J.H. Degnan- Compression of Field Reversed Configurations for Magnetized Target Fusion

8/3/2019 J.H. Degnan- Compression of Field Reversed Configurations for Magnetized Target Fusion

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COMPRESSION OF FIELD REVERSED CONFIGURATIONS

FOR MAGNETIZED TARGET FUSION

presented by

Dr J. H. Degnan

Air Force Research Laboratory

Directed Energy Directorate

Presented at Symposium on Current Trends in International

Fusion Research7-11 March 2005


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COMPRESSION OF FIELD REVERSED CONFIGURATIONS

FOR MAGNETIZED TARGET FUSION

J.H.Degnan, A. Brown (2), T.Cavazos (1), S.K.Coffey (2), M.Frese (2), S. Frese (2), D.Gale (1),

C.Gilman (1), C. Grabowski (1), B. Guffey (2), T.P.Intrator (3), R.Kirkpatrick (3), G.F.Kiuttu,

F.M.Lehr, R.E.Peterkin, Jr (1), N.F.Roderick (4), E.L.Ruden, R.E.Siemon (5), W.Sommars (1), Y F.

Thio (6), P.J.Turchi (3), G.AWurden (3), S. Zhang (3)

Directed Energy Directorate, Air Force Research Laboratory, Kirtland AFB, NM, USA

(1) SAIC, Albuquerque, NM, USA

(2) NumerEx, Albuquerque, NM, USA

(3) Los Alamos National Laboratory, Los Alamos, NM, USA

(4) Permanent address: Department of Chemical and Nuclear Engineering, University of New Mexico,

Albuquerque, NM, USA

(5) University of Nevada Reno, Reno, NV, USA

(6) DOE-OFES

This research was sponsored by DOE-OFES


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Elements Of Magnetized Plasma Compression, akaMagnetized Target Fusion (MTF)

Thin i mploding liner

Mega-ampere current

10 k eV plasma

Magnetic

guide field

Typical parameters:Initial Final

n 10 17 cm-3 10 20 cm-3

T 300 eV 10 keVB 100 kG 10 MG

Guide-field co ils

Plasma preheater and i njector Liner implosion sys tem

FRC

Conical theta pinch

Thin i mploding liner

Mega-ampere current

10 k eV plasma

Magnetic

guide field

Typical parameters:Initial Final

n 10 17 cm-3 10 20 cm-3

T 300 eV 10 keVB 100 kG 10 MG

Guide-field co ils

Plasma preheater and i njector Liner implosion sys temPlasma preheater and i njector Liner implosion sys tem

FRC

Conical theta pinch

~10


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MTF Is A Hybrid Of ICF And MFE

ICF relies on rapid imploding boundary to achieve adiabaticcompression of fuel

- requires driver to deliver megajoules in nanoseconds

- requires several 10s cm/microsecond implosion velocity

- validated by underground tests

MFE relies on magnetic field to confine modest density, hightemperature plasma for seconds or longer

- problems are instabilities and impurities

- has achieved gain ~ 0.5 (gain = energy out/energy in)

MTF uses magnetic field to suppress thermal conduction , imploding

boundary to compress plasma

- requires 10s of megajoules in ~1 to 10 microseconds- requires ~ 1 cm/microsecond implosion velocity

- greatly reduced driver power (x100 to 1000) relative to ICF


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Magnetized Target Fusion

Magnetized target fusion (MTF)

identified in US and Russia as an

alternate approach intermediate between

MFE and ICF parameter regimes

Closed magnetic field configurations

reduce electron thermal conductionlosses

Enables (slower) adiabatic compression

with modest driver requirements

~10X radial compression required

Typical precompression plasma

parameters: 100 eV, 1017 cm-3, 5 T

Required Plasma Energy vs. Density

for various transport assumptions

1

103

106

109

1012

1014

1016

1018

1020

1022

1024

1026

Density (cm-3)

PlasmaEnergy(Joules)

CT Classical

CT Bohm

ICF electron

thermal cond.

Chi=1m2/sec

MFE

MTF

ICF

LANL


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Closed magnetic field lines

Magnetic field line tension squeezes axially when radially compressed

Particles that drift across flux surfaces are lost to open field lines beyond

separatrix

Equilibrium lifetime is anomalously long (many Alfven times), but nottheoretically understood

LANL

Field Reversed Configuration

Self Organized Magnetic Equilibrium


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Initial diagnostics for FRC formation Diamagnetic field exclusion magnetic probe

array

Radial view laser interferometry

Axial view fast photography Current and voltage probes on all discharges

Later additional FRC formation diagnostics Vacuum ultraviolet (VUV) probe arrays for

purity monitoring and temperature, density

information

LANL

Diagnostics


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AFRL eight chord laser interferometer installed on

FRC formation system at LANL


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time (Qs)10 12 14 16 18 20 22

n

/1016(cm-3

)

0

2

4

6

8

10

12r! 0.0 cm

r! 0.7 cm

r!1.9 cm

r!2.4 cm

r!3.0 cm

r!3.4 cm

r!3.6 cm

r!4.2 cmr!5.2 cm

Density vs. time at various radii via Abel Inversion.

The radii chosen correspond to the closest approach of each laser

chord to the FRC axis (impact parameters). Shot 1973


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radius (cm)0 1 2 3 4 5

n

/1016(c

m-3

)

-2

0

2

4

6

8

10

10 Qs

12 Qs

14 Qs

16 Qs

18 Qs

20 Qs

impact parameters

Density vs. radius at various times for FRC

inferred from Abel Inversion algorithm.


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FRC

parameter

How

measured

goal Experiment

peak

Experiment

equilibrium

comments

density laser

interfer-

ometry

1017 cm-3 ~ 6 x 1016 ~ 2 x 1016 has toroidal

profile

Temperature

Ti } Te

via

density

and

pressure

from field

exclusion

~ 200 eV~ 200300

eV

~ 100 eV

lifetime via

n, p vs t

~ 20 Qsec ~ 10 Qsec may be

limited by

crowbar

ripple

FRC status as of mid 2003: achieved parameters are

approaching pre-compression goals


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ASSEMBLY DRAWING

SOLID LINER

PP-99028-1A

1999 SHOT SERIESr = 5 cm, 1 m/m < t < 2 m/m

30 cm TALL CYLINDRICAL LINERENGINEER:

CHECKER:

DRAFTSMAN: U.S. AIR FORCE

SCALE:

DRAWING NO.

TITLE:

PL-WSP

D.GALE

COMPUTER FILE NAME: :

D.GALE

1/3S99ASY6A.DWG

SHT 1 OF 1

FRC Compatible Imploding

Liner Hardware Design

- The 30 cm long liner

implosion experiments

extend our experience to

longer liners

- The diagnostics on these

initial shots include flash

radiography, interior

magnetic field

compression, dischargecurrent and voltage, and an

interior instrumented

impact package


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Shiva Star Facility at AFRL

Shiva Star Capacitor Bank (up to 9 Megajoules, 3 Qsec)

available now for implosion - compression experiments

82 kV, 1300 uF, 44 nH

for first Z-pinch driven

long liner experiments

~12 Megamp, ~10Qsec

risetime discharge

implodes 30 cm long, 10

cm diameter, 1.1 mm

thick Al liner in 24Qsec

4.4 MJ energy storage

gives 1.5 MJ in liner KE


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Radiographs from FRC compatible

Liner Implosion on Shiva Star

t = 0.0Qsec, diam = 10 cm

Achieved velocity, radial convergence, symmetry, stability

needed for compression of FRCs to MPC conditions

13 x radial

convergence

Shot 1

20.0Qsec

Shot 2

22.0

Qsec

Shot 2

23.0Qsec

Adjacent

lower

electrodeMid-gap

Central probe

package (1

cmdia.)

LinerLower electrode

Liner

Central probe

package

(0.64 cm dia.)

Shot 1

23.5Qsec


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Avoiding Sliding Liner-electrode

Contact

Avoiding the sliding liner-electrode

contact is desirable in order to:

- Avoid impeding FRC injection into

interior of liner- Improve purity of injected FRC

- Improve axial diagnostic access

Two approaches to achieving this are:- Using deformable liner-electrode

contact for Z-pinch driven liner

- Using a theta-pinch driven liner


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Connecting current to the liner

Uniform-thickness liner Variable-thickness or shaped liner

Glide-plane electrodes

used in 1999 Shiva-Star experiments

would interfere with FRC injection Shaped liner recently tested

Liner


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2D-MHD simulations indicate feasibilty of

deformable liner-electrode concept

Deformable Liner-Electrode Contacts Offer Advantages in Purity of the

Compressed Plasma and Diagnostics Access for Z-pinch Driven Liner;

these examples are for8 cm diameter electrode apertures

Double frustrum and smooth liner

initial thickness profiles

Double frustrum profiled

liner density contours at ~ 1

Qs before peak compression

Smooth profiled liner

density contours at ~ 1 Qs

before peak compression


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2D-MHD simulated density contours for similar

parameter liner implosion, at 0.5 Qs before stagnation.

Experimental radiograph for portion of liner

adjacent to electrode, at 22 Qs after start of current,

approximately 0.5 Qs prior to peak compression.

Bottom of liner to top of field of view is

approximately 4.5 cm.

Static radiograph of portion of liner adjacent

to electrode, prior to experiment. Innerdiameter = 9.78 cm.

Overlay of 2D-MHD simulation density contours and radiographs at

approximately same size scales.

Deformable contact liner implosion performed with 8 cm

diameter electrode apertures; results indicate that Z-

pinch imploded liner approach is feasible


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Top: radiograph of liner at t=0, near mid-gap,

ID = 9.78 cm, OD = 10.0 cm.

Bottom: radiograph of liner at t = 22 Qsec, near

mid-gap. ID of non-m=0 portion $ 0.58 cm,

corresponding to radial compression of innersurface ~ 17. We believe that the m=0 portion

is right at mid-gap. If there had been an FRC

inside, it would be compressed > 10x radially

prior to significant growth of this instability.

Mid-gap radiograph indicates ~ 17 x radial

compression of inner surface

We suspect this late m = 0 feature is due to release of initial axial compression,

combined with thickness derivative discontinuity (from double frustrum thickness

profile) at 9 cm from mid-gap. Both the initial axial compression and the thickness

derivative can be removed by design change.


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Left: 200 nanosec optical framing photo, axial view, of load. Inner

diameter of opening is 8.0 cm. Photo used Xenon flash backlighting.

Right: 200 nanosec optical framing photo, axial view, of load at

21Qsec into implosion discharge. Inner diameter of smallest part of

liner (most imploded part) is 1.5 cm.

Axial view fast optical photos indicate symmetric

implosion of inner surface of liner with inner

diameter consistent with simulation


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Mach2 2D-MHD simulation density contours for half height of liner at t =21 Qs and 22 Qs for double frustrum liner thickness profile from z = 0 to 6

cm, uniform thickness 1.1 mm from z = 6 to z = 14.5 cm, thickness tapers

from 1.10 to 1.075 mm from z = 14.5 cm to mid-gap. Electrode aperture

radius is 4 cm.

t = 21 Qs t = 22 Qs

R = 4.0 cmR = 0 cm

Z = 0 cm

Z = 15 cm = mid-gap

An ~ 1 mil (.025 mm) thinning of liner over central cm

near mid-gap would explain late m = 0 feature


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Alternative liner thickness vs profiles are being

examined via Mach2 simulations

A family of such simulations uses an analytic profile which includes Gaussian

thinning region a few cm from electrodes

-

-

(

E

-

!2

00n/1n/1

3zz

exp1

zB

A

zB

ARzr

Z0 = distance from liner midplane. Zo = 11.5 corresponds to 3.5 cm up from electrode. Z00 = 3.5

( is the half width at half max and E is a measure of the amplitude.

Other parameters are defined in following table (next slide)


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4 cm electrode inner radius

Baseline 01 03 05 06 07

07-1 07-2 08 08-1 09 09-1

Contour plots show half (15 cm) of 30 cm tall, 5 cm initial outer radius, Al liner position and shape at 21

microseconds after start of 1300 microfarad, 80 KV, 44 nanoHenry initial inductance Shiva Star discharge,

with standard safety fuse. Initial liner thickness is 1.1 mm at mid-gap (15 cm above lower electrode).

2D-MHD simulations indicate that use of Gaussian thinning

regions a few cm from electrodes controls divergence of liner

ends; variants of this are being investigated computationally

15 cm

mid-gap


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Current peaked at ~ 12 megamps, at ~ 10 Qs after start of current

rise. Insulator crowbar occurred at ~ 17 Qs, as expected.

Normal current delivery to liner and symmetry were

obtained for experimental Bi-frustrum profile)case

1.40E+7

-1.10E+7

-7.50E+6

-5.00E+6

-2.50E+6

0.00E+0

2.50E+6

5.00E+6

7.50E+6

1.00E+7

1.25E+7

30.000E-60.000E+0 5.000E-6 10.000E-6 15.000E-6 20.000E-6 25.000E-6

I_corrected CCW.dat

I_sum_arms.dat

I_bdot1.dat

I_bdot2.dat

I_bdot3.dat

MTF shot on Dec 09, 2003


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Simulation Details: FRC Formation

and Translation

The FRC formation uses a flux-basedresistive diffusion model.

The simulation includes

Thermal diffusion Radiative emission

After about 2 Qs, the forming FRCtranslates itself down the formation region

into the liner implosion region. We generally use an FRC from ~ 4 Qs into the

formation simulation to insert (interpolate) intothe imploding liner simulation.


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FRC Formation and Injection Setup

Formation

And

TranslationRegion

Implosion

Region

Schematic

(not to scale)

axis

axis

Liner (not in

formation/translation

phase)

Actual Block Structure

Flux Input: 1

Flux Input: 2

Flux Input: 3

Flux Input: 5

Flux Input: 4

m


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FRC Formation and Translation: Te

& Flux

t = 0Qs t = 1Qs t = 2Qs t = 3 Qs t = 4Qs t = 5Qs

Liner

Implosion

R

egion


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Integration of the Two Simulations

Around 13 to 14 Qs, we interpolatethe FRC simulation data into theliner implosion simulation andcontinue the implosion.

We can vary the time of the insertion(relative to the liner implosion) andthe age of the FRC.

The following series of figuresshows the liner (in white), the

temperature, and the flux lines asthe liner implodes.

In this particular simulation, an FRC4.2 Qs old is inserted into the liner at

13 Qs as shown at right.


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Early Liner Evolution with Injected FRC

t = 13 Qs t = 13.5Qs t = 14Qs t = 14.5Qs

The downwardmomentum of theFRC tries to forceit out the bottomof the liner.

The mirror fieldtrapped in theimploding linercaptures it, butsome mass

escapes.

The white line is the liner.


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Liner Evolution with Injected FRC

t = 15Qs t = 16Qs t = 17Qs t = 18Qs t = 19 Qs

This combination of timings seems to captureand re-center the FRC.

The grid motion is stopped at 17.4Qs

The lower portion of the grid is shown in the inset


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Late Liner Evolution with Injected FRC

By 20Qs, theliner has com-pressed to aninner radius of0.5 cm. The temperature

in the center ofthe FRC is over8 keV.

There are

temperatures ashigh as 13 keVwithin the FRC,near the axis.

t = 19.5Qs t = 20Qs


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Design concept for integratedFRC formation hardware with

imploding liner compression

hardware is evolving

- adequate space for existing

FRC formation load hardwaredesign in vertical orientation

under Shiva Star center section

with implosion load hardware

- even more space available with

re-positioning of FRC vacuumpump


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Presently planned layout of FRC Formation

Hardware Under and Around Shiva Star

Main = single re-configured

Shiva Star module

PI = pre-ionization bank

Bias, guide, and cusp banks

in NE sextant of floor space

rail mounted FRC formation

train is under Shiva Star B

transmission line when mated

to implosion chamber

rail mounted FRC formation

train is withdrawn to NE

corner of workspace for FRC

formation experiments with

greater formation diagnostics

complement, allowing other

uses of Shiva Star

Re-configured Shiva Star module

FRC formation load in axial orientation


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Can Imploding Liner Magnetized Plasma

Compression Be Made Repetitive?

Implosion-compression of several-cm-radius shells on the 1 to 10 microsecond timescale can be used for magnetized target fusion (MTF)

This can be done in a manner with standoff of the driver, e.g., using arrays of laseror particle beams, which enables repetitive operation (for power plants orpropulsion)

Similar to inertial confinement fusion (ICF) drivers, but with 103 to 104 times

slower pulses, hence easier There are also schemes for repetitive operation of magnetic pressure driven liner

implosions (R.W. Moses et al, LA-7683-MS, 1979), and for pneumatic pressuredriven implosions of rotationally stabilized, re-usable liquid Li liners (P.J. Turchi etal, Phys. Rev. Lett. 36, 1613 (1976))

A plasma jet spherical array compression scheme has also been proposed(Y.C.F.Thio et al, Proceedings of Second Symposium of Current Trends inInternational Fusion Research, 1999)

Single shot versions of such implosion-compression can be done now via magneticpressure implosions, using our existing large capacitor bank

Such single shot implosion-compression experiments can be used to investigatecritical technical issues before developing and building more expensive, repetitivedrivers

Documents

J.H. Degnan- Compression of Field Reversed Configurations for Magnetized Target Fusion