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during_experiments [2015/10/27 16:00] pereira [Mask calibration] |
during_experiments [2017/06/17 14:53] pereira [Efficiency of OBJ Scintillator] |
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====== During experiment ====== | ====== During experiment ====== | ||
+ | This section describes support tasks that are typically requested during the course of an experiment. Some of them, like Mask calibration, | ||
+ | * [[#Mask calibration]] | ||
+ | * [[#Particle identification corrections]] | ||
+ | * [[# | ||
- | ==== Mask calibration ==== | + | |
+ | ===== Mask calibration | ||
CRDC mask calibrations are used to relate channel numbers and true physical distances in mm for the position-sensitive cathode readout drift chambers. A mask with a distinct and well-determined pattern of slits and holes can be inserted remotely in front each CRDC. The particles passing through the holes leave the pattern of the mask in the position spectrum of the detectors. First-order polynomials are used for the calibration. In x direction, where the position is determined from the charge induced in the pads, the slope of the first-order polynomial is fixed by the geometry of the detector to 2.54 mm/pad. The offset has to be set to center the "beam hole" at 0 mm. Since the drift time depends on the drift voltage, the gas composition and pressure, the y slope will change from experiment to experiment. | CRDC mask calibrations are used to relate channel numbers and true physical distances in mm for the position-sensitive cathode readout drift chambers. A mask with a distinct and well-determined pattern of slits and holes can be inserted remotely in front each CRDC. The particles passing through the holes leave the pattern of the mask in the position spectrum of the detectors. First-order polynomials are used for the calibration. In x direction, where the position is determined from the charge induced in the pads, the slope of the first-order polynomial is fixed by the geometry of the detector to 2.54 mm/pad. The offset has to be set to center the "beam hole" at 0 mm. Since the drift time depends on the drift voltage, the gas composition and pressure, the y slope will change from experiment to experiment. | ||
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{{: | {{: | ||
- | The following process describes how to improve the PID resolution. This correction is supposed to be done " | + | The following process describes how to improve the resolution |
- | * The SpecTcl | + | The SpecTcl |
- | | + | The SpecTcl parameters **s800.tof.xfpcorr1**, |
+ | |||
+ | The process described below describes to improve the resolution of the PID based on the **OBJ-FP** ToF from the ORTEC TAC. The correction process for the PID spectra based on other ToFs is similar | ||
+ | |||
+ | | ||
{{: | {{: | ||
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* In [[s800 SpecTcl|SpecTcl GUI]], click **Attach to File** and select data file **run-xxxx-xx.evt** in directory **/ | * In [[s800 SpecTcl|SpecTcl GUI]], click **Attach to File** and select data file **run-xxxx-xx.evt** in directory **/ | ||
- | * Looking at the spectrum **PID:TAC.OBJ2_TRACK.AFP** (figure below, | + | * Looking at the spectrum **PID:OBJCORR2_TRACK.AFP** (figure below, |
* Enter a new value (typically in the range 500-1000) | * Enter a new value (typically in the range 500-1000) | ||
* Click **Set** | * Click **Set** | ||
* Re-scan the data file | * Re-scan the data file | ||
- | * Keep trying different values, until the dependence is eliminated. The figure below (right) shows the corrected spectrum (for this particular case, **s800.tof.obje1Correction** = 450) | + | * Keep trying different values, until the dependence is eliminated. The figure below (bottom) shows the corrected spectrum (for this particular case, **s800.tof.obj2Correction1** = 450) |
- | {{: | + | {{: |
- | {{: | + | {{: |
- | * Repeat the process looking now at the spectrum **PID:TAC.OBJ2_CRDC1.X** (figure below, | + | * Repeat the process looking now at the spectrum **PID:OBJCORR2_CRDC1.X** (figure below, |
- | * Enter a new value for the variable **s800.tof.obje2Correction** (typically in the range 0.01-0.1) | + | * Enter a new value for the variable **s800.tof.obj2Correction2** (typically in the range 0.01-0.1) |
* Click **Set** | * Click **Set** | ||
* Re-scan the data file | * Re-scan the data file | ||
- | * Keep trying different values, until the dependence is eliminated. The figure below (right) shows the corrected spectrum (for this particular case, **s800.tof.obje2Correction** = 0.05) | + | * Keep trying different values, until the dependence is eliminated. The figure below (bottom) shows the corrected spectrum (for this particular case, **s800.tof.obj2Correction2** = 0.05) |
- | {{: | + | {{: |
- | {{: | + | {{: |
- | * The figure below shows the spectrum **PID:TAC.OBJ2_IC_SUM** after the right corrections were included in SpecTcl | + | * The figure below shows the spectrum **PID:OBJCORR2_IC_SUM** after the right corrections were included in SpecTcl |
- | {{: | + | {{: |
- | * The correction process described above can be used for other ToF. SpecTcl includes a set of corrected ToF parameters: | + | * The correction process described above can be used for other ToF. SpecTcl includes a set of corrected ToF parameters |
- | | + | * **s800.tof.objcorr1**, **s800.tof.obj1Correction1**, |
- | | + | * **s800.tof.objcorr2**, **s800.tof.obj2Correction1**, |
- | | + | * **s800.tof.objcorr3**, **s800.tof.obj3Correction1**, |
- | | + | * **s800.tof.xfpcorr1**, **s800.tof.xfp1Correction1**, |
- | * Note that although the SpecTcl | + | |
+ | * **s800.tof.xfpcorr3**, **s800.tof.xfp3Correction1**, **s800.tof.xfp3Correction2**: | ||
- | ===== Beam blocker use ===== | ||
- | ===== Handling detectors | + | ===== Efficiency of OBJ Scintillator |
+ | At relatively high rates (~0.5 MHz), the OBJ scintillator will be gradually damaged. Experimenters should check the efficiency of this detector continuously during the course of the experiment. Whenever the rates drop below ~90%, they may request the Device/Beam Physicist to shim the detector. | ||
+ | |||
+ | |||
+ | |||
+ | Before shimming, make sure that the thresholds are set properly (not too high) (refer to section " | ||
==== Shimming OBJ scintillator ==== | ==== Shimming OBJ scintillator ==== | ||
- | Shimming of the OBJ scintillator is required when the efficiency (measured by the experimenters) drops to about 85%. Please, refer to the operations [[https:// | + | Shimming of the OBJ scintillator |
- | ==== Replacing OBJ scintillator ==== | ||
- | The replacement of the OBJ scintillator is described in this [[https:// | ||