Wire Scan GUI
Introduction
The wire scanner GUI can be used in conjunction with another application or independently to determine beam size at the location of the selected wire scanner. When launched by another application like theEmittace GUI it can make measurements to obtain twiss parameters from the Emittance application. In general, a wire is passed through the beam reflecting the particle beam in the direction of a photomultiplier tube (PMT) which then measures the signal in counts. This "gaussian" signal at full width half max is interpreted as a beam size. If this signal is saturated, the beam size is meaningless and you may want to pick another PMT that does not show a 'flat top' signal to achieve a better beam size measurement which will lead to a better emittance measurement.
RED BOX
- Start by selecting the sector that you would like to measure the beam size in. IN20, LI21, LI28 or LTU.
- Below these choices are buttons that allow the operator to Save the generated data to disk for further analysis, Load previously saved data, Export the data to an external MatLab figure for fast analysis and save/load a Config to recall past configurations of this GUI. The Config feature is convenient for repeating a previous measurement without taking the time to set it up from scratch.
- You may choose a Scan Mode of either: Wire, Corr or Step. This...........
MEASUREMENTS BOX
- You may select a particular wire in the region that was selected above by pulling down the menu at the top of this section and clicking the desired wire. PV names look like, WIRE:LIXX:###. This can be useful if you would like to only scan one wire as opposed to the collection of them, say, to correct a single bad wire measurement.
- Start Scan will initiate the GUI as evidenced by the green scrolling bar and text below the abort button. If the GUI was previously ran to measure the Y beam size, and X is now selected, the measurement will take longer as the GUI must retract the Y wire before starting the X measurement. So to save time, operators should scan the plane that the GUI is all set up for before switching to the other plane, if measurements in both planes are desired. Scan at 30 Hz.
- Abort scan will hault the GUI form continuing the measurement in progress. You should also see this at the scrolling bar and text.
- Operators may toggle the Wire button IN and OUT which will inject or extract the selected wire, respectively. If Retract is selected the GUI will retract the wire.
- The Logbook button will print the generated image to the LCLS physics E-Logbook.
PROCESSING BOX
- Jitter correction can be selected and corrects for signal jitter generated by the wire, picked up by the PMT.
- Charge norm. ???? dont know what it does...
- Select the desired PMT for receiving signal from the selected wire by pulling this menu down and clicking the PMT. Default PMTs can work most of the time but not always. PV names look like, PMT:LIXX:###. In the graph to the right are many traces and IDs of different colors for different PMTs/BPMs/TOROs. You may visualy determine which PMT is receiving the proper amount of signal and select that one for measuring beam size. This is where you would see the saturated PMT or the "not enough signal" PMT. Be sure to pick one with high signal to noise ratio.
- Select the desired BPM or TORO in the menu below that of the PMTs. These devices are used in jitter correction and charge normalization.....????????????????????
- A list of BPMs used???????????????????????
DISPLAY BOX
- Method Select is a slider with 7 options of methods to fit the data plotted. 1 = Gaussian
2 = Asymetric Gaussian
3 = RMS
5 = RMS Cut Peak
6 = RMS Cut Area
7 = RMS Cut Floor - X Plane, Y plane and U Plane can ONLY be selected individualy for the GUI to measure beam size in that plane, unlike the OTR scans.
- Check the Show Selected box if you would like to see JUST the selected PMT signal in the graph to the upper right.
- Check the Show Dispersion box if you would like to see the effects of dispersion on the measurement. ???????????????
WIRE PARAMETERS BOX
- X Wire, Y Wire and U Wire can be selected by checking the associated box. Only one plane at a time can be selected. The range of the wire can be chosen by either typing numerical values or by clicking 'Pick'. This will bring up a dotted line in the lower graph (left side if inner is selected and right side if outer is selected) showing the current inner/outer limit of the wire range (in microns). Place the cursor over the desired X axis value and click to change the limit. You may click in the grey area if the range must be wider. This is useful after making a measurement and noticing the scan did not pick up the complete distribution.
- check the Auto Center box if you would like the scan to be centered in the lower graph.
- Scan pulses is the number of beam pulses incident on the wire from the begining to the end of the scan range.
- Set width will save the current range of the wire selected (X,Y or U) as a default range.
- Offset???????????????????????????