Volume 34A. n u m b e r 4
PIiYSICS
LETTERS
8 March 19~1
a T = 3.2 × 10 -14 c m 3 ' s e c . T h e y o b t a i n e d a n e x p e r i m e n t a l v a l u e of 2.7 × 10 -14 c m 3, ' s e c f o r a at a t m o s p h e r i c p r e s s u r e , w h i l e A l e k s a n d r o v et al. [3] o b t a i n e d a v a l u e of 4 × 10 -11 c m 3 , ' s e c at an e l e c t r o n d e n s i t y 2 × 1016 c m -3 and a t e m p e r a t u r e of 9 0 0 0 ° K . T h e a g r e e m e n t b e t w e e n e x p e r i m e n t a l a n d t h e o r e t i c a l v a l u e s i s good. This preliminary result indicates a useful techn i q u e f o r s t u d y i n g d e c a y p r o c e s s e s in d e n s e p l a s ma.
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One of u s , A. S h a m i n , i s g r a t e f u l to t h e G o v e r n m e n t of P a k i s t a n f o r g r a n t i n g s t u d y l e a v e . T h e a u t h o r s e x p r e s s t h e i r g r a t i t u d e to M e s s r s . J . H e n l e y , W. H o w e l l a n d J . T a y l o r f o r a s s i s t a n c e in constructing apparatus.
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Fig. 2. Variation of plasma t e m p e r a t u r e with time a f t e r the application of a pulsed magnetic field. The t e m p e r a t u r e was m e a s u r e d 0.3 em above the top of the rf coil.
References [1] D.W. Hughes and E. R. Wooding. Phys. L e t t e r s 24A (1967) 70. [2] R. V. Mitin and K. K. Pryadkin. Sov. Phys. Techn. Phys. 13 (1969) 1398. [3] V. Ya. AIeksandrov. D.B. Gurevich and I. V. Podmoshenskii. Opt. and Spectrosc. 24 (1968) 178.
a n d P r y a d k i n [2] d e d u c e d a t h e o r e t i c a l f o r m u l a f o r t h e r e c o m b i n a t i o n c o e f f i c i e n t w h i c h , at the m e a n t e m p e r a t u r e of 11 1 0 0 ° K e x i s t i n g i n the p r e s e n t p l a s m a , l e a d s to a v a l u e :
ANOMALOUS PROPERTIES
EFFECTS OF
TYPE
OF
LENGTH
ON
I SUPERCONDUCTING
THE
FIELD HOLLOW
TRAPPING CYLINDERS
*
D. G. S C H W E I T Z E R Brookhaven National Laboratory, Upton. New York, USA Received 15 F e b r u a r y 1971
Thin walled hollow cylinders of type I superconductors in which the walls are annealed and etched exhibit a maximum in the trapped field with length of the cylinder. The effect does not occur in the same s a m p l e s when the s u r f a c e s are strained.
E x p l a n a t i o n s [ 1 - 4 ] of t h e f i e l d t r a p p i n g p r o p e r t i e s of f i n i t e t y p e I s u p e r c o n d u c t i n g h o l l o w c y l i n d e r s h a v e f o c u s s e d on g e o m e t r y e f f e c t s a s sociated with the intermediate state. In r e c e n t w o r k [5] it w a s f o u n d t h a t a l o n g w i t h geometry factors, the shielding and field trapp i n g p r o p e r t i e s of t h i n - w a l l e d t y p e I s u p e r c o n ducting hollow cylinders are markedly dependent * This work was p e r f o r m e d under the auspices of the US Atomic Energy Commission. 220
on s u r f a c e s t r a i n s . T h e b e h a v i o r of t h e s e s y s t e m s i s a n o m a l o u s in t h e s e n s e t h a t a n n e a l e d high purity hollow cylinders exhibit properties t h a t d e v i a t e f r o m t h e o r y [6] w h i l e s a m p l e s in w h i c h the s u r f a c e s a r e s t r a i n e d s h o w p r o p e r t i e s m o r e c o m p a t i b l e w i t h t h e o r e t i c a l p r e d i c t i o n s . In p r e v i o u s s t u d i e s [5] t h e d e v i a t i o n s in s h i e l d i n g and field trapping properties were studied as f u n c t i o n s of w a l l t h i c k n e s s . H e r e we s u m m a r i z e work showing that additional anomalous behavior is associated with the field trapping properties
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Fig. 1. Field trapping versus length in thin walled hollow cylinders of type I superconductors with etched and strained surfaces. v e r s u s length in thin walled high p u r i t y annealed type I s u p e r c o n d u c t i n g hollow c y l i n d e r s . Again, the a n o m a l i e s do not o c c u r in thick walled (> 0.1 cm) s a m p l e s or in thin walled s a m p l e s in which the s u r f a c e s a r e s t r a i n e d . The methods f o r p r e p a r i n g the s a m p l e s and the techniques f o r s t r a i n i n g and annealing a r e the s a m e as those r e p o r t e d e a r l i e r [5]. The p a r a m e t e r m e a s u r e d in t h e s e s t u d i es is the field r e t a i n e d in the void of a hollow c y l i n d e r a f t e r an e x t e r n a l f ie ld e x c e e d i n g H c is applied and r e m o v e d . The applied f i e l d s w e r e g e n e r a t e d by a solenoid which was 35 cm long and t h e r e f o r e much l o n g e r than the s a m p l e s . In al l c a s e s it was v e r i f i e d that the s a m p l e was c o m p l e t e l y n o r m a l b e f o r e the a p pl i e d f i el d was reduced. The data shown in fig.1
8 March 1971
for san d b l ast ed s a m p l e s co n f i r m the p r o p e r t i e s expected f o r finite hollow c y l i n d e r s ; n a m e l y , that the field trapping i n c r e a s e s with length and a p p r o a c h e s H c in long c y l i n d e r s . The data f o r the annealed and etched s a m p l e s a r e noticeably different. In t h ese c a s e s the field trapping goes through a m a x i m u m with length. Both the m a g nitude of the r e t a i n e d field and the length at which the m a x i m u m o c c u r s depend upon wall thickness. Th e r e t a i n e d fields o b s e r v e d in Pb and Sn hollow c y l i n d e r s a r e plotted as f r a c t i o n s of the c r i t i c a l field to i l l u s t r a t e that the b e h a v i o r is c h a r a c t e r i s t i c of type I m a t e r i a l s at d i f f e r e n t t e m p e r a t u r e s . In a m o r e c o m p l e t e study in which the field d i s t r i b u t i o n along the axis was d e t e r mined, we will show that the b e h a v i o r is not due to fall off at the ends. F o r the p r e s e n t we e m p h a s i z e that t h ese a r e unexpected g r o s s p r o p e r ties that depend upon s u r f a c e conditions r a t h e r than m a c r o s c o p i c g e o m e t r y effects.
References [1] D. Schoenberg, Superconductivity (Cambridge University Press, Cambridge, New York, 1952) pp. 27-34. [2] D. L. Coffey, W. F. Gauster and H. E.Rorschach Jr., Appl. Phys. Letters 3 (1963) 75. [3] C.P. Bean and M. V. Doyle, J. Appl. Phys. 33 {1962) 3334. [4] J.D. Livingston and H. W. Schadler, Progr. Mater. Sci. 12 (1964) 209. [5] D. G. Schweitzer, Phys. Rev. 173 (1968) 461. [6] F. London, Superfluids (Dover Publications Inc., New York, 1960) Vol. ], plc. 11, 47-51, 125-30.
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