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Effects of Microchannels in IEC devices
S. Krupakar Murali,* J. F. Santarius and G. L. KulcinskiUniversity of Wisconsin, Madison
*Lawrenceville Plasma PhysicsWork carried out at UW Madison
1999-2004
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Outline• Introduction
– What is an IEC? And how does it work?• Motivation
– Why are we interested in Microchannels• Poissor Structure• How are microchannels studied ?
– Eclipse disc experiments– Single loop experiments– Grid rotation experiments
• Previous experiments in support of Poissor structures– Gamma collimation results– Proton collimation results– Observations by Kiyoshi Yoshikawa
• Poissor structure and relation to microchannels• What are its consequences and implications to IEC research?• Conclusions and Future work
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What is an IEC device ? How does it work ?
• IEC Inertial Electrostatic Confinement Device
• Laverent’yev (1963, USSR) and Philo Farnsworth (1966, USA) independently proposed inertial electrostatic confinement of fusion plasma
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Scale: 30 cm
Schematic of UW IEC Advanced Fusion Device up until August 2004
Proton Detector
Fusion Reactions
High VoltagePower Leads
Neutron Detector
AdvancedFuelsInput
RGA
Pyrometer &
Camcoder
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IEC Operation
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Eclipse diagnostic for fusion source regime characterization
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Fusion Source Regimes
Wall-Surface(Embedded)
CX-neutral(Volume Source)
Beam-Background(Volume Source)
Beam-Target(Embedded)
Beam-Beam(Converged Core)
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Eclipsing Experimental Setup
Annulus
View through the detector port
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Eclipsed Data Suggests Significant
Converged Core D-D Reactions (error ~ 5%) D-3He (100 kV, 30 mA)
Noeclipse
24% 9% 1% 1%
9%14%
37%
78%
100%
Small OffsetSmallMediumLarge
Volume eclipsed
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Relevant conclusions
• Mostly D-D reactions occur in the core of the device.
• A proton detector can see converged core reactions.
• In other words, if you put something infront of the cathode obstructing the view of the proton detector, it will pick this up.
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Sequential grid construction
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Single loop grid experiments
• Single loop acts like a line source and provides a higher proton rate than a spherical grid at some locations
• Easiest way to compare different materials for grid construction.• Can be used to project performance of a spherical grid at higher input power
30o
60o
90o
0o
0
1
2
3
4
5
6
0 20 40 60 80 100
Orientation of the grid (degrees)
P/N
rat
io
30 kV 10 mA
40 kV
0.0E+00
2.0E+05
4.0E+05
6.0E+05
8.0E+05
1.0E+06
0 10 20 30 40 50 60 70
Voltage (kV)
Neu
tron
s/s
Re Expt. No. 1146
W Expt. No. 1147
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Sequential grid construction for studying the influence of grid symmetry on the fusion rate
S. Krupakar Murali, J. F. Santarius, and G. L. Kulcinski, Phys. Plasmas, 15, 122702, (2008).
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Neutron rate Vs Configuration
(90o)
5002500450065008500
10500125001450016500
0 1 2 3 4 5 6
Configuration
Raw
co
un
ts/6
0s
40 kV60 kV80 kV
Proton rate Vs Configuration
(90o)
0
2000
4000
6000
8000
10000
12000
0 1 2 3 4 5 6
Configuration
Raw
co
un
ts/6
0s 40 kV60 kV80 kV
P/N ratio Vs Configuration
(90o)
0
5
10
15
20
25
0 1 2 3 4 5 6
Configuration
P/N
rat
io 40 kV60 kV80 kV
1. XWLoopRe-12. XWLoopRe-23. XWLoopRe-34. XWLoopRe-75. XWLoopRe-C
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Neutron rate Vs Configuration
(0o)
5002500450065008500
10500125001450016500
0 1 2 3 4 5 6
Configuration
Raw
co
un
ts/6
0s
40 kV60 kV80 kV
Proton rate Vs Configuration
(0o)
0
500
1000
1500
2000
2500
3000
0 1 2 3 4 5 6
Configuration
Raw
co
un
ts/6
0s
40 kV60 kV80 kV
P/N ratio Vs Configuration
(0o)
0
5
10
15
20
25
0 1 2 3 4 5 6
Configuration
P/N
rat
io 40 kV60 kV80 kV
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Conclusions of single loop grid experiments
• A single loop grid generates a cylindrical line source of protons. • The eclipse scan of the loop grids showed a positive fusion reaction
gradient as we move from the edge• to the center of the XWLoopRe-1 single loop grid. • With improving symmetry added wires, the fusion rate increases and
eventually saturates. • The gradual transformation of a line source to a volume source is observed
with the increasing symmetry obtained by the addition of more loops to the grid.
• The ionization source must be placed away from the cathode for efficient performance.
• The presence of the grid wires seems to affect the fusion rate more drastically than previously thought. This prompted the next set of experiments – Grid rotation experiments.
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Grid Rotation Experiment
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Grid rotation experiment
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Results of Grid rotation experiment
Consequences of this experiment -
• Grid has to be oriented properly every time an experiment is conducted. If not, almost 50% variation is to be expected.
• New calibration factor for the Si detector needs to be developed, accounting for the microchannels as the fusion source.
• Theory should accommodate this non-uniformity in ion flow.
• This new technique could be used to characterize the three modes of operation of an IEC device namely-star, halo and converged core modes.
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Proton rate calibration assuming all volume source reactions occur within the
microchannels
• Fusion rate has three contributors– Converged core (MCNP)*
– Embedded source and
– Volume source Microchannel source
dA
r
214 2
214 2
dA
r
* M. A. Sawan, University of Wisconsin, Madison, Private Communications, (2002)
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Microchannels form the volume source
• Fusion rate from a single microchannel is given by:
c
ccy
tV
r
ffdx
rxxr
rf
AF
2
v
22
22
v )]cos(2[
)'(cos
4
(a)
(b)
Cathode
2rrc
hd
2rcy
l
1
2
3
a
c
bPole
S. Krupakar Murali, J. F. Santarius, and G. L. Kulcinski, submitted to IEEE transactions on plasmas
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Surface area (A) visible to the protons
x
h
r
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