From: VAXK::LAO
Date:  7-DEC-1994  11:37:47
Description: C Coil and Diamagnetic Flux Compensation from LaHaye    

From:	VUSC::LAHAYE        7-DEC-1994 11:33:07.69
To:	LAO LAHAYE
CC:	
Subj:	CHANGES TO EFIT AND GETDIA
 
 
(1)  EFIT
  THE SWITCH LANG HAS PUT INTO THE EFITSNAP FILE ALLOWS SUBTRACTION
OF THE VACUUM PICKUP FROM THE C-COILS ON THE 67 AND 322 PROBES.
C-COIL PAIR "C79" HAS AN N=1 FIELD BTHETA COMPONENT WHICH THE 67 DEG PROBES SEE.
C-COIL PAIR "C139" HAS A SECTION AT 319 DEGREES WHICH HAS PICKUP ON THE
322 DEG PROBES.  THE POLOIDAL FIELD OF THE C-COIL SECTIONS IS RATHER
LIKE SIN(X)/X WHERE X IS THETA.  AT TYPICAL CURRENTS THERE ARE PICKUPS OF
UP TO +/- 50 GAUSS WHICH CHANGE SIGN ABOUT THE AXIS.  SUBTRACTION OF
THESE NON-AXISYMMETRIC FIELDS FROM THE PROBE ARRAYS BEFORE DOING THE EFIT
SHOULD MAKE A BETTER N=0 EQUILIBRIUM FIT. A SIMILAR SWITCH WAS EARLIER
PUT IN FOR THE N=1 COIL AND WAS IMPORTANT IN GETTING BETTER AGREEMENT ON
THE UPPER SEPARATRIX AND THOMSON.
 
(2)  GETDIA
  LANG HAS IMPLEMENTED AN AUTOMATIC, IE NO SWITCH, UPDATE OF THE DIAMAGNETIC
FLUX WHICH EFIT USES.  THE UPDATE HAS C-COIL PICKUP CORRECTIONS WHICH ARE
SIGNIFICANT AND ARE NOT HARDWIRED INTO DIAMAG3 POINTNAME FOR EXAMPLE BUT ARE
COMPENSATED FOR ONLY IN SOFTWARE.  IN ADDITION, NEW ABSOLUTE CALIBRATIONS
WHICH INCREASE FLUX BY 5% (TAKING INTO ACCOUNT BETTER MEASUREMENTS OF THE 
RESISTIVE DIVIDERS) ARE INCLUDED, UPDATED LINEAR COMPS FOR ALL F-COILS, 
ECOIL, ETC
AND A NON-LIEAR COMP FOR ECOIL AND BCOIL TOGETHER WHICH IS SIGNIFICANT
ONLY FOR HIGH ECOIL CURRENT, IE OHMIC SHOTS FOR EXAMPLE AT END OF FLATTOP.
FOR BEST DIAMAGNETIC STORED ENERGY ON OLD SHOTS EVEN WITHOUT THE C-COIL,
IT IS RECOMMENDED TO RERUN THE EFITS AS EARLIER COMP WAS BASED ON 1986
MEASUREMENTS AND WAS ONLY UPDATED IN 1989 TO ADD N=1 COIL COMP.
EXCEPT WHERE THE C-COIL IS ON, RESULTS WITH NEW CAL AND COMPS WILL NOT
BE SIGNIFICANTLY DIFFERENT IN GENERAL.
  NOTE THAT SOME SHOTS WITH PARTIAL C-COIL IN THE FIRST HALF OF 1994 BEFORE
ITS GENERAL USE USE NAMES INTSP1 AND INTSP3 RATHER THAN C79, C139, AND C199
AND WILL THUS NOT HAVE THE NEW C-COIL COMP.