Difference between revisions of "G2p optics procedure"

Revision as of 17:55, 14 June 2011

Initial Conditions

Beam Energy:             1.160 GeV (first pass beam)
Septum angle:            5.7 Degrees
Beam inclination:        5.7 Degrees
HRS and septum polarity: negative
Sieve-slit:              IN
Raster:                  Off
Target:                  No Target
Target Field:            2.5 T
Left HRS Momentum:       1.159 GeV/c (elastic carbon)
Right HRS Magnets:       1.159 GeV/c (elastic carbon)

(This plan assumes that the raster size and nominal beam position have already been previously established.)

General Notes

0) I would strongly suggest to perform the delta scan (sieve slit IN) with the target field at 0 T and 2.5 T. This will provide invaluable
information on how the target field changes the optics. I am not sure how easy it is to do this change and take into account the beam
inclination angle.

1) The optics runs with raster should be with the maximum raster size the experiment plans to use. However, it may not make sense to use
3 cm on the foil target. Hence, Jixie suggestion of 1 cm is probably adequate to check the raster affect on the optics.

2) We should probably do optics for both target angles: 20 degrees and 90 degrees. The two field directions should affect the scattered electrons differently.

3) At 1.16 GeV, I assume the septum saturation effect will probably be negligible. At the higher energies and momenta settings, we should make
a plan to study saturation affects. Do we need to decouple this affect from the target field affect?

4) Having an "extended" foil target with one foil at z = -5 cm and z = +5 cm will allow the full reactz (ytg) acceptance for g2p to be
calibrated. This will also allow us to check the vertex z position reconstruction at all momentum settings. A 10 cm separation for E97-110
was found to be adequate at scattered angles of 6 degrees. However, I have been told due to space limitations and field uniformity this option is impractical.

5)

Procedure

1) Request the desired current (100 nA). Perform beam diagnostics to verify that beam profile and positions are
reasonable. Fast feedbacks MUST be on and working.

2) Verify that the OTR's are out (both target and arc!) before taking optics data.

3) Before beginning a measurement in any kinematics, the shift workers must log the Hall A Tools screen and the magnet strip tool! Waiting for
the dipole magnets to settle is one of the key parts in taking good optics data.

  Remember to cycle the quadrupoles Q2 and Q3 when increasing momentum!

4) Start with delta=0% with the both spectrometers at 1.159 GeV/c and target field at 2.5 T.

  For all data runs optimize the rate such that the DAQ collects data at or below the maximum rate (4-8 kHz) by adjusting
  * beam current (~ 100 nA if possible)
  * keep prescale factors as low as possible with deadtime < 20%.
  Raster should be OFF at this point.

5) Take one 250k data run with this setup using the carbon foil target. Please analyze the data and verify you can see the foil and sieve slit pattern.

6) Perform elastic delta scan with one run at each setting for the optics target. Each file should have AT LEAST 250k.

  Remember to cycle the quadrupoles Q2 and Q3 when increasing momentum!
  The quality of this test is very important.  Please check all runs with the analyzer.  
  (central momenta are for 12C elastic)

(a)  4%    Momentum = 1.205 GeV/c (one run with raster on and off)
(b)  2%    Momentum = 1.182 GeV/c 
(c)  0%    Momentum = 1.159 GeV/c (one run with raster on and off)
(d) -2%    Momentum = 1.136 GeV/c 
(e) -4%    Momentum = 1.113 GeV/c (one run with raster on and off)
(f) -10%   Momentum = 1.043 GeV/c (one run with raster on and off)

7) Take an access and rotate the sieve slits to the OUT position.

8) Repeat delta scan. Take data with the optics target.

  Remember to cycle the quadrupoles Q2 and Q3 when increasing momentum!
  The quality of this test is very important.  Please check all runs with the analyzer.  
  (central momenta are for 12C elastic)

Again take a run with 250k each:

(a)  4%    Momentum = 1.205 GeV/c (one run with raster on and off)
(b)  2%    Momentum = 1.182 GeV/c 
(c)  0%    Momentum = 1.159 GeV/c (one run with raster on and off)
(d) -2%    Momentum = 1.136 GeV/c 
(e) -4%    Momentum = 1.113 GeV/c (one run with raster on and off)
(f) -10%   Momentum = 1.043 GeV/c (one run with raster on and off)