Welcome to the wiki page of the NSCL S800 spectrograph. The page provides technical information about the S800, as well as instructions to operate the S800 prior to and during an experiment.

• Introduction
• Stations
• Magnets
• Modes of Operation
• Determination of Angles and Momentum
• Detectors
• Electronics
• Data Acquisition (DAQ)
• S800 Software
• Coupled Devices
• Types of Experiments

• Preparation for tuning the S800
• Experiment Device Tuning)
• During experiments
• Division of operation responsibilities

PILOT BEAM (XDT)

Unreacted beam

Send beam to FP

Ensure that crad04 is enabled with a rate limit of 20 kHz (crad04 looks at E1 up)
FP rate limit:  6 kHz
Bias S800 FP scintillators
Set bias to best guess based on previous experience for the fragment Z being used
Typical values:
1500 V E1 up/down
1200 V E2 up/down
Have a good expectation of rate from A1900 group information or from timing scintillators
remove stops to look for beam at S800 FP with scalers and adjust beam rate with attenuators
Look at FP scintillator scalers
There are typically a few scaler counts without beam
Ion chamber does not have scalers

Object scintillator setup

Use scope to look at signal patched out to data-U6
This signal is a copy of what goes to cfd in vault
Good signal height:  400-500 mV
Typical bias:  1200-1800V (up to 2200 V)
Typical current:  _________
Watch for no rate change on scaler display with a bias adjustment up or down of ~50-100 V

FP scintillator setup

Set trigger to “s800 trigger”
Start trigger GUI by clicking icon in “Operations” area
Under trigger tab select “s800 trigger” (which is E1 up by definition)
Deselect experiment trigger
SAVE TO FILE
Stop and start daq to assert new trigger condition
start spectcl
Adjust bias looking at down vs. up 2D spectra for each scintillator
See sketch below
Bias changes stretch curve (i.e. shift spot corresponding to typical unreacted beam)
Adjust biases so that unreacted beam are at 1/3 to ¼ of dynamic range
Reaction product will typically be similar enough to unreacted beam particles
Different particles with different e-loss will shift the curve corresponding to particles covering whole FP
Biases for K-48 @ ~95 MeV/u
E1_UP/DOWN:  1550/1500V
E2_UP/DOWN:  1350/1390V

Ionization Chamber setup

Gas should be flowing
Bias detector
Start alarm server under “operations”
Start HV application under “operations”
Typical bias
Anode:  200V (should not draw current after bais reached)
Drift:  800V (typical current:  <80)
K-48 at ~95 MeV/u:  Anode/Drift:  800/200V
This is not a sparky detectors
Adjust pad gains
There are 16 pads each providing dE information in the Z (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”
Gains are controlled in “s800shpini.tcl” file in the current directory
This file can be edited with the bbedit editor by double clicking on the file in the browser
1st shaper is for ion chamber
typically only coarse gains are used

FP CRDC setup

Bias CRDCs
Look at anode signal on scope while biasing drift and anode
Patched to data-U6 on labeled connector
200 – 500 mV signals are good
Typical starting values:
Drift:  500 V (800 V used for K-48)
Should draw current with bias applied
Anode:  500-600 V (800 V used for K-48)
Should not draw current after set value reached
Watch signal as setting in 100 V steps
Gate: 20-40V (adjust to optimize signal height compared to noise)
K-48 @ 95 MeV/u
CRDC1 Anode/Drift:  800/800 V
CRDC2 Anode/Drift:  800/800 V
Gate:  26V
Not a sparky detector
Should see counts on scalers
Count rate a little higher than on scintillator due noise or thresholds
Check spectra
 “crdc1.raw” and “crdc2.raw”
224 pads in dispersive direction
Sketch shows typical spectra
Width of beam peak is proportional to A1900 p-acceptance in focus optics
Width is narrower in match optics

Adjust anode to bring fuzzy maximum to around 600-700 channels
ADC full range for each pad is 1000
Can look at y vs. x 2D spectra as a sanity check
Remember that the y-parameter is not reliably calibrated at this point
“crdc1.tac” and “crdc2.tac” provide raw y-parameter (confirm these spectra titles _____________________)
Mask calibration
Unreacted beam does not provide good conditions for performing the mask calibration, but sometimes it provides the only option
To cover mask
Detune non-dispersive y quad (ratio=0.5) in spectrograph to spread beam in y
Sweep beam across dispersive direction using spectrograph dipole

Timing setup

See http://groups.nscl.msu.edu/s800/Technical/Electronics/Electronics_frameset.htm for background information on the trigger setup
The TDC delays can only be changed when the run control is stopped; must SAVE settings before starting run control not to overwrite adjustments being made
The “S800” trigger is from E1 up signal
Trigger the scope with the “Live Trigger” signal patched to data-U6
There are 4 trigger inspect channels patched to data-U6 that can be assigned using the trigger GUI
Examine the timing of each of the selectable listed signals with respect to the “Live Trigger” signal
There are 4 TDC inspect channels patched to data-U6 that can be assigned using the trigger GUI
The full range of the TDC is 400 ns
Set each timing to 200 ns
TDCs of last 4 listed signals (including XF and object scintillators) are bypassed with cable delays inside the vault and thus their delays cannot be controlled with the GUI
They can be inspected, however using the GUI
Information
The signal delays controlled by the GUI (and not by cable delays) are not “pipelined” – i.e., any new signals that arrive during the delay time of a previous signal are lost and thus deadtime is introduced into the system.  The signals delayed passively by cables are “pipelined” and thus are not subject to deadtime losses
All of the trigger signals are not pipelined and are thus subject to deadtime

Checking Particle ID and rate at S800 FP

Establish PID
Refer to information on setting from A1900 FP
dE-TOF
dE signal from Ion Chamber
TOF from XF or Object scintillator to S800 FP
Not necessary to implement dE- or TOF-based corrections
Document rate of fragment of interest with run to disk
Measure beam current with appropriate Faraday cups
Timed run

Analysis line classic PPAC setup (Focus optics only)

“Classic” PPACs are the default detector, not TPPACs or CRDCs
Classic PPACs have rate limitations from pileups
TPPACs are not as efficient as CRDCs for low Z because it is not currently setup to set thresholds on individual pad readouts
Checking PPACs with beam
Scalers do not provide reliable diagnostic information because of noise
Bias PPACs while looking at patched out anode signal on scope to check for sparking
Typical starting value:  400V
K-48 @ 95 MeV/u biases:  PPAC1=580V, PPAC2=540V
Look at spectra of raw up, down, left, right, anode to decide on bias
Run with smaller p-acceptance (e.g., 0.5%)
Efficiency against Focal plane CRDCs should be 100%
Optimize bias setting based on raw signals
Check that position spectra look reasonable
Run with larger p-acceptance (e.g., 2%)
Efficiency against Focal plane CRDCs should be 100%
Record run showing tracking
Confirm angular dispersion: ~50 mrad/% (not an absolute measurement)
Confirm correlations between dispersive angle at intermediate image and p in FP (e.g., crdc1x)
This correlation will be somewhat washed out by straggling in the target; in principle, this should be checked without the target, but the benefit vs. cost in time to remove the target is not worth it.

Setup beamline

Object and XF scintillators and intermediate image PPACs inserted if they will be used
If Object scintillator will not be used, there is no reason to look at beam on it unless to debug a problem with the transmission
Set spectrograph Brho for unreacted fragment

Start scalers

Use s800 account
Make sure experiment daq is:
Stopped
Gone
Open terminal window (from bottom of mac)
ssh to spdaq20
ps auw | grep Readout
Does not get restarted
Under operations folder on mac
scalers (gives error if no bridge)

Setting Optimization

Focused optics
Expectations for A1900 FP to S800 FP transmission
80% or better for mid-Z fragments
>60% for low-Z fragments with large angles
40% transmission might be a cause for concern for high-Z beam with charge state losses in detectors/targets depending on the charge state distribution and how many charge states reach the S800 FP
Strategy for optimizing transmission
Want to balance losses between S800 analysis line and Transfer Hall (the S800 analysis line is typically slightly worse)
Best diagnostic is scalers from S800 FP, object scintillator and XF scintillator
Tweak y-quads (while watching scalers) in front of dipole gaps (this works both for Transfer Hall and analysis line); choose elements that have biggest effect with smallest ratio change
Matched optics
Typically much more time is invested for optimizing optics for matched optics than for focused optics
One input is optimizing for transmission
For tritons a scintillator is required at the pivot position since fragments at 5 Tm will not reach S800 FP
The last two analysis line triplets are used to tweak for the desired optical properties

Document optimized transmission with another run to disk to measure rate of fragment of interest at S800 FP

Reaction Settings and Coincidences

Setting up Reaction Settings

Calculating reaction setting
Center unreacted beam at S800 FP
Adjust spectrograph Brho to center beam at S800 FP
Requirements for a beam to be “Centered”
Spectrograph dipoles matched
Beam position within about 1 cm of center as judges by 0 point on crdc1x spectrum or on track.xfp spectrum
Record run to disk to document centered unreacted beam setting
Calculate reaction setting using “effective” beam energy and the nominal target thickness
Ideally, experimenters should be the ones making this calculation
This approach assumes that the target thickness is known
Reaction setting to FP
Start with Attenuator setting of unreacted beam and step up in intensity
Set up beam blocker, if necessary
Expect to see unreacted beam if reaction setting is within +/- 3% of unreacted beam setting
Should have to move only one of the two blockers unless charge states are present
A graphic tool is available to help (not yet calibrated)
Try to cut only as much as necessary; depends on
What rate limits allow
What experimenters want (e.g., if they want singles, the cut has to be more restrictive to limit acquisition deadtime)
Move blocker, decrease attenuator, repeat

Coincidences

Overview
Most experiments at the S800 involve setting up an auxiliary detector system (e.g. SeGA, HiRA, etc) to be used in coincidence with the standard detectors of the S800.
The auxiliary detector provides a secondary trigger that is fed into the S800 trigger system
A key part of setting up the S800 for such experiments is getting proper timing setup between the S800 and any auxiliary detectors
For cases where the Secondary detector has a slow response relative to the S800, the coincidence timing must be reset to the S800 timing by delaying the S800 trigger using the third gate and delay generator on the trigger GUI
A typical S800 delay for SeGA is 450 ns
Probably smaller typical S800 delay needed for HiRA
An example of experiments where auxiliary detectors are not used and, thus, setting up coincidence timing is not an issue are the experiments with tritons run by the charge exchange group
It is not clear whether coincidence setup gets logged as “XDT” or “EXR”
Choice of setting to be used for coincidence timing setup
The reaction of interest for the experiment can be used to setup coincidences only if the rate of coincidences is high enough
Sometime the pilot beam is used for setting up the coincidence timing in cases where the intensity of the secondary beam is too small
Example:  Reaction of interest 2p knockout to make Mg-36 from Si-38 (Si-38 rate was 1000 pps)
Setup
Coincidence signals are usually visible on scope without running scope in acquire mode
Adjust the width of the early signal (S800 or secondary) should be wide enough to catch coincidences with the late signal (width of late signal is not critical)
Readjust TDC delays based on changes made to S800 trigger delay
Experimenters will need to adjust their delays based on delay made to S800 trigger
Have experimenters record a run with coincidences on their account
S800 trigger TDC channel should show a peak (which corresponds to coincidences)
“secondary” TDC channel should have a peak
This check is required for verification in cases of low beam intensity (e.g. 1000 pps)
Length of run required is typically about 10-15 minutes
To be resolved:  whether or not to this run copied from experiment account for documentation of device tuning
Sample timing for running S800 with SeGA
SeGA trigger is late with respect to S800 trigger
Timing schematic to show how to
Setup of the S800 trigger to recover timing needed for proper functioning of S800 FP detectors
Set up the coincidence trigger
See:  http://groups.nscl.msu.edu/s800/Technical/Electronics/Electronics_frameset.htm

A double peak structure will appear in the TDC for the S800 trigger between the coincidence events and the singles events; the groups are separated by 25 ns because of the delay introduced by the downscaler used for the singles

Followup

Before leaving beam with experimenters
Set up current trip points on Linux HV controls
Values used for K-48
5 for CRDC and Ion Chamber anodes and intermediate image ppacs
50 for CRDC drifts
80 for IC drift
Ensure alarms are running
Make sure Linux HV GUI alarms are enabled
Make sure threshold on isobutane level is set up (not currently connected to alarms because they give too many false alarms when communication is lost)
All logs are being recorded
There is no log file for biases controlled by Labview
Linux HV
LabView gas handling system
Note in logbook
Scintillator biases
IC gate biases
Post reference printouts for experimenters
HV status:  a snapshot of HV GUI
Gas handling system status:  a snapshot of LabView window
Create window configuration with summing regions to make it easier for experimenters to track efficiency/performance of all detectors
Setting up coincidences for additional reaction settings in an experiment
Do not need to redo coincidence settup if secondary beam does not change
Might need to redo coincidence setup if secondary beam changes drastically
To watch during experiment
Look for isobutene running out – messes up data over several hours

Experimenters responsibilities

Implementing dE- or TOF-based corrections is part of EXR

More detail needed

Minimum rates required for coincidence setup
Selection of appropriate substitute reactions for coincidence setup
How to feel comfortable that there will not be a problem with FP detector gases running out
Starting alarms
Starting logging

Not covered

Details of mask calibration
Details on implementing dE- and TOF-based corrections

Index
Introduction
Experiment Types
Experiment planning
NMR
Operations software (Barney, QTChan, BLkq...)
Tracking setup
Device Tunning  Process (Focus mode, Dispersion-matching mode, Reaction setting, Unreacted beam)
Mask calibration
Beam blocker use
Setting optimization (tweaks)
Electronics
DAQ
Analysis
Operation Environment System Overview
Dump Switches
Experiment preparation (S800 checklist prior to experiment)
Login strategy
Detectors (TPPACs, CRDCs, IC, OBJ_SCI, S800_SCI, Hodoscope)
Overview 
HV
Gas Handling system 
Vacuum control
Special considerations for each detector
Shimming OBJ
Replacing OBJ

Advance preparations