RESEARCH N e w Routes to Fusion Power? AEC r e v e a l s three new Project S h e r w o o d a p p r o a c h e s t o c o n t r o l l e d thermonuclear reactions
STELLARATOR (Pretzel Type)
MIRROR
HOT 34
C&EN
MACHINE
ION MAY
INJECTION 19,
1958
T HE VEIL OF SECRECY
around
U . S.
research on controlled thermonuclear reactions has lifted slightly. AEC scientists gave delegates t o the American Physical Society m e e t i n g in Washington, D . C , a peek at some of the fusion research u n d e r way in Project Sherwood. But it was only a peek; details will b e revealed a t the Geneva Atomsfor-Peace Conference next September. At the time A E C a n n o u n c e d achievement of a controlled fusion reaction using the "pinch effect" to contain the reaction (C&EN, F e b . 3, page 23) A E C spokesmen said work was being done on three other approaches to the problem. At t h e APS meeting, AEC for the first time revealed w h a t these approaches are: the Stellarator (often mentioned, b u t never d e s c r i b e d ) , the mirror machine, a n d h o t ion injection. But AEC disclosed little more than the basic principles of operation of these devices. Spokesmen refused t o answer questions on w h a t temperatures h a v e been reached, w h e t h e r a thermonuclear reaction has been achieved, of w h a t the outlook is for power production. According to AEC's Arthur E. Ruark chief of Project Sherwood, more details will be disclosed at Geneva where some 60 papers on fusion research are scheduled for presentation. It is far too soon to guess what the future fusior p o w e r producer will b e like, Ruark says. Perhaps one of t h e new approaches will do the trick; perhaps a combination of methods will work. Here's how t h e new systems work: • Mirror Machine. T h i s machine, developed at University of California's Radiation Laboratory at Livermore Calif., consists of a long straight tube surrounded by coils of wire. Current passed through the coils produces a magnetic field inside the t u b e . At the ends of the t u b e , a much stronger than average current is applied; this squeezes the lines of force at the ends of the tube. Result: Lines of force in the tube look like an elongated foot ball. Hot plasma is confined in the center of the football-shaped region. The constricted lines of force at the e n d s act like magnetic mirrors to reflect plasma particles, h e l p prevent them from escaping die reaction zone.
Unlike t h e pinch effect, p l a s m a in t h e mirror machine is very stable, says UC's Richard F . Post. Another advantage: Design of the machine p e r m i t s considerable control over the p l a s m a . F o r example, currents in the e n d coils can b e altered to move t h e mirrors toward each other, squeezing t h e plasma. However, there is o n e p o t e n t i a l drawback. F o r efficient operation, Post says, t e m p e r a t u r e s of a b o u t 1 billion degrees centigrade must b e a t t a i n e d . • Stellarator. Although AEC has been working with Stellarators since 1951, basic principles of operation have been kept under wraps. According to L y m a n Spitzer, Jr., of Princeton, t h e plasma in the Stellarator i s kept away from the t u b e walls b y a m a g n e t i c field induced b y external coils. T w o designs are used. In one, t h e endless tube is b e n t into a figure-eight design (pretzel m a c h i n e ) . Simple circular coils around t h e t u b e produce t h e field. In the other, t h e tube is doughnut-shaped. T w o kinds of external coils are needed —an outer circular set, and an inner set of helical coils. Plasma in t h e Stellarator is heated initially b y passing a current through the gas along t h e center line of the t u b e . B u t to g e t to t h e h i g h operating t e m p e r a t u r e s n e e d e d , extra heat must b e a d d e d by magnetic p u m p i n g . To do this, p a r t of the magnetic field is pulsed a t very high frequencies. Most heat is p u m p e d into the g a s when the pulsation period coincides with the natural period of the g a s . • Hot Ion Injection. So far, this system h a s been used to feed super-hot d e u t e r i u m ions to a mirror machine, says Albert Simon of O a k Ridge National Laboratory. In t h i s system, a b e a m of molecular d e u t e r i u m ions is injected through a high v a c u u m , high current a r c and trapped i n a "magnetic bottle" (mirror m a c h i n e ) . In the arc, the molecular deuterium i o n breaks u p . dissociating into a n e u t r a l deuterium atom a n d a singly-charged deuterium ion. T h e neutral atom flics o u t of orbit, b u t t h e high energy d e u t e r i u m ion is t r a p p e d in a circular orbit, stays in the magnetic field. Big a d v a n t a g e of this system, says Simon, is that it is a steady state device, furnishes a continuous stream of hot ions. According to S i m o n , hot ion injection combined w i t h a mirror machine has great p o t e n t i a l as a fusion power producer. H o w e v e r , he says, it is possible that t h e infection system alone could p r o d u c e a t h e r m o n u c l e a r reaction.
Different Method, Isotope California researchers make short-lived isotope of 1 0 2 , cannot duplicate results reported last year SOME
QUESTIONS are still u n a n s w e r e d
this week as scientists plan their next research moves against element 1 0 2 . Researchers a t University of California, unable t o duplicate results of last year's discoverers of the element (C&EN, July 22, 1957, page 1 5 ) , say they h a v e "definitely discovered" a short-lived isotope of it. Paul R. Fields of Argonne National L a b o r a t o r y , a member of the international discovery team, stands on results published by the group, says b o t h he and the Swedish scientists involved plan further experiments to clear up any discrepancies. T h e s e discrepancies arose last fall when nuclear scientist, Albert Ghiorso, Torbjorn Sikkeland, exchange nuclear scientist from Norway, a n d chemists John R. Walton and Glenn T. Seaborg tried to p r o d u c e element 102 in the University of California's heavy ion linear accelerator (Hilac). They b o m b a r d e d curium-244 with carbon-13 nuclei—the m e t h o d used b y Fields a n d his coworkers last year. Although they used t h e same sort of curium target and a b e a m of carbon-13 nuclei with the same e n e r g y range in "repeated, careful experiments," they could not find any 102. ( T h e i r beams of nuclei w e r e about 10 times as intense as those produced in the Swedish machine.) They were successful, however, w h e n they switched to curium-246 as a target. T h e isotope they made is not t h e same as the o n e reported last year. It h a s a mass n u m b e r of i254, a half-life of t h r e e seconds, a n d decays t o fermium-250 by alpha emission. (Last year's isotope h a d a mass number of 253, a half-life of 10 to 12 minutes, a n d is also an alpha emitter.) • The Details. Ghiorso a n d his coworkers make their isotope b y beaming carbon-12 at 68 m.e.v., or carbon-13 at 7 5 m.e.v., at a target of curium deposited on a thin nickel foil and enclosed in a helium-filled container. W h e n a curium atom captures a carbon nucleus, a n e w nucleus is formed, four neutrons come off, a n d t h e resulting nucleus (of 102) flies o u t of the target. It is slowed by the helium a n d attracted t o a metallic conveyor belt h a v i n g a negative charge that moves just under the target. This belt
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