Glo

w D

ischarg

e Clean

ing

for L

DX

Sarah

Dag

enM

IT P

lasma S

cience an

d F

usio

n C

enter

Darren

Garn

ier and

Eu

gen

io O

rtizC

olu

mb

ia Un

iversity

Presented at the 44

th Annual M

eeting ofthe D

ivision of Plasm

a Physics

Orlando, F

lorida

Novem

ber 11-15, 2002

Ab

stract

Sarah D

agen (MIT

PS

FC

), Darren G

arnier, Eugenio O

rtiz (Colum

bia

University)

Th

e L

ev

itate

d D

ipo

le E

xp

erim

en

t (LD

X) h

as

co

mp

lete

d

desig

n o

f its g

low

dis

ch

arg

e c

lea

nin

g (G

DC

) sy

ste

m. G

DC

will

be

u

se

d

be

fore

firs

t p

las

ma

s

in L

DX

, a

s

we

ll as

be

twe

en

ex

pe

rime

nta

l op

era

tion

s, to

elim

ina

te im

pu

rities

from

the vacu

um

vessel. Th

e glo

w is created

by a m

ovab

le

ano

de p

rob

e inserted

thro

ug

h a flan

ge o

n th

e un

dersid

e of

the

ve

ss

el. T

he

an

od

e is

bia

se

d w

ith u

p t

o 8

00

V w

ith

res

pe

ct to

the

ve

ss

el w

all w

ith 1

2k

W D

C p

ow

er availab

le

for p

lasma fo

rmatio

n.

Aw

ay from

the an

od

e, a biased

tun

gsten

filamen

t will b

e

ins

talle

d to

aid

in d

isc

ha

rge

bre

ak

do

wn

an

d re

du

ce

the

like

liho

od

of a

rcin

g[1

]. Th

e fila

me

nt m

ay

als

o b

e u

se

d

for p

reio

niza

tion

du

ring

ex

pe

rime

nta

l op

era

tion

s. G

DC

will b

e im

ple

me

nte

d w

ith d

eu

teriu

m g

as

follo

we

d b

y a

sh

orte

r pe

riod

of

he

lium

ga

s. A

re

du

ce

d c

on

du

cta

nc

e

pu

mp

ing

pa

th w

ill be

inc

orp

ora

ted

into

the

vacuu

m

sy

ste

m in

ord

er to

be

tter c

on

trol p

res

su

re d

urin

g G

DC

op

era

tion

. Th

e c

om

ple

ted

de

sig

n a

nd

p

lan

s fo

r initia

l

tests of th

e GD

C system

will b

e presen

ted.

[1] H.W

Kugel, W

. Blanchard, G

. D'A

mico, R

. Gernhardt, a

nd

T. P

rovo

st, "NS

TX

Fila

me

nt

Preionization A

nd Glow

Discharge C

leaning System

s", PP

PL R

eport (2000).

LD

X V

acuu

m V

essel

Sp

ecification

s:

•5 m

eter (198”) diam

eter, 3 mhigh, elevated off cham

ber floor

•11.5 T

on weight

•7.5 x 10

-8 Torr base pressure

–M

anu

factured

by V

acuu

mT

echn

olo

gy A

ssociates / D

ynaV

ac

•C

om

pleted

Sep

t. 1999

Interio

r of V

essel- Initial C

leanin

g

LDX Experiment Cross-Section

Wh

y dip

ole co

nfin

emen

t?•

Sim

plest

con

finem

ent field

•S

teady state

•H

igh

-b con

finem

ent

occu

rs natu

rally inm

agn

etosp

heres

(b ~ 3 in

Jup

iter)•

Po

ssibility o

f fusio

np

ow

er sou

rce with

near-classical

energ

y con

finem

ent

•O

pp

ortu

nity to

stud

yn

ew p

hysics

relevant to

fusio

nan

d sp

ace science

Th

e Io P

lasma

To

rus aro

un

d Ju

piter

J. Spencer

Dip

ole C

on

finem

ent an

d L

DX

:•C

on

cept is b

ased o

n o

bservatio

ns o

f the p

lasma p

rop

erties arou

nd

Jup

iter, created b

y a dip

ole co

nfin

emen

t

• b~ p

lasma p

ressure/ m

agn

etic pressu

re

Glo

w D

ischarg

e Pro

cess

An

od

e

An

od

e Sh

eath

Vacu

um

Vessel W

all(C

atho

de)

Large E (space charge

limited current flow

)

Electron density Æ

0

Quasi-neutral region;

Ions accelerate

Cath

od

e Sh

eath(m

inim

al ion

ization

)

Secondary

electrons

Fast electrons

Ions accelerate throughsheath

Neg

ativeG

low

(Plasm

a)

An

od

e Sh

eath

• Un

iform

ion

den

sity

• Co

llision

lessreg

ion

• No

ion

ization

• Accelerates

secon

dary electro

ns

back in

to g

low

Cath

od

e Sh

eath

• Min

imal io

nizatio

n

• Fast electro

ns take

collisio

nless p

athth

rou

gh

glo

w an

d h

itan

od

e

• Ion

s acceleratedÆ

kno

ck imp

urities o

ffvessel w

all

Po

tential D

rop

across G

low

Th

e GD

C P

rocess

•Gas and V

acuum pum

pingsystem

s:

•Vessel pum

ped down to

~10

-3 Torr

•Gas pum

ping systemintroduces H

or He gas

into vessel

•Glow

initiated Æim

purities liberated fromvessel w

alls

•Continual pum

pingrem

oves liberatedim

purities from vessel

Imp

ortan

ce of G

DC

for L

DX

•LD

X requires pure

hydrogenic plasma

Æexperim

ental objective isto exam

ine limits of

stability in high pressure(high b) plasm

as

•Large volum

e of plasma

and limited pow

eravailability

•Im

purities on the interior ofLD

X vessel w

all (such asoxygen, nitrogen, etc.)ejected into confinedplasm

a by plasma and

neutral bombardm

ent

•E

jected atoms radiate

power, causing the plasm

ato cool

•Im

purities can dissipatepow

er enough to severelylow

er confined plasma

pressure

•T

hus, LDX

vessel must be

free of impurities to obtain

experimental objective!

GD

C A

no

de P

rob

e•

GD

C anode probe enters and retracts from

main vessel via m

ounting system connected

to pre-existing flange on vessel

•P

robe attached to rigid, insulated stainlesssteel rod

•E

nd of rod outside vessel connects to fullnipple flange

•V

acuum-operated bellow

s encloses rodbetw

een exterior of vessel and full nippleflange

Filam

ent

entry

An

od

ep

rob

een

try

GD

C F

lang

e

* Draw

ing by Eugenio O

rtiz, Novem

ber 10, 2002

GD

C A

no

de P

rob

e

Em

issive Pro

be

GD

C A

no

de P

rob

e

An

od

e Su

pp

ort S

haft

•B

iggest concern in design:arcing!

•S

haft design takes into carefulaccount possibility of arcing

•1/8

” copper conductor shieldedw

ith 1/4” O

D alum

ina tube

•3/4

” OD

stainless steel main

support rod shielded with

1”OD

, 40” long alum

ina tube

•S

teel rod is welded to a blank

flange at lower end

•S

haft housed in bellowsÆ

mechanism

for insertion andretraction of G

DC

probe•V

iew of shaft upper end-- w

ill go inside probe

•Provides pow

er to anode via copper wire-

copper wire is attached to the inside of anode

•Stainless steel anode inserted into

vacuum vessel for G

DC

Insid

e An

od

e Pro

be

•K

ey to in

side o

f pro

be is b

oro

nn

itride cylin

der

•C

ylind

er pro

vides in

sulated

termin

ation

po

ints fo

r all shaft

com

po

nen

ts•

1/8” cop

per co

nd

ucto

r exits top

of

cylind

er and

is attached

to in

side o

fsteel p

rob

e•

BN

cylind

er is sup

po

rted in

side

sph

erical ano

de via steel d

iskw

elded

insid

e ano

de

Bo

ron

Nitrid

e Cylin

der

Cro

ss-section

of an

od

e pro

be

Stain

less Steel

Ho

llow

Sp

here

Set screw

Co

pp

er con

du

ctor

Half o

f steel ano

de

An

od

e Po

wer S

up

ply

•10.5

” H x 19

” W x 19” D

rack mount supply

•O

utput:–

800V D

C

–U

p to 7.5 A

•F

loating ground isolatespow

er supply from chassis

ground

•S

elected for high currentoutput, rem

ote operationcapability, and frontconsole design

•Manufactured by

Spellm

an HV

, Oct. 2002

12 kW P

ower S

upply

Po

wer T

ransfer C

on

nectio

n

Full

Nipple

Flange

Main S

teel Support R

odcom

ing down from

anode

1/4” alumina

Copper conductor

from anode

Copper from

feedthrough

Insulation fromfeedthrough

Copper connector

tube

Alum

inaencasing entire

connection

•1/8” copper conductor

attached internally toanode m

ust make solid

connection with pow

ersupply

•Very high risk of arcing

inside full nippleflange

Æ m

any regionsw

here ‘line of site’betw

een copper andother m

etals couldcause arcing and effectdischarge

Prein

oizatio

n F

ilamen

t

175 VA

VA

RIA

C

DC

Bias P

ower

Supply

Output:300V

, up to30m

A6V

, 24A

Filam

entT

ransformer

IsolationT

ransformer

To F

ilament

115V A

C in

115V A

C in

Lighted fuse holder with

2A fuse

Lighted fuse holder with

.1A fuse

On/O

fftogglesw

itch

GN

D

Po

wer tran

sfer system to

Filam

ent

Bias P

ower S

upply and Tungsten

Filam

ent

•Biased tungsten

filament inserted near

anode

•Aids in glow

dischargeby providing addedelectron source

•Also useful for

illuminating inside of

vacuum vessel

GD

C O

peratio

n P

lan

•P

reionization filament m

aynot be used in first G

DC

plasmas in order to test

only anode and high-voltage pow

er supply

•V

ery long period of glowdischarge w

ill run beforefirst LD

X plasm

as tothoroughly clean vessel

•G

DC

will use hydrogen

gas and then a shorterperiod of helium

gas

•C

urrently do not have Z-

detector to monitor w

hatis rem

oved from vessel

during GD

C

•D

o have 2-pi bolometer

(photodiode with green

filter)

•T

his will be used to

assess GD

C

GD

C O

peratio

n P

lan

•R

esidual Gas A

nalyzer(R

GA

) will m

onitor vacuumconditions betw

eenplasm

a shots

•O

ption to run GD

Cbetw

een shots will be

determined by vacuum

conditions as indicated byR

GA

•G

DC

will run for

approximately 7 hours total

in between run days

•G

DC

operates atpressure ~

10-3 T

orr

•F

uture Goal:

–W

ould like to automate

GD

C system

in the future-anode pow

er supply iscapable of rem

oteoperation

–T

his would also require

modifications to gas and

pressure systems

Co

nclu

sion

s

•G

DC

uses unconfined plasma to rem

oveim

purities from inside of LD

X vacuum

vessel•

Rem

oval of impurities essential for LD

Xexperim

ent•

GD

C design based on pre-existing flanges in

LDX

vessel•

Largest issue in design was to avoid arcing

•G

DC

first plasmas expected in D

ecember

2002!

Fo

r mo

re info

rmatio

n/u

pd

ates on

LD

X G

DC

,co

ntact S

arah D

agen

: dag

en@

psfc.m

it.edu

Referen

ces

1.H

.W K

ugel, W. B

lanchard, G. D

'Am

ico, R.

Gernhardt, and T

. Provost, "N

ST

XF

ilamen

t Preio

nizatio

n A

nd

Glo

wD

ischarg

e Clean

ing

System

s", PP

PL

Report (2000).

2.IT

ER

report, 1999