Electromagnet Designs on Low-Inductance Power Flow Platforms

860_31524964

Magnetization Hea ingCompr s ion

Electromagnet Designs on Low-Inductance Power

Flow Platforms for the Magnetized Liner Inertial

Fusion (MagLIF) Concept at Sandia's Z Facility

D. C. Lamppa, M. R. Gomez, L. M. Lucero, D. C. Rovang, R. J. Kaye Sandia National Laboratories*, Albuquerque, NM USA

J. Meissner, M. Ales

Milhous Company, Amherst, VA USA

2018 IEEE International Power Modulator and High Voltage Conference

" Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering

Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, lnc., for the U.S. Department of Energy's

National Nuclear Security Administration under contract DE-NA0003525. SAND2018-XXXX C.IISMCW.1SAND2018-5911C

This paper describes objective technical results and analysis. Any subjective views or opinions that might be expressed

in the paper do not necessarily represent the views of the U.S. Department of Energy or the United States Government.

Outline of today's discussion

n Sandia's Z Machine and the MagLIF concept n Pre-magnetizing the fusion fuel with the Applied B on Z (ABZ) system n Making a more efficient inefficient coil: Designing an electromagnet for Low-L n The path forward to 20 - 25 T

El Page...t.

SANDIA'S Z MACHINE AND THE MAGLIF CONCEPT

Sandia's Z Machine uses large currents (>25MA) to generate 100-MBar pressures for HEDP experiments II r -0441 1 10 4 -NI 6,

751111 ari a t

'.1 33 m
diameter 80
605

1(5 40

ci 20

Marx generators

pulse-forming lines insulator stack 67 TW 20TW

0.51 1.5

time (vs) 2.5

SandiaNationalLaboratories

Magnetically-Driven Implosion

MBar drive current Implosion time - 50 ns; stagnation - 0.1-1 ns100 MBar at 26 MA and 1 mm Magnetized Liner Inertial Fusion (MagLIF) combines three stages that reduce fuel compression requirements to achieve fusion conditionsApplied + B-field A Laser entrance hole Liner

Cold DT fuel

Axial B-field

Pre-Magnetization

Compressed

B-field

Current A

AAA

Current-

generated

B-field

''.......-...." &

Z-Driven lmplosion

Liner unstable but

sufficiently intact

Compressed fuel reaches

fusion temperatures r

AppliedLaser heated B-field

fuel

Liner beginning

compression

Azimuthal

drive field

Laser Pre-Heat

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Laser 20(a)

B-field

L /j.....,--- ->.

29503000 3050Time [ns]3100

S.A. Slutz et al., Phys Plasmas (2010); A.B. Sefkow et al., Phys Plasmas (2014); M. R. Gomez et al., Phys. Rev. Lett. (2014). 5

Pre-Magnetization relaxes implosion convergence

requirements by helping confine heated fuel

Without Magnetic Field

With Magnetic Field

Time-integrated x-ray

self-emission seen in radiographs Low B L._ A 1-Z

High B

When magnetized, MagLIF Liners have reduced x-ray

self emission (left) and particles are confined within fuel on cyclotron orbits (right)

Neutronsil

.e12 100

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10 L 1 0 derv±0.7 den=1.1 1=1.8 den=3.0 30 20 20 30
ti i Energy Deposited (kJ) 10 Fusion yield trends for various fuel density, laser preheat energy benefit from increased magnetic flux density • A highly magnetized fuel inhibits loss by trapping electrons to axial field lines and reducing radial thermal conduction to cold liner wall • The usual azimuthal MRT instability becomes helical; initial B-field may stabilize the liner during compression to improve fusion conditions 6

PRE-MAGNETIZING THE FUSION FUEL WITH THE

APPLIED B ON Z (ABZ) SYSTEM

The Applied B on Z (ABZ) capacitor and coil system designed to provide 10 30 T within liner volume • Two 4-mF, 15-kV capacitor banks store 900kJ total. • Paralleling diodes, 125mQ overcurrent protection per bank. • Switchyard dummy load inductor available for system checks. • 0.8 - 3mH coils ensure 2-6ms risetimes for magnetic diffusion •Vacuum feedthrough utilizes encapsulated transition between coaxial cable drive and coil loads /

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Z Center Section Vacuum Chamber

Magnetic Field Coil

Assembly on Z

Center Section

• •

Cable Header

Capacitor Bank #1q

C=4 roF

R = 11.8 rnri

ABZ Bank 1

ABZ Bank 2

6.2 roCI

6X 24' DS2168

6X 28' OS2168

Capacitor Bank #2q

Switchyard Test load

124rn0

Current limiting

resistors 124m0
l 19.1 mr) 13.6 mLi0.9-2mH

8X 182X 35'R -132-1140ID5.2323 1SC3052323

Junction

Box /Switchyard and protection circuitry

Verification

coil

Vacuum

feedthrough

Junction

box

C=4 ttIF

=11.8 mr1

6.2 mC1

D. C. Rovang, et al, Rev. Sci. lnstrum. 85, 124701 (2014)8

Integrating electromagnets onto the target

geometry requires changes in Z power flow • Initial guidance was to prioritize radial diagnostic access and • field uniformity in liner

1Top Coil

X-ray diagnostics

Ir-Bottom

L Coil

Anode

L - 17MA Drive Current

r=2.5cm • We designed coil pairs with 1-2.5cm axial spacing • An Extended Power Feed was needed to raise target above the bottom coil of a split pair into uniform field region • ABZ coil pairs consist of an 80-turn top coil and either a 60- or

80-turn bottom coil

MagLIF

Liner

SandiaLIM NationalLaboratories

• Helmholtz-like pairs provide <1% field uniformity • 5cm-bore coils magnetize - 75cm3 region to 10 - 20 T

Magnetic

Field

(T) 10.12 10.1 10.08 10.06

10.040 2 4 6 8

Axial Distance (mm)

10.06 - •

7, 10.04

u: c 10.02

10 0 2 4 6

Radial Distance (mm)

2D Transient magnetic calculations axial and radial

lineouts showing -1% field variation within liner9

The Extended Power Feed platform was designed

with three coil configurations in mind

Full-Access Spacinq (60-80)

• 10-T Operating point • - 25-30mm coil spacing for radial diagnostic access • 90+ shots on Z since 2013

Limited-Access Spacinq (80-80)

15-T Operating point

- 10-14mm coil spacing for radial diagnostic access

15+ shots on Z since 2013

No-Access Spacinq (230-turn)

20-25-T Operating point

No radial diagnostic access

Never shot on Z in this

configuration ...

SandkiNationalLaboratories

10

The Extended Power Feed limits achievable drive

pressQures from the Z current pulse 10r 0 -10 E -20 o o • -300_ -40 -50 -60 -70

Bottom Coil

10 20 30 40 50 60

radial position [mm]

Sandiaa mit NationalLaboratories

• Each additional nH of initial feed inductance reduces deliverable machine current by -0.8 MA • Higher power feed voltage drives nonlinear loss mechanisms • Z's magnetic drive pressure should increase in step with ABZ field and laser preheat energy to maintain liner convergence • We are also already near the Z Facility's peak charge voltage

The extended power feed results in

initial load inductance of 7.2nH 100.0
1.0 0.1

Imax=17.4 (7.2 nH 80 kV)

Imax=21.1 (4.5 nH 90 kV)

lirrax -22.6 (3.5 nH 95 kV)

010 20 30 40 50

Bz Tesla

Fusion yield increases with magnetic field and drive current11

By reducing feed inductance, Z can deliver

more current to a Ma • LIF liner -20 -25 0 10 20 30 40 50 60 radial position [mr] E 0 o o0_

Ei -10

-15 -20 -250 10 20 30 40 50 60 radial position [mm] (C) 4.0nH -250 10 20 30 40 radial position [mm] Initial inductance is reduced by lowering axial extent of feed (A), reducing power feed A-K gap (B), and return can volume (C)

25.0

20.0 15.0

10.0 -

5.0 -

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2.5 nH

3.5 nH

4.5 nH

5.5 nH

6.5 nH

0.0 2950 3000 3050 3100

Time (ns)

Simulated load current profiles for varying final

power feed inductances and imploding MagLIF liner Hutsel, et a ., PhyRev AccelBeams, 21, 030401 (2018) 12 The " 5 . 1 n H Low-Inductance (Low-L) platform uses

230-turn coil to magnetize MagLIF linerg_

-1cm

Diagnostic

accessAnode

Current Flow

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AO622A1 Calculated IN for 7.5mm tall target - ABZ Vein, 110.5kit, !peak = 8.4 kA 14 12 • p 10 c 8 LT_ 6 czi)co24

I z=7.5mm 2

z=3.8mm z= Omm •

X: 4.7

Y: 12.99

X: 4.7

Y: 10.34

-z=ornm z=3.75mm z=7.5mm

0 0.6 11.5 2 2,6 3 3.6 4 4.5 5 5.5

Ti me (ms)

ANSYS Maxwell Transient-Magnetic calculations predict -23% axial variation of field in 7.5mm tall target (above); -32% for lOmm tall target 13

It is remarkably inefficient to utilize the

external field of the 230-turn coil like this

B [tesia]

1 26.0
24.3
22.6
20.8
19.1 17.4 15.6 13.9 12.2 10.4 8.7 7.0 5.2 3.5 1.8 0.0

Coil Envelope

Field distribution at 4.2ms (time of Z trigger)

• • . • .

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Coil was designed to produce 25-T at coil midplane for No Access configuration Not enough headroom in bank voltage for Bz_ayg > 12-T By reducing coil height by 50% (230 4 115 turns), average Bz at target drops by only 6%! Adding 2 outer radial layers would increase field by 18%!

We can design a better coil for this application.

24.00

Coil Midplane Lineout

Curve Info

- 1131

Liner Top

(z = lOmm)

NameXY

m 137.7450.12..9014 m247.54149.2923

Liner Bottom

= Dm m) " I '10.0030.00

Distance [r-nr-n]

I '4000I '50.00 60.00

MAKING A MORE EFFICIENT INEFFICIENT COIL:

DESIGNING AN ELECTROMAGNET FOR LOW-L

Program guidelines dictate ABZ coil design path

The MagLIF program looks to increase constituent parameters in lockstep • Integration by September 2018: • ABZ field between 15 - 20 T • Z Machine delivering 19 - 20 MA • Laser preheat of 1 - 2 kJ • Integrated by September 2020: • ABZ field between 20 - 25 T • Z Machine delivering 20 - 22 MA • Laser preheat of 2 - 4 kJ

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16

Coil Design Requirements

• Flux Density: • Low-L Coil shall be able to magnetize target to 15-T average across the liner. • Low-L Coil should be able to magnetize target to 20-T average field across the liner. • Liner Uniformity: Equal or lower than existing Low-L platform: - 32% across 1.0mm target. • This is a lower priority than flux density. • Bank Dynamics: • Rise time should be < 6.1 ms

• Low-L Coil shall achieve requirements with one-bank operation at 13.5kV max (limits coil inductance)

• Lifetime and pulsed behavior: • Low-L Coil should achieve required field strengths using - 10kA current

Enables coupling to 60- and 80-turn coils

• Demonstrate coil lifetime of n=10 shots at required field strengths

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17 Loosely constrained parameter space required staged analysis SandiaNational approach to "optimize" output design Laboratories

Parameters

• Initial coil diameter • Axial layers (how "tall" is it) • # of zylon internal reinforcement shells • Thickness of zylon reinforcement shells • Outer coil radius rMATLAB field calculations - Calculate Bz(0, z) - Calculate Rpc, Lijc - Turn geometries (r,z)

RDC, LDC

lGeometries,

Shell pressures

. .

Drive V, I

MATLAB ABZ bank modeler

- Time of peak current (Tpk) - Vchg required - Ohmic heating of coil - Emag, Ealec, and efficiency

1000s of runs

Maxwell 2D Magnetostatic Geometries

- Confirm Lijc - Verify Bz (0, z) - Bulk Lorentz forces (r,z)

Surveyed parameter space yielded

-3400 design variants

Distributed Lorentz Forces

lOs of runs t-

Maxwell 2D Time-harmonic

- Confirm Rpc

Estimate RAc

\

ANSYS Mechanical Static Structural

Utilizing nonlinear solver, nonlinear Cu alloy model, orthotropic zylon model - Stress as a function of radius - Elastic, plastic strains as a function of radius - Bulk Lorentz forces (r,z)

1 f ,,1 o vi 1 uno

3- and 4-shell variants of 13-axial-layer coil advanced to detailed design

10 -10E -20-c -30 • -40 -50 -60

1010131313131313131310101313131313131313101013131313131313131013131MIMEMIMI1013131MIMIMMI1013131MIMEMIMI1013131MIMEMIMI1013131MIMEMIMIE113131EMMIMI

AIMIMIE1131313131313•113131311111111113131313

020 40 60

Radius (mm)

80
10

WEIMIMEIMEMODZIMMIDDIMIDZIDIDZIMODZI

-10DO DODO DODIDZIMODZIDIDZIMODZIDO DODIDZIMODZIDO DODIDZIMODZI -20 c3)

DO DODO DOmM

DIDZIMODZIDIDZIMODZIDIDZIMODZIoDIDZIMODZI-30 DODIDZIMODZIxxxx XX XXX XXX -40 -50 -60

0 20 40 60

Radius (mm)

80

MATLAB-generated 3-shell and

4-shell Low-L coil geometries

n

Etesla]

• 1 28.0
26.1
24.3
22.4
20.6
18.7 16.8 15.0 13.1 11.2 9.4 7.5 5.7 3.8 1.9 0.1

I IL Dr.:4111%N wirhr.

1.11 0.9mm

ANSYS Maxwell-Generated

magnetic field strengths and

JxB distributed force loadings

[ a NiIrr3frffrh...

1)....1-1.1. 411

;:.id. 7re.! 110,..., r...

0.3mm I

_

ANSYS Mechanical-generated total deformation

using elastic-plastic nonlinear copper model for

20-T average field at liner location

Z hardware imposes unique winding requirements to enable novel internal reinforcement, coil connection scheme •.

3-shell Low-L Coil

111".1.!!!!timiniasieshwr

e"-

4-shell Low-L Coil

• Designs minimize material below coil • Inter-coil connections made via crimps above coil in lower-field regions • Requires a "down-wind" and "up- wind" to get wire out of way for zylon

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3-shell Low-L Coil

Delrin flange captures coil• Allows for internal reinforcement transitions and leads for final around clean breaks in conductor wind epoxy encapsulation process o

3-Shell and 4-Shell Low-L Coils perform similarly in simulation

Parameter3-Shell4-Shell

Coil Inductance

DC Resistance

Drive current to achieve 15-T avg.

1-Bank Voltage Vchg for Bavg = 15-T

Field Uniformity for lOmm liner

2.14mH

143mQ

9.05kA

9.9kV 30%

2.27mH

153mQ
9.3kA

10.5kV

29%

Shell 1 Zylon Peak Stress1.15 GPa1.16 GPa

Shell 2 Zylon Peak Stress

Shell 3 Zylon Peak Stress

Bavg linearly scaled to 13.5kV max Vchg

Shell 1 Zylon Peak Stress at 13.5kV Vchg

Shell 2 Zylon Peak Stress at 13.5kV Vchg

Shell 3 Zylon Peak Stress at 13.5kV Vchg

1.12 GPa

1.10 GPa

20.5 T

2.14 GPa

2.08 GPa

2.04 GPa

1.10 GPa

1.04 GPa

19.3 T

1.66 GPa

1.57 GPa

1.48 GPa

Shell 4

0.62 GPa

Shell 4

0.88 GPa

Zylon fibers measured to have 3.3 GPa ultimate tensile strength for 77.5% fill fraction [Y.K. Huang et al / Composites: Part B 33 (2002)]. We assume we have less than this fill fraction.

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Zylon shell

Zylon shell

Zylon she I

3-shell sectioned prototype shows well-

filled zylon reinforcement shells, tightly- packed winding journals

3-Shell Low-L coil seems superior to 4-shell in

theory, but ... • Passing orthotropic "thick-shell" zylon ultimate tensile strength calculations is necessary for "good" designs • But not sufficient to predict coil failure. • We've never failed a zylon shell. • 3rd coil conductors are observed to move. • Observed failures always occur at wire- to-wire interfaces • Predicting lifetime would require 3D modeling based on local wire loading • Also need to consider 3D effects on layer- to-layer transition, lead-to-wire

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• A third internal reinforcement shell: • Reduces field 5% (1T out of 20T) • Increases inductance (lower Ipk at 13.5kV) • More complex to produce per unit • But it also: • Reduces calculated peak wire strain by 67% • Reduces compliance in winding journal and resultant deformation • Is likely necessary for higher-field shots (>15-T) First 3-shell coil prototype (Delrin flange removed) after 10 shots at 17-T average B-field. r 22 Prototype 3-shell coils have demonstrated n"10 for Bavg > 15-T • 15-T Bavg 100% design stress • Test coil 1: • 1 shot each at 50%, 70%, 80%, 100%, 120% • 10 shots at 133% • (Dissected after 10th shot) • Test coil 2: • lea. at 50%, 3ea. at 67%, lea. 85%, 100% • 14 shots at 120% • Soft failure of 14th shot • Test coil 3: • lea. at 50%, 67%, 85%, 100% • 9ea. at 120% • Soft failure on 9th shot (after peak current)

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Shhoot 3t 1

- Shot 2 s

Shot 4

Shot 5

Shot 6

Shot 7

Shoth8S10oJu

2 4

Time (ms)

6810
Prototype 1 pulsed ten times at 10.4kA (Bavg - 17T) before post-mortem MMI

4590 (rnm)

Coils tested in surrogate geometry that mimics Z hardware23 Observed failures have been "soft"; result from conductor movement shorting between layers during pulse n 3-shell Low-L coil is observed to accumulate large radial displacement in outer coil n This trend is observable in coil inductance (Leg oc d) n The two nested 2-layer coils see no change throughout testing n This movement eventually shorts out turns during pulse n Typically occurs after peak current (peak mechanical strain) n Does not destroy the coil (it remains intact for post-mortem)

Shotinner CoilMiddle CoilOuter CoilFull Assembly

21.6 uH 33.9 uH 1.554 mH 1.98 mH

1100.0%100.0%100.0%100.0%

299.7%100.0%100.3%100.2%

100.4%100.3%100.6%100.4%

4100.2%100.2%100.9%100.6%

5100.1%100.0%101.1%100.7%

6100.3%100.2%101.3%100.9%

799.7%100.2%101.6%101.1%

899.4%100.1%101.7%101.2%

999.8%100.2%101.9%101.3%

10 99.5%100.2%102.0%101.4%

Sandia'Mil National---.P Laboratories

Unscaled

dl/dt (V) 0.2 0.15 0.1 0.05 0 -0.05

I Shot 1

Shot 2

Shot 3

Shot 4

Shot 5

Shot 6

Shot 7

Shot 8

Shot 9

024 6 8 10

Time (ms)

Rogowski probe (di/dt diagnostic) shows gentle short after Ipk on shot 9

Test coil is nested and total coil inductance change per shotTurn movement (left arrow) and increase in inner diameter (right arrow)4

The 3-Shell Low-L coil has been fielded for 10-T

Z experiments, ready for 15-T Bavg

Experiment Z3207 (05Feb2018) utilizing 3-Shell

coil on Low-L platform for MagLIF experiment

SandiaNationalLaboratories

• We have fielded these coils on Low-L platform Z experiments at 10-T • Experiments performed in February 2018 • 15-T average field experiments currently scheduled for July 2018 • The lifetime data with the 3-shell prototypes gives us confidence in our readiness • We can increase pre-magnetization field level in standard feed experiments • Replacing 80-turn coil with 3-Shell Low-L coil to increase from 15 to 20T 25

THE PATH FORWARD TO 20 25 T

Low-L coil provides three configurations for MagLIF scaling studies

100(mm)

Low-L Coil on Low-L Platforms

15 - 20T avg. field

with 19-20MA feed designs r- rin Inn pin

80-turn Coil + Low-L Coil

20 - 22T avg. field in Standard Feed

(-17 MA drive current) 70
60
50
40
E E 30
o o0_

To 20•R

10 0 -10 -20

SandiaNationalLaboratories

I-I00 00000003000000I

I I I 1 I O 00 00 00 00 no nn O O

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O OO OOI

1 ' i I I I oo oo00 00 00 00 nn nn oc00003000000000003000000

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1 II ir_ xxxxxx_1xxxxxxxxxix i xxxxxxxxxxxxxx- xxxxxxxxxxxxx•xxxxxxxxxxxxx•xxxxxxxxx_xxxxxxxxxx•i i_ i i _ _ __ _ _ i i•

10 20 30 40 50

radial position [mm] 6070

New conformal bottom coil to increase field,

provide better field uniformity for 20-30T goal 27

Design underway to complement Low-L coil with new

bottom coil "Cheyenne" for 20-30 T operation axial position [mm] 70
60
50
40
30
20 10 -10 -20

11 IO 0 0

I 0

I 0 0 0

. 0 0 0 i 0 0 o ,,11 O 0 0 O 0 0 O 0 0 O n n O 0 0 O 0 0 O 0 0

O 0 0 0 0 0

O 0 0 0

O 00000

O 00000

O 0 0 0 0 0

O 00000

O 00000

O 00000

n nonnn

O 00000

O 00000

O 00000

3000
3000

3 0 0 0

3 0 0 0

--) n n n O 0 0 oO 0 0 O 0 0 O 0 0 O 0 0 O 0 0 O 0 0 O n n

0 00000 0

0 00000 0

3 00000 0

hiX x xx xx xx xx xx x xx xx xx xx

X XXXX XXXX

X XXXX XXXX

X XXXX XXXX

X XXXX XXXX

X XXXX XXXX

X XXXX XXXX

or 4-shell Coil

11111111

v L -. v -+ -. v -, v -. v -, , . _ 1111
1

New conformal

bottom coil "Cheyenne"

0 10 20 30 40 50 60 70

LI Fik LaboratodesNati°1Sandkilei

$k:1 {: .4: .:, k: o40 111
1 Superposition of calculated coil fields look encouraging for "25T experiments in 2020 35
30
25
ca2 10

Axial Field Lineout for 2020 design point

J

Notional MagLIF

liner location -20 0 20 40 60 80 100

Axial Distance (mm)

I= • • • • 71 • ,111 • NM •

SandiaNationalLaboratories

X: 35.75 LY: 26.72

X: 25.£Y: 23.6

. .• • Conceptual coil pair can generate 25.2-T average field at the same operating current (10kA) as the existing Low-L coil • Need to evaluate transient coil self-forces, coil attraction, and repulsion from anode Cheyenne concept requires new winding capability, fabrication process, and detailed analysis to converge on design ........

NIMINSONNM MUNN.

040

Conceptual coil design with support flange and

notional internal reinforcement shells • Tight geometric constraints prevent coil-coil transitions like in Low-L coil • Coil cross-section must follow power flow contour • Minimize Z power feed inductance • Maximize field strength per turn • Power feed and bottom coil must be designed in tandem to achieve optimized performance for both

SandiaNationalLaboratories

Machine with orbital winding functionality currently in fabrication by collaborators at Milhous Company • Space constraints require the ability to wind zylon while maintaining conductor feed under tension • Zylon winding heads must "orbit" stationary coil mandrel while wire feed remains unbroken • Orbiting heads must be preloaded with zylon • Hoping for Cheyenne prototypes by February 2019 30
Summary of today's discussionSandiaNationalLaboratories n Sandia's MagLIF program on Z requires electromagnets to pre-magnetize the fusion fuel n The magnetic field reduces thermal conduction losses in fuel, relaxes convergence requirements

n The ABZ subsystem on Z regularly delivers 10 - 15 T to Z experiments with - 16-17 MA machine current.

The ABZ team works to meet program goals for integrated MagLIF experiments: n 19-20 MA machine current, 15 - 20T pre-magnetization, 1-2kJ laser preheat

n The Low-L platform increases machine current by dropping extended power feed, reducing load inductance

n We have designed an internally reinforced magnet that can deliver 15 - 17 T average field in MagLIF liner

n Coil prototypes have demonstrated acceptable lifetime and are ready for Z experiments n Our first 15-T experiments are scheduled for July 2018 on Z n 20-22 MA machine current, 20 30T pre-magnetization, 2-4kJ laser preheat

n Our team is designing a coil pair to meet this field requirement also while providing radial diagnostic access

n A coupled design effort for the Z power feed and bottom ABZ coil is required to optimize performance

n A new winding methodology is currently in development to enable production of Cheyenne prototypes 31

Questions?