effects of microchannels in iec devices s. krupakar murali, * j. f. santarius and g. l. kulcinski...

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

2

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

3

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

4

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

5

IEC Operation

6

Eclipse diagnostic for fusion source regime characterization

7

Fusion Source Regimes

Wall-Surface(Embedded)

CX-neutral(Volume Source)

Beam-Background(Volume Source)

Beam-Target(Embedded)

Beam-Beam(Converged Core)

8

Eclipsing Experimental Setup

Annulus

View through the detector port

9

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

10

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.

11

Sequential grid construction

12

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

13

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).

14

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

15

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

16

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.

17

Grid Rotation Experiment

18

Grid rotation experiment

19

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.

20

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)

21

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

22

Surface area (A) visible to the protons

x

h

r

23

24

25

26

27

28

29

30

31

32