Table of Contents

Timing

In a typical S800 experiment, there are different time-of-flight (ToF) measurements that can be used to identify the fragments of interest. The most common timing-signal sources used are the RF cyclotron (vetoed by the B6 output from the ULM Trigger module); the thin plastic scintillator at the A1900 focal plane box (XFP); the thin plastic scintillator at the S800 Object station (OBJ), and the S800 FP scintillator (E1) with two signals, one from the “up” and one from the “down” photomultipliers.

Although it is possible to measure the ToF between any pair of timing sources, there are three “standard” measurements provided to any experiment, namely, between the cyclotron and the S800 FP (RF-FP); between the A1900 FP and the S800 FP (XFP-FP); and between the S800 OBJ and FP (OBJ-FP). These ToFs are electronically recorded in a Phillips 7186 TDC, a Mesytec TDC (MTDC), and a group of Ortec 566 TACs, all them located in the electronic racks in S3, near the FP box.

Although the timing reference (“start”) in the all the ToF modules is given by the FP scintillator E1 up, the electronic path from the detector to each module is different (see main electronics diagram for more details).

Some important things to know about each of these modules:

MTDC

Ch. name Ch. number Electronic path (from detector)
E1 up 0 LeCroy Var. ampl. → Mesytec MCFD ch #0 → ECL-NIM → Fan in/out → Fan in/out → Fan in/out → Gate Generator → NIM-ECL
E1 down 1 LeCroy Var. ampl. → Mesytec MCFD ch #1 → ECL-NIM → Fan in/out → NIM-ECL
XFP 2 Patch #1 (dU6) → CANBERRA CFD (dU6) → Patch #70 → Fan in/out → Mesytec MCFD ch #2 → ECL-NIM → Fan in/out → NIM-ECL
OBJ 3 Patch #94 → LeCroy Var. ampl. → Mesytec MCFD ch #3 → ECL-NIM → Fan in/out → NIM-ECL
Free 4
RF 5 Patch #69 → Fan in/out → Logic Unit → ECL-NIM → Fan in/out → NIM-ECL
CRDC1 Anode 6 Tennelec Ampl. → CANBERRA CFD → ECL-NIM → Fan in/out → NIM-ECL
CRDC2 Anode 7 Tennelec Ampl. → CANBERRA CFD → ECL-NIM → Fan in/out → NIM-ECL
XFP 8 Patch #1 (dU6) → CANBERRA CFD (dU6) → Patch #70 → Fan in/out → NIM-ECL
OBJ 9 Patch #54 (dU6) → CANBERRA CFD (dU6) → Patch #62 → Fan in/out → NIM-ECL
Free 10-11
Hodosc. OR 12 Splitter att. → CANBERRA CFD → Fan in/out → NIM-ECL
Free 13, 14
E1 up 14 LeCroy Var. ampl. → Mesytec MCFD ch #0 → ECL-NIM → Fan in/out → Fan in/out → Fan in/out → NIM-ECL
E1 up 15 LeCroy Var. ampl. → Mesytec MCFD ch #0 → ECL-NIM → Fan in/out → Fan in/out → NIM-ECL

The multi-hit capability requires some special attention. Let's imagine a situation where the rate from OBJ detector is much higher than from the FP detector. During this window, the MTDC will record one hit from the FP scintillator (E1 up, which SpecTcl uses as the start ToF reference) and multiple hits from the OBJ scintillator (stops). As a results, SpecTcl will generate an array of OBJ-FP ToFs called s800.fp.vmetdc.obj.i, where i=0 stands for the first hit, i=2 second hit and so on (the corresponding array for XFP-FP TOF is s800.fp.vmetdc.xfp.i).

At moderate rates, or in an unreacted-beam setting, the first hit typically provides the “good” ToF (i.e. start and stop signals come from the same event in a given RF cycle). This is seen as a sharp single peak in the first figure below (showing a SpecTcl “gamma” spectra with all the hits from the array s800.fp.vmetdc.obj.i included). However, in a reaction setting (where the rates in the XFP and OBJ detectors are much higher than in the E1 up detector), the same spectrum will show multiple peaks (see next figure below); a very intense one corresponding to the “good” ToF (start and stop coming from the same event in the RF cycle), and many lower ones coming from ToFs generated by “random” coincidences between the start signal from E1 up and the OBJ stops generated from previous or later RF cycles.

Spectrum with s800.fp.vmetdc.obj.i for unreacted-beam setting Spectrum with s800.fp.vmetdc.obj.i for reaction setting

The two figures below show summary spectra with the OBJ-FP ToF (vertical axis) vs. hit number (horizontal axis). The first spectrum was recorded in an unreacted-beam setting, and the next one corresponds to a typical reaction setting. Note that in the former case, the “good” ToF peak (at ~-77 ns) is always given by the first hit, whereas in the later case, the good ToF (~-77 ns) can be given by any of the first five hits.

Summary spectrum with s800.fp.vmetdc.obj.i for unreacted-beam setting Summary spectrum with s800.fp.vmetdc.obj.i for reaction setting

Tennelec TACs

Signal Ch. ID Electronic path (from detector)
S800 trigger start LeCroy Var. ampl. → Mesytec MCFD ch #0 → ECL-NIM → 4x Fan in/out → Logic Unit→ 300 ns delay
OBJ stop Patch #54 (dU6) → CANBERRA CFD (dU6) → Patch #62 → Fan in/out
Signal Ch. ID Electronic path (from detector)
S800 trigger start LeCroy Var. ampl. → Mesytec MCFD ch #0 → ECL-NIM → 4x Fan in/out → Logic Unit
XFP stop Patch #1 (dU6) → CANBERRA CFD (dU6) → Patch #70

Phillips TDC

Ch. name Ch. number Electronic path (from detector)
E1 up 0 LeCroy Var. ampl. → Mesytec MCFD ch #0 → ECL-NIM → 2x Fan in/out → NIM-ECL → XLM Delay
E1 down 1 LeCroy Var. ampl. → Mesytec MCFD ch #1 → ECL-NIM → Fan in/out → NIM-ECL → XLM Delay
Free 2-7
S800 trigger 8 LeCroy Var. ampl. → Mesytec MCFD ch #0 → ECL-NIM → 3x Fan in/out → NIM-ECL → XLM Delay
Free 9, 10
Secondary trigger 11 Fan in/out → NIM-ECL → XLM Delay
RF 12 Patch #69 → Fan in/out → Logic Unit → NIM-ECL → XLM Delay
OBJ 13 Patch #54 (dU6) → CANBERRA CFD (dU6) → Delay → Patch #67 → NIM-ECL → XLM Delay
XFP 14 Patch #54 (dU6) → CANBERRA CFD (dU6) → Delay → Patch #66 → Fan in/out → NIM-ECL → XLM Delay
Free 15