charles w. hartman et al- flow-through z-pinch study for radiation generation and fusion energy...

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UCRGJC-117669PREPRINT

Flow-Through Z-Pinch Study for Radiation Generationand Fusion Energy Production

Charles W. Hartman, James L. Eddleman, Ra lph Moir, U. Shu mlak

to th e11th

June 19423,1994

June 20,1994

Thisisapreprintofapaperintendedforpublicationina ournalorproceedinga Sincechanges may be made befo re publication, t his preprint is made available with theunderstanding hat it will not be cited or reproduced with out the permission of the


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FLOW-THOUGH Z-PINCH STUDY FOR RADIATION GENERATION AND FUSIONENERGY PRODUCTION

Charles W. Hartman, James L. Eddleman, Ralph Moir

Lawrence Livermore National Laboratory, P.O.Box

808, L-637Livermore, CA 94551(510) 22-1568

U. ShumlakPhillips Laboratory, PL/WSP

3550 Aberdeen SEKirtland AFE3, New Mexico 87117-5776

(505) 846-5078

ABSTRACT

We discuss a highdens ity fusionreactor which utilizes a flow-through Z pinchmagnetic confinement configuration.Assessment of this reactor system is motivatedby simplicity and small unit size (few hundredW e ) nd immunity to plasma contaminationmade possible at high density. The typereactor discussed here would employ a liquid Livortex as the first wall/blanket to capturefusion neutrons with minimum inducedradioactivity and to achieve high wallloading and a power density of 200 w/cm3.

I. INTRODUCTION

A renaissance is occurring in the field ofZ-pinch research based largely on the use of Z -pinches to produce keV radiation and onrecently disclosed Russian results.( l) Althoughmany pinch configurations continue to exhibitstrong MHD instabilities, certain notable andimportant exceptions have been observed(2)which depend mostly on pressure-profilecontrol, and when coupled to early-observedstable 2-pinches with flow suggestreconsideration of the Z-pinch as a highdensity thermonuclear fusion system. It haslong been recognized(3) that the high densityZ-pinch has enormous advantages as a fusionreactor candidate - no external magnets, highpower density, immunity to impurities, thepossibility of using liquid Li walls for very

high wall loading and low induced reactivity,and small unit size (-100 M W )- making thereactor potential qualitatively improved overpresent approaches. This paper is apreliminary evaluation of the flow-through Z -pinch as a magnetic confinement system and astudy of fusion reactor embodiments.

11. FLOW-THROUGH 2-PINCH FLOWSTATES AND STABKITY

We consider a flow-through Z-pinch(FZP) configuration as shown in Fig 1. Plasmaand B0 field a re injected to produce radially

hward flow to form FZF's directed along k Z.(This double pinch configuration avoidsimpurity generation at small r, high p, B f anelectrode were used to back a single Fa.) Totake advantage of the large B-fieldenhancement possibilities of the Z-pinch, andto maintain slow axial flow (VCCVA), theradial inward convection must be subsonic.Some flow properties are:constant for hizh conductivitv.

&/pr =" ,,

c= v z 2.V ? + S +.- dA6 constant

rn vA: ( V z ' 1 for the finale ( x + 7 ; ) ,2

szr!g flow-lines, and,

pinched state. Here V x o 2 is theAlfven speed at large radius, C s is thesound speed, and V is the flow velocity.


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Li

N m

Z lcml

Fig 1. Basic cell of a FZP. Symmetry planes areat Z = 0,9 an, e and plasma are duded in andou t as shown. Recirculating flow is shown withcomputed velocity vectors.

The FZP configuration of Fig. 1 s undercalculation using 2-D, 4HD code, TRAC?*).The calculations will serve as a basis to specifyelectrode configurations and initial conditionsto achieve the desired pinch state.

If the flow speed V is small, the pinchstate approaches the Kadomtsev, marginalstability profile(5) (to m=o, sausageinstability). Kadomstev also shows tha t theonly remaining unstable MHD mode of themarginal stability profile is an internal kink(m=l) which occurs in the region where $ > 1.Internal kinking is observed(6) but the effectsappear to be benign. We have recentlyexamined (7) he stability of a peaked-profile,spinning Z-pinch to the kink and fi id atendency towards stabilization 6.e. reducedgrowth rate) when &3 p . calc~lationsof kinking for an m=o, marginal stabilityprofile with spin are underway and may givethe result of a Z-pinch completely stable to allMHD modes.

The FZP provides a means ofadiabatically establishing a diffuse profile Z-pinch in contrast with early snow-plowpinches, exploding wire pinches, etc. whichtend to have more of a sharp boundary profile.

In general, sharp profile pinches exhibit strongsausage, and sometimes kink instability, whileearly FZPs and more recent wire-array6) andgas-puff pinches with diffuse profiles tend toshow very little M HD activity.

111. CONTROLLED THERMONUCLEARFUSION REACTOR

The main objective of FZP research isapplication to fusion energy production wherethe advantages of self-generated B-field (noexternal magnets), immunity to impurities andvery high power density because of highplasma density, and inherent simplicity canlead to a Qualitative mprovement in CTreactor possibilities. Ultimately it is hopedthat a high power density reactor with liquidLi walls and low unit power can be developed.

For aFZP

with Te=Ti=lO keV D/T plasma, thetotal fusion power Pf and fusion Qf areapproximately,

where the quantities are measured in units ofDeka MA, an, m/micro SIX, and eu (1 eu =.lW . Here VZ is the axial flow speed and theBennett equilibrium with a quadratic pressurepmfile pzp,(l-a>+%bbeenused. Itis

seen that large Qf requires large I/ a and lowVz. Since Uext/Up is typically 5-10, the flowof magnetic energy external to the pinch cansignificantly lower Qf. For the reactorconfigurations discussed here, the externalmagnetic field energy Uext is assumed to berecirculated with no energy loss.

Two reactor configurations appearpossible, always retaining the back-to-backgeometry of Fig 1. A linear reactorconfiguration like Fig 1 in which the parasiticmagnetic energy would recirculate and only thepinch plasma and internal field would beducted in and out to provide for the injection ofimpurity-free fuel and a scrape-off layer.

A second, closed reactor configurationwould retain the linear formation geometry ofFig 1 with curved pinch regions as shown in Fig. 2. An external field Bext 10 KG would be


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applied to breaks in the Li vortex system asshown. The two possible reactor configurationscan be operated in a pulsed, or possibly,cont inua mode

A pulsed reactor with relaxed flowvelocity requirements and higher Qf is possibleat higher pinch current. For the aboveexample, if I = 3. MA,

injectorPf = 100 GwthVz Qf = 10.

Li

VortexLi

Vortex

extractor

Fig 2. A closed pinch configuration withinjector, extractor, and two Li vortices. Pinchcurvature in the injector and extractor regions is

obtained with a vertical B field.At low I- 1 MA, and with sufficiently

low flow speed, V s .05-0.1 cm/microsec, itmay be possible to design a continuous FZPreactor. For L = w ) cm, = 1. cm, = 0.1 DMA,

so hat V, = S 1. cm/microsec for the same Qfas above. If a 1% duty factor is used to have 1Gw average power, as above, the reactor couldoperate for - 100 microsec at each peak of a 60cycle current waveform. Switching voltages ofa few 10% of KV would be required.

ACKNOWLEDGMENTS

This work was performed under the auspices ofthe U.S. Department of Energy by LawrenceLivermore National Laboratory under contractNo. W-7405-Eng-48.

REFERENCES

1. See proceedings, 3rd InternationalConference on Dense Z-pinches London,U.K. 9-23 Apr. 1993.

2. R. Spielman, private communication 8/93.3. A Conceptual Fusion Reactor Based on the

High-Plasma-Density Z-Pinch*4. J. Eddleman, et a1 A New Modeling Tool

for the RACE Experiment, 1989 FallMeeting of the APS Division of PlasmaPhysics, Anaheim, CA., Nov. 13-17. 1989

5. In Reviews of Plasma Physics v2 p. 153.Hydromagnetic Stability of a Plasma B.B.Kadomstev.

6. R. Spielman, private communication 8/937. U. Shumlak, private communication 11/93.

Since a major end-loss power, I Te

Gw, considerably exceeds Pf, the continuous FZPreactor would have to be closed as shown in Fig2, which would have an overall fusion powerdensity of - 200 w/cm3.

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charles w. hartman et al- flow-through z-pinch study for radiation generation and fusion energy...

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