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S800 Tuning (XDT)
This page gives the steps that are followed when tuning the S800. The two possible tuning modes are included, namely, the Focus mode and the Dispersion-matching mode.
Before proceeding, it is mandatory to complete all the steps of the to-do list necessary to prepare the S800 for tuning. The preparation of the S800 for tuning is covered by the A1900 prior to every experiment.
Focus Mode
For most of the experiments in the S800, the analysis line is run in focus mode. In this optics, the analysis line is achromatic, i.e. the dispersive position of the beam focused in the target area (pivot point) does not depend on the momentum. Thus, this mode provides the biggest momentum acceptance (4%). On the other hand, since the spectrograph focal plane is chromatic, the resolution is limited to about 1 part in 1000 in energy.
Unreacted beam
In the first part of the XDT, the rigidity of the S800 is typically set to match the value of the fragment beam (selected in the A1900) after passing through the S800 target. This is where the term “unreacted beam” comes from.
Send beam to FP
Bias S800 FP scintillator photomultipliers
Remove stops to look for beam at S800 FP with
scalers and adjust beam rate with attenuators
Look at FP scintillator scalers (E1 up, E1 down)
There are typically a few scaler counts without beam
Object scintillator setup
Use
scope to look at signal patched out to data U6 (channel #54 in data U6 patch panel)
This signal is sent to the CANBERRA 454 Quad CFD in data U6
One of the output from this CFD is sent (via patch panel #62) to the TAC and scaler (channel OBJ.Scint) in S3. The other output goes through a passive delayed, and is sent (via patch panel #67) to the Phillips TDC
Check raising time and amplitude. Good signal: ~10 ns raising time; 400-500 mV amplitude
Adjust MCFD threshold:
Open configuration file MCFD16.tcl in /user/s800/operations/daq/usb/Configs
The OBJ signal feeding this module is not patched out to data U6
The OBJ signal from MCFD-16 module goes to the Mesytec MTDC32 module and scaler (channel OBJ.MCFD.Scint)
Make sure that the threshold of the XFP MCFD channel is reasonable. Rates in scaler channels XFP.Scint and XFP.MCFD.Scint should be comparable
Adjust MCFD OBJ threshold looking at scalers. The ratio of OBJ to XFP scaler rates (channels OBJ.MCFD.Scint and XFP.MCFD.Scint) should reflect the transmission of the cocktail beam
Save new threshold in configuration file MCFD16.tcl
FP scintillator setup
Select
Spectcl window
S800_SCINT.win
Adjust
bias looking at 2D spectra
e1.deup_e1.dedown (showing the parameters s800.fp.e1.de_down vs. s800.fp.e1.de_up) for the FP E1 scintillator
See spectrum below. Changing bias of this detector stretches the curve (i.e. shifts the blob in the middle of the curve corresponding to typical unreacted beam)
Different particles with different energy loss will shift the curve corresponding to particles covering whole FP
Ionization Chamber setup
Adjust pad gains
There are 16 pads each providing energy-loss information in the beam direction
The idea is to make sure the dynamic range is OK so that heavy particles do not saturate the spectra; the pad gains do not have to be matched
Use summary 2D spectra IC.raw (see spectrum below)
Gains are controlled in
s800shpini.tcl file in directory
s800/operations/daq/usb/Configs (an example of the content of this file can be seen
here).
CRDCs setup
-
Look at anode signal on
scope while biasing drift and anode
Patched to data-U6 on labeled connector
200 – 500 mV signals are good
CRDC1 anode is noisier (digital noise) than CRDC2
Bias CRDC1 and CRDC2. Typical starting values:
For He-3 @ ~130 MeV/u: CRDC1 (Anode=1120 V, Drift=1000 V); CRDC2 (Anode=1120 V; Drift=1000 V)
For Be-12 @ ~30 MeV/u: CRDC1 (Anode=970 V, Drift=1000 V); CRDC2 (Anode=970 V; Drift=1000 V)
For Ar-34 @ ~80 MeV/u: CRDC1 (Anode=860 V, Drift=1000 V); CRDC2 (Anode=840 V; Drift=1000 V)
For Zn-58 @ ~44 MeV/u: CRDC1 (Anode=740 V, Drift=1000 V); CRDC2 (Anode=740 V; Drift=1000 V)
For Rb-74 @ ~40 MeV/u: CRDC1 (Anode=650 V, Drift=1000 V); CRDC2 (Anode=650 V; Drift=1000 V)
For U-238 (88+) @ ~70 MeV/u: CRDC1 (Anode=570 V, Drift=1000 V); CRDC2 (Anode=570 V; Drift=1000 V)
Gate bias:
~20-30 V (adjust to optimize signal height compared to noise)
Should see counts on scalers
Count rate is a little higher than on scintillator due to noise or thresholds
Check
Spectcl window
S800_CRDCS.win (see figure below) to verify the good performance of the detectors. (The spectra for each CRDC can be checked separatelly in windows
s800_CRDC1.win and
S800_CRDC2.win)
Timing setup
At present, there are three electronic “sources” with time information for ToF calculation: ORTEC TACs, Phillips TDC, and Mesytec MTDC. Some background information can be found here.
Checking Particle ID and rate at S800 FP