# Presentation: 683035

## SD17 SNS Dipoles Measurements

**Animesh Jain**
*Superconducting Magnet Division*Brookhaven National Laboratory, Upton, NY 11973
- March 20, 2002

## Measuring Equipment

** ****	**Rotating coil to measure ***integral*** field harmonics. 	(2.49 m long; 163.8 mm diameter; 5 windings)
-  	Magnet is placed on a level stand.
-  	Measuring coil is nominally centered axially in 	the magnet.
-  	Measuring coil can be moved laterally to scan the 	entire magnet aperture.
-  	Measuring coil has survey fiducials to locate its 	position relative to the magnet.

- Animesh Jain, BNL

- March 20, 2002

## Field Scans at a Fixed Current

** ****	**The entire aperture region is scanned in 5 separate	measurements at different lateral positions of the 		measuring coil (Center, ±2” and ±4”)
-  	5 readings are taken at each position to ensure data 		quality. Typical noise in integral T.F. is ~0.002%
-  	Entire scan is done for two currents:		*I* = 4395A  (1.11 T.m, 1.0 GeV), and		*I* = 5409A  (1.33 T.m, 1.3 GeV)
-  	Measurements are done on the down ramp after one cycle 	to         (        = 4834A for 1.0 GeV and 5450A for 1.3 GeV).

- Animesh Jain, BNL

- March 20, 2002

## Field Quality as a Function of Current

** **	The field quality is also measured as a function of 	current in the central region of the magnet.
-  	Measurements are done on a down ramp after 	cycle to        (4834A for 1.0 GeV and 5450A for 1.3 GeV).
-  	Measurements are done at 4395A, 4300A, 4200A, 	4100A, 4000A, 3900A and 3770A for 1 GeV cycle.
-  	Measurements are done at 5409A, 5350A, and 	5300A to 4500A in 100A steps, in addition to the 	currents listed above,  for the 1.3 GeV cycle.

- Animesh Jain, BNL

- March 20, 2002

## Integral Transfer Function Problems

** **	After the first few magnets were measured, the 	integral transfer function began to show large magnet 	to magnet variation (up to ~0.25% from mean).
-  	Possible sources of measurement errors were ruled 	out by incorporating redundant current readouts, 	carrying out NMR measurements and measuring a 	previously measured magnet again.
-  	Possible role of remnant magnetization of iron was 	ruled out by carrying out measurements for negative 	polarity of current, and then for the positive polarity 	again. The results were insensitive to the polarity.

- Animesh Jain, BNL

- March 20, 2002

## Slide 6

- Animesh Jain, BNL

- March 20, 2002

## Shimming of the Dipoles

** **	After carefully considering several correction options, it 	was decided to use iron shims to correct the integral 	transfer function in all dipoles.
-  	The transfer function could be either reduced (by adding 	shims to the return legs) or increased (by adding shims 	under the pole), without requiring expensive and risky 	machining operations.
-  	POISSON (2-D) and TOSCA (3-D) calculations were 	carried out to verify that no unwanted harmonics were 	generated by shimming, even for the extreme cases.
-  	Two dipoles (one low and one high ITF) were shimmed on 	an experimental basis to verify the effectiveness of the 	shimming procedure. The results were as expected.

- Animesh Jain, BNL

- March 20, 2002

## ShimmingStatus as of20 Mar 2002

- Animesh Jain, BNL

- March 20, 2002

## Slide 9

- Animesh Jain, BNL

- March 20, 2002

## Slide 10

- Animesh Jain, BNL

- March 20, 2002

## Slide 11

- Animesh Jain, BNL

- March 20, 2002

## Slide 12

- Animesh Jain, BNL

- March 20, 2002

## Slide 13

- Animesh Jain, BNL

- March 20, 2002

## Slide 14

- Animesh Jain, BNL

- March 20, 2002

## (10 mil shims)

**(10 mil shims)**

- Animesh Jain, BNL

- March 20, 2002

## Slide 16

- Animesh Jain, BNL

- March 20, 2002

## Conclusions

** **	Shimming has been demonstrated to be an inexpensive 	and 	feasible solution to the transfer function problem.
-  	50% of all dipoles (100% of one lead configuration) 	have been measured, and shimmed.
-  	Measurements of shimmed magnets are in progress.
-  	As of today, eight magnets are “OK to use.”
-  	Shimming is optimized for 1.0 GeV operation (16X 	reduction in standard deviation).
-  	Standard deviation at 1.3 GeV operation is also 	reduced, but only by a factor of ~2.7.

- Animesh Jain, BNL

- March 20, 2002