LANL MagnetizedTargetFusion 1994

Los Atamoe Mtronal Lt~boratory m opmted

by me Universw of CMiorrtie for the Urrrfed Statee Oepertment of Enertw under contracl W-7405-Ef4G-3S

TITLE:

AUTHOR(S):

SUW41TTEDTO:

Byacceplance

thepublmwd

Irvin R. Lindemuth, X-1

MAGNETIZED TARGET FUSION - AN ULTRA HIGH ENERGY APPROACH IN AN UNEXPLORED PARAMETER SPACE

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Proceedings, 1st International Symposium for Evaluation of Current Trends in Fusion Research, Washington, DC, November 14-18, 1994

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An Ultrahigh Energy Approach in an Unexplored Parameter Space

TARGET FUSION:

@AU-Irvin R. Lindemuth @AD-Los Alamos National Laboratory

X-1, MS F645 Los Alamos, NM 87545 USA

However, the crucial

Among for doing this is an ultrahigh energy approach

Magnetized target fusion is a concept that may lead to practical fusion applications in a variety of settings. first step is to demonstrate that it works as advertised. the possibilities to magnetized target fusion, one powered by explosive pulsed power generators that have become available for application to thermonuclear fusion research. the All-Russian Scientific Institute for Experimental Physics (VNIIEF) a very powerful helical generator with explosive power switching has been used :0 produce an energetic magnetized plasma. diagnostics have been fielded to ascertain the properties of this plasma. and calculationally

We are intensively studying the results of the expertients

In a collaborative effort between Los Alamos and

analyzing the performance of this experiment.

Several

Abstract

@H1-INTRODLICTION

@CTITLE=MAGNETIZED

“l’hephysical characteristics of inertial confinement. fusion and magnetic confinement fusion differ by about ten orders of magnitude. The approach to creating the fusion plasma by these two methods are equally different. Because of the extreme differences and the vast parameter space that separates these two approaches, it is logical to consider the possibility of an intermediate approach to fusion. We believe that an idea suggested many years aao, and sporadically investigated over the past 20 years may provide an approach to fusion energy that avoids the difficulties of the previous extremes, if one is able and willing to accomplish a requisite first step to accommodate this intermediate approach. to accomplish such a first step. fielded jointly by Los Alamos and the All-Russian Scientific Institute for Experimental Physics (VNIIEF) promises to provide the n%cessary components for that first step. has fielded many experiments, and Los Alamos has joined the effort only lately, but has also brought to the effort advanced diagnostic and computational capabilities that sho~ld greatly improve our understanding of the plasma creation process and the properties of the plasma created.

We are now studying one attempt

The MAGO experiment

In fact, VNIIEF

This intermediate approach to thermonuclear fusion is called magnetized target fusion (MTF) . We coined this phrase only about two years ago, but in the past the same concept has been called variously magnetized fuel, fast liner fusion, and magnetothermally insulated fusion. Below we will present the salient facts for MTF and describe the US/Russian joint effort to take the first step toward realizing magnetized target fusion.

@Hl=WHAT IS MAGNETIZED TARGET FUSION?

MTF 1s a relatively untried approach to fusion ignition, requiring two elements: a) a means of preheating and magnetizing the thermonuclear fuel and b) a compression system. are 1) an embedded a ~mnrll]ct{vlt.v

field is used to reduce the thermal

not to confine the Dlasma, and 2) the

The key aspects

magnetic nlasima.

h~t.

ignition conditions are achieved.

For ICF, compression of the fusion fuel is called implosion and involves very strong shocks to accelerate a shell (or ‘pusherH that contains the fusion fuel) to high implosion velocity. This is because as fusion ignition conditions are approached the enezgy loss rates become high, ana a high work rate is necessary to overcome them until fusion energ!y production is sufficient to overcome them. The major energy loss process for typical ICF targets is thermal. conduction, but for targets with high fuel density the bremsstrahlung radiative loss from the fvsion fuel can be more important. discussed in a previeus paper in this symposium 11].

The details of ICF +argets are

The strategy of MTF is to suppress the losses from the fusion fuel, first by reducing the density of the fuel to reduce radiative losses, making the conduction losses dominant, and then by using a magnetic fi~-.d to suppress the conduction losses. of thermal condv~tivity should be classical [2]. This strategy drastically reduces the overall losses, which means that the work rate necessary to overcome the reduced losses can be much smaller, greatly relaxing the need for high implosion velocity.

We think that this reduction

Because at high temperature the plasma electrical conductivity is high, the embedded magnetic field is plasma, so that they move together, and as the plasma is compressed, so is the magnetic field. will be amplified by a factor of about 100 in the course of about a thousand fold compression, which corresponds to a convergence of a factor of ten for a spherical target.

This means that the magnetic field

effectively frozen into the

The MTI’ parameter space is shown in Figure 1. It is presented as an initial condition parameter npace, that is, contours of unity gain plckted in the initial density, initial implosion velocity space. condition space: Bo - 16, 40 and 100 KG. for specified DT mass, initial temperature, and implosion energy [3]. @FIGURE-Fig 1 The initi~l conditisu space for MTF based on results

Three sets of contours are plotted in this initial

The plots are made

derived f ~m a “zero-dimensional survey code that follows the dynawcs of an imploded magnetized fusion target [3]. The target plasma starts at 50 ev.

Also,

It is clear that MTF region in the lower left lies far from the ICF region in the upper right hand corner of the plot. This survey result suggests that MTF allows extremely low implosion velocities. the two fusion regions connect, so that there is a continuum between the two. The survey code used to produce Figure 1 did not allow for fusion energy deposition, so that fusion ignition was not possible. What Figure 1 shows is that even without ignition MTF still provides a net gain in an accessible part of parameter space.

Howev-r, ignition is a pos~ibility for MTF.

as the initial magnetic field is increased,

to raise the

Thie

This means that it is necessary to heat

Because MTF does not need high implosion velocities, there are no strong shocks involved that serve temperature of the fusion fuel prior to continued compression by the pusher or liner. the fusion fuel by an auxiliary means befoz.1 compression. In Figure 1 the initial temperature of 50 ev was used. Ohmic heating is a convenient chuice because it is a.Lso desired to have a magnetic However, ohmic heating alone may not suffice, because as the plasma temperature rises, the resistivity falls. There is a limit to the temperature It is also possible to attainable by simple ohmic heating. employ allMHD means of shock heating the fusion fuel, which 4” A-----4” the m-l,.—< +k- Mfi(Y7

field in the plasma.

nvmm~ir.>ent

will

@H1-ACC2SS TO THE MTF pWETER

Because the MTF target plasma is low density, for the same mass target., an MTF target must be larger than its ICF counterpart. This coupled with the fact that the MTF fusion region is accessible with lower implosion velocities means that the ~mplosion times for MTF are much longer than for ICF. and intensity on target for MTF are much Zower than for ICF. @FIGURE-Fig 2 Lines of constant power in the MTF initial condition space. @FIGURE=Fig 3 Lines of constant intensity in the MTF initial condition

This means that the power

space.

This is shown in Figures 2 and 3 as lines of constant values of power and intensity in the same initial condition space as Figure 1. It should be noted that the ICF reqion is extended to lower density in this diagram than would be the case for B - 0. two or more orders of magnitude separate the extremes of the two regions in power, and four i.~ intensity. factors that should make a substantial difference in the requirements for realizing fusion energy. accessed than ICF. magnetic confinement instabil:tiesm @FIGURE-Fig 4 The MTF parameter space for a small target (20 ug),

At the sane time it avoids many of the claasical

These are significant

The MTF fusion region is much more easily

In fact fully

requiring 100 K J implosion energy.

@FIGURE-Fiq 4 The MTF parameter space for a larger target (200 ug), Notice the expansion

requiring 1 MJ implosion energy. of the initial conditions that provide significant MTF gain.

Figures 4 and 5 show how the size of the MTF fusion region changes as the DT mass and ~mplosion energy are increased. is the unity gain contour. initial condition space plots that there is no DT alpha energy This means (i.e., no “self heating” in the plasma). deposition that for these survey calculations, ignition was not allowed to occur . Therefore, the gains calculated were a lower limits, and the sizes of the MTF fusion regions should be larger. of the survey calculations from which these figures were derived are given in the 1983 paper [3].

It should be noted that for all these

The details

The so~.id contour

SPACE

It should be clear that MTF is not a simple matter of just adding a magnetic field to a conventional ICF target. necessitates target pla3ma preparation, in a lower initial density fusion fuel, which means a larger target. fact result that the target can be imploded much slower means that the target can operate at much lower power and intensity on target. The lower implosion velocities mean more massive pushers and longer dwell times near maxim~m compression that matches the longer fusion burn time due to the lower density. required, but there iS implosion.

No pulse shaping should be for plasma preparation before

This coupled with the

The magnetic field

requirement

@H1-DT ALPHA ENERGY DEPOSITION

compressed along with the fusion fuel,

Because the magnetic field is the gyro radius of the charged fusion reaction products decreases. For DT the one charged reaction product is the DT alpha with an initial energy of 3,5 Mev, an atomic mass of 4 and a charge of 2. If the gyro radius is much smaller than the distance from where the DT alpha is born to the pusher, or if the mean free path is sufficiently short, then most of the fusion energy carried by that reaction product will be deposited in the fusion fuel, However, most of the fusion energy escapes with the DT 14 Mev neutron. fusior fuel, it can ignite, meaning that the temperature will keep on increasing even after the implosion has reversed and expansion “—1 4”n —,-,.4A- thn tinnwm,,Inma =vn~amanm 4n +hm

If sufficient fusion energy is redeposited in in the

ftlq~nn

FIIP1

plasma with uniform current density. the field in the target can be amplified, and possibly sufficiently to reduce the Larmor radius of the DT alpha and thereby significantly e~.hance the fusion energy ‘self-heating”.

During the implosion,

An example of the complex trajectory of a D’1 alpha in a magnetized DT fusion fuel is shown in Figure 6. in the rhoR, temperature plane where DT ignition is possible for MTF. Notice that it is greatly extended to lower values of areal density rhoR form the ICF region on the far right. fusion regions for several values of target plasma masses. For a magnetic field of 5 MG, the MTF ignition region disappears for DT mass below a&JUt necessary for MTF ignition. @FIGURE-Fig 7 Mass dependence of the new MTF region in a Lindl-Widner

This sets a lower limit on the energy

Figure 7 shows the region

This figure shows the

1 ug.

diagram. 5 MJ is required to to drive 1 mg of DT to fusion temperature.

The specific heat of DT is 100 J/ug.Kev, so about

Second,

+arrret

@Hi-PREVIOUS EXPERIENCE kITH MTF

It is ~lear that the basic

Because both Edward Teller and Andrei

Two years later Mokhov and his colleagues published

The basic ideas for MTF seem to have had their origins both in the US and in Russia. Sakharcv were engaged in nuclear weapons work, the genesis of the ideas are not completely documented. ideas came from the groups they worked with during those secret times. The first published work on this topic did not appear until the lace 1970’s, and probably independently of the secret sources of information. Sandia National Laboratory published an early report on th Phi-target work in 1977 [4,5]. a very sketchy paper on a device intended to realize fusion with a magnetic implosion [6]. Because the actual fusion target was not discussed, many doubted it coold work. that this scheme could riot work without a magnetized fusion fuel. When the Soviet Union dissolved, we learned that this conclusion -was correct. Sakharov at the premier Soviet nuclear weapons laboratory from the earliest days of their nuclear weapons work. 1970~s there have been several advances in our understanding, but the Sandia Phi-targets have remained the single best example of an integrated MTF experiment. Figure 8 shows various geometries for MTF, including the Phi-target. @FIGURE-Fig 8 Examples of possible magnetized fusion targets.

Indeed, we now know that Mokhov had worked with

These drawings are not to scale.

Years later, we deduced

Since the late

range from a few millimeters to several the geometries from cylindrical to spherical.

centimeters, and

The Phi-target had a diameter of 3 mm. radius of 10 cm.

The MAGO experiment has a No dimensions were given for the Mokhov device.

The scales

We believe that developments in the last decade warrant a renewed examination of MTF. First, modeling of Sandia Phi-target provided a better understanding of the essential physics. survey code results put the MTF into a perspective against the back-drop of other fusion ccncepts [3]. In addition, there are now many new plasma diagnostics, pulsed power facilities, and improved computational tools. We think that one item that may be most important is the development of new methods for producing a hot, magnetized target plasma. the Russian MAGO experiment is another. other methods for creating a target plasma.

The high density Z-pinch is one, and We are also considering

The acronym MAGO is properly translated magnetic compression. It has became the acronym used for a variety of related activities which include explosive pulsed power and the creation of a hot, magnetized target plasma. explosive pultied power (HEPP) drivers, and has coupled 25 MJ into -.-…—.A&4”-11,.A..l..nm4rn-la.4fim w~+h +ha{w !!nimlla

VNIIEF has demonstrated 200 MJ high

mla.qma

they have produced up to 5 x 10A13 neutrons (without implosion) . Now an unprecedented US/Russian collaboration in ultrahigh magnetic fields and pulsed power is familiarizing US scientists with Russia~s remarkable accomplishments.

In September of 1993 the first joint experiment involving the scier.tists from the US and Russian nuclear weapons design laboratories was performed at VNIIEF in Arzamas-16 was the first tangible result of an unprecedented scientific collaboration established through the support and encouragement of the highest levels of the governments of both nations. followed by a series of joint high magnetic field experiments in December 1993 and August 1994, and also a series of MAGO experiments in April 1994 and Jctob>r 1994.

That first joint experiment was

(Sorova), Russia.

The experiment

@Hl=EXP1.OSIVE PULSED POWER

The mi~~gnetic flux compression technique for converting the chemical energ:~~ of h~.gh explosives to intense electrical pulses that can provide intensely concentrated nlagnetic energy, is one of the legacies of Ar,drei Sakharov, father of the Soviet H-bomb and winner of the Nobel Peace Prize. created unmatched magnetic flux compression capability: 200 MJ at 200 MA, to produce fields in excess of 10 MG (1000 T). This advanced capability was not entirely unknown to the US, but rather unbeliever until recently in the US, so US researchers are just now pondering possible applications. Through the LANL/VNT[EF collaboration, VNIIEF is familiarizing US scientists with its ‘mique capabilities.

Beg~nning with his leadership, VNIIEF has

The principls of magnetic flux compression is based on Lenz’s Law, Electrical current in an inductive circuit stores energy in the form By decreasing of a magnetic field ?.nthe inductance of the circuit. the inductance in the circuit, the inactively stored energy can be amplified:

Lo.10 = Lf.If If = Lo.10

1/2 Lf.IfA2 = 1/2 Lo.10”2 .Lo/Lf

This can also be viewed from the standpoint of flux conservation in a resistanceless current loop. This is increased by decreasing the area cf the current loop. the principle has been applied to two general types of magnetic flux compression generators.

The magnetic energy density is

/ Lf

f?FIGURE=Fig ? A 3-module disk explosive magnetic generator (DEMG).

Each module consists of a disk shaped explosive sandwiched between twc cavities that feed a low inductance transmission line along the outer periphery of the mcdul.es. The disk explosives are initiated at the center.

Figure 9 illustrates a DEMG.

Each module consists of a shaped disk of high explosive

The helical explosive magnetic generator (HEMG) is the one pursued most extensively in this country, but VNIIEF has also developed the disk explosive magnetic generator (DEMG) , which has several advantages over former generators, are modular. sandwiched between tw~ inductive cavitizs. The high explosive is iilitiated on axis and feeds a transmission line at the periphery. This makes a very low inductance transmission line possible. can be stacked to increase the energy supplied without significantly effecting the delivery time. have been developed at VNIIEF, an{i a 3 module, 1 meter diameter VNIIEF system has delivered 100 MJ at 256 MA into a 3.3 nH load, Scaling directly to a 10 module 1 meter diameter system would produce 269 MJ at 196 MA into a 14 nH load,

Systems using as many as 25 modules

These gener~tcrs

The mciules

In September of 1993 the first joint US/Russian experiment involoved implosion of a thin liner using explosive pulsed power. @FIGURE=Fig 10 Configuration for the DEMG line= implosion e~~eriment. An equivalent circuit for the system is showq as well. The capacitor bank shown in the equivalent was remotely located (not shown in the experiment

configuration) .

A DH4G was coupled to a liner load through an electro-exploded (fuse) opening switch. circuit are shown in Figure 10. (not shown in the configuration, but shown in the circuit) that provides an initial current for (2) a helical generator provides an initial current for (3) the DEMG, which is coupled through (4) switches to (5) the liner load at the top of the configuration.

The experimental configurat~on and equivalent It consists of (1) a capacitor hank

35 MA was supplied to the load in 1 us.

(HEMG), which

foil

hr-al.rinwn

a,-i-m

There weze four B-dot probes in the glide plane, thirty

An extensive system of diagnostics were fielded to measure the liner motion. contact (shorting) pins, configured as columns of 5 probes each at six azimuthal locations, thirty-six fiber optics probes with four probes monitoring light from the inner surface and 32 probes monitoring liner transit along 8 radial spokes of 4 recessed probes. @FIGURE-Fig 11 The liner assembly fo~ the DEMG liner implosion experiment.

Two cross sections of the ‘ssembly show the diagnostic arrangemen”~s.

The configuration and equivalent cir~cit are illustrated in Figure 11. The HEMG, DEMG, fuse and closing swit=-h operated as expecsed, but a transmission line insulation breakdown limited the curxent to the liner and led to some asynunetry ill the implosion. Los Alamos optical current measurement confirmed the DEMG performance, and the joint experiment provided the first opportunity for VNIIEF to familiarize Los Alamos personnel with their assembly and operating procedures. to significant improvement % the LoaiAltimos theoretical and computational moc!eLs.

This experiment has led

@Hl=THE MAGC EXPERIMENT

The MAGO experiment is an approach to creating a hot, magnetized target plasma that has been under development at VNIIEF for several years, but was first ar.nounced as a contributed paper at an IEEE pulsed power conference in 1951. meeting, but rather was first presented 7 months later at the Zababakin Scientific Talks in Russ.-a. Since then we have learned a lot abo~t this complex and interesting experiment. capabilities to produce a transient wall confined plasma. this experiment is shown in Figure 12 together with a circuit diagxam. @FIGURE-Fig 12 The MAGO target plasma creation experiment chamber wzch an

However, the paper was not presented at that

It employs the VNIIEF HEPP The qeometry of

equivalent circuit for the HEMG, switches, and chamber.

The HEPP system works thus:

This puts a seed current in the helical generator.

The experiment consists of an HEPP system that drives the i4AG0 experiment chamber through a complex explosive switching module. No DEMG ‘.sused for this experiment, since the energy and current needed to create the plasma are not very high. A capacitor is discharged through the entire system, including the experiment chamber. Then, the capacitor is isolated by closing switch S1. explosives are initiated to operate the HEMG, thus amplifying the current through the chamber. isolate the experiment chamber while the HEMG continues to operate, achieving a very much higher current (approaching 9 MA). Bec~use the time constant for the isolated chamber is long, the current continues to flow there with little or no decay. explosively operated opening switch indicated as a variable resistor in series with with S2 is triggered. This suddenly introduces the very Li _L ..__..Lk- &kA -..—.d-tintnh—nk~~

Then, the switch S2 is operated to

At maximum current the

Next, the high

ant-l

next paragraph. approximately ten times higher current to the experiment chamoer as an inductive kick, is important is determining the continued time history cf the current.

One might consider the sudden introduction of the

The dynamic behavior of the plasm~ in the chamber

~he early current

No ionization occurs because

The experiment chamber is divided into two chambers by a barrier mounted on a rod along the axis of the ckm~er. through the rod and walls of the chamber sets up a magnetic field in the 10 torr DT gas in the chamber. the voltage across the insulator is not vezy high and is changi,?g only slowly with time. When the high current is suddenly switched into the chamber, breakdowns occur in the chamber, first across the gap (or “nozzle”) between tne barrier and the cylinder wall. The current path broadens and the heated plasma expansion sends a shock into the second chamber. the B-dot probes that the breakdown across the insulator occurs some time later. provides a ponderamotive the plasma in the gap to high velocity. runs into the previously shocked (and thereby ionized) gas in the second chamber, producing a stationary second shock. high values in hot spots in the region between these two shocks. The temperature of the bulk plasma is much lower, but it is the hot spots that are mainly responsible for the neutron output of up to 5 x 10”13.

As the dynamics develop, the current across the nozzle

The process is not fully understood, but we see from

force on the plasma in the nozzle, accelerating

This high velocity plasma

The temperature rises to

Because there were no

for the bulk electron temperature in the plasma.

The MAGO 11P experiment was a pure deuterium experiment, fielded in tihe same way as other MAGO experiments. primary 14 Mev neutrons, this experiment afforded an opportunity I.O make a neutron ratio measurement that provided a rough lower lmit the tritons produced in the DD reaction are energetic, and while being slowed down in the plasma (mainly by electrons), they can undergo fusion reactions with the deuteriurn nuclei, thus producing a 14 Mev neutron. from the branch of the DD reaction that has one neutron and a light helium nucleus as its products is greater for higher electron temperatures because the range of the triton is longer for hotter electrons. It is a lower limit because the less reactions than otherwise will if the range is longer than the distance to the wall, or the OCCur ions substantially S1OW the using activation detectors for the 14 Mev neutrons. of “,1Oev seemed to be indicated for the electron temperature.

The ratio of these 14 Mev neutrons with the DD neutrons

A rough measurement was made by

That. is because

A lower limit

~rj.tons.

On the basis of computations done for our i~ost recent experiment it appears that the p.erfolmance of the MAGG experiment is somewhat sensitive to the ratio of the early current to the later high current. In that experiment, the two currents had a smaller difference, so the neutron output was some what down (- 10A13) and the computed bulk temperature was only about half that of a previous DT experiment The computed bulk temperatures were about 270 ev in MAGO I and 160 ev in MAGO II.

In the MAGO I experiment we made time resolved neutron measurements, obtained neutron activation, did optical interferometry for electron density, obtained time resolved visible spectroscopy, did time integrated near-UV spectroscopy, and many obtained current a.~d field measurements. Much of this data is still being analyzed, but we know that about, 8 x 10A12 neutrons were produced, the activation agreed with the time of flight measurements, the interferometry saw electron densities up to about 8 x 10’16, and ti)e spectroscopy saw mostly continuum. While the analysis O: the data is still in progress, the results so far are reasonably consistent

with cor,putations,

(MAGO II),

(14AG01) .

to correctly correlate features in the various measurements. In the MAGO II experiment we also got a similar neutron yield to

that of MAGO I (about 10’13).

The visible spectroscopy in correlation

with the interferametry and features in the B-dot probes looks very We now see more than continuum. interesting. filtered X-ray me~sure.ments were made, which should contain spectral information rn the emission from the plasma. The data reduction will take some the.

Time resolved,

@Hl=A PROOF-OF-PRINCIPLE

The reasonably high bulk temperature in the MAGO experi,unt~ lakes it interesting as a vehicle for a proof-of-principle experiment. We are currently examining the measurements made on MAGO II and analyzing them with our MHRDR code to ascertain whether or not this plasma is suitable for suhaequent implosion. bulk plamna thermal the for compression. 1 cm/us, the time scale must be about 10 us. that any impurities in the bulk plasma will reduce this tfie scale, especially as the plasma density increas~s [7].

scale must be greater than the time required For MAGO with an implosion velocity on the order of Yakubov has pointed out

To be suitable, the

@FIGURE- Fig 13 Adiabatic cor~p::essionof the hot, magnetized plasma

to fusion conditions requires only a mcdest convergence.

Two such methods are illustrated

Depending on dimensionality of the compression

VNIIEF has from the very beginning of this collaboration suggested methods of accomplishing a compression of the second chamber of the MAGO experiment. in Figure 13. and the temperature cf the bulk plasma, it may take only a modest However, the convergence to reach fusion ignition temperatures. temperature, field, and rhoR of the MAGO plasma are too low for fusion ignition if cylintiical compression used. is in acccrd with the calculations, a cylindrical compression of the existing design of the MAGO second chamber should provide a very convincing proof-of-principle compressed from about 6 cm down to about 1.5 cm, with the central ’.-odunchanged in diameter, then neglecting losses, the plasma ‘+ould de driven from 300 ev tc 2.7 Kev, and the field would be pumped to tens of megagauss. implosion cylindrically compressed should settle into a Kadomtsev stable wall-confined

Computations predict a plasma suitable for

If the bulk plasma were

If the plasma life the

Z-pinch profile.

@Hi-THE PROSPECT FOR FUSION IGNITION

EXPERIMENT

experiment.

sunerco~ductor

himh

An attempt to achieve fusion ignition would require a

Besides offering a vehicle for an MTF proof-of-principle the MAGO experiment may also provide a route to demonstrating ignition. redesign of the MAGO second chamber so that convergence along the axis as well as radially occurred. a convergence of ten would more than suffice for ignition if the initial temperature were 300 ev and the compression was reasonably adiabatic. We must emphasize that this discussion is very stage, because neither the bulk plasma temperature or the life time of the bulk plasma has been established with certainty yet.

Assuming hemispherical compression,

experiment, fusion

speculative at this

@Hi-THE VNIIEF PIECES

VNIIEF high explosive pulsed power and ultrahigh magnetic field capability works as advertised. exceeds existing US capability. completed to date simply could not have been performed using off-the-shelf (JS technology. a variety of potential physics applications, beyond their successful \Ja= tm A=t-rmin-

This capability significantly The three experimental campaigns

field generators have

VNIIEF high

critical

tmmrature

the

MTF permits a complete rethinking of the entire driver/target configuration. Conventional target drivers (lasers, light ions, etc.) are optimized for conventional targets and are probably not appropriate for MTF in its extremes. For sufficiently strong magnetic fields, there is a continuum between conventional ICF target space and MTF space, suggesting a possible role for existing drivers. If the MAGO experiments confirm our calculations, the VNNIEF 200 MJ HEPP systems should allow a fusion ignition experiment to be attempted in the near future with a minimal capital outlay.

The September 1994 DEMG/liner experiment

a higher energy alternative source for present and future US pulsed power applications. coupled with the MAGO series of experiments suggest that VNIIEF may have all the pieces required to achieve thermonuclear fusion ignition, but almoat certainly provide the essentials for an If ignition is unambiguous MTF prwf-of-principle possible, then it can be demonstrated without a billion dollar capital investment.

experiment.

@Hi-FUSION SYSTEM CONFIGURATION

While the beam on target configuration is appealing for a fusion research program and possibly for other applications, it does put a very touchy high technology component between the necessary pulsed power supply and the target. MTF using the high explosive pulsed power capabilities of VNIIEF would eliminate the “middlemen”.

@Hi-AN PITF PROGRAM

up to about 10.

An MTF program should focus on three major goals: We must have a convening quasi-adiabatic heating (Tf > 2 To) of a magnetized plasma by a magnetically driven liner. (> 4 Kev) and high neutron yield (> 10A14) should be the next step. Finally, it is necessary to demonstrate thermonuclear fusion ignition and a significant burn-up fraction.

Achievement of fusion ignition temperatures

proof-of-principle

demonstration of

There are two reasonable candidates for an implosion

The obvious target plasma formation candidates are the

Both Los Alamos and VNIIEF have had extensive experience

Each goal requires both a hot, magnetized target plasma and a target implosion system. VNIIEF MAGO plasma for which characterization is in progress, and the Los Alamos cryogenic fiber Z-pinch for which only the early stages are characterized. system: with cylindrical liners magnetically driven to velocities in the range of 0.3 to 1.0 cm/us with convergence A quasi-spherical 3 has been demonstrated by VNIIEF (?) and Phillips Lab (?). This could satisfy conditions necessary for a proof-of-principle experiment. Each goal requires extensive computations to evaluate the trade-offs between initial temperature of the target plasma, the convergence required, the liner (or pusher) velocity, and the energy ;equired.

implmsion at 0.5 cm/us with a convergence of about

In addition,

We believe that a six year program costing about $ 3-6 M per year may suffice to demonstrate fusion ignition for MTF. ~‘or this programeachof the goalswouldrequire about three years with a computational effort defining each of the necessary experiments and providinq analysis of their results. overlapped to some degree, so that three years is a reasonable estimate of the time needed to accomplish all three goals. With more resources the time to demonstration could be shortened,

The tasks for each goal can be

@Hl=PROSPECTS 170R A FUSION PEACTOR

What are the prospects for an MTF reactor? We recoanize that the maanetic flux compression generators cannot be

These include

fusion ignition at low operating cost and no All these features make MTF very attractive as a

Magnetized target fusion has many attractive features. low implosion velocities, low convergence ratios, enhanced self-heating, the use of existing drivers with excess energy, and the possibility of demonstrating capital cost. future research direction in our quest for controlled fusion. They also point toward the possibility of a -cry economical fusion power technology. demonstrate fusion ignition. to this effort, that first major step could be accomplished at a much earlier date than is currently projected for the mainline fusion efforts and at a much lower cost.

Depending on the resources committed

However, the first major step is to

Puby lasers first demonstrated lasing,

Nor d~ transoceanic airlines still use

Based on our present knowledge, existing

Is to demonstrate fusion ignition. but they are rarely used today. internal combustion engines. 200 MJ L)EMG capabilities are more than adequate to achieve thermonuclear fusion ignition via MTF. MTF does not require a major capital equipment investment before the very first ignition experiment can even be attempted. been achieved can we truly say that controlled fusion is just an engineering problem. not have been predicted long before lasing was demonstrated, the potential of MTF (or any other fusion concep~) cannot be realistically evaluated until ignition is demonstrated.

Just as the myriad of laser applications could

Only when a large fusion burn-up fraction has

eHl=suMMARY

@Hl=ACKNOWLE!)GEMENTS

@REFNUM”2 @REFNUMSTY=Dawson,

@REFNuM=4 @REFNUMSTY=Widner,

@REFNuM=3 @REFNUMSTY=Lindemuth,

Beam Targets”,

@Hl=REFERENCES

@REFNUM=6

Bull. Am, Phys. Sot. 22 (1977) 1139.

R.C., Proceedings, First Inter

in Methods in Computational

@REFNuM=I @REFNUMSTY=Kirkpatrick, national Symposium for

J.M., Okuda, H., and Rosen, B., “Collective

Transport in Plasmas”, Physics 16 (1976) 281.

Electron

Space

The author thanks R.C. Kirkpatrick, R.E.Reinovsky, and P.T. Sheehey for comments, research support, and computations that contributed to the work presented here. Los Alamos and VNIIEF teams for their excellent performance in accomplishing the collaboration on the MAGO series of experiments.

We also wish to commend and thank the

@REFNUM=5 @REFNUMSTY=Sweeny M.A., Proceedings, First International Symposium for the

Evaluation on Current Trends in Fusion Research, Washington, D.C., November (1994).

for Magnetized Fuel Targets in Inertial Confinement Fusion, ” Nucl. Fusion 23 (1983) 263.

I.R., and Kirkpatrick, R.C., “Parameter

the Evaluation on Current Trends in Fusion Research, Washington, D.C., November

(1994).

M.M., v\Neut~~on producti~~jn from Relativistic

SOV. Phys. Dokl. 24 (i.979) 55-).

V.B., Los Alamos National Laboratory Seminar,

October (1994).

@REFNUt4-7

” @REFNUMSTY=Yakubov,

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