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High-density field-reversed configuration plasma for magnetized target fusion

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IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 32, NO. 1, FEBRUARY 2004

T. P. Intrator, Member, IEEE, Jaeyoung Y. Park, James H. Degnan, Senior Member, IEEE, I. Furno, Chris Grabowski, S. C. Hsu, Edward L. Ruden, Member, IEEE, P. G. Sanchez, J. Martin Taccetti, M. Tuszewski, W. J. Waganaar, Glen A. Wurden, Senior Member, IEEE, Shouyin Y. Zhang, and Zhehui Wang

A High-Density Field Reversed Configuration Plasma for Magnetized Target Fusion

Abstract—We describe a program to demonstrate the scientific basis of magnetized target fusion (MTF). MTF is a potentially low-cost path to fusion which is intermediate in plasma regime between magnetic (MFE) and inertial fusion energy (IFE). MTF involves the compression of a magnetized target plasma and pressure times volume (PdV) heating to fusion relevant conditions inside a converging flux conserving boundary. We have chosen to demonstrate MTF by using a field-reversed configuration (FRC) as our magnetized target plasma and an imploding metal liner for compression. These choices take advantage of significant past scientific and technical accomplishments in MFE and defense programs research and should yield substantial plasma perfor- 5 keV) using an available mance ( pulsed-power implosion facility at modest cost. We have recently shown the density, temperature, and lifetime of this FRC to be within a factor of 2-3 of that required for use as a suitable target plasma for MTF compression for a fusion demonstration.

cm before cm after com- compression and is expected to have pression. As plasma equilibrium it has high power density and is the ratio of plasma particle pressure to ex- ternal confining magnetic field. There is a large confining mag- netic field, 5 T prior to compression, and 500 T after compres- sion. The auxiliary heating power level from the theta-pinch for- mation is on the order of 100 MW, and approximately 1000 GW during flux conserver compression.

demonstrate the scientific basis of magnetized target fusion (MTF). MTF could be a reduced-cost path to a more attractive fusion energy system that takes advantage of a plasma regime between magnetic (MFE) and inertial fusion energy (IFE). Adiabatic compression of a magnetized target plasma would yield PdV heating to fusion relevant conditions inside a converging flux conserving boundary. We are exploring an innovative approach for creating compact pulsed plasmas with high

Our proposed physics demonstration of MTF requires a field-reversed configuration (FRC) magnetized target plasma and its translation into a region where an imploding metal shell can compress the plasma. A schematic is shown in Fig. 1. This strategy takes advantage of significant past sci- entific and technical accomplishments in MFE and defense programs research and should yield substantial plasma perfor-

Among alternate fusion concepts, the choice of the FRC con- figuration for MTF also confers the following other advantages:

small size which results in reduced total construction cost;

T. P. Intrator, J. Y. Park, I. Furno, S. C. Hsu, P. G. Sanchez, J. M. Taccetti, M. Tuszewski, W. J. Waganaar, G. A. Wurden, S. Y. Zhang, and Z. Wang are with the P-24 Plasma Physics Group, Los Alamos National Laboratory, Los Alamos, NM 87545 USA (e-mail: [email protected]).

repetition rate of 0.1 Hz, so that there would be time to clear the reactor chamber after each power pulse event;
most of the initial physics research can be conducted with

WE DESCRIBE a primarily experimental program to

Manuscript received July 30, 2003; revised September 16, 2003. This work was supported in part by the Department of Energy—Office of Fusion Energy Sciences under Contract W-7405-ENG-36.

We are not far from what is needed for a suitable target plasma for MTF compression and a fusion energy demonstra-

heat exhaust handling includes a natural axial divertor;
advanced fuel potential could be realized at high

mance pulsed-power implosion facility at very modest cost.

Fig. 1. MTF schematic showing plasma formation region and liner implosion section.

magnetic simplicity, because no toroidal magnetic field,
in a reactor, each pulse would utilize a fresh liquid first
geometric simplicity, because no captured magnetic coils

Index Terms—Field-reversed configuration, fusion energy, mag-

J. Degnan, C. Grabowski, and E. L. Ruden are with the Air Force Research

or center stack ohmic transformer are required;

the heart of the device sits on a table top;

This FRC has high-plasma density,

existing facilities and technology.

Digital Object Identifier 10.1109/TPS.2004.823974

or linked magnets are required;

5 keV using an available

Laboratory, Kirtland, NM 87117 USA.

netized target fusion (MTF).

and high temperatures.

large ion temperature;

I. INTRODUCTION

near 10

1, where

wall;

s-cm

and

153

A. MTF

plasma energy

, we can roughly estimate the cost as

II. BACKGROUND: SCIENCE AND TECHNOLOGY

Since system cost and size scale approximately with the

INTRATOR et al.: HIGH-DENSITY FIELD REVERSED CONFIGURATION PLASMA FOR MAGNETIZED TARGET FUSION

Fig. 2. FRC schematic of cylinder geometry including poloidal magnetic fields, toroidal current, theta-pinch coil, cusp/mirror coils, closed and open magnetic surfaces.

tion experiment. We show the high density and temperature of this FRC to be within a factor of 2-3 of that required, and found the lifetime to be within 2/3 of the design goal. This integrated project benefits from multiple collaborations with the Los Alamos National Laboratory (LANL), Air Force Research Laboratory-Kirtland (AFRL), Lawrence Livermore National Laboratory (LLNL), and General Atomics (GA).

MTF is a subset of magneto-inertial fusion (MIF), which includes all pulsed, high-pressure approaches to fusion in- volving inertial confinement of a plasma that require magnetic field in an essential way. For example MIF concepts include laser-heated solenoid plasmas, cryogenic fiber Z-pinches, flow-stabilized stabilized Z-pinches, and the composite Z- pinch. MTF specifically requires an imploding pusher to compress and PdV (where pressure P acts on a differential volume change dV) heat a magnetized target plasma, such as a spheromak or FRC, to fusion conditions. MTF involves plasma 5 keV) regimes intermediate ( between MFE and IFE and seeks to capitalize on the advantages of this intermediate regime (described in the following) [1]-[3]. Various flux conserving materials have been considered for the imploding pusher, including metal liners, gaseous or plasma pushers [4], and compressible liquid shells [5], [6].

For a D-T fusion scenario, the right-hand term on the right-hand side is relatively constant because 10 keV, is important, is fixed. Thermal diffusivity but relatively difficult to improve. Only density remains as the variable that we can use to influence the energy of a fusion system. Compared with MFE research, the necessity of reducing thermal diffusivity is relaxed because MTF operates at much higher densities than the MFE approach. Using conven- tional magnet technology and the engineering of steady-state power handling, the “conventional MFE density” typically is in cm . Inertial fusion scenarios are conceived the range of 10 as working with pulsed systems at much higher density and no magnetic field. On the other hand, a pulsed approach like MTF that takes advantage of magnetic thermal insulation could have much larger density than MFE and smaller

MTF invokes the compression of a magnetized target plasma to fusion conditions. Compact toroids such as the spheromak and FRC have been identified as candidate target plasmas candi- dates for MTF because of several potentially favorable features:

closed field line topology; 2) lack of internal material objects facilitating compression within a liner; and 3) ability to be trans- lated from the plasma formation region into a liner for compres- sion. LANL has a long history of toroidal confinement exper- iments, including the reversed-field pinch (RFP), spheromak, and FRC. We have chosen the FRC as the candidate that can best survive formation, translation, and compression [7], [8], [38], and which also offers some unique advantages over other pos- sible targets.

The FRC is an elongated, self-organized compact toroid state that has toroidal plasma current and poloidal magnetic field. In Fig. 2 we indicate the FRC as a closed-field-line torus inside a with an open-field-line sheath outside the separatrix radius separatrix. FRC equilibrium balances plasma pressure with ra- dial magnetic field pressure and axial field-line “tension.” For an ideal straight cylinder it has been shown [9], [10] that volume

Density is one of the few adjustable free parameters in the design of a fusion system, particularly when seeking a lower cost development path [2]. The fusion energy production per unit volume scales as density squared

where m s per unit volume can be characterized with a loss time

is the fusion reaction rate is the energy per fusion reaction. The losses so that

(probably anomalous) then the energy confinement time can be defined

is the characteristic ion temperature. The ratio of , which depends only upon the temperature

B. Motivation: A Potential Low Cost Route to Fusion

is the density m , , and

and the well known Lawson product

If we assume the systems have size

C. FRC as a Target Plasma

and diffusive losses

cm and

than ICF.

where

(2)

(3)

(4)

(1)

(5)

(8)

(7)

(6)

where

so that

In practical units

is the density and

IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 32, NO. 1, FEBRUARY 2004

averaged pressure inside the separatrix normalized to the external magnetic field pressure, is

Our theta-pinch formation method takes advantage of a large 1 kV cm azimuthal electric field which increases implosion velocity and consequently the the radial Green-Newton [11], [21], [22] magnetic field. This field drift speeds at the edge corresponds to equal Alfvén and

forms closed flux surfaces. Formation (2-3 s) and translation 10 cm s into the liner region can be accomplished [12] in a few s, a time short compared to the expected FRC lifetime (20-25 s). Two-dimensional magnetohydrodynamic (MHD) simulations [14] suggest that FRC compression could be underway 5 s after implosion.

and is the ex- is the coil radius, is the ternal separatrix magnetic field, , evalu- temperature. The FRC has high plasma beta ated with respect to . Active worldwide FRC research has resulted in significant experimental and theoretical progress, re- sulting in stable plasmas with good confinement properties.

The FRC offers many potential advantages as an MTF target plasma, including the promise of robust, closed flux surfaces that maintain their topology during compression, as has been observed [11] in compression, translation [12], stability ex- periments [13], and models [14]. Formation of an FRC using high-voltage theta-pinch technology is well established, and the plasma characteristics of the FRC (i.e., stability, transport, and impurity content) in the density and temperature range of interest are reasonably well characterized. Early reversed-field theta pinches formed FRC’s exceeding our target density [15]-[18], but the diagnostic methods and theoretical under- standing were less complete in the 1960s-1970s. The following are other desirable features.

is the ion mass in proton units, and for FRX-L opera- where is desir- 0.5-0.7 T. A high tion at limits the maximum trapped flux and, hence, able because the maximum plasma pressure in a theta pinch formed FRC. In- that is trapped (when the creasing magnetic liftoff field main field reverses and the FRC “lifts off” the wall) relative to can also increment resistive flux dissipation heating over the usual radial shock heating. The desired initial temperature 250 eV and trapped flux correspond to a bias field T. There is experimental evidence [23], [24] that a pressure bearing sheath forms which slows the flux loss during formation from convective to diffusive. Simple estimates of the magnetic lift-off field that is trapped (when the main field reverses and the FRC “lifts off” the wall) may be unduly pes- 0.5 where we operate simistic for large values of FRX-L. On the other hand, our collisional FRC (ion mean-free 2 cm) 1-2 cm compared to separatrix radius path may have worse flux retention properties during formation than those observed at lower density.

For MTF, the FRC plasma must survive long enough to translate into the liner volume for implosion. Fusion energy breakeven at expected implosion convergence factors requires sufficient plasma pressure. The key physics governing both lifetime and pressure is determined by magnetic flux retention during the FRC formation process. Theta-pinch FRC formation [8] uses an initial bias magnetic field (0.3-0.5 T for field reversed configuration experiment-liner (FRX-L) that is frozen in during preionization (PI), and then radially shocked by another reversed main bank field that is much larger (3-5 T in FRX-L). The radial jump in magnetic field induces a plasma toroidal image current. Field line reconnection at the ends then

Because of field line tension, the FRC undergoes axial contraction during radial compression [19]. A cylindrical contracts) obeying (6) and con- adiabatic implosion ( serving particles yields an FRC volume that scales as , i.e., more strongly than a two-dimensional (2-D) compression given by [20]. A full three-dimensional (3-D) compression could be achieved with shaped liners.
FRCs are formed inductively and are largely free of im-
stability that defies MHD predictions. Consequently, the FRC is a valuable platform for exploring fundamental plasma physics which gives rise to these proper- ties. One example is to understand the effect of strong flows on plasma equilibria and stability. Another is to explore the va- lidity of generalized relaxation principles which may govern FRC formation and equilibria, such as minimum dissipation

Although this research is focused on achieving MTF using an FRC, it also offers a strong plasma science component. The FRC configuration is unique among magnetic configurations. Among its unique properties are

high plasma
no or very little toroidal field;
dominant cross-field diamagnetic current and flows;
vanishing rotational transform, magnetic shear, and he-
The open field lines outside the separatrix act as a natural divertor that isolates plasma loss flux from wall bound- aries.

The latter two attributes may substantially reduce impurity mixing, a concern for MTF.

The FRC has been shown to exhibit resiliency during

E. Fundamental FRC Physics

translation and deformation.

D. Theta-Pinch Formation

purity line radiation.

40-80 mT,

kV cm

licity;

mtorr

(9)

;

F. Liner Implosion Technical Issues

III. TECHNICAL PROGRESS OVERVIEW

INTRATOR et al.: HIGH-DENSITY FIELD REVERSED CONFIGURATION PLASMA FOR MAGNETIZED TARGET FUSION

theory [25]-[27]. Some of these fundamental plasma physics questions reach beyond MHD single fluid models and may be related to geophysical and astrophysical phenomena.

During the last four years, we have made major progress in creating a high-density FRC target for MTF. We also successfully imploded two aluminum liners onto vacuum at AFRL-Kirtland, demonstrating parameters appropriate for our proposed liner on plasma experiment [28]-[30].

The broad utility of high-energy liners in defense programs and high-energy density programs has led to significant invest- ment in liner physics studies and technology advancement that will be useful for MTF. A flux conserving shell (liner) will be used to implode the MTF target. The interactions of the liner with the plasma interior involve physics and engineering ques- tions that also need to be investigated in the final stages of this project, which culminate in an integrated liner-on-plasma ex- periment [1], [2], [28]-[30].

The first three years of the past four-year project were con- sumed by the design, construction, testing, and integration of a high-voltage, high-current, pulsed-power experiment. By year two, we had assembled the essential FRC apparatus, including a low-inductance transmission line header that coupled the cable connections from the main capacitor bank to the single turn theta coil. Shakedown activities included finding a feasible compro- mise between good grounding, inductive connections, charging and firing configurations. We characterized the preionization process, and worked on suppression of electrical noise. Initially, we had no position control of the FRC that formed, and the ap- parent quick “loss” of the plasma indicated by midplane diag- nostics was a symptom of the FRC squirting out axially. The addition of cusp/mirror coils to each end of the theta coil along with capacitor banks and control systems aided magnetic recon- nection during the FRC formation and kept the FRC centered underneath the theta coil. These resulting FRC equilibria had rotational long lifetime, allowing growth of the classic instability which finally terminates the FRC.

We have formed high density FRCs that are within factors of 2-3 of the desired target parameters [8] and have fielded an array of diagnostics to measure many important characteristics. At the time of the peak current for the main bank, the formation parameters are quite acceptable, but they deteriorate as the FRC main bank rings later in the shot. The decompression of the FRC is due to crowbar switch modulation of the theta coil magnetic field, which results in large flux losses, and particle and stored energy losses as the FRC expands beyond the length of the theta coil. Typical current waveforms for cusp coils, theta-coil current in Fig. 3(a) and a time expanded view of the bias, PI, and main bank with ringing crowbar modulation in Fig. 3(b). The crowbar modulation was improved during the summer of 2003.

We benchmarked the PI startup plasma using only the bias and PI banks, when the main bank system was still under con- struction. The initial ringing theta-pinch behavior has good az- imuthal symmetry until late times. As seen in Fig. 3, our chosen -pinch coil at high frequency, induces a large azimuthal field which breaks down the gas.

The inductively coupled -PI method is very clean ( historically) compared to a Z-pinch axial current discharge PI approach with internal electrodes. It provides a high ( 100%) level of ionization, and is more likely to work at our high fill pressure (40-80 mtorr).

Even though high density FRCs were discovered 35 years ago, much has been forgotten about how to specifically operate in this regime. To prepare for translation and fast liner compres- sional heating, we require guidance from our suite of diagnostics cm ), temperature (to to increase the FRC density (to 10 s). The key to all of these goals relies on increasing the magnetic flux that is trapped during formation.

proved operation requires an increase in the trapped FRC equi- librium flux. The path to this end depends mostly on incremental improvements in the pulsed-power systems to increase the bias and PI fields, increases of gas prefill pressure, exploration of pre-PI schemes, and optimizing the timing sequence.

Fig. 4 shows a series of images for a bias and PI shot 87, cap- tured with an Imacon 750 fast framing camera on film, at a fill

Typical formation (and equilibrium) parameters are density

Fig. 3. Waveforms of cusp/mirror, PI, bias, and main bank currents. Cusp coils fire on the slowest time scales.

mWb (1 mWb), and 0.4 mWb (0.2 mWb); as will be shown later. Im-

cm 3 eV (200 eV), excluded

eV) and energy confinement time (to

-PI technique rings the theta

A. PI and Formation

cm , temperature

internal flux

(13)

B. Density Measurements

s, a flute like instability can be seen.

IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 32, NO. 1, FEBRUARY 2004

1.5 mWb. The internal flux estimated from the relation [11]

0.3 be- compressed and has small normalized radius cause the trapped flux is low. Peak formation excluded flux is 3 mWb and during decompressed equilibrium

Fig. 4. Framing camera images of end-on visible emission, taken at 1-(cid:22)s intervals, showing initial annular plasma breakdown, followed by radial breathing of the ringing theta pinch (PI+ bias) phase. Notice the high order flute structure developing late in time.

pressure of 43 mtorr . The zero crossings of the magnetic field due to the PI cancellation of the bias field are estimated to s. The light emission profile occur at can be seen to breathe radially as the confining magnetic field changes. At

is approximately 0.4 mWb at formation and 0.15 mWb during equilibrium. Here, is the measured axial magnetic field used for the excluded flux data, is a profile dependent param- eter that falls between 0 (high flux sharp boundary limit) and 0.25 1 (low flux sharp boundary limit). We have chosen consistent with past FRC experiments at LANL [11]. The liftoff is taken to be the value of estimated internal flux at the flux is assumed to be the moment liftoff time. The liftoff time when the density from the interferometer starts to increase, e.g., 10 s. The equilibrium internal in Fig. 5 density trace at flux is a smaller (15%) than expected fraction (30%) of the lift off flux, compared with a scaling estimate

which favors large radius experiments instead of FRX-L. The from the crowbar switch can also be seen at modulation of the bottom of column 2 in Fig. 5. The apparent modulation of the estimated internal flux (phi-int, bottom of right hand column) indicates that this estimate is suspect. It is physically reason- able to suppose that flux is lost, but not that it could be regained during the shot, as Fig. 5 would have us believe. Problems with the separatrix radius data lead to this and a similar apparent but 15 s. suspect oscillatory behavior in temperature at time half length, top of Flux loss may occur when the length (2 right hand column) of the FRC separatrix exceeds the coil length (36 cm), thus eliminating the cylindrical flux conserving radial boundary that confines the equilibrium. If the closed flux sur- faces bulge out the end of the theta coil and touch the quartz tube vessel, large particle losses would ensue. It is hard to estimate or conclude whether it is consistent a flux confinement time with

condition and pressure balance yields 300 eV for for- for Fig. 5 an average temperature 200 eV for the equilibrium period. The apparent mation and modulation in temperature after s is probably not real, but follows because we divide the calculated beta by the rotational mode. The par- modulated density during the 10 s can be estimated ticle e-folding confinement time from the time history of particle inventory (right-hand column), inferred from interferometer density multiplied by an assumed data ellipsoidal separatrix volume constrained by measured at different axial locations. The particle inventory estimate shows an average monotonic decrease after formation, in spite , which is a of the large crowbar modulated variations in physically reasonable behavior. This gives confidence about measurement, our physical assumptions (elliptic shape,

In Fig. 5, we show one typical shot with many FRC char- acteristics that can be inferred from the magnetics and density measurements. The left-hand column displays line density and density derived from the multichord interferometer. The central ro- (solid line) and off-axis (dotted line) chords show the s that triggers the demise of many tational instability at axis. FRCs, consistent with an oval shape spinning about the For this shot, peak formation density exceeds 4 10 cm and cm . There exist other shots equilibrium density is 2 with larger density but lower temperature, i.e., similar plasma pressure. The separatrix shape is estimated by fitting an ellip- data at four axial locations. Particle inventory soidal shape to follows from this volume times the density measured by the in- terferometer.

The encouraging data typified by Fig. 5 followed installation of cusp/mirror coils at either end of the theta coil. A cusp config- uration is created with respect to the initial bias field that evolves to a mirror 2-3 s later with respect to the reversed main bank field. The X-point field nulls enable consistent magnetic recon- nection and good FRC formation. The mirror centers the FRC under the theta coil instead of “squirting” it out axially. Next year, the translation experiment will take advantage of asym- metric mirrors to allow the FRC to exit one end and translate axially to a liner experimental region.

Flux Trapping: The theta-pinch approach tends to trap less than half [10] of the initial bias field. The disadvantage fol- lows from the contradictory requirements between high peak current (i.e., large capacitance) necessary to cancel out the bias field (i.e., create zero crossings for bias), and a fast ringing fre- quency (i.e., small capacitance). [21], [31]-[34]. Visible light diagnostics were used initially to optimize the timing and mag- netic field settings.

We had thought that our single main bank module would be marginal to attain these parameters, but our FRC pressure seems to be more constrained by how much bias flux is trapped than the main bank compression field. This FRC is slightly over

C. Improvements in Cusp Formation

D. Confinement of Particles

) built into this estimate.

Using the average

mtorr

(14)

INTRATOR et al.: HIGH-DENSITY FIELD REVERSED CONFIGURATION PLASMA FOR MAGNETIZED TARGET FUSION

Fig. 5. Analysis of one shot showing many quantities that can be inferred from excluded flux and interferometer (0-on axis; 1-2 cm—off axis) data. For the internal flux plot (phi int) indexes 1, 2 represent flux loops that straddle the midplane axially and 0, 3 loops are closer to the ends of the theta coil.

Multichord interferometer data can be inverted to estimate the density profiles. Fig. 6 shows crude radial profiles, one each mi- crosecond from formation through equilibrium and decompres- sion. The estimated major and separatrix radii from the excluded flux array are also indicated on the plots. During the equilibrium phase, the density profiles tend to be as expected. Eventually, hollow at the new Thomson scattering diagnostic will provide an inde- pendent measurement of the electron temperature at six axial spatial points on each shot. This point data will be compared with the results inferred from the excluded flux data bulk tem- perature derived from pressure balance, excluded flux, and line density. We also will soon cluster more interferometer chords in the central and edge regions of the FRC, yielding the resistivity at the field null and separatrix [35]-[37].

Separatrix radii for four axial locations are inferred from ex- cluded flux data. The excluded flux array together with the mul- tichord interferometer provide essential information on FRC can be in- formation and equilibrium. The separatrix radius ferred from axial magnetic flux loop data and a local magnetic in the region between the separatrix and the in- field value terior theta coil wall radius . Using radial and axial pressure [9], [10] balance, (6) for volume-averaged beta and interferometer density, we can back out the total tempera- The plasma particle energy is estimated from ture the product of the Fig. 5 particle inventory and average energy per particle (temperature).

mtorr. The PI bank been carried for 20 mtorr voltage has been pushed to 55 kV. The bias field has been in- 0.3 T. From a database of 35 shots, for “typical” creased to operation, FRC lifetimes are shown in the histogram of Fig. 7, 10 s, but extend toward 20 and are mostly in the range of s in a few cases. For these shots, we varied fill pressure from 30 to 60 mtorr, as well as the trigger timing for PI and crowbar relative to the main bank trigger. We expect this to improve as fields/fluxes are increased.

Trigger timing is also important. As the pulsed power systems become more robust, we can operate closer to the voltage limits. Typical number of shots per week is on the order of 30, with

Several campaigns have been undertaken to explore the ex- perimental knobs available to us. Surveys of fill pressure have

Fig. 6. Polynomial fits to multichord interferometer density data. Squares indicate chord locations.

H. Survey of Typical Operating Regimes

E. Equilibrium Characteristics

F. Radial Profiles of Density

G. Configuration Lifetimes

0 and flat near

TABLE I

REFERENCES

IV. CONCLUSION

IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 32, NO. 1, FEBRUARY 2004

SUMMARY OF TYPICAL SHOT PARAMETERS FOR FRX-L DATA AS OF MAY 2003, FOR PEAK AND EQUILBRIUM VALUES. DESIGN GOAL PARAMETERS ARE LISTED IN THE LEFT-HAND COLUMN

Fig. 7. Histogram summarizing 35 shots and the typical FRC lifetimes. For these shots, we varied fill pressure from 30 to 60 mtorr, as well as the trigger timing for PI and crowbar relative to the main bank trigger.

We have given an overview of the goals and status of the FRX-L experiment, as of spring 2003. This experiment represents a start on the road toward one realization of the MTF concept. MTF could be a relatively inexpensive and short term approach to an alternate fusion energy concept. Significant progress toward a target plasma has been achieved, with FRC parameters within a factor of 2-3 of the design goals. An outline of the technical achievements required to get to this experiment to its present state was briefly presented. A synopsis of typical recent data for the past year is shown. One shot was shown in detail and many plasma parameters are extracted from the dataset.

[8] J. M. Taccetti, T. P. Intrator, G. A. Wurden, S. Y. Zhang, R. Aragonez, P. N. Assmus, C. M. Bass, C. Carey, S. A. deVries, W. J. Fienup, I. Furno, S. C. Hsu, M. P. Kozar, M. C. Langner, J. Liang, R. J. Maqueda, R. A. Martinez, P. G. Sanchez, K. F. Schoenberg, K. J. Scott, R. E. Siemon, E. M. Tejero, E. H. Trask, M. Tuszewski, W. J. Waganaar, C. Grabowski, E. L. Ruden, J. H. Degnan, T. Cavazos, D. G. Gale, and W. Sommars, “FRX-L: A field-reversed configuration plasma injector for magnetized target fusion,” Rev. Sci. Instrum., vol. 74, pp. 4314-4323, Oct. 2003. [9] D. C. Barnes and C. E. Seyler, “Compact torus theory—MHD equilib- rium and stability,” in Proc. US-Japan Joint Symp. Compact Toruses and Energetic Particle Injection, Princeton, NJ, 1979, p. 110.

approximately 30% being main bank shots. We have brought the experiment to the point where the pulsed power systems generally work and we can take 5-10 main bank shots on a good day. We would like to increase both the initial bias and PI field by approximately 50%, and trap considerably more flux in the FRC. The main bank operating voltage is at the low end of its capability, and can be increased without a problem.

Incremental pulsed power improvements along with explo- ration of the operating parameters in November 2002-April 200 main bank shots 500 shots with 2003 have resulted in and 60 good “typical” shots. The average shot parameters are summarized in Table I. The columns indicate from left to right, parameters for design goal, peak, and equilibrium FRCs. The measured parameters have been used to estimate the internal flux.

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[16] A. Kaleck, H. Kever, L. Könen, P. Noll, K. Sugita, F. Waelbroeck, and H. Witulski, “Study of trapped reverse field configurations in a linear thetapinch experiment,” in Proc. Topical Conf. High Beta Plasma, 1967, pp. A4-1-A4-7.

[6] P. J. Turchi, A. L. Cooper, R. D. Ford, D. J. Jenkins, and R. L. Burton, “Review of the NRL liner implosion program,” in Megagauss Tech- nology and Pulsed Power Applications, P. J. Turchi, Ed. New York: Plenum, 1980, pp. 375-386.

[10] W. T. Armstrong, R. K. Linford, J. Lipson, D. A. Platts, and E. G. Sher- wood, “Field-reversed experiments (FRX) on compact toroids,” Phys Fluids, vol. 24, pp. 2068-2089, 1981.

[15] E. A. McLean, A. D. Anderson, and H. R. Griem, “Measurement of plasma density and particle losses in a large theta pinch,” in Proc. Top- ical Conf. High Beta Plasma, 1967, pp. A5-1-A5-5.

[7] G. A. Wurden, K. F. Schoenberg, and R. E. Siemon et al., “Magne- tized target fusion: a burning FRC plasma in an imploded metal can,” J. Plasma Fusion Res. Ser., pp. 238-241, 1999.

[5] P. J. Turchi, A. L. Cooper, R. Ford, and D. J. Jenkins, “Rotational sta- bilization of an imploding liquid cylinder,” Phys. Rev. Lett., vol. 36, pp. 1546-1549, 1976.

[3] D. D. Ryutov and R. E. Siemon, “Magnetized plasma configurations for fast liner implosions: a variety of possibilities,” Comm. Plasma Phys. Control. Fusion, vol. 2, pp. 185-201, 2001.

[11] M. Tuszewski, “Field reversed configurations,” Nucl. Fusion, vol. 28,

[13] M. Tuszewski, “Excluded flux analysis of a field-reversed plasma,”

[14] R. D. Milroy and J. U. Brackbill, “Numerical studies of a field-reversed

theta-pinch plasma,” Phys. Fluids, vol. 25, pp. 775-783, 1982.

Phys. Fluids, vol. 24, no. 2126, pp. 2126-2127, 1981.

pp. 2033-2091, 1988.

INTRATOR et al.: HIGH-DENSITY FIELD REVERSED CONFIGURATION PLASMA FOR MAGNETIZED TARGET FUSION

[19] M. Tuszewski, D. P. Taggart, R. E. Chrien, D. J. Rej, R. E. Siemon, and B. L. Wright et al., “Axial dynamics in field, reversed theta pinches. II: Stability,” Phys. Fluids, vol. B3, pp. 2856-2870, 1991.

[22] A. L. Hoffman, R. D. Milroy, J. T. Slough, and L. C. Steinhauer, “For- mation of field-reversed configurations using scalable, low-voltage tech- nology,” Fusion Technol., vol. 9, pp. 48-57, 1986.

[24] M. I. Kutuzov, V. N. Semenov, and V. F. Strizhov, “Trapping of magnetic flux during the formation of a compat toroid,” Sov. J. Plasma Phys., vol. 7, pp. 520-525, 1981.

[21] T. S. Green and A. A. Newton, “Diffusion of antiparallel bias magnetic field during the initial stages of a theta-pinch,” Phys. Fluids, vol. 9, pp. 1386-1388, 1966.

[18] A. Eberhagen and W. Grossmann, “Theta pinch experiments with trapped antiparallel magnetic fields,” Z. Phys., vol. 248, pp. 130-139, 1971.

[23] W. T. Armstrong, D. G. Harding, E. A. Crawford, and A. L. Hoffman, “Flux-trapping during the formation fo field-reversed configurations,” Phys. Fluids, vol. 25, pp. 2121-2127, 1982.

[20] R. L. Spencer, M. Tuszewski, and R. K. Linford, “Adiabatic-compres- sion of elongated field-reversed configurations,” Phys. Fluids, vol. 26, pp. 1564-1568, 1983.

Dr. Intrator received the LANL Student Mentor Award in 2001. He is a member of the American Physical Society and the American Geophysical Union.

T. P. Intrator (M’03) was born in New York City in 1952. He received the B.S. degree in physics from the State University of New York, Albany, in 1976, and the M.S. and Ph.D. degrees in physics from the University of Colorado, Boulder, in 1981 and 1982, respectively.

[25] D. Montgomery and L. Phillips, “Minimum dissipation rates in magne- tohydrodynamics,” Phys. Rev. A, vol. 38, pp. 2953-2964, 1990. [26] R. Bhattacharyya, M. S. Janaki, and B. Dasgupta, “Field-reversed con- figuration (FRC) as a minimum-dissipative relaxed state,” Phys. Lett. A, vol. 291, pp. 291-295, 2001.

[17] A. Kaleck, L. Könen, P. Noll, K. Sugita, F. Waelbroeck, K. Watanabe, and H. Witulski, “Limitation of the confinement of plasma in a linear theta-pinch with trapped reverse magnetic field,” in Plasma Physics and Controlled Nuclear Fusion Research (Proc. 3rd Int. Conf. Novosibirsk, 1968). Vienna, Austria: Int. Atomic Energy Agency, 1969, pp. 581-593.

Recently, he joined Los Alamos National Labo- ratory (LANL), Los Alamos, NM, as a Member of Technical Staff and is leading the effort to create a high-density field reversed configuration for magne- tized target fusion. He also has built a magnetic re- connection scaling experiment at LANL to study astrophysics issues in the lab- oratory. After research at the Cyclotron at the University of Colorado, Boulder, the tantalizing dream of a fusion power solution to our energy crisis inspired a plasma physics career. Subsequent physics, engineering, and teaching work at the University of Wisconsin included a host of basic physics tabletop experi- ments and nonlinear wave particle interactions in magnetic fusion devices such as mirrors, tokamaks, and a reversed field pinch. A sojourn as visiting scientist at Bell Laboratories, Murray Hill, NJ, in 1987 was followed by a year as Vis- iting Professor at the Université de Grenoble, France, in 1989.

I. Furno received the M.S. degree in nuclear engi- neering (summa cum laude) from the Politecnico di Torino, Torino, Italy, in 1995, and the Ph.D. degree in plasma physics from the Ecole Politechnique Fed- erale de Lausanne, Lausanne, Switzerland, in 2001. While pursuing the Ph.D. degree, he studied heat and particle transport induced by magnetic recon- nection during sawtooth activity in radiofrequency heated tokamak plasma. During the last year, he worked on RSX and FRX-L in P-24 as a Postdoctoral Appointee, where he developed plasma diagnostics and acquisition systems, and acquired a broad knowledge of the innovative plasma gun technology used to produce the plasma in the device. Currently, he is a Postdoctoral Appointee in P-24 at the Los Alamos National Laboratory, Los Alamos, NM. His research work mainly focuses on experimental plasma physics in magnetically confined laboratory plasmas for thermonuclear fusion and for basic plasma physics research. He has an extensive knowledge of plasma diagnostics and has designed and successfully implemented a number of systems fully integrated into the Tokamak á Configuration Variable, Lausanne. Currently, he is also involved in a project to develop miniature (submillimeter size) magnetic detectors in collaboration with the National High Magnetic Field Laboratory, Los Alamos National Laboratory, and Sandia National Laboratory, Albuquerque, NM. He has published about 40 works (26 on international refereed journals).

Since 1973, he has been with the Air Force Re- search Laboratory (AFRL) and its predecessors, Air Force Weapons Laboratory and Phillips Laboratory. There he designed, conducted, and directed research on high energy density plasmas, radiation diagnos- tics, and pulsed power. His recent work includes mag- netic pressure implosions of cylindrical and spherical metal shells for plasma compression. He is presently a senior physicist (GS-15 = DR-IV) and Technical Advisor of the Pulsed Power Branch (DEHP) in the High Power Microwave Di- vision of the Directed Energy Directorate of the Air Force Research Laboratory (AFRL/DEH).

[29] T. Intrator, J. M. Taccetti, D. A. Clark, J. H. Degnan, D. Gale, S. K. Coffey, J. Garcia, P. Rodriguez, W. Sommars, B. Marshall, F. Wysocki, R. Siemon, R. Faehl, K. Forman, R. Bartlett, T. Cavazos, M. H. Frese, D. Fulton, J. C. Gueits, T. W. Hussey, R. Kirkpatrick, G. F. Kiuttu, F. M. Lehr, J. D. Letterio, I. Lindemuth, W. McCullough, R. Moses, R. E. Pe- terkin, R. E. Reinovsky, N. F. Roderick, E. L. Ruden, K. F. Schoenberg, D. Scudder, J. Shlachter, and G. A. Wurden, “Experimental measure- ments of a converging flux conserver suitable for compressing a field reversed configuration for magnetized target fusion,” Nucl. Fusion, vol. 42, pp. 211-222, 2002.

[28] J. H. Degnan, J. M. Taccetti, T. Cavazos, D. Clark, S. K. Coffey, R. J. Faehl, M. H. Frese, D. Fulton, J. C. Gueits, D. Gale, T. W. Hussey, T. P. Intrator, R. C. Kirpatrick, G. H. Kiuttu, F. M. Lehr, J. D. Letterio, I. Lin- demuth, W. F. McCullough, R. Moses, R. E. Peterkin, R. E. Reinovsky, N. F. Roderick, E. L. Ruden, J. S. Shlachter, K. F. Schoenberg, R. E. Siemon, W. Sommars, P. J. Turchi, G. A. Wurden, and F. J. Wysocki, “Implosion of solid liner for compression of field reversed configura- tion,” IEEE Trans. Plasma Sci., vol. 29, pp. 93-98, Feb. 2001.

[34] R. J. Commiso, W. T. Armstrong, J. C. Cochrane, C. A. Ekdahl, J. Lipson, R. K. Linford, E. G. Sherwood, R. E. Siemon, and M. Tuszewski, “The initial ionization stage of FRC formation,” in Proc. 3rd Symp. Physics and Technology of Compact Toroids, 1980, pp. 184-187.

[37] A. L. Hoffman, R. D. Milroy, and L. C. Stienhauer, “Poloidal flux loss in a field reversed theta pinch,” Appl. Phys. Lett., vol. 41, pp. 31-33, 1982. [38] G. A. Wurden, K. F. Schoenberg, and R. E. Siemon et al., “Magnetized target fusion: A burning FRC plasma in an imploded metal can,” pre- sented at the 9th Intl. Toki Conf., Toki, Japan, Dec. 7-11, 1998.

He is currently a Technical Staff Member at Los Alamos National Laboratory, Los Alamos, NM, working on applied plasma physics and innovative confinement concepts for nuclear fusion. His research interests include plasma diagnostics, atmospheric pressure plasmas, and plasma-based neutron source development.

[30] J. M. Taccetti, T. P. Intrator, F. J. Wysocki, K. C. Forman, D. G. Gale, S. K. Coffey, and J. H. Degnan, “Magnetic field measurements inside a converging flux conserver for magnetized target fusion applications,” Fusion Sci. Technol., vol. 41, p. 13, 2002.

[32] H. Kever, “Theory of dynamical behavior of plasmas with internal magnetic fields during magnetic compression: Comparison with experiments,” Nucl. Fusion 1962 Suppl., pt. 2, pp. 613-616, 1962. [33] T. S. Green, “An investigation of the theta pinch using magnetic pick-up

James H. Degnan (A’90-M’99-SM’99) received the Ph.D. degree in physics in 1973 from the Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA, where he did his thesis work on ex- perimental nuclear reaction studies.

[36] R. E. Chrien and S. Okada, “Field reversed configuration profiles and resisitivities inferred from radial line density profile,” Phys. Fluids, vol. 30, pp. 3574-3578, 1987.

Jaeyoung Y. Park received the Ph.D. degree in astrophysical sciences from Princeton University, Princeton, NJ.

[35] M. Tuszewski and R. Linford, “Particle transport in field reversed con-

[27] L. C. Steinhauer and A. Ishida, “Relaxation of a two-specie mag-

[31] G. B. F. Niblett and T. S. Green, “Radial hydromagnetic oscillations,”

figurations,” Phys. Fluids, vol. 25, pp. 765-774, 1983.

netofluid,” Phys. Rev. Lett., vol. 79, p. 3423, 1997.

loops,” Nucl. Fusion, vol. 2, pp. 92-101, 1962.

Proc. Phys. Soc., vol. 74, pp. 737-743, 1959.

IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 32, NO. 1, FEBRUARY 2004

W. J. Waganaar studied electronics at New Mexico Highlands University, Las Vegas, NM.

Dr. Tuszewski is a Los Alamos National Labora- tory Fellow and a Fellow of the American Physical Society.

M. Tuszewski received the Ph.D. degree in nuclear engineering from the University of California, Berkeley, in 1976.

He is a noted authority on field reversed configu- rations, and more recently has been interested in in- ductively coupled plasmas and space plasmas. He has obtained four patents.

Chris Grabowski was born in Dayton, OH, on October 8, 1966. He received the B.S. degree in electrical engineering from Texas Tech University, Lubbock, in 1988 and the M.S. and Ph.D. degrees in electrical engineering from the University of New Mexico, Albuquerque, in 1990 and 1997, respectively.

During 1991 and part of 1992, he was a Re- search Student in the Pulsed Power Laboratory at Kumamoto University, Kumamoto, Japan, studying inductive energy storage pulsed power generators. After graduation, he worked as a Postdoctoral Researcher at both the Weizmann Institute of Science, Rehovot, Israel, and at Cornell University, Ithaca, NY, studying plasma spectroscopy and high-power traveling wave tube amplifiers, respectively. Currently, he is a Senior Staff Engineer with Science Applications International Corporation, Albuquerque, where he has had the opportunity to work on a wide variety of pulsed power projects.

For ten years, he was an Electronics Technician with Eberline Instrument Corporation, Santa Fe, NM. He is currently the Lead Operator and Electro- mechanical Technician for the FRX-L Magnetized Target Fusion Experiment at the Los Alamos National Laboratory (LANL), Los Alamos, NM. He has been responsible for or involved with most aspects of pulsed-power experimental operations at LANL for 20 years including design, fabrication, and trouble-shooting. He served in the U.S. Navy for four years as an Aviation Electricians Mate.

S. C. Hsu received the B.S. degree in electrical en- gineering from the University of California, Los An- geles, in 1993 and the Ph.D. degree in plasma physics from Princeton University, Princeton, NJ, in 2000. His thesis research was on the experimental investi- gation of ion heating during magnetic reconnection. After graduation, he brought a U.S. Department of Energy Fusion Energy Postdoctoral Fellowship to the California Institute of Technology, Pasadena, where he built and used a simple magnetized coaxial gun to study the dynamics of spheromak formation and also magnetic collimation related to astrophysical jets. In December 2002, he joined the P-24 Plasma Physics Group, Los Alamos National Laboratory, Los Alamos, NM, as a Reines Fellow in Experimental Sciences. He is now continuing basic experimental plasma physics research with an eye toward magnetic fusion en- ergy and plasma astrophysics applications.

After receiving the Ph.D. degree, he became Principal Investigator on tokamak plasma physics and diagnostics on HT-series tokamaks, ASIPP. He joined the P-24 Plasma Physics Group at Los Alamos National Laboratory (LANL), Los Alamos, NM, as a Postdoctoral Research Associate in 2001. After that, he was working on plasma diagnostics and plasma physics experi- ments on HT-series tokamaks. His research experiences and accomplishments on Tokamak plasma physics are illustrated by his publications, national awards, and approved China Patent. He is presently studying the formation of high-density field reversed configuration (FRC) plasma for Magnetized Target Fusion program at LANL.

Since then, he has performed research in the area of high-energy density states of matter for the Air Force Research Laboratory’s Directed Energy Directorate, Kirtland AFB, NM, and its organizational predecessors. He has developed several interferometric systems for the diagnosis of plasmas using coherent radiation sources across a broad spectrum: millimeter wave, far IR, visible, and UV. In addition, he has extensive experience in experimental, analytic, and computational efforts involving continuum dynamics of all phases of matter.

From 1998 to 2001, he was a Postdoctoral Researcher. He was then promoted to a Technical Staff Member with the P-24 Plasma Physics Group, Los Alamos Na- tional Laboratory, Los Alamos, NM, in 2001. He has had broad experience with developing plasma sources, and patented with C. Barnes for a new configuration for effectively producing directed plasma flow in coaxial channels in 2002. His research interests include fundamental plasma physics research, such as plasma dynamos, plasma interaction with magnetic fields, plasma-based electric propul- sion, innovative concepts for plasma confinement, and plasma technologies.

Glen A. Wurden (M’94-SM’00) was born in Anchorage, AK, on Sept. 9, 1955. He received three simultaneous B.S. degrees, in physics, mathematics, and chemistry (summa cum laude) from the Univer- sity of Washington in 1977, and the M.S. and Ph.D. degrees in astrophysical sciences (plasma physics) from Princeton University, Princeton, NJ, in 1979 and 1982, respectively.

Dr. Zhang received the Chinese National Award of Academician/Prof. CAI Shidong Plasma Physics Prize from China Plasma Physics Society in 2000 for his Ph.D. dissertation on developing an innovative fast-scanning millimeter wave heterodyne radiometer system for ECE measurements on HT-7 superconducting tokamak.

for magnetic fusion experiments in the P-24 Plasma Physics Group at Los Alamos National Laboratory, Los Alamos, NM. His research interests include magnetized target fusion, plasma diagnostics, alternate confinement concepts, including burning plasma issues.

J. Martin Taccetti (M’88) was born in Buenos Aires, Argentina. He received the B.S. degree in physics from The State University of New York, Stony Brook, in 1990 and the Ph.D. degree from the University of Maryland, College Park, in 1998. He performed his thesis work on free-electron lasers at the Naval Research Laboratory, Washington, DC.

Shouyin Y. Zhang received the B.S. degree from the University of Science and Technology of China, Hefei, in 1988 and the Ph.D. degree in plasma physics from the Institute of Plasma Physics (ASIPP), Chinese Academy of Sciences, Hefei, in 2000.

Zhehui (Jeff) Wang received the B.S. degree in space physics from the University of Science and Technology of Chin,a in 1992 and the Ph.D. degree in astrophysical science (plasma physics) from Princeton University, Princeton, NJ, in 1998.

He has many years of experience in electrical engineering, and has designed and built analog, digital, pulsed-power control, computer control, and interface electronics.

Dr. Wang was awarded the U.S. DoE fellowship for five years to support his graduate study at Princeton University. He received the American Vacuum Society Graduate Research Award in 1998.

He is presently a Staff Member of the Plasma Physics Group, Los Alamos National Laboratory, Los Alamos, NM, where his research involves the study of magnetized target fusion as an approach to

Edward L. Ruden (M’96) received the Ph.D. degree in physics studying plasmas from the University of California, Irvine, in 1988.

P. G. Sanchez received the B.S. degree from New Mexico State University, Las Cruces.

Dr. Wurden is a member of the American Physical Society and Phi Beta

Dr. Hsu was a corecipient of the 2002 Award for Excellence in Plasma Physics

Research, given by the American Physical Society.

He is the team leader

Kappa.

fusion.

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