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

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0.0E+00

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Voltage (kV)

Neu

tron

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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

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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

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co

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Proton rate Vs Configuration

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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

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