development of micro-pattern gaseous detectors – gem - LMU

34 Chapter 3 The Triple GEM Prototype 1.0
photomultiplier
Protection Circuit
Charge sensitive
Preamplifier
●CATSA 82 82
●Canberra 2004
●Elab 2010
SIGNAL
scintillator 1
Flash ADC
GEM
Timing Filter
Amplifier
(ELAB LMU)
(C.A.E.N. V1779)
TRIGGER
scintillator 2
USB to VME Interface
(Struck SIS3150USB)
photomultiplier
I / O Register
(C.A.E.N. V977)
charge
Discriminator
(C.A.E.N. N845)
Discriminator
(ELAB LMU)
- - 87,0 mV mV
Discriminator
(ELAB LMU)
- - 87,0 mV mV
Timer
(C.A.E.N. N93B)
∞
Timer
(C.A.E.N. N93B)
RESET
1.0 1.0 µs µs
START
AND
(C.A.E.N. N455)
DELAY
(ELAB LMU)
140 140 ns ns
AND
(C.A.E.N. N455)
Scaler 1
(C.A.E.N. N1145)
Scaler 2
(C.A.E.N. N1145)
TRIGGER
DETECTOR
TRIGGER
SCINTILLATOR
TRIGGER
SCINTILLATOR
+
DETECTOR
Figure 3.9: Schematics of the readout chain with Flash ADC, trigger and signal lines.
unit resets the timer for the next event.
Further trigger lines are generated by two scintillators, connected to photomultipliers, that are placed
beneath and above the GEM and are sensitive to cosmic muons. After discrimination of their signal
at a threshold of −87.0 mV with a discriminator by the ELab, the scintillators signals are fed to a
CAEN N455 coincidence unit. If coincident within 20 ns, this NIM signal provides the second trigger
line.
Combining this trigger line trough a ELab delay unit of 140ns with the detector’s signal, one derives
the triple coincidence trigger line with another CAEN N455 coincidence unit. Putting a CAEN
N1145 scaler in each of the last two trigger circles, the ratio of three- to twofold coincidences can be
detected, as it is necessary for efficiency measurements. Since the scintillator’s sensitive surface of
160 × 90 mm 2 is larger than the GEM’s active area, one has to consider this difference for efficiency
or
or