WORKS ON CHINESE PRIMARY FREQUENCY STANDARDS

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WORKS ON CHINESE PRIMARY FREQUENCY STANDARDS

Yang Xiaoren

To cite this version:

Yang Xiaoren. WORKS ON CHINESE PRIMARY FREQUENCY STANDARDS. Journal de

Physique Colloques, 1981, 42 (C8), pp.C8-257-C8-260. �10.1051/jphyscol:1981832�. �jpa-00221727�

page

WORKS ON CHINESE PRIMARY FREQUENCY STANDARDS

Presented by : YANG XIAOREN

rime and Frequency Laboratory, National I n s t i t u t e of MetroZogy, Beijing, China.

A b s t r a c t : T h i s p a p e r g i v e s some s p e c i f i c f e e t u r e s and t h e eva- l u a t i o n r e s u l t s of t h e Chinese p r i m a r y f r e q u e n c y s t a n d a r d s . Some i n v e s t i g a t i o n s on t h e f r e q u e n c y s h i f t s due t o t h e Plillman e f f e c t and t h e Majorana e f f e c t a r e d i s c u s s e d .

The Chinese P r i m a r y Frequency S t a n d a r d s :

I n t h e E l e v e n t h Annual P r e c i s e Time and Time I n t e r v a l Applica- t i o n s and P l a n n i n g Meeting ( 1 9 7 9 ) , we had r e p o r t e d t h e cesium p r i - mary f r e q u e n c y s t a n d a r d Cs-2 developed by t h e N a t i o n a l I n s t i t u t e of Metrology (IJIM) ,China. I t s t o t a l u n c e r t a i n t y was 1 . 2 ~ 1 0 - ~ ~ ( 1 ~ ) , and

i t s f r e q u e n c y s t a b i l i t y was s ( T = l hour)=5x10-'~.

I n t h e beam t u b e of (2.3-2, Y we used d i p o l e s t a t e - s e l e c t o r mag- n e t s , a n i n t e r a c t i o n l e n g t h of 3.68 m e t e r s , a niobium r i b b o n i o n i z e r and a t w o - d i r e c t i o n beam o p e r a t i o n . i;e a p p l i e d s q u a r e wave phase m o d u l a t i o n t o t h e e g s t a t i o n s i g n a l s , s o t h s t by s h i f t i n g t h e phase of t h e r e f e r e n c e s i g n a l s we might d e t e r m i n e whether t h e r e was any phase d i f f e r e n c e o r n o t between t h e two e n d s of t h e microwave c a v i t y . I n s t e a d of t h e commonly used twin-T s e l e c t i v e a m p l i f i e r , we used a synchronous i n t e g r a t o r f o r t h e f i l t e r i n g of n o i s e s i n t h e e r r o r s i g - n a l s , s o t h a t c r i t i c a l r e q u i r e m e n t s o n t h e s t a b i l i t y of t h e modula- t i n g f r e q u e n c y a s w e l l a s on t h e v a l u e s of t h e R , C components and t h e i r t e m p e r a t u r e s t a b i l i t y might be g r e a t l y reduced. I n o r d e r t o o b t a i n s u f f i c i e n t phase s h i f t f o r t h e r e f e r e n c e s i g n a l s , we used a monostable t r i g g e r e d phase s h i f t e r t h a t p o s s e s s e d a d u t y r a t i o of a b o u t 0 t o 1. A 1 1 of t h e beam t u b e components and t h e e l e c t r o n i c c i r c u i t s were d e v e l o p e d i n o u r l a b o r a t o r y .

I n t h e y e a r 1980 w e made some improvements on t h e magnetic f i e l d d i s t r i b u t i o n i n t h e two t r a n s i t i v e s e c t i o n s i n t h e beam t u b e t o r e d u c e t h e Majorana e f f e c t i n t h e s e two r e g i o n s , s o t h a t t h e C f i e l d p o l a r i t y e f f e c t might be l e s s e n e d . A s t h e a c c u r a c y of o u r cesium p r i m a r y f r e q u e n c y s t a n d a r d was n o t s o h i g h and t h e r e was y e t no b e t t e r method t o manage t h e C f i e l d p o l a r i t y e r r o r f o r t h e moment,

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1981832

C8-258 JOURNAL DE PHYSIQUE

t h e s g s t e m a ~ i c f r e q u e n c y e r r o r was adopted a s zero while t h e A,B,C magnetic f i e l d s were i n t h e same s e n s e with t h e h o r i z o n t a l component of t h e E a r t h ' s magnetic f i e l d . To e v a l u a t e t h e second o r d e r Doppler e f f e c t , we used t h e method of a n a l y s i n g t h e r e c o r d e d Ramsey p a t t e r n and c a l c u l a t i n g t h e e f f e c t from it by t h e u s e of e l e c t r o n i c computer. 1 A t t h e end of 1980 we made a r e e v a l u a t i o n of Cs-2, t h e r e s u l t s of which were l i s t e d i n t a b l e 1 , and t h e t o t a l u n c e r t a i n t y was reduced t o 4 . 1 x 1 0 - ~ ~ ( 1 c r ) . A t t h e same time t h e frequency s t a b i l i t y of Cs-2 was reduced -Lo o- ( T = l h o u r ) = 3 ~ 1 0 - ~ ~ due t o t h e u s i n g of a lower- phase-noise f r e q u e n c y m u l t i p l i e r c h a i n and a l a r g e r s e r v o l o o p g a i n . Y

I n o r d e r t o make a b e t t e r comprehension of t h e r e p r o d u c i b i l i t y of t h e cesium primary f r e q u e n c y s t a n d a r d a s w e l l a s i t s frequency d r i f t and t o e s t a b l i s h a mutual r e f e r e n c e s t a n d a r d f o r t h e a c c u r a c y e v a l u a t i o n , we developed a n o t h e r cesium primary f r e q u e n c y s t a n d a r d Cs-3 of t h e same d e s i g n a s Cs-2. A t t h e end of 1980 we a l s o made a n e v a l u a t i o n of Cs-3, t h e r e s u l t s of which were a l s o l i s t e d i i n table 7 ,

and t h e t o t a l u n c e c t a i n t y was ~ . ~ x I o - ~ ~ ( I u - ) . Thus, i n c a s e we should want t o make some m o d i f i c a t i o n s i n t h e cesium primary f r e q u e n c y s t a * d a r d , we could s t i l l keep one of them i n normal o p e r a t i o n .

TABLE I

The e r r o r s of Cs2 an6 Gs3

B i a s s o u r c e s

?.Cavity phase s h i f t 2.RF spectrum

2-order d o p p l e r j ' s h i f t

4.Servo system e r r o r 5.Hc

6.- $ KC2

7.'m 4 Rqr)

P u l l i n g by neigh- 8'bouring t r a n s i t i o n s

9. C a v i t y p u l l i n g T o t a l

c s 3 Cs2

B i a s (XIO-12) -14.0 -29.6 -5.9

0 +6.2

0 O 0 0 -43=3 B i a s

( x ~ ~ - 1 2 ) +5.48

-1.11 -0.7

0 +I. 94

0 O 0 0

+5.6

U n c e r t a i n t y (XIO-13)

*2.5 23.2 ao. 3 t1.3

t o * ³

k0.2

;to. 0 3 t0.02

~ 0 . 6 k4.5 ( 1,) U n c e r t a i n t y

( x ~ ~ - 1 3 ) b2.5

a2.5

kfJ

5 k2.0 20.1 10.2 rt0. I k0.02

~ 0 . 6

k4.1

( 1 5 )

quency s h i f t s due t o t h e Piillman e f f e c t and t h e E~ajorana e f f e c t . W e a l s o concluded i n t h a t , i n o - t r a n s i t i o n s t h e r e would be no such M i l l - man e f f e c t ,as mentioned by S.L.Hahn 2 .

Although t h e Majorana e f f e c t i n t h e t r a n s i t i o n s e c t i o n i n t h e beam t u b e would n o t d i r e c t l y c a u s e any frequellcy s h i f t i n t h e (4,O) t*(3,0) t r a n s i t i o n , b u t it d i d cause t h e frequency s h i f t s mentioned by D.W.Allan 3 through t h e mixing of t h e energy s t a t e s . Moreover,

atoms between t h e ( 4 , O ) and t h e ( 4 , - 4 ) s t a t e s , i n d u c e d by t h e Majorana e f f e c t , would a r r i v e a t t h e i o n i z e r t o g e t h e r w i t h t h e f l o p - i n atoms, o r p a r t l y a r r i v e a t t h e i o n i z e r t o g e t h e r w i t h p a r t of t h e f l o p - o u t atoms (due t o i m p e r f e c t beam o p t i c s ) . This would change t h e o r i g i n a l v e l o c i t y d i s t r i b u t i o n of t h e (4,O)-(3,O) t r a n s i t i o n atoms, and s o change t h e velocity-dependent f r e q u e n c y s h i f t s .

I n t h e e x c i t a t i o n s e c t i o n and t h e d r i f t s e c t i o n i n t h e beam t u b e , t h e c o u p l i n g of t h e Majorana t r a n s i t i o n s with t h e (4,O)-(3,O) t r a n s i t i o n would cause f r e q u e n c y s h i f t . I n t h e c a l c u l a t i o n we chose a six e n e r g y - s t a t e approximation model a s shown i n f i g u r e 1. Consi- d e r i n g of a l l t h e p o s s i b l e microwave and r . f . n t r a n s i t i o n s among t h e s e (4,1),(4,0),(4,-1),(3,-1),(3,0) and ( 3 , l ) s t a t e s , we used t h e m u l t i - s t a t e m u l t i - t r a n s i t i o n method t o f i n d t h e i r f r e q u e n c y s h i f t i n g e f f e c t on t h e (4,0)-(3,O) t r a n s i t i o n . The work was n o t y e t f i n i s h e d .

FIGURE 1

Six-energv s t a t e model

C8-260 JOURNAL DE PHYSIQUE

B e s i d e s , i n some p r a t i c a l c i r c u m s t a n c e s , owing t o t h e Majorana e f f e c t i n t h e t r a n s i t i v e s e c t i o n i n t h e beam t u b e snd owing t o t h e d i f f e r e n t f o r c e s e x e r t e d by t h e d e f l e c t i n g magnetic f i e l d , o n t h e atoms i n d i f f e r e n t energy s t s t e s , t h e atoms i n d i f f e r e n t i n i t i a l e n e r g y s t a t e s might have d i f f e r e n t o ~ u p a t i o n s . T h i s would g i v e r i s e t o t h e f r e q u e n c y p u l l i n g of t h e ( 4 , 0 ) 6 ( 3 , 0 ) t r a n s i t i o n by t h e ^7T t r a n s i t i o n s . We had used t h e method of ~ . ~ a r r a c h ~ t o g e t a formula s i m i l a r t o h i s e q u a t i o n (25), and found t h a t t h e f r e q u e n c y s h i f t c a l c u l a t e d from i t would be much l a r g e r t h a n t h a t c a l c u l a t e d by t h e method of N.F.Ramsey . ( H e r e i n , t h e f r e q u e n c y s h i f t caused b.y t h e Millman e f f e c t of t h e microwave-rf t r a n s i t i o n s might i n c r e a s e c o r r e s - pondingly.) A t t h e moment, we had a l s o a p p l i e d t h e m u l t i - s t a t e m u l t i - t r a n s i t i o n method t o t h e c a l c u l a t i o n of t h i s frequency s h i f t .

R e f e r e n c e s :

I.C.Audoin, e t a l , IEEE Trans., IM-23,(1974), 501.

2. Hahn S.L., B u l l . Acad. Pol. S c i . Tech., 3 (1975) 249-

3. A l l a n D..d., e t a l , Proc. 3 1 s t Symp. on Freq.Sontro1 (1977) 10.

4. Harrach d., NBS Tech. Note 343 (1966).