D0 Radiation Monitoring and SMT Safety System
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Radiation Monitors
The radiation monitors consist of silicon diode detectors and are physically located in the SMT. This enables the measurement of the dose received by silicon inside the SMT and naturally provides advantage over the BLM approach which measures the radiation outside the endcaps of the detector. The whole system consists of 24 so called fingers each of which houses two silicon diodes. To exploit the full dynamic range of the input signal (radiation dose), the signal from each channel is passed through a low gain and a high gain amplifier. In addition the fast electronics allows the generation of fast signals for alarm/abort decisions.
Each radiation monitor finger consists of two silicon diodes, passive and active components (preamps), mounted on a flex circuit, laminated onto a beryllium plate for heat transportation. Dimensions of the beryllium plates are the same as those of the flex prints. In addition, each finger also holds an NTC temperature sensor.
The layout of F-disk fingers can be found
here.
The layout of H-disk fingers. can be found
here.
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Radiation monitor fingers are mounted on the beryllium support structure. A base plate with mounting pins is glued onto the support. The fingers are then mounted on the plate. The support plate is also made of beryllium. Positions of the radiation monitor fingers are listed in this table.
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The diodes for the radiation monitors were cut from the H-disk test structures. Each diode measures 8mm x 8mm (effective area) x 300um thickness. Guard rings increase the breakdown voltage of the diodes. The diodes were tested at Nijmegen and selected according to the following criteria:
- I_leak < 15nA (one 18nA used, H05)
- V_depletion > 20V initially
- V_breakdown > 400V (no breakdown during testing up to 400V)
- Stability of leakage current over 24 hour period
High depletion voltage diodes were selected because of the characteristic behaviour with radiation damage (depletion voltage decreases with radiation until type inversion occurs; after type inversion, depletion voltage rises with radiation up to values much higher than the initial depletion voltage).
The most probable charge collection from one MIP is 3.8fC.
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The F- and H-disk fingers have the same schematic
and components.
Each finger holds an NTC temperature sensor
with certain temperature
characteristics. The loading diagram for H-disk type radiation monitors
can be found here.
The diagram for F-disks is identical but for the shorter length of the
finger.
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The custom low mass cable connects to the flex circuit through a 33-pin Hirose connector. The other end is terminated by a Robinson-Nugent P50-034S-RR1-TG (or "RN34") connector. Pinouts on the connectors can be found here. The prints holding the connectors are shown in radmon_finger_hirose.ps (Hirose connector) and radmon_finger_rn34.ps (RN34 connector).
One cable connects to each radiation monitor module. The F-disk cables run along the SMT support cylinder to the endcap, and radially outward to positions on the horseshoe.
The high mass cables run radially outward from the horseshoe to a beam running allong the West side of the detector. From there they run along the beam to the NW corner of the detector, and to the rack the movable counting house (MC303). Lengths of the high-mass cables are listed here. The curvature of the face of the calorimeter was not taken into account. Numbers are conservative (i.e. safe) estimates. N.B. 166.5ft is the distance to rack 214 in the movable counting house.
The cables are numbered S1-S6 for South, N1-N6 for North end of the detector, starting at phi=0 (looking towards z=0) and counting counterclockwise along the horseshoe.
The low mass cable is custom made by Habia and contains:
- 5x shielded twisted pair (Habia UBT 3607 ST 2)
- signal cable ( D1:hg, D1:lg, D2:hg, D2:lg, NTC: )
- Imax = , Vmax = (source: )
- 2x wire wrap wire (Habia M-WET3001, art.nr. 581443001)
- bias voltage ( HV:1, HV:2 )
- AWG30, PFTE isolation
- Imax = , Vmax = (source: )
- 3x thick wire (diameter = 0.44mm)
- +5V, -5V, GND
- Imax = , Vmax = (source: )
- 2x thin wire (diameter = 0.23mm)
- offset voltage (D1, D2)
- Imax = , Vmax = (source: )
- 1x woven braid (Habia art.nr. 0000010703) shield
Low- and high mass cable compositions are shown in radmon_finger_cabel.ppt.
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The signals are received at a custom 9U crate in the movable counting house (rack MC303). The custom crate contains:
- 8 receiver cards with 3 channels each (one for each finger). The receiver cards integrate the signals from the radiation monitors and subtract the offset.
- 2 ADC interface cards.
- 1 fast response card, with comparators for beam alarms.
- 1 power distribution card.
- 1 receiver card for the BLMs (not yet implemented)
- 2 ADCs
- 1 MVME-2604 Power PC
- 1 36-channel discriminator
- 1 scaler module
crate.ps shows an overview of the front-end.
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Each receiver card has three identical channels.
Channel input is an RN34-terminated high
mass cable from a radiation monitor finger. The input signals are:
- D1 low gain
- D1 high gain
- D2 low gain
- D2 high gain
- NTC temperature sensor
- D1 offset
- D2 offset
- D1 bias
- D2 bias
- +5V
- -5V
- GND
radmon_receiver_sch.ps
shows the complete schematic of the receiver card.
radmon_receiver_dia.ps
shows the loading diagram.
radmon_receiver_bom.txt
is a list of components.
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Two buffer cards drive the signals for the ADC. There are 16 channels on each card (in 2 groups of 8), so the cards can be used for the BLMs as well. The schematic can be found here.
The commercially made ADCs are housed in VIPC616 VMEbus IP carrier modules manufactured by Greenspring.
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A custom power distribution crate delivers power to the receiver cards and to the diodes.
Schematic: radmon_finger_psch.ps
Diagram: radmon_finger_pdia.ps
Components: radmon_finger_pcomp.txt
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A custom card delivers bias voltages to the diodes. The voltages have to be adjusted manually. The schematic of the card can be found here.
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A VME scaler and a VME counter module provide an alternate method of measuring the dose rate and consequentley facilitate the cross-calibration with ADC data.
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The motorolla Power PC MVME2604 is the main processor for data acquisition and processing. The operating system being used is the VxWorks.
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An uninterruptible power supply is being used to ensure continuous operation even in case of general power failure. All the equipment in the rack (except Rack Monitor Interface) is being powered through this UPS.
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All the susceptible power and signal lines have been accordingly fused.
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The online software has been written in c language. The software runs at ~10kHz for the fast signals, ~10Hz for the slow radiation level signals, and ~1Hz for the scaler output. Details can be found here.
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A fast electronics card will generate a beam abort trigger if the radiation level exceeds safe values. Only the low gain channels are used. Each channel has two threshold levels - an alarm level and an abort level. A combination of alarm and abort signals from different diodes will generate an overall trigger. The combination can be changed.
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