by Mark Jones and Arun Saha
Last updated on 5/29/2002
Data taking STEPS
run harps with more than 5 microA CW
This is an invasive
On the HAC computer from Hall A Main Menu
click on blue menu near ARC Scanners and select Scanner Control Screen.
This wiindow will pop up:
Harp 5 (1HA1H03A ) is next to bpmA and harp
6 (1HA1H03B) is next to bpmB on the beam line
Harp 5 and 6 are SEM devices and do not need
PM tube HV
The above is after a scan of the harp for
an energy measurement. The following describes how to set it up for just
using harps 5 and 6.
Run with conditions (set
these conditions or the analysis code has trouble discriminating signal
Current: 5.0 microA
Arc Tuning: ACHRO
Command file name: data56 ( The example
above is for arc energy measurement where they used harps 1,2,3 and 4)
Make sure to hit the return button in the
entry space for the value to register
Don't worry about the Running command .
This is just feed back on the commands that have been carried out
after START button is pushed.
When everything is ready, click on the START
For command data56, the harp #5 will first
do a forward scan and at the end a red profile with 3 peaks will show up.
Then harp #6 will do a forward scan. Then harp#5 will proceed to
do a return scan and a green profile will show up. Both the profiles should
overlap each other. Then harp #6 will do a return scan. You can repeat
the scans as many times as you like, just save the good ones for later
analysis. The harp consist of three wires : the first into the beam
is a vertical wire ( this will give the horizontal width of the beam directly),
the next two are at 45 degrees to the vertical ( this will give a combination
and x and y width. If it is a circular beam of radius A then width of the
next two peaks will be A*sqrt(2) .
A good scan will have the signal strength
of the peaks between 5 and 10 volts. The gain of the signal can be adjusted
by selected an amplification from the blue box just below the plot. Typically
an amplification factor of 4 will work, but it is trial and error to find
the right factor.. If signal is saturated a red spot will appear next to
the plot and this flags a bad run.
Once you have conditions for a good run. If
you want to calibrate espace parameters: Start of CODA so that we have
a data on tape with the BPM information. Then start a HARP run. Once
you can a good run click on the Save button and stop CODA run.
On the NCD xterm hiresxt20
using the Accerlerator Main Screen:
One click on the blue
menu with the ! in it next to "Hall A" and select "Hall A Scanners and
Arc Intergral Analysis" and a window pops up
Click on Run arc-scan
and the window pops up:
First it only ask for
the run number. Type in the Run number and hit return. Then after a few
seconds , A the line for plot option appears. Click on button next
The following plot will
The top plot is for harp 6 and the bottom
plot is for harp 5. The x axis is microns. The harp consist of three
wires : the first into the beam is a vertical wire ( this will give the
horizontal width of the beam directly), the next two are at 45 degrees
to the vertical ( this will give a combination and x and y width. If it
is a circular beam of radius A then width of the next two peaks will be
A*sqrt(2) . The peak at the far right is for the vertical wire ,
so its width is directly the horizontal beam width. The two peaks ( countin
from the left ) are from the wires at 45 degrees and the width is a convolution
and the x and y width of the beam. If the beam is very small in y so y
width << x width then the widths of all the peak will be the same.
If the beam is very small in x so y width >> x width the width will be
the y width of the beam. In general the analysis program assumes the beam
spot is an ellipse and extracts the tilt angle and the size of the major
and minor axis and the y width of the beam is extracted from these numbers.
For the quality of the data one should zoom
in on the picture and check that the back and forth scans lie on top of
each other. If the beam moved during the scan then there might be two peaks:
the first for when wires went forward and then second when they were retracted.
Another possible problem is that fast feedback is off and the peaks look
Click on exit button
in HIGZ window. Then a window pops up with the results.
These results are not
corrected for the offset of the harp position relative to beam line. Click
on the OK button and then the quit button in the ARC-SCAN window. If one
to see details of the analysis click on the DATA1 and DATA2 buttons
that appear. Results for DATA1 (for this run the proper info of beam
current, tune was not set when taking data)
The results for DATA2:
One interest in looking
at DATA2 window is if the raster is on then one can get the baseline width
of the raster. For raster: Wire #3 is the vertical wire and so the
peak base width give the baseline width of the raster in the x direction.
For wires #1 and #2 the average peak base width
should agree and
it is the x width + the y width of the raster.
To get the corrected
position click on the Correct Arc-Scan button in the Beam Energy Measurement
window, then the window
enter the run number and hit return and then the window shows the survey
harp offset positions :
Select the latest survey ( in this case #24).
Then the results are shown
The run number is automatically updated to the next run. Quit by closing