A PERMANENT MAGNET UNDULATOR FOR FREE ELECTRON LASER

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A PERMANENT MAGNET UNDULATOR FOR FREE ELECTRON LASER

C. Bazin, J. Ortega, D. Deacon, C. Depautex, P. Elleaume

To cite this version:

C. Bazin, J. Ortega, D. Deacon, C. Depautex, P. Elleaume. A PERMANENT MAGNET UNDULA-

TOR FOR FREE ELECTRON LASER. Journal de Physique Colloques, 1984, 45 (C1), pp.C1-317-

C1-319. �10.1051/jphyscol:1984164�. �jpa-00223720�

JOURNAL DE PHYSIQUE

Colloque C1, suppl6ment au

1, Tome 45, janvier 1984 page CI-317

A PERMANENT MAGNET UNDULATOR FOR FREE ELECTRON LASER

C. Bazin, J .M, Ortegar, D.A.G. Deaconrr, C. Depautex and P. ~ l l e a u m e * ~ ~ L.U.R. E., BCt. 209 C, Universite' Paris-Sud, 91405 Orsay, France

IE.

S. P.C., 10 rue VauqueZin, 75231 Paris Cedex 05, France

rr Deacon Research, 3790 EZ C&no ReaZ, N o 162, Palo A l t o , CA 94306, U.S.A.

rr*Dpt. de Physico-Chimie, C.E.N. SacZay, 91191 Gif-sur-Yvette, France

R6sum6

Optimisation du champ magnbtique d'un onduleur pour laser & 6 l e c t r o n s libres & partir d e mesures magn6tiques d e s aimants constituant l'onduleur.

Abstract

A magnetic study o n 3 0 0 REC magnets allows us a magnetic field optimization of the undulator built w i t h these magnets.

A undulator h a s b e e n designed w i t h permanent magnets in order to replace t h e previous superconducting magnet (I).

T h e magnet structure is the classical arrangement defined by

H A L B A C H . The magnets are rotated by f r o m one position to the

following a l o n g the undulator. 2

CHARACTERISTICS

Undulator

- f u l l length - period

- n u m b e r of periods - transverse p o l e width

- m i n i m u m gap Individual magnet

- Samarium-cobalt - dimensions

- Remanence - coercive f o r c e - specific energy

Recoma 2 0

5 0 x 19 x 19 m m 3 0.9 T

7 0 0 k A / m 160 k J / m '

The permanent magnets a r e n o t perfect and present imperfections.

In first approximation w e only consider the remanent field dispersion.

I n order to study the effect of this dispersion w e arranged randomly the different magnets along the undulator

the electron trajectory is d i s t o r t e d , the magnitude and shape of the spontaneous emission a r e modified.

F o r example

for + 7% FWHM dispersion o n field remanent,25 % of spontaneous emission is lost (2)

Individual measurements :

The magnets have b e e n measured w i t h a H A L L p r o b e f o r all the field By in t w o points A and B , and for some a measure of the field profile By(X) at a distance of 2 0 m m a b o v e and b e l o w the magnet

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984164

CI-318

f a c e s (fig I )

JOURNAL DE PHYSIQUE

A x By (gauss)

t=20-

.o o '0 5--A'

W e c a n see two types of imperfection :

- a discrepancy in m a g n i t u d e (inhomogeneities in the magnetiza- tion)

- a shift in position (the remanent field is n o t parallel to the magnet block vertical side. T h e r e s u l t of the A , B measurements a r e put in a diagram w h i c h the shape of the distribution looks like an ellipse. With the aid of this diagram (fig

w e arrange the magnets into the undulator in such a way to compensate the field dispersion between magnets. T h e vertical magnets a r e chosen to h a v e the narrowest possible field distribution n e a r the a v e r a g e and each vertical magnet is surrounded by a weak-strong pairs of horizontal magnets. F o r m o r e details s e e ref (3)

U n d u l a t o r magnetic measurements

M a g n e t i c measurements h a v e b e e n carried out a l o n g the undulator a x i s with a H A L L probe d r i v e n by a stepping motor. T h e output of the p r o b e w a s digitized and the electron trajectory inside the undulator w a s calculed in real time using the equations :

W h e r e Vx and X a r e the transverse speed and d e v i a t i o n of the

electron in the undulator

T h e s u c c e s s o f our optimization method i s demonstrated by the measured field dispersion w h i c h is less than

1 % except f o r the first and last oscillation and the spectral distribution f o r the first h a r m o - nic of the emitted radiation (fig 3 ) w h i c h agrees w e l l with the theory and magnetic simulation. (the full width i s w i t h i n 1 % of the calculated v a l u e f r o m the measured field distribution ( 4 ) .

-

g $

Ez237.5 MeV K.2.07

A

References

( 1 ) B A Z I N C . , F A R G E Y . , L E M O N N I E R M . , P E R O T J . , P E T R O F F Y . , N I M 1 7 2 ( 1 9 8 0 ) 6 1 ( 2 ) O R T E G A J . M . , B A Z I N C . , D E A C O N D . A . G , D E P A U T E X C . , E L L E A U M E

N I M 2 0 6 ( 1 9 8 3 ) 2 8 1

( 3 ) O R T E G A J . M . , B A Z I N C . , D E A C O N D . A . G . J . of Applied P h y s i c s to be published

( 4 ) B I L L A R D O N M . , D E A C O N D . A . G . , E L L E A U M E P . , O R T E G A J . M . ,

R O B I N S O N K . E . , B A Z I N C . , B E R G H E R M . , MADEY J . M . J . , P E T R O F F Y . , and V E L G H E M .

J . P h y s i q u e 4 4 ( 1 9 8 3 ) C I - 2 9