MAGNETIC MEASUREMENTS FOR TUNING AND OPERATING A HYBRID WIGGLER

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MAGNETIC MEASUREMENTS FOR TUNING AND OPERATING A HYBRID WIGGLER

D. Nelson, M. Green, K. Halbach, E. Hoyer

To cite this version:

D. Nelson, M. Green, K. Halbach, E. Hoyer. MAGNETIC MEASUREMENTS FOR TUNING AND

OPERATING A HYBRID WIGGLER. Journal de Physique Colloques, 1984, 45 (C1), pp.C1-957-C1-

960. �10.1051/jphyscol:19841195�. �jpa-00223672�

JOURNAL DE PHYSIQUE

Colloque Cl, supplCment au no 1, Tome 45, janvier 1984 page Cl-957

MAGNETIC MEASUREMENTS FOR T U N I N G AND OPERATING A H Y B R I D WIGGLER

D.H. Nelson, M.I. Green, K. Halbach and E.H. Hoyer

Magnetic Measurement Engineering Group, L a w r e m e Berkeley Laboratory, University of CaZifornia, Berkeley, California 94720, U.S.A.

Usumk - Un wiggler hybrid,,vanadium-permendurlterre-rare-cobalt a dt6 dessing, construit et mesure au Lawrence Berkeley Laboratory (LBL) c o m e projet conjoint avec le Stanford Synchrotron Radiation Laboratory (SSRL) et le Exxon Research and Engineering Company. Cet article dkcrit deux tech- niques de mesures magnetiques utilisdes pour caractkriser et r6gler le wig- gler. Nous dkcrivons des mesures & l'aide d'un gaussmetre & effet Hall qui:

(1) confirmsrent et quantifisrent les distributions du champ sinusoidal du wiggler, et ( 2 ) calibrerent les ajustements du shunt B flux variable ce qui peut fournir un "reglage fin" pour les pbles individuels. Nous dkcrivons aussi les mesures des intkgrales de l'induction magnktique avec des bobines dtint6gration et des integrateurs Qlectroniques. Des bobines et intggrateurs furent utilisks pour (1) calibrer les courants "end-pole" requis pour annuler les intkgrales 2 demi-aimant, (2) mesurer l'intkgrale de la com- posante horizontale, et ( 3 ) mesurer les variations dans la position longitudinale dans le wiggler.

Abstract - ^{A hybrid,} vanadium-permendrirlrare-earth-cobalt (REC) wiggler has been designed, built, and measured at the Lawrence Berkeley Laboratory (LBL) as a joint project with the Stanford Synchrotron Radiation Laboratory (SSRL) and the Exxon Research and Engineering Company. This paper describes two magnetic measurement techniques used to characterize and tune the wiggler.

We describe Hall effect gaussmeter measurements that: (1) confirmed and quantified the wiggler sinusoidal field distributions, and ( 2 ) calibrated variable-flux-shunt adjustments, which can provide "fine-tuning" for indi- vidual poles. We also describe measurements of integrals of magnetic induc- tion with integral coils and electronic integrators. Coils and integrators were used to: (1) calibrate the end-pole currents required to zero the half-magnet integrals, (2) measure the horizontal-component integral, and ( 3 ) measure variations in single period integrals as functions of longitu- dinal position in the wiggler.

I - INTRODUCTION

A hybrid, vanadium-permendurlrare-earth-cobalt wiggler has been designed 111, built 121, and measured 131 at LBL as a joint project with SSRL and the Exxon Research gnd Engineering Company. This wiggler magnet will be the source of syn- chrotron radiation for Beam Line V 1 at SSRL 141. The wiggler has 27 periods each 7 cm long. The hybrid magnet design incorporates rare-earth-cobalt material in conjunction with vanadium-permendur poles to achieve high magnetic fields with short periods. It achieves peak fields of 1.21 T at a 1.2-cm gap and a 1.64 T at a 0.8 cm gap. An elevation section of the wiggler magnet is shown in Fig. 1.

(The measurement coordinate system is included in Fig. 1.)

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19841195

JOURNAL DE PHYSIQUE

I1 - MEASUREMENTS A. Equipment

The LBL general purpose Data Acquisition System (DAS), used for magnetic measure- ments of the wiggler is described elsewhere 151. Six data acquisition and five data processing programs were written for the wiggler measurements. Commercial Hall effect probes were used to measure three orthogonal components of magnetic induction. The three probes were calibrated to 0.1% and the effective centers were located to + ^{0.1 mm. A} holder located the three probes at common vertical and lateral positions, but separated longitudinally by a quarter "wiggler period"

(17.5 mm). The holder was mounted on a sled which moved 2.5 m longitudinally and 80 mm laterally. Additionally, three "line-integral coils" were designed, fabri- cated, and calibrated at LBL for measuring magnetic induction integrals.

B. Hall Effect Gaussmeter Measurements

1. Full z-range; -1100 1< z

+I100 mm, Az = 1 mm

A primary measurement objective was to characterize the periodic magnetic field distribution on a plane of symmetry (y = 0). The approach used was to measure on a uniform grid, to save large quantities of data, and then to use post-processing programs to extract and display details of interest. Figure 2 shows a real-time plot of By(x,O,z) at 2201 z-positions and 3 x-positions. Of immediate interest were accurate determinations of the peaklvalley magnitudes and positions and the values of the minor components Bx and BZ at the 53 z-positions where By = 0.

The DAS provided processed data minutes after these data were collected; addition- ally, the raw data are saved (with a backup), so that they are readily available for further analysis.

2. Stud Tuning Calibration Measurements

The calibration of the "variable-flux tuning studs" was accomplish'ed with the DAS programmed to function in a prompting mode, collecting data on command, and pro- viding imediate feedback of processed data so the operator could direct the next operation.

Each of the 57 vanadium-permendur pole pairs is equipped with 4 threaded holes that may accept tuning studs. The tuning studs for pole 129 are shown in Fig. 1.

Threading studs toward the poles reduces the local reluctance, thereby reducing flux-density in the corresponding working gap and simultaneously increasing the flux density in the working gaps of the adjacent pole pairs. This effect alter- nates and diminishes with distance from the adjusted poles, and magnitudes depend on both the gap and the stud position. Calibration involved positioning the ver- tical component Hall probe to the center of the working gap of a pole pair and measuring magnetic field changes due to adjusting sets of 4 tuning studs associ- ated with the five closest pole pairs. Because the field quality of the wiggler was adequate the tuning studs will not be used initially; however, to better equal-

ize the magnitudes of the peaks and valleys, the calibration data may be used in conjunction with an algorithm to determine the appropriate tuning stud positions.

C. Magnetic Induction Integral Measurements

Integral coils connected to electronic integrators determine magnetic field inte- grals more accurately than is practical by numerically integrating point measure- ments. The line-integral coils used for these measurements were conservatively designed to meet a 25 G-cm resolution requirement with a LBL Mod 71 electronic integrator capable of resolving 1 U V sec 161.

1. Half-Magnet, y-Component, z-Integral Measurements

The wiggler's two end pole pairs are equipped with coils to null the respective

half-magnet i n t e g r a l s (of t h e y-component). A technique was developed t h a t mini- mized t h e e f f e c t of m i s p o s i t i o n i n g t h e i n t e g r a l c o i l 171.

A combined d a t a a c q u i s i t i o n l d a t a processing program ( 1 ) prompts t h e o p e r a t o r t o measure t h e uncompensated i n t e g r a l , (2) allows t h e o p e r a t o r t o s u c c e s s i v e l y s e t end-pole c u r r e n t s , ( 3 ) measures and saves shunt p o t e n t i a l and i n t e g r a t o r o u t p u t p o t e n t i a l , and ( 4 ) p r o c e s s e s , p l o t s , and p r i n t s t h e h a l f magnet i n t e g r a l v s end pole c u r r e n t . Figure 3 i s a copy of t h e real-time p l o t a s s o c i a t e d with an h a l f - magnet i n t e g r a l measurement.

2. Full-Magnet, x-Component, z - I n t e g r a l Measurements

The h o r i z o n t a l ( x ) component was measured by f l i p p i n g (180° about t h e z-axis) a

+m

long i n t e g r a l c o i l and measuring changes i n flux-linkage due t o / ^Bxdz.

3 . F u l l Wiggler Period (70 mm) y-Component z - I n t e g r a l P r i o r t o mating t h e

s e p a r a t e l y t o check

upper and lower h a l v e s of t h e wiggler they were measured f o r sub-assembly e r r o r s . A s e n s i t i v e f u l l ( z ) - ~ e r i o d ( " n u l l " )

P

z+35 mm

c o i l was used t o d e t e c t v a r i a t i o n s i n _{2-35 mm} / B dz v e r s u s z a s t h e c o i l was ^y moved along t h e z-axis. No assembly e r r o r s were d e t e c t e d .

111 - SUMMARY OF RESULTS

A t t h e wiggler midplane, t h e v e r t i c a l magnetic f i e l d i s s i n u s o i d a l along t h e beam a x i s a s expected. The averaged maximum midplane magnetic f i e l d s , f o r 53 p o l e s (peaks and v a l l e y s ) a t v a r i o u s gap p o s i t i o n s a r e summarized below. The maximum e f f e c t s of a d j u s t i n g t u n i n g s t u d s a r e t a b u l a t e d . Since f o r small gaps t h e v a r i a - t i o n was b e t t e r than t 2 % , t u n i n g s t u d s have n o t been used. The end pole c u r r e n t s e t t i n g s were determined f o r 6 gaps, s o t h a t t h e v e r t i c a l f i e l d i n t e g r a l was l e s s than 50 gauss-cm f o r each h a l f of t h e wiggler. Below a r e given t h e uncorrected h a l f magnet f i e l d i n t e g r a l s . A t a 1.2 cm gap, a t o t a l c o r r e c t i o n range of 2740 gauss-cm o r 137 gauss-cmlampere i s a v a i l a b l e . End pole c o i l s e n s i t i v i t y i s given.

The measured midplane h o r i z o n t a l f i e l d i n t e g r a l of t h e e n t i r e w i g g l e r , which i s not a d j u s t a b l e , i s a l s o t a b u l a t e d .

Table I. Summary of s i g n i f i c a n t measurement r e s u l t s

Gap Peak/valley data Tuning-stud Uncorrected half End pole Wiggler 55-point Standard max. effect wiggler vertical coil horizontal

average deviation field integrals sensitivity field integral

(cm) (T) (T) (T) ofl'm) (aTm/A) OITm)

z < o

z > o

Acknowledgments

The a u t h o r s thank R. Avery, P. Eisenberger, T. E l i o f f , E. C. Hartwig, W. Hartsough,

H. P. Hernandez, D. A. S h i r l e y , L. J. Wagner, and H. Winick f o r p r o j e c t s u p p o r t .

W e a l s o a r e indebted t o R. Barton, L. Callapp, J. Chin, S. K l i n g l e r , J . Hodges,

C. S i l v a , J. Wirth, and t h e e n t i r e LBL Assembly Shop f o r t h e i r a s s i s t a n c e . This

work was supported by t h e D i r e c t o r of Energy Research, O f f i c e of Basic Energy

Sciences, M a t e r i a l s Sciences Division of t h e U.S. Department of Energy under

Contract No. DE-AC03-76SFOOC98.

Cl-960 JOURNAL DE PHYSIQUE

--SSRL UICCLER ZllaP

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FULL RUN

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Pig. 2. R e a l time p l o t of 6603 d a t a p a i r s : B (x,O,z) v s z; x = 0, x = -10 m, and x Y = +10 m; Az = 1 mm.

F i g . 1. Beam L i n e V I Wiggler, showing measurement c o o r d i n a t e system w i t h o r i g i n

c e n t e r e d a t p o l e p a i r 29.

--SSRL UltCLER B i L v r I

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C$:8n? !:!u~E%R!:::Ek"~D % E > l t ! k ~ S THRICE

Fig. 3. Half magnet i n t e g r a l c o i l d a t a .

R e f e r e n c e s

1. HALBACH, K., T44 (1983) C1-211.

2. HOYER, E. e t a l . , LBL r e p o r t LBL-15115 (March 1983).

3. NELSON, D.H. and GREEN, M.I., LBL E l e c t r o n i c s E n g i n e e r i n g Report MT 327, LBID-755 (May 1983).

4. HOYER, E. e t a l . , N I M 208,(1983) 117-125. Also a v a i l a b l e a s LBL r e p o r t LBL-14773 (1983).

5. GREEN, M.I. and NELSON, D.H., MT 8 , S e c t i o n 1E3-02 (September 1983). Also a v a i l a b l e a s LBL r e p o r t LBL-15365 (1983).

6. NELSON, D.H., LBL E l e c t r o n i c s E n g i n e e r i n g Report M T 329, LBID-768 ( J u l y 1983).

7. NELSON, D.H., LBL E n g i n e e r i n g Report MT 324 ( J a n u a r y 1983).