LCLS 001047 Fast Feedback corrector Dc current measurements. 

Physical Coil Length = 21.438 inches or 54.45 cm

Magnet alignment on Test stand:  The magnet coils are vertically aligned and the magnet was measured  on the East West line with the power leads on the west end of the magnet. Looking from West to East the magnetic field in the middle of the magnet points to the left and this gives a positive hall probe reading.  Looking the same way the positive terminal is on the right and the negative terminal is on the left.

The background field is -0.000065 Tesla.  ( Earth’s field is ~4.5 gauss, so there is a 2 gauss extra field from the test stand area)

The average effective length using the coil and hall probe data is: 4.8071e-001 +/- 6.6634e-004 .
This uses all of the data below which has the test stand background field (earth’s field plus a bit more) taken out of both measurements.

Current 	Integrated Field         Hall Field             Effective Length
(Amps)		    (Tm)		    (T)                      (m)

-2.0		2.9894e-003		-6.2175e-003		4.8080e-001
-1.0		1.4942e-003		-3.1067e-003		4.8095e-001
-0.5		7.4504e-004		-1.5493e-003		4.8090e-001
-0.25		3.7319e-004		-7.7427e-004		4.8198e-001
0		0.0	    		    0.0			    N/A
0.25		3.3372e-004	     	7.7600e-004	    	4.7960e-001
0.5	        7.1369e-004	     	1.5480e-003	    	4.8054e-001
1.0		1.4788e-003	   	 3.1058e-003		4.8043e-001
2.0		3.0061e-003       	 6.2141e-003		4.8048e-001

The measurements were done with the magnet pointed in the direction of the LCLS.  When the test stand background field of 0.65 (earth’s field plus a bit extra from the test stand) is left in, the effective length changes with the sign of the current.  The mean effective length for all the currents is: 4.8016e-001 +/- 1.2581e-002 m.  If the background field is on the order of the earth’s field where the corrector is placed, the field strength of the corrector  strength could be effected by +/- 2.5%.  The raw data is below.  

Current 	Integrated Field         Hall Field             Effective Length
(Amps)		    (Tm)		    (T)                      (m)

-2.0 		3.0359e-003 		-6.2832e-003 		4.8318e-001
-1.0		1.5407e-003 		-3.1725e-003		4.8566e-001
-0.5		7.9159e-004 		-1.6150e-003  		4.9015e-001
-0.25		4.1975e-004 		-8.4000e-004  		4.9970e-001
0.0 		4.6811e-005 		-6.5727e-005  		7.1220e-001
0.25 		3.2569e-004 		 7.1027e-004  		4.5854e-001
0.5 		6.9737e-004 		 1.4823e-003 		4.7047e-001
1.0 		1.4456e-003		 3.0401e-003  		4.7552e-001
2.0		2.9393e-003		 6.1484e-003  		4.7805e-001