and available for the
processing of an external signal, or a signal from a second detector (e.g. a
DET40 timing detector with
FT4-TP signal
decoupling).
If the signals shall not be digitized
with a TDC but with fast ADC system (FADC,
see below), we recommend amplifying the
signals from the FT12(16)TP-type
signal
decoupler by a FAMP8
and or FAMP1
module
(possibly followed by a
MIXA8). Also if a different CFD
than the internal circuit on the DLATR
board shall be used (e.g.
the
new CFD8),
the FAMP
amplifiers shall be used for pre-amplification.
The combination FAMP8
and the new CFD8
(and TDC8HP)
represents the optimal readout electronics of
RoentDek
delay-line detectors for advanced
performance demands.
The TDC choice is very important for the
application. So far, the TDC is limiting some performance characteristics of
the detector system like particle throughput and position resolution (and
thus the number of pixels in an image, also depending on the active detector
size).
Currently there is the choice of two
TDC-types:
a) the HM1-B
can be operated in several modes. It is
mainly used for fast imaging or imaging&timing applications (not multi-hit)
with DLD-type
detectors and allows in the
limit 1 MHz
particle rate.
The HM1-B’s
analog output can produce an on-line
image on an oscilloscope screen (oscilloscope not included). The
HM1-B has also an option to
acquire up to 3 (multi-) hits at a particle rate of up to 15 kHz.
b) the TDC8HP
is a module dedicated for
high resolution imaging and for
multi-hit acquisition. It can
achieve a particle throughput over 100 kHz (CPU-dependent), but does not
have an analog output option.
For detailed advice on the best-suited TDC
choice for your application please contact
RoentDek.
Advanced digital read-out:
For advanced applications (e.g. extreme
multi-hit conditions) the use of CFDs and TDCs can become inadequate due to
dead-time limitations and lack of desired
information on the pulse height and shape of the detector signals. For such
demands it is possible to record the signal sequence from the detector by a
fast ADC system (FADC).
RoentDek
supports this technique with adequate
front-end electronics (see above) and data analysis software (please contact
RoentDek for
details).
If a complete detector system is purchased,
it can be considered complete concerning all “special” items. Connection
cables (“lemo”)
between electronic modules are included if both modules to be connected by
the cables have been purchased.
Only standard
SHV connection cables between the
high voltage power supply HV2/4
and the feedthroughs are NOT included, but can
be ordered separately.
Standard tools as screw drivers or wrenches,
which are necessary to assemble and mount the detector heads (the detector
heads and mounting gear come as an assembly kit) and for adjusting the
electronic settings are NOT included. Also NOT included is a PC for the TDC
operation . However, the data acquisition software
CoboldPC (for but without Windows
OS) is part of the TDC delivery.
A fast oscilloscope (300 MHz) for single
pulses is necessary for initial signal verification and performance control
(trouble shooting).
For using auxiliary monitoring, operating
several detectors in coincidence or correlating detector signals to external
signals, additional pulse-shaping and multiplexing electronic circuits can
be of necessary. The
RoentDek
products
COIN4, MIXA8, NIM2ECL
and ECL2TTL
can be useful complementary electronic units in
this respect.
7 Coincidence setups and COLTRIMS/spectrometer
assemblies:
RoentDek is
able to provide advanced setup for operation of two (or more) detectors and
support the correlation between the detector signals and other recordings
from the experiments.
COLTRIMS
setups or custom
time-of flight spectrometers can be
assembled from standard components.
Since such setups are strongly
application-depended it is necessary to contact
RoentDek for details.
To contact
RoentDek
please send an e-mail to:
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