DIAGNOSTICS PROGRAM FOR A MAGNETICALLY INSULATED ION DIODE FOR INERTIAL CONFINEMENT FUSION

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Submitted on 1 Jan 1979

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DIAGNOSTICS PROGRAM FOR A

MAGNETICALLY INSULATED ION DIODE FOR INERTIAL CONFINEMENT FUSION

E. Burns, D. Johnson, A. Farnsworth, Jr, D. Fehl, R. Leeper, L. Mix, G.

Kuswa

To cite this version:

E. Burns, D. Johnson, A. Farnsworth, Jr, D. Fehl, et al.. DIAGNOSTICS PROGRAM FOR A

MAGNETICALLY INSULATED ION DIODE FOR INERTIAL CONFINEMENT FUSION. Journal

de Physique Colloques, 1979, 40 (C7), pp.C7-775-C7-776. �10.1051/jphyscol:19797374�. �jpa-00219371�

tTOURflAL DE PHYSIQUE Colloque C7, suppliment au n07, Tome 40, J u i l l e t 1979, page C7- 775

DIAGNOSTICS PROGRAM FOR A MAGNETICALLY INSULATED ION DIODE FOR INERTIAL CONFINEMENT FUSION

E.J.T. Burns, D.J. Johnson, A.V. Farnsworth, Jr., D.L. Fehl, R.J. Leeper, L.P. M i x and G.W. Kuswa.

Sandia Laboratories, Albuquerque, flew Mexico, 87185.

I n e r t i a l confinement fusion (ICF) schemes require an ion power density of 1 0 ' ~ - 1 0 ~ ~ watts/cm 2 on t a r g e t . 1 A t Sandia Laboratories, magnetically

insulated ion diodes a r e being developed f o r pos- s i b l e use as a source of a s u i t a b l e beam t o drive ICF The i o n range i n t h e t a r g e t places an upper l i m i t t o the usable ion energy of s e v e r a l MeV f o r protons and a few t e n s of MeV f o r carbon.

Both proton and carbon beams are being generated and evaluated. We describe here some of t h e diag- n o s t i c s used t o study ion beam composition and p r o f i l e s from t h e diode, through t h e d r i f t s e c t i o n t o t h e t a r g e t .

The proton md caxbon fluence and f l u x a r e measured with carbon a c t i v a t i o n samples and biased charge c o l l e c t o r s , r e ~ p e c t i v e l y . ~ ' ~ I n t h e a c t i - vation technique, a portion of t h e beam i s i n t e r - cepted by a carbon o r hydrogen t a r g e t allowing

12 13

t h e r e a c t i o n C ( P , ~ ) N t o occur. The positron decay of i s measured a f t e r i r r a d i a t i o n allow- ing determination of t h e incident beam. Correc- t i o n s f o r t h e n a t u r a l l y occurring deuterium must be made depending upon t h e beam r e l a t i v e voltage and current p r o f i l e s . The a c t i v a t i o n technique i s u s e f u l f o r proton energies above 460 keV and carbon energies above 6 MeV. The biased charge c o l l e c t o r s a r e u s e f u l f o r measuring proton and carbon current d e n s i t i e s f o r beam voltages g r e a t e r than 100 keV.

The carbon i s separated from t h e proton beam by ion time-of-flight or f i l t r a t i o n by t h i n polymer f o i l s . The biased charge c o l l e c t o r s and a c t i v a t i o n

technique a r e limited t o current d e n s i t i e s of a few hundred ~ / c m 2

.

current d e n s i t i e s require f l u x screen attenuation.

A time resolved x-ray pinhole camera6 has been used t o observe t h e focused proton and carbon beam p r o f i l e s v i a induced atomic e x c i t a t i o n and thermal emission from t a r g e t s , respectively. This camera used f i v e pinholes and f i v e independently gated CEMA detectors with e f f e c t i v e exposure times of l e s s than f i v e nanoseconds. The r e s u l t i n g e l e c t r o n images were transported along a 2 kG, pulsed t o r - o i d a l magnetic f i e l d , amplified i n a second CEMA p l a t e , then accelerated i n t o a phosphor t o produce v i s i b l e images. These pBot0n images were transpor- t e d by a f i b e r o p t i c p l a t e d i r e c t l y t o Polaroid film. The pinholes were covered with l i g h t t i g h t windows which separated t h e vacua of t h e camera and t a r g e t chamber. The s p a t i a l resolution of t h e camera i n t h i s configuration i s l i m i t e d by t h e pin- hole array, t y p i c a l l y 0.5 t o 1 mm. This system was successful i n observing t h e e a r l y time proton- induced atomic K-line e x c i t a t i o n i n an aluminum t a r - get followed by l a t e time carbon ion heating of an expanded low density aluminum plasma.

Time resolved o p t i c a l s p e c t r a l measurements of t h e anode plasma a r e used t o determine i t s tempera-' t u r e which i s c o r r e l a t e d t o t h e charge s t a t e o f t h e carbon ion accelerated. The spectrometer system i s a Cerny-Turner o p t i c a l spectrograph coupled t o an image converter camera. The o p t i c a l spectrometer i s capable of viewing 70 nm between 225 and 700 nm

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19797374

on a given shot. Coupled w i t h e l e c t r o n d e n s i t y measurements from a holographic interferometer sys

-

tern estimates of t h e d i f f e r e n t casbon i o n popula- t i o n s i n t h e anode plasma a r e made. These carbon i o n populations a r e compared with t h e populations measured i n t h e d r i f t s e c t i o n and t a r g e t a r e a by a Thomson p a r a b o l i c mass spectrometer system. 7

Holographic i n t e r f e r o m e t r y i s an important t o o l f o r studying various phenomena a s s o c i a t e d with i o n beam generation and t h e implosion of thermo- nuclear t a r g e t s . The system i n u s e a t Sandia Lab- o r a t o r i e s employs a 3 ns ruby l a s e r f o r holographic exposures. Using beam s p l i t t e r s and time-of-flight delays, each output pulse from t h e l a s e r i s divided i n t o f o u r c o l i n e a r pulses, separated i n time by a s much a s 28 ns, t o provide i n t e r f e r o m e t r i c d a t a a t f o u r times. For ruby l i g h t , a f r e e e l e c t r o n density

17 2

of 3 x 10 /cm w i l l produce one f r i n g e s h i f t i n t h e i n t e r f erogram. I n t e r f erometric measurements a r e being made of t h e diode plasma formation w i t h t h e hope of reducing t h e divergence of i o n beams through a b e t t e r understanding o f t h e formation and s p a t i a l development of anode plasmas.

S o f t x-ray, vacuum u l t r a v i o l e t (XW) spectros- copy has been used t o determine t h e response of approximately one proton range planar and c y l i n d r i - . c a l t a r g e t s t o an i n t e n s e beam of hydrogen and

casbon ions. E l e c t r o n temperatures were deduced

*om l i n e i n t e n s i t y r a t i o s from a carbon i o n heated, o p t i c a l l y t h i n plasma with a high r e s o l u t i o n , 1200 lineslmm g r a t i n g , one meter grazing incidence spectrograph. Brightness temperatures and t o t a l r a d i a t e d power from proton deposition were d e t e r - mined w i t h a t r i p l e t a r r a y of p h o t o e l e c t r i c o r x-ray diodes (XRDS). This d a t a was used i n con- junction with coupled radiation-hydrodynamic calcu- l a t i o n s t o deduce t h e i n c i d e n t i o n c u r r e n t density.

References

M. J. Clauser, Phys. Rev. Letts.

3,

D. J. Johnson, A. V. Farnsworth, Jr., D. L.

Fehl, R. J . Leeper, and G. W. Kuswa submitted t o J. Appl. Phys.

D. J, Johnson, G. W. Kuswa, A. V. Farnsworth, Jr., J. P. Quintenz, R. J. Leeper, E.J.T. Burns.

and S. Hunphries, Jr., t o b e published i n Phys. Rev. L e t t s .

F. C. Young, J. Golden, and C. A. Kapetanakos, Rev. Sci. Instrum.

48,

C. Eichenberger, S. Humphries, Jr., J. Maenchen, and R. N. Sudan, J. Appl. Phys.

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C. W. Mendel, ( t o b e published).

J. N. Olsen, G. W. Kuswa, and E. D. Jones, J. Appl. Phys.

3,

L. P. M i x and R. W. Kessler, unpublished Sandia Report No. 77-0209.

E. J. T. Burns, D. J. Johnson, A.V.Farnsworth, Jr., and G. W. Kuswa, submitted t o Appl. Phys.

Lett.