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5IAEA Technical Committee Meeting onDrivers for Inertial Confinement Fusion

November 14-18,1994Paris, France

ABSTRACT

Pulsed Power Drivers for ICF nd High Energy Density Physics"

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Juan J. Ramirez, M. Keith Matzen, Dillon H. McDaniel,

Sandia National LaboratoriesMS-1178 (Department01204)

P.O.Box 5800, Albuquerque, New Mexico 87185-1178

Nanosecond Pulsed Power Science and Technologyhas ts origins in the 1960s and over thepast decade has matured into a flexible and robust discipline capable of addressing key physicsissues of importance to ICF and High Energy Density Physics. The major leverage provided bypulsed power is its ability to generate and deliver high energy and high power at low cost and highefficiency. A low-cost, high-efficiency driver is important because of the very large capitalinvestment required for multi-megajoule ignition-class systems. High efficiency is of additional

importance for a commercially viable inertial fusion energy option. Nanosecond pulsed power has

been aggressively and successfully developed at Sandia over the past twenty years. This effort has

led to the development of unique multi-purpose facilities supported by highly capable diagnostic,calculational and analytic capabilities.

The Sandia Particle-beam Fusion Programhas evolved as part ofan ntegrated national ICFProgram. It applies the lowv-cost, high-efficiency leverage provided by nanosecond pulsed powersystems to the longer-term goals of the national program, i.e., the Laboratory h&rofusion Facilityand Inertial Fusion Energy. A separate effort has led tolhe application of nanosecond pulsed powerto the generation of intense, high-energy laboratory x-ray sources for application to x-ray laser andradiation effects science research. Saturn is the mostpowerful of these sources to date. It generates- 500 kilojoules of x-rays fiom a magnetically driven implosion (Z-pinch). This paper describesresults of x-ray physics experiments performed on Saturn, plans for a new Z-pinch drive capabilityfor PBFA-II, and a design concept for the proposed -15 MJ Jupiter facility. The opportunities forICF-relevant research using these facilities will also be discussed.

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DISCLAIMER

Portions of this document may be illegiblein electronic image products. Images are

produced from the best available original

document.



Introduction

Th e near-term g oal o f the US ICF program is to achieve thermonuclear ignition ofdeuterium-tritium @-T) fuel in the laboratory. The long-term goal is to achieve high-yield

thermonuclear bum for both defense and energy applications. The National IgnitionFacility (MF) has been adopted as the preferred approach to ignition. It consists of a 1.8

MJ glass laser system designed primarily for indirect drive. Sandia’s role in the nationalICF Program has emphasized the development of ion beams for the long-term goal ofhigh-yield I CF using light-ions and ind irect drive [I-31.

The pulsed-power-based particle beam IC F program a t Sandia builds on technologiesinitially developed during the late Six ties and early Seventies for radiography and for thegeneration of bremsstrahlung radiation. Rapid advances made in pulsed power technologyat Sandia during the mid Seventies to the mid Eighties were mainly driven by the needs o f

the evolving ICF program. This period led to the development of fast water-dielectricpulse forming lines, the precision synchronization of a large number of pu lse formingmodules, and the efficient transport of high-power pulses through self-magneticallyinsulated vacuum transmission lines (MITLs)[4].

The PBF A-I accelerator was built in 1980 [5 ] . It was originally intended as an electron

beam accelerator but was converted to investigate the generation of high pow er ion(proton) beams once it became clear that electron beams w ere unsuitable for driving anICF pellet. PBFA-11 was com pleted in late 1985 [6 ] as a power so urce for 24 MeVlithium beams. In this design, currents fi-om 36 pulse-forming modules were added a t each

of eight layers of a vacuum insulator stack as shown in Figure 1. Each layer adds half of

the current from nine separate pulse-forming modules. A set of MITLs within the vacuuminsulator stack adds th e voltage fi-om the four top and bottom layers to feed pow er to acomm on ion diode located at the m idplane of the stack. Progress in ion beam pow er

coup ling and ion-driven hohlraums o n PBFA-11 is described in a paper by F duk et al. in

this conference [7].

The long te rn goal of high-yield IC F requires a configuration where multiple ion beams

are generated and extracted from he accelerator and propagated several meters to a pelletlocated at the cen ter of a target chamber. The evolving ICF driver strategies for LMFand ETF are described in a paper by Olson et al. in this conference [SI.

The SABRE accelerator at S andia is being used to extend the light-ion beam technology

developed in PBFA-11 to an extra ction geometry [9]. This work could be extended to

higher voltage and power levels on H e m e s III [IO] and PBFA-II. Figure 2 shows theoriginal PBFA-11 configuration used for the barrel diode experiments aswell as how the

PBFA-11 MITL.s could be reconfigured to support extraction ion diode experiments.

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Magnetically Driven Implosions

In 1987 PBFA-I w as converted into the Saturn accelerator [113. Saturn is used as a

source of -1 M eV bremsstrahlung radiation. It is also used as a power source for fastmagnetically driven implosions and generates -0.5 UT of X ays in this mode. Figure 3 depic ts the various stages of the plasma implosion process. A pulsed pow er high voltagegenerator produces a number of individual output pulses. The current from theseindividual pulses are added, through a set of MITLs, nd delivered to a cylindrical plasmaload located a t the cen ter of the test chamber. The magnetic forces generated by the drivecurrent cause the plasma to implode thus converting electrical energy into kinetic energy.The kinetic energy is then converted into radiation when th e plasma stagnates on axis.

Magnetic energy stored near the load region can continue to drive the collapsed plasmaproducing additional radiation. The implosion system thus represen ts an additional stageof power compression and the radiation pulse from -100 ns implosion can be - 15 ns in

duration. The entire process can also be made to be very efficient [121.

The work on magnetically driven plasma implosions has been motivated by applications toradiation effects science research, X-ray lasers and high-energy-density physics. Work on2-pinch physics dates back several decades. Pro gress has been arguably limited byproblems associated with control of instabilities in the imploding system. The advent of

fast pulsed po wer drivers in the Eighties resulted in fimdamental changes. An analysis ofthe scaling of MHD instabilities in imploding plasma liners by Hussey et al. [131 shows

tha t the Rayleigh-Taylor instability dominates in the worst, most unstable implosions. Theresult is that short high-temperature radiation pulses can be more readily obtained withshorter implosion times. The use of high-power, short-pulse generators such as Saturn todrive plasma implosions shifts the problem emphasis from plasma dynamics towards high-efficiency, fast pulsed power systems. This line of research thus benefits greatly by using

systems that tak e maximum advan tage of the substantial progress in fast pulsed powerscience and engineering made over the past 15-20 years.

The Saturn Experiments

Th e experiments on Satu rn were preceded by x-ray laser experiments on Proto-11 [141

which themselves built on the results of the SCORPIO 2-pinch program [IS ]. The

configuration used for the X-ray laser experiments is shown in Figure 4. In this scheme anannular shell surrounds an X-ray laser rod which sits on the cylindrical axis of symmetry ofthe 2-pinch implosion. The annular shell serves both to stagna te the imploding plasma,converting plasma kine tic energy into radiation (the flashlamp), and to hydrodynamically

isolate the laser rod from the imploding plasma. With this geometry the lasant can remainhomogeneous for a time before being destroyed by the imploding plasma. Theseexperiments on Saturn were successful in demonstrating a population inversion in helium-like neon [16].

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developing a 2-p inch drive capability for PBFA II. This capability will be obtained by

redirecting the o utput fkom the 36 individualPFLs through a short vacuum insulator stackand using a set o f MITLs, similar to those used on Saturn, to deliver the summed currentpulse to a single 2-pinch load. A sketch of the PBFAII-2 configuration is show n in Figure

7. Calculations indicate that PB FA II-2 should be capable of driving 20-25MA implosionswith - 100 ns implosion times. PBFAII-2 should be completed during FY96 and willenable - 2MJ implosion experiments. These experiments Will validate ou r understanding

of pow er flow and implosion dynamics and will provide the necessary confidence forscaling to Jupiter level parameters.

Applications to ICF

The pulsed pow er R&D, ICF, and Radiation Science programs at Sandia are highlyinterdependent. T he individual programs have benefited greatly fiom the strong linkage

betw een them. Sandia is a leader in developing laboratory X-ray sou rces using fastmagnetically driven implosions and has initiated a comprehensive assessment of how the

rapid progress being made with these systems can be leveraged for the benefit o f the ICFprogram.

The motivation for this study is best seen in Figure 8 which show s the measured hohlraumtemperatu res achieved to date on existing facilities and an ex trapolation of these data toPB FA II-2 and Jupiter. Although this approach does not allow for stand-off, and thus is

not a candida te for the long-term goals of high-yield ICF, it is possible to conceive of anumber of important radiation transpo rt and internal pulse shaping experiments using thistechnology. The ultimate promise is the potential to drive a pellet. Achieving this promise

however will require developing concepts that transform the radiation fiom the cylindricalconverter into a spatially uniform, temporally programmed pulse to drive the imploding

capsule.

Conclusions

Magnetically driven implosions using fast pulsed power generators form th e basis for agrow ing international collaboration on X-ray physics. This technology has proven capableof converting electrical energy into X-ray energy with an overall efficiency of 15-20

percent. The Saturn and h g a r a V experiments will be extended to include2

0Mq -2M J implosion experiments on PB FA II-2 during FY96. A design concept fo r Jupiter thatmakes use o f inductive voltage adder technology has been developed and would enable -55MA, 15MJ implosion experiments. Sandia has initiated an assessment of howsuccess with hohlraums generated on PBFAII-2 and Jupiter could best be used for the

study of ICF implosion physics.

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AcknowledPments

W e would like to thank our colleagues at Sandia,Los Alamos,Law rence Livermore, theUK, and the CIS for their contributions to the X-ray physics results discussed here. Wewould also like to acknowledge our colleagues atDOE nd DoD aboratories, universities,and industry who have been key con tributors to the development of fast pulsed pow ertechnology and who have contributed many of the ideas now being integrated intomagnetic driven implosions and its applications.

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References

1. J. P. VanDevender and D. L. Cook, Science, 232,831 (1986)

2. 5. P. Q uintenz, et al. “Progress in Light Ion Fusioq” Proc. IAEA TechnicalCom mittee Meeting on Drivers for Inertial Confinement Fusion, Osaka, Japan, April15-19, 1991.

3. M. K. Matzen, et al. “Progress in Ion Beam Target Design and Experiments,” in

Proceedings of the 15thInternational Conference on Plasma Physics andControIledNucIear Fusion Research, Seville, Spain, Sept. 26-Oct. 1, 1994.

4 J. J. Ramirez, et al., “Very High Pulse-Energy Accelerators,” Proc. 1989 ParticleAccelerator Conf., Chicago,E, arch 20-23, 1989 , 1446.

5 . T. H. Martin, e t al., “Particle Beam Fusion Accelerator I,” IEE E Trans. on Nucl.

Sci. NS-28, No. 3,3 368 (1981).

6. B. N. Turman, et al., ‘TBFAII-A 100TW Pulsed Power D river for the Inertial

Confinement Fusion Program,” P roc. 5th IEE E Pulsed Pow er Conf., Arlington,VA,June 10-12, 1985, pp. 155-161.

7. A. B. Filuk, et al., “P rogress in Ion Beam Coupling and Ion-Driven Hohlraum s on

PBFAII,” in Proceedings of this Conference.

8. C. L. Olson et al., “ICF Driver Strategies for IFE,” in Proceedings of thisConference.

9. D. L. Hanson, et al., “Improved Field Geometries for SABRE Extraction Ion Diode

Operation With P assive Ion Sources,” Beams 94 10th International Conference onHigh Pow er Particle Beams, SanDiego, C& June 20-24, 1994.

10. J. J. Ramirez, et al., “H em esProc . 7th International Conference on High Power Particle Beams, Karlsruhe, West

Germany, July 4-8, 1988, pp. 148-157.

- A 16 TW, Short Pulse, Gamma Ra y S imulator,”

11. D. D. B loomquist, et al., “Saturn,A Large Area X-Ray Simulation Accelerator,”Proc. 6th IEEE Pulsed Power Conf., Arlington,VA, June 29-July 1, 1987, pp. 310-3 17.

12 . P. J. Turchi and W. L. Baker, J. Appl. Phys. 44 ,493 6 (1973).

13. T. W. Hussey et al., J. Appl. Phys. 51, 1452 (1980).

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.

14. M. K. Matzen, et al., J. Phys. Colloq. (Paris) 47, C6-135 (1986).

15. M. J. Clauser, L. Baker, D. H. McDaniel, R. W. Stinnett, and A J. Toepfer,“Magnetic Implosion of Plasmas with Short Pulse, High Pow er G enerators,” SandiaReport, SAN D78-1387C.

16. J. L. Porter et al., Phys. Rev. Lett. 68. 79 6 (1992).

DISCLAIMER

This report was prepared as an account of work sponsored by an agency of the United StatesGovernment. Neither th e United States Government nor any agency thereof, nor any of their

employees, makes any warranty, express or implied, or assumes any legal liability or responsi-bility for the accuracjj, completeness, or usefulness of any information, apparatus, product, orprocess disclosed, or represents that its use would not infringe privately owned rights. Refer-

ence herein to any specific commercial product, process, or service by trade name, trademark,

manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recom-mendation, or favoring by the United States Government or any agency thereof. The views

and opinions of authors expressed herein do not necessarily state or reflect those of the

United States Government or any agency thereof.

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FigureCaptions

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Artist Drawing of PBFA 11

PBFA IIMITL configuration for barrel and extractor diode experiments

Conceptual stages for magnetically driven implosions

Idealized target configuration for X-Ray laser experiments

Hohlraum temperatures achieved with ion beams and magnetic implosions

Design concept for Jupiter

Des ign concept for Z-pinch drive capability on PBFA II

Extrapolation of hohlraum temperature to higher current drivers

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