Difference between revisions of "G2p optics procedure"

Revision as of 16:45, 14 June 2011

Initial Conditions

Beam Energy:             1.160 GeV (first pass beam)
Septum angle:            5.7 Degrees
HRS and septum polarity: negative
Sieve-slit:              IN
Raster:                  Off
Target:                  No Target
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.)

Procedure

1) Once beam has been sent back to the Hall, 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.

4) Start with delta=0% with the both spectrometers at 1.159 GeV/c.

For all data runs optimize the rate such that the DAQ collects data at or below the maximum rate (4 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 two 500k data runs with this setup using the carbon foil target.

6) Perform elastic delta scan with two runs at each point for both optics and Ta targets. Each file should have AT LEAST 500k.

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

(a)  0%    Momentum = 1.16 GeV/c (one run with raster on and off)
(b) -1%    Momentum = 1.150  GeV/c
(c) -2%    Momentum = 1.1383 GeV/c (one run with raster on and off)
(d) -3%    Momentum = 1.1266 GeV/c
(e) -4%    Momentum = 1.1150 GeV/c (one run with raster on and off)
(f) -10%   Momentum = 1.0454 GeV/c (one run with raster on and off)

7) To check for the effects of cross talk between the HRS's and while the sieve is in, we should also:

(This step assumes that the right HRS Q1 is operational. If it is not, then skip to step 8.)

(a) return left HRS to delta = 0 and take a run
(b) turn RHRS Q1 on (Momentum = 1.16 GeV/c) and take a run
(c) turn RHRS Q1 off and flip polarity to positive
(d) set RHRS Q1 50% of delta = 0 and take a run
(e) set RHRS Q1 100% of delta = 0 and take a run
(f) return Q1 polarity to negative, set to delta = 0 and take a run

8) Leaving the spectrometers in negative polarity, take an access and rotate the sieve slits to the OUT position.

9) Repeat delta scan. Take data with the optics target and possibly with the Ta foil. The beam current might have to be limited to 20-30 nA.
(The current limitation depends on the VDC performance at high rate).

Again take two runs with 500k each:

(a)  0%    Momentum = 1.16 GeV/c (one run with raster on and off)
(b) -2%    Momentum = 1.1383 GeV/c
(c) -4%    Momentum = 1.1150 GeV/c (one run with raster on and off)
(d) -10%   Momentum = 1.0454 GeV/c (one run with raster on and off)

If we are short on time, the (*)'ed points could be left out, but we should really try to get the data if we can.