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Six Ion Gun Fusion Experiment

(SIGFE) Findings and Future Work

Matt K. Michalak, Brian J. Egle* Gerald L. Kulcinski, John F. Santarius

Presented at

13th US-Japan IEC Workshop

7-8 December 2011 in Sydney, NSW

*At ORNL

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Presentation outline

• Review of past information presented on

the SIGFE

• Most recent results

• Diagnostics used – 2 Si proton detectors, 1 3He neutron detector

– Fusion Ion DOppler shift (FIDO)

• Next steps

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IEC fusion reaction modes

• Basic IEC operation modes – Beam-background

– Beam-embedded

– Converged core

– Multiple virtual electrode formation (Poissors)

• Beam-background and beam-embedded shown to dominate in gridded systems with mid to high pressure (>0.3 Pa)

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Experimental results of Hirsch

showed tri-modal distribution

Source: Hirsch, R.L. (1967). Inertial-electrostatic confinement of

ionized fusion gases. Journal of Applied Physics,

38(11), 4522-4534

Data taken at pressures between

0.3 to 1 Pa (2 to 8 mTorr)

• Hirsch-1967 reported a tri-modal spatial

distribution of fusion neutrons and

bremsstrahlung radiation inside the

cathode

• Theory of virtual electrode formation

(poissors) used to explain these results

Hirsch-1967

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

-2.0 -1.0 0.0 1.0 2.0

Re

lative

In

ten

sity [n

eu

tro

ns]

Re

lative

In

ten

sity [x-r

ay]

Radial Position [cm]Neutron data X-ray data

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Comparison of the SIGFE to Hirsch

geometry

• SIGFE’s design attempted to replicate the geometry of Hirsch-1967 as close as

possible

• Major differences that may affect electric fields include:

• Grounded ring in SIGFE replicates chamber wall as anode

• Addition of focusing lens

• Electron suppression on cathode

Hirsch SIGFE

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Design to reality

December 2007 December 2008 September 2009

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8 mm

SIGFE can operate in a

large parameter space

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• Stable -150 kV operation achieved

• 2 mm ion beam width at cathode

center at cathode voltages from

-50 to -150 kV

• 2 to 31 mA total cathode current

• 5 to 270 mPa chamber pressure

(deuterium)

SIGFE Run 266, 9/14/2009

110 kV, 10 mA, 44 mPa (330 µTorr )

0

5

10

15

20

25

30

35

0 50 100 150 200

Tota

l ca

thod

e cu

rren

t [m

A]

Cathode voltage [kV]

8

75

750

7500

1

10

100

1000

0 10 20 30 40C

ha

mb

er p

ress

ure

[µ

Torr

]

Ch

am

ber

pre

ssu

re [

mP

a]

Total cathode current [mA]

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0.0E+00

5.0E+06

1.0E+07

1.5E+07

2.0E+07

2.5E+07

3.0E+07

10 100 1000

Neu

tron

rate

[n

/s]

Chamber Pressure [mPa]

100 kV cathode voltage

10 mA total cathode current

SIGFE neutron rate scaling with

pressure is dependent on focus

8

70% Vfocus

130% Vfocus

Unfocused

100% Vfocus

Hirsch

UW Gridded

• Well focused

SIGFE n/s has

weak pressure

dependence

• Over focused

SIGFE has direct

n/s pressure

dependence

• Under focused

SIGFE has

inverse n/s

dependence

• Under focused

SIGFE has

similar scaling to

Hirsch

1 mPa = 7.5 µtorr

Ion direction

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Defocused SIGFE data matches

Hirsch D-D neutron rates

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0.0E+00

5.0E+06

1.0E+07

1.5E+07

2.0E+07

2.5E+07

3.0E+07

3.5E+07

4.0E+07

4.5E+07

5.0E+07

20 30 40 50 60 70 80 90 100 110 120 130 140 150

Neutr

on R

ate

[n/s

]

Cathode Voltage [kV]

SIGFE 13 mPa

focus: 70%

SIGFE 150 mPa

focus: 70%

Hirsch 13 mPa

Hirsch 150 mPa

Hirsch 1040 mPa

UW Gridded 270 mPa

10 mA of total cathode current

SIGFE 13 mPa

focus: 0%1 mPa = 7.5 µtorr

Vfocus 70%

Vfocus 70%

Defocused

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FIDO diagnostic measured <0.2% of

total D-D fusion from cathode center

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43% 64% 85% 106% 128% 149%

1.0E+03

2.0E+03

3.0E+03

4.0E+03

5.0E+03

6.0E+03

7.0E+03

8.0E+03

9.0E+03

1.0E+04

1.0E+06

2.0E+06

3.0E+06

4.0E+06

5.0E+06

6.0E+06

7.0E+06

8.0E+06

9.0E+06

1.0E+07

2.0 3.0 4.0 5.0 6.0 7.0

Focus voltage percentage

Ca

lib

ra

ted

D-D

pro

ton

ra

te [

p/s

]

Cali

brate

d D

-D n

eu

tron

rate

[n

/s]

Focus voltage [kV]

D-D proton rate

from cathode center only

4 cm3

D-D neutron rate

from entire chamber volume

75000 cm3

100 kV cathode voltage

5 mA total cathode current

80 mPa (600 µTorr) pressure

Linear trend lines

• Large difference in protons

from center and neutrons

from entire volume

• Virtual potential well

formation is not a

significant fusion

mechanism within the

SIGFE parameter space

50%

D+D

50%

p+3He

n+T

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• D-D fusion rate scaled linearly with current at total

cathode currents within the 2-31 mA operation space

• D-D neutron rate is highly dependent on the focusing of

the ion beams

• Highest neutron rates in the SIGFE observed with

defocused ion beams

• 4.2 x 107 n/s

• at -130 kV cathode voltage, 10 mA total cathode

current, 13 mPa chamber pressure

Conclusions from SIGFE D-D

experiments

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Evidence of virtual potential well

formation not observed in SIGFE

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Within the parameter space explored

(<31 mA total cathode current,-50 to -150 kV, 13 to 270 mPa)

• Less than 0.2% of the D-D fusion reactions are from center of

SIGFE device

• Virtual potential well structures and other space-charge related

physics at the center of the SIGFE cathode are not a

significant source of fusion

• D-D and D-3He fusion protons observed from center are

consistent with beam-background fusion

• The results of the SIGFE imply that beam-embedded fusion in

the cathode lenses is the dominant D-D fusion mechanism in

the SIGFE

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Rational for SIGFE diagnostics

• Measure energy of reacting particles

• Determine location of fusion reactions

within the cathode

• Identify the mechanism for high neutron

production efficiency

– Hirsch device was the most efficient IEC, until

SIGFE, on a neutron production rate per

kilowatt basis

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Proton detector designed to only

observe fusion from center

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Proton detection volume

4 cm3 Fusion Ion Doppler Shift

(FIDO) diagnostic1

• Energy of reactant particles

determined from detected

fusion proton spectrum

• x-ray noise reduced by

bending protons out of line-

of-sight of chamber

• 8 µm of Al foil at cathode

edge

• Designed to detect protons

from the center of cathode

only

• Calibrated as a point source

of protons at the center of

the SIFGE

1. Developed by David Boris

60 cm

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Protons from center consistent with

beam-background fusion

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• Doppler shift of D-D protons

can be from D1+, D2

+, and

D3+ ion species

• Experimental proton

spectrum consistent with

near full cathode energy

ions on stationary targets

(beam-background)

Note: protons from 4 cm3 volume

at cathode center only

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D-3He proton detector

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D-3He proton detector

• Collimated to detect

14.7 MeV protons only from

center of cathode

• Calibrated as a point source

of protons at the center of

the SIGFE

• 360 µm of Pb and 8 µm of Al

foil between center and

detector

D+3He p+4He

90 cm

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Doppler shift is consistent with

D-3He beam-background fusion

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0

50

100

150

200

250

6.5 7 7.5 8 8.5 9 9.5

Cali

brate

d p

roto

n r

ate

[p

/s p

er e

nergy b

in]

Energy deposited in detector [MeV]

150 kV cathode voltage

100 kV

70 kV

10 mA total cathode current

133 mPa (1000 µTorr) pressureTrend line: 5 pt moving avg

100% focus voltage

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Summary

• SIGFE has been operated with different

fuels and multiple diagnostics over a large

parameter space

• Matched Hirsch results

– Most likely operated in a beam-embedded

mode

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Next steps for the SIGFE

• Operate in a pulsed mode to achieve higher

currents

• Explore new operating parameters

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Ohnishi, M., Sato, K. H., Yamamoto, Y., &

Yoshikawa, K. (1997). Correlation between

potential well structure and neutron production

in inertial electrostatic confinement fusion.

Nuclear Fusion, 37(5), 611-619.

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Questions?