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The PEM Cosmic Ray Detectors
LIGO-T010088-00-H R. Frey, U. of Oregon The LHO and LLO cosmic ray detectors each have 4 photomultiplier tubes PMTs. The speci c descriptions below apply only to LHO. The setup for LLO is identical, but with di erent details. The detector is located on the oor below BSC1. Each PMT requires 1 high voltage input about 1 kV and one analog signal output. The analog signals are carried by4 RG58 coax cables with BNC connectors. The cables are 34 m long and terminate at rack 1X4. The 4 high voltage cables are terminated with MHV connectors. They also go to rack 1X4 at LHO. The analog signals terminate in analog electronics which uses one slot in a Eurocrate 4U ? in rack 1x4. This electronics, built at UO, provides two functions: 1 shape the analog signals and convert I to V for subsequent digitization; 2 provide a logic trigger signal if the input is above threshold. The fast few ns PMT signals are shaped to a few sby this electronics, which is compatible with LIGO timing and the 100 kHz sampling rate of the A D. The shaped signals are passed to a VME-VMIC 3123 A D which is in a slot in the 68040 side of VME crate 1 in rack 1X5. The trigger signal goes to a Brandywine GPS slave module in this crate, whichisto provide a time stamp for the event. Special VxWorks-based software running in the 68040 will readout the A D and include the time stamp in an "event record" which is then shipped to a le on CDS disk. We expect the average event ratetobeabout 1 per hour, or so. The high voltage is provided by a unit 2U which resides in 1X4. This unit was built at UO. It is based on Bertan modules for the high voltage. We provide the controls and spigots for monitoring. We would liketo have 8 slow EPICs channels to monitor the voltage and current for each PMT. The high voltage can be set remotely via this box, but we do not expect to use this capability initially.


S1, S2 : 31"x31"x1" plastic scintillator A1, A2 : 10-stage PMT B1, B2 : 11-stage PMT D : Discriminator Test Mass Chamber A/D : 3123 voltage sampling follows ~10 us shaping

Cable Trays and Pipes S1 A1 B2 S2 Floor

B1 A2

6"

A1 A2 B1 B2

D D

~1 Hz

Calibrate Trigger Run Hz Time Stamp

VME Timing Module
(CDS Rack 2X5)

D D

~10

-3

4 /

VME A/D (CDS Rack 2X5)

Event Record(MVME)

LDAS MetaDataBas

Figure 1: Schematic of cosmic ray detector and readout path.