Recent Progress of Recent Progress of Researches in Mirror Researches in Mirror

DevicesDevices

IAEA FEC 2004IAEA FEC 2004November 1 ~ 6, 2004November 1 ~ 6, 2004VilamouraVilamoura , Portugal, Portugal

EX/9-6RcGOL-3

Heating and Confinement of Ions at Multimirror Trap GOL-3

V.S. Koidan, A.V. Arzhannikov, V.T. Astrelin, A.V. Burdakov, G.E.Derevyankin, I.A. Ivanov, M.V. Ivantsivsky, S.A. Kuznetsov, K.I. Mekler, S.V.

Polosatkin,V.V. Postupaev, A.F. Rovenskikh, S.L. Sinitsky, Yu.S. Sulyaev, A.A. Shoshin, Eh.R. Zubairov

Budker Institute of Nuclear Physics, Novosibirsk 630090, Russia

GOL-3 facilityGOL-3

GOL-3 Introduction

Recently magnetic system of the GOL-3 facility was converted into completely multimirror one.

Multimirror plasma confinement

lL

Full solenoid length L exceeds mean free path of the particles λi. If, at the same time, the mirror cell length l< λi then the longitudinal confinement time increases essentially compared to classical single mirror trap.

τ ~ R2 L2

λiVTi= R

2 Lλi

τ0R =

BmaxBmin

τ ~LVTi

0-confinement time in solenoid

GOL-3 facility

sheet beam diode

U-2 generator of the electron beam

corrugated magnetic fieldexit unit

plasma

GOL-3

Electron beamEnergy - 1 MeVCurrent - 50 kAEnergy content - Pulse duration - 8 µs

0.3 MJ

Magnetic field•multimirror•55 cells•4.8/3.2 T

PlasmaLength ~Density -Temperature ~

12 m10 - 10 m20 22 -3

1 keV

GOL-3 Plasma heating and confinementHeating by the electron beam

Confinement

• Collective plasma heating by E- beam results in Te~2 keV at ~0.5⋅1021 m-3 density. High Teexists for ~10 µs.

• To this time Ti reaches 1-2 keV and keeps at the high level long enough time.

• Duration of the ion heating is much less than classicalelectron-ion energy transfere time.

• In order to explain this phenomenon the mechanism of fast ion heating is suggested.

0 0.1 0.2 0.3 0.4 0.5time, ms

0

1

2

Ti, k

eV

0

1

nT, 1

015 k

eV/c

m3

D0209

PL5372

time, ms

Ti,

keV

nT, 1

021ke

V/m

3

Dynamics of ion temperature measured by Doppler broadening of Dα spectral line . Initial density is 0.5⋅10 21 m-3.

Neutron generation

0

50

100

150

200

0

50

100

150

200

a) neutrons+gamma

b) neutrons

AD

C re

adou

t

0 0.2 0.4 0.6 0.8 1.0 time, ms

GOL-3

Waveforms of signal of digital PSD stilbene detector (Z=4.3 m).a) original signal, which contain neutron and gamma components of fusion product emission. Digital pulse shape discrimination (dPSD) was used for analysis of stilbene detector signals.b) signal of fusion neutrons (after separation by dPSD). Initial density is 1.9⋅1021 m-3.

Progress in GOL-3 parameters

dia_

reco

rds

0 0.2 0.4 0.6 0.8time, ms

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6neTe+niTi, 1021 keV/m3

full corrugation, 1.5⋅ 1021 m-3, D improved heating, PL5871, 2.08 m

full corrugation, 0.8⋅ 10 21 m-3 , D PL5221, 3.57 m

4 m corrugated ends, 0.3⋅ 1021 m-3 , D PL4710, 2.08m

uniform, 0.9⋅ 1021 m-3 , H PL2285, 3.73m

1997

2001

2002

2004

GOL-3

Waveforms of the plasma pressure in the GOL-3 facilityat different magnetic configurations

ResultsGOL-3

• Conditions for stable creation and effective heating of plasma in the range (0.2÷6)⋅1021 m-3 are experimentally found.

• Electron and ion plasma temperatures up to 2 keV at density ~1021 m-3 are achieved.

• Macroscopical stability and long confinement of the dense plasma in multimirror system is obtained.

• The value nτE ~ (1.5÷3)⋅1018 m-3s at ion temperature ~1 keV is attained.

Advances inAdvances in PotentialPotential Formation Formation and Findings in Sheared and Findings in Sheared Radial ElectricRadial Electric--Field Effects on Turbulence and Loss Field Effects on Turbulence and Loss

Suppression in GAMMA 10Suppression in GAMMA 10T. Cho, H. Higaki, M. Hirata, H. Hojo, M. Ichimura, K. Ishii, M. K. Islam, A. Itakura,I. Katanuma, J. Kohagura, Y. Nakashima, T. Numakura, T. Saito, Y. Tatematsu,

M. Yoshikawa, M. Yoshida, T. Imai, V. P. Pastukhov*, and S. MiyoshiPlasma Research Centre, University of Tsukuba, Japan

GAMMA 10GAMMA 10

φφcc

ThreeThree--Times ProgressTimes Progress in in IonIon--Confining PotentialConfining Potential φφcc

AfterAfter IAEA 2002 IAEA 2002 (Lyon)(Lyon)

Plug ECH PowerP PECH (kW)

Barr

ier E

CH P

ower

P BEC

H (k

W)

Hot-ion mode Ti =several keV

New RecordNew Recordφφcc= = 2.1 kV2.1 kV

1992-2002

20032003

20042004

To C

ent r

a lC

e ll

T o E

ndIo

nIo

n --C

o nfi n

ing

P ote

ntia

lC

o nfi n

ing

P ote

ntia

lφφ cc

(kV)

(kV)

ScalingScaling

The advance in φc produces strong radially sheared electric fields Er .

GAMMA 10GAMMA 10

ion

rc=2.6 cm00 10 20 30

(g)

1

2

3 96-101 ms

Frequency (kHz)

Clear Up

ComparisonComparison::Strong and

WeakEErr ShearShear

effectseffects

(n)

(o)

(q)

(p)

012

012

510

-50

0 5 10 15

02

4(j)

(i)

(h)

(k)

012

012

510

-50

0 5 10 15

02

4

TurbulenceTurbulence

00 10 20 30

1

2

3

rc=2.6 cm

(m)

TurbulenceTurbulence

70-75 ms

Frequency (kHz)

Suppression of Drift Waves and Turbulent Turbulent FluctuationsFluctuationsby Radially Sheared Electric Fields EErr

StrongEr Shear

0

2

45

0 50 100 150 200

3

1

Shot No. 185221

PlugECH

(a)

ICH

FourierAmplitude

Time (ms)

Frequency (kHz)

Time (ms)

Central Line

Density(1017m-2)

Radius rc (cm)Radius rc (cm)

0

2

45

0 50 100 150 200

3

1

Central Line

Density(1017m-2)

Drift Wave

Turbulence

(l)Shot No. 185628

PlugECHICH

WeakEr Shear

Radius rc (cm)

FourierAmplitude

Drift Wave

Turbulence

Vorticity Wr=[∇×nVE]z/n0

Er SheardEr/dr

105-110 ms

01

2 (c)

0

12 (d)

510

-50

0 5 10 15

(f )02

4 (e)

Rise saturated

WeakEr Shear

GAMMA 10GAMMA 10

m=1

0

1

0 10 20 30

2

3

rc=2.6 cm

(b)2 3 4

Vorticity Wr=[∇×nVE]z/n0

Er SheardEr/dr

Observations ofObservations of Turbulent VortexTurbulent Vortex StructuresStructures,,and and theirtheir SuppressionSuppression due todue to aa strong Estrong Err ShearShear

formed by formed by HighHigh--PotentialPotential productionproduction..

X-Ray Tomography

Clear UpClear Up0

1

2

0 10 20 30

rc=-4.3 cm95 ms(e)

a Vortexappears

growth

decrease

outwardshift

EE××BBdrift

Strong EStrong Err ShearShear Weak EWeak Err ShearShear

TurbulenceTurbulence0

1

2

0 10 20 30

(d) rc=-4.3 cm70 ms

Frequency (kHz)

X-ra

y Fo

urie

rA

mpl

itude

(rel

.uni

t)

Frequency (kHz)

X-ra

y Fo

urie

rA

mpl

itude

(rel

.uni

t)

peaked

GAMMA 10GAMMA 10

τp//=95 ms, τ⊥>4 τ// for φc =0.84 kV; a few tens % a few tens % improvementimprovement inin ττ⊥⊥ due due to a to a strong shearstrong shear

Finite I⊥Negligible II⊥⊥

nlc

(101

7m

-2)

Confinement Improvement by Turbulent Vortex Suppression due to a Strong Er Shear

Time (ms) Time (ms)70 90 110

(a)

0

1

2

Cur

rent

s (1

0-2

A)

Time (ms)80 120 160 200

End

Loss

Cur

rent

sI //

(10-

4A

/cm

2 )

0

2

4

6

PlugECH

(b)

Cen

tral

-Cel

l Li

ne D

ensi

tynl

c(1

017

m-2

)

0

2

4 (c)

edN/dt

(e)

I //(1

0-4

A/c

m2 )

0

6

200

4 (f)

Calculationsfrom Eq. (1)

2

4PlugECH

Time (ms)80 120 160

0

2 Calculationsfrom Eq. (1)

70 90 110

Cur

rent

s (1

0-2

A) rc=0 -1 cm

Plug ECH

IsI//

0

1

2

e dNdt

Particle Balance Equation (1);

=Is −I// −I⊥

dN/dt ; density riseIs ; source current

(Hα data) I// ; endloss currentI⊥; transverse-loss current

from Eq.(1).

((Nonambipolar loss is Nonambipolar loss is suppressed with suppressed with floated endplates.)floated endplates.)

ττ⊥⊥>>>>ττ////

((τE-Pastukhov=50 ms; consistent)

DiscrepancyDiscrepancy from from PastukhovPastukhov’’ss TheoryTheory

(Extra(Extra I⊥⊥))

ConsistentConsistent withwithPastukhovPastukhov’’s s

TheoryTheory(no(no I⊥⊥))

Weak ShearWeak Shear

rc=0 -1 cmPlug ECH

IsI// edN/dt

(d)

Strong ShearStrong Shear

22ττ⊥⊥==ττ////

ScalingsScalings for High PotentialHigh Potential and the associated Strong EStrong Err ShearShear FormationFormation

Validity of our proposed theoretical surfaces for potential formationfor potential formation [1]

covering various modes including covering various modes including (a) (a) highhigh--potentialpotential and (b) and (b) hothot--ion modesion modes..

Data well fit to the extended scaling surfaces with auxiliary heatings; i.e.,

(c) and (d) (c) and (d) with central ECHwith central ECH(d) along with (d) along with plug NBIplug NBI.

[1] T. Cho et al., Phys. Rev. Lett. 86, 4310 (2001).

A preferable scaling of aaweak decreaweak decreasese inin φφcc with with increasing nincreasing ncc

together with the recoveryrecoveryof of φφcc with with increasing increasing ECH powersECH powers(a hot-ion mode having Ti>keV)

Ther

mal Bar

rier

Potenti

als

Ion

Con

finin

gP

oten

tials

Plug to Central Density Ratio Central Density

GAMMA 10 GAMMA 10

[1] ThreeThree--timestimes ProgressProgress in IonIon--Confining PotentialsConfining Potentials φφcc as compared to φφcc in 1992-2002 is achieved in the hot-ion mode.

[2] The advance in the potential formation leads toleads to a findingfinding ofremarkable effects of radially produced radially produced EErr ShearShear,, dErr/dr.

[3] Turbulent VortexVortex structures are observed with a weak EErrshear formation.

[4] Suppression of the turbulent vortexvortex structures due to a strong due to a strong EErr shearshear leads to Confinement ImprovementConfinement Improvement in the transverse direction (typically a few tens %).

[5] TheThe progressprogress in the in the potential formationpotential formation is made in line with the extension of our proposed physics scaling.

[6] A scalingA scaling of of φφcc with nwith ncc (ranging in achieved ncc~1019 m-3 with Ti ~ keV for φφcc >hundreds V) is found to have preferable dependence of a a weak decreaseweak decrease in in φφcc with increasing nwith increasing ncc along with the recoveryof φφcc with increasing ECH powers.

Summary in GAMMA 10

HANBIT Mirror Device and Recent Research Activities

Major Recent Research Activities (after Lyon Conference) :- Identification of discharge characteristics in HANBIT - Development of stable reference operation scenarios in HANBIT- Basic physics study of plasma heating, stability, and confinement- Hot electron-ring experiments in plug region, KS in cusp region.- ECH preionization or heating experiments in central cell

Two distinct operation regimes observed in HANBIT

- Big density jump observed near ω ~ ωci during initial HANBIT experiments

(the density jump point is Bcc ~ 107% or ~ 0.23 T, where ωci ~ ω (f= ω/2π=3.5MHz)

(IAEA2002, Lyon)

• A possible scenario of the improvement

- Slow wave ion heating at ω < ωci =>Ti , Ti / Te increase => confinement improvement => density, beta increase

- Hot ions => fast neutrals by charge exchange => increased wall-recycling => self-sustainment of discharge without fueling100 101 102 103 104 105 106 107 108 109 110

0

1

2

3

4

5

6

72000.11.15 KBSI

Line

Den

sity

(1013

cm

-2)

Magnetic Field (%)

Shot: 9852-9865Slot: 3.5 MHz 150 KwDHT: 3.75 MHz 70 kW

• Measurements show also the jump in plasma beta and ion temperature

** MHD mode stabilization by RF ponderomotive or side-band coupling may be also a possible trigger.

Studies on StabilityPower excursion experiments were done to find

threshold power below which the plasma discharge is terminated.

Power excursion experiments reproduced the characteristics of operation window found in normal operation.

0.00 0.05 0.10 0.15 0.20 0.25 0.300

1

2

3

4

5

6

dP/dt=-1 kW/msec rf p

ower

(kW

)

γ=1.03 γ=1.01 γ=0.99

Line

den

sity

(1013

/cm

-3)

Time (sec)

0

50

100

150

200

250

rf power

2 4 6 8 10 12 140.000

0.005

0.010

0.015

0.020

Am

plitu

de (A

.U.)

Frequency (kHz)

50 msec < t < 100 msec 100 msec < t < 150 msec 150 msec < t < 200 msec

FFT of edge probe data for different time periods shows the onset of a strong MHD activity (~ 3 kHz ) before/during the plasma termination.

180.0 180.2 180.4 180.6 180.8 181.00.0

0.2

0.4

0.6

0.8

1.0

1.2 Probe 7 (array 1) Probe 7 (array 4)

Den

sity

(1011

/cm

-3)

Time (msec)

Array probe data show m=-1 (ion diamagnetic direction), n=0 interchangemode is excited.

Freq

uenc

y (k

Hz)

20

0.51.02.04.0

0

5

10

15

Edge probe at r = 160 mm

Wavelet Transformation

18301

• The instability onset time of both probes are the same about 82 ms and finishes at 137 ms.• Plasma column movement in the radial direction is not observed.• A fundamental 3.3 kHz and its second harmonics are shown in both probes.• Wavelet power spectrum of the edge probe is much smaller than that of the inner one.

0 5 0 1 0 0 1 5 0 2 0 0 2 5 00

1

2

3

4

5

6

7 L i n e i n t e g r a t e d d e n s i t y R F p o w e r E d g e i o n s a t u r a t i o n c u r r e n t D i a m a g n e t i c f l u x

S h o t 1 8 3 0 1

T i m e ( m s e c )

Nor

mal

ize

d V

alue

s (A

U)

Freq

uenc

y (M

Hz)

Am

plitu

de (A

U)

0.120 0.125 0.130 0.135 0.140 0.145

0.050.10.20.4

0.0

-0.5

-1.0

0.5

0

15

1.0

5

10

20

0.150Time (sec)

Interchange mode Quiescent plasma

• About 3.5 MHz frequency is dominant.• Wavelet power spectrum during interchange mode is much weaker than that of the quiescent plasma.- RF power was reduced by factor of 2- wave coupling effects are efficient during

interchange instability

Magnetic probe at r = 160 mm

Ponderomotive Theory

0 50 100 150 200 250 300 350 4000

2

4

6

8

10

12

14

16

18E+

-2E-5-1.667E-5-1.333E-5-1E-5-6.667E-6-3.333E-62.541E-213.333E-66.667E-61E-51.333E-51.667E-52E-5

z (cm)

r (cm

)

0 50 100 150 200 250 300 350 4000

2

4

6

8

10

12

14

16

18 E-

-1.75E-5-1.437E-5-1.125E-5-8.125E-6-5E-6-1.875E-61.25E-64.375E-67.5E-61.063E-51.375E-51.688E-52E-5

z (cm)

r (cm

)

0 2 4 6 8 10 12 14 16 180.0

5.0x10-6

1.0x10-5

1.5x10-5

2.0x10-5

2.5x10-5

3.0x10-5

|E| (

A.U

.)

r (cm)

|E+| |E-|

Full wave simulation taking into account the density profile and realistic mirror field geometry showed that ponderomotive forcedestabilizes interchange modes when γ=0.97 and stabilizes whenγ=1.03 disagree with experiments

Fp+ > 0 : destabilization

Fp- < 0 : stabilization

0 2 4 6 8 10 12 14 16 180.0

4.0x10-6

8.0x10-6

1.2x10-5

1.6x10-5

2.0x10-5

|E| (

A.U

.)r (cm)

|E+| |E-|

0 50 100 150 200 250 300 350 4000

2

4

6

8

10

12

14

16

18E-

-8E-6-6.5E-6-5E-6-3.5E-6-2E-6-5E-71E-62.5E-64E-65.5E-67E-68.5E-61E-5

z (cm)

r (cm

)

0 50 100 150 200 250 300 350 4000

2

4

6

8

10

12

14

16

18

E+

-9E-6-7.417E-6-5.833E-6-4.25E-6-2.667E-6-1.083E-65E-72.083E-63.667E-65.25E-66.833E-68.417E-61E-5

z (cm)

r (cm

)

Fp+ < 0 : stabilization

New Theory : EPM + SBCLow-frequency electrostatic interchange mode

( ) αωααωαααωαωωω

ωαω

ωαωωα

ωαωααωαα

ωαωα

ν gΓBΓ

EBΓ

EΓVΓ

Γ

nmmc

nc

nqmt

m

tn

+−Π⋅∇+⎥⎥⎦

⎤

⎢⎢⎣

⎡⎟⎠

⎞⎜⎝

⎛ ×++×+=∇⋅+∂∂

=⋅∇+∂

∂

∑=′′+′

′′′

′′′000

0 Total ponderomotive force densityCentrifugal force

Collisionalfriction

Plasma fluctuation driven by RFSideband waves

αωααωαωαω

ωααωα

αωαω

ν±

±

±±

±

±

−⎟⎟⎠

⎞⎜⎜⎝

⎛+×+=

∂∂

=⋅∇+∂

∂

± ΓEBΓ

EΓ

Γ

mnc

nqt

m

tn

s 000

0 Nonlinear coupling

αωαααω

ωααωα

αωαω

ν0

0

00

0

0

00

0

ΓBΓ

EΓ

Γ

mc

nqt

m

tn

−⎟⎟⎠

⎞⎜⎜⎝

⎛×+=

∂∂

=⋅∇+∂

∂

+ Maxwell equations for RF and SB waves

0.90 0.95 1.00 1.05 1.10

-15000

0

15000

30000

45000

60000 P (Ef=5V/cm) P/2 P/3 P/4

-Im(ω

)

ω0/Ωi

Stable Operation Window:

The stable operation window and its dependence on RF-power and ω0/Ωi agree well with experimental results.

02.195.0 0 ≤Ω

≤i

ω

Idea for Improving Stability••••••

••••••

Hot Electron Ring Formation• D’Ippolito, et al. proposed the creation of hot-electron rings and disks in the end cells of a tandem mirror. • The intent was to maximize the line bending of the mode.• Maximizing the stabilizing mode line bending energy is equivalent to minimizing the parallel connection length between the central cell and the line-tying point.

• Theoretical arguments suggest that a high-β hot electron ring will support a higher central cell β for a ring beta, βr <0.6.

• But a high-β hot-electron disk should support a higher central cell beta for βr >0.06

D. A. D’Ippolito,et al., Plasma Physics, 24, 707, (1982)

There is little evidence that a high-β hot-electron disk has ever been made in a mirror machine

RF Heating Studies

dispersion relation of magnetized cylindrical plasma

fast wave

slow wave

n=1012 cm-3

plas

ma

resi

stan

ce (W

)

magnetic field (Gauss)

SLOT

1e-5

1e-4

1e-3

1e-2

1e-1

1

2100 2150 2200 2250 2300 2350 2400 2450 2500

m = +1 m = +1 m = -1m = -1

Uniform PlasmaDispersion Relation

fast wave cavity resonance

slow wave

plasma impedancefor uniform plasma

calculated by in theplasma volume.

∫ ⋅ 3*2

1 drEJI a

rrcalculated by on the plasmavacuum boundary.

danS∫ ⋅ˆr

The plasma resistances calculated two ways are well coincident. This is necessary condition for exact solution.

0.95 1.00 1.0510-5

10-4

10-3

10-2

10-1

Rtotal Rion Relectron

ω/Ωc0

plas

ma

resi

stan

ce (O

hm)

0.94 0.96 0.98 1.00 1.02 1.04 1.06 1.08 1.100.0

2.0x1013

4.0x1013

6.0x1013

8.0x1013

1.0x1014

high pressure low pressure

line

dens

ity (c

m-2)

ω/Ωc0

• The numerical results show that the RF wave can deliver its power to plasma more effectively as w/Wc0 < 1 for both of electron and ion (left figure).

• The trend of power absorption into electron coincides very well with the trend of the plasma density (right figure).

Application to HANBIT Mirror Devicerepresentative wave patterns, m= +1, Im(Er,θ,z)

0 50 100 150 200 250 300 350 40002468

1012141618

-9E-6-8.15E-6-7.3E-6-6.45E-6-5.6E-6-4.75E-6-3.9E-6-3.05E-6-2.2E-6-1.35E-6-5E-73.5E-71.2E-62.05E-62.9E-63.75E-64.6E-65.45E-66.3E-67.15E-68E-6

z (cm)

r (cm

)

SLOT

ICR

0 5 10 15 20-5000

0

5000

10000

15000

20000

25000

30000

35000

40000

pow

er d

ensit

y (a

.u.)

r (cm)

electron

0 5 10 15 20

0

5000000

10000000

15000000

20000000

25000000

powe

r den

sity

(a.u

.)

r (cm)

ion

0 50 100 150 200 250 300 350 40002468

1012141618

-2.5E-5-2.225E-5-1.95E-5-1.675E-5-1.4E-5-1.125E-5-8.5E-6-5.75E-6-3E-6-2.5E-72.5E-65.25E-68E-61.075E-51.35E-51.625E-51.9E-52.175E-52.45E-52.725E-53E-5

z (cm)

r (cm

)

SLOT

0 5 10 15 20

0

100000

200000

300000

400000

500000

600000

powe

r den

sity

(a.u

.)

r (cm)

electron

0 5 10 15 20

0

2000000

4000000

6000000

8000000

10000000

12000000

powe

r den

sity

(a.u

.)

r (cm)

ion

0 50 100 150 200 250 300 350 40002468

1012141618

-6E-8-5.3E-8-4.6E-8-3.9E-8-3.2E-8-2.5E-8-1.8E-8-1.1E-8-4E-93E-91E-81.7E-82.4E-83.1E-83.8E-84.5E-85.2E-85.9E-86.6E-87.3E-88E-8

z (cm)

r (cm

)

DHT

ICR

0 5 10 15 20

0

5000

10000

15000

20000

25000

30000

powe

r den

sity

(A.U

.)

r (cm)

B

0 5 10 15 20

0

2000000

4000000

6000000

8000000

10000000

12000000

Powe

r den

sity

(A.U

.)

r (cm)

C

0 50 100 150 200 250 300 350 40002468

1012141618

-6E-5-5.5E-5-5E-5-4.5E-5-4E-5-3.5E-5-3E-5-2.5E-5-2E-5-1.5E-5-1E-5-5E-6-5.082E-215E-61E-51.5E-52E-52.5E-53E-53.5E-54E-5

z (cm)

r (cm

)

DHT

0 5 10 15 20

0

100000

200000

300000

400000

500000

powe

r den

sity

(a.u

.)

r (cm)

electron

0 5 10 15 20

0

5000000

10000000

15000000

20000000

25000000

30000000

powe

r den

sity

(a.u

.)

r (cm)

ion

)( θEIm

Effect of Neutral Pressure

0 2 4 6 8 10 12

100

200

300

ω/Ωc0=1.31 ω/Ωc0=1.04 ω/Ωc0=1.03 ω/Ωc0=1.01 ω/Ωc0=0.97 ω/Ωc0=0.97

, 100 kW

T || (

eV)

gas puffing rate( # of 2msec pulse)

Low pressure discharge is effective to enhance the ion temperature.

Each point is time averaged T|| for each shots to achieve representative value. It shows that temperature is increases as the reducing the number of puffing pulses.

0.98 1.00 1.02 1.04

100

200

300

400

ω/Ωc0

T || (eV

)

T|| Iloss

0

200

400

600

Iloss /nline

RF: 150 kWPuffing rate: 1 x pulse (2m sec)

We performed time average for each shots again to achieve evident behavior of T|| & Iloss on external magnetic field. We can see that at ω/Ωc0< 1 case, parallel ion temperature is higher than ω/Ωc0 > 1 case and also temperature anisotropy becomes larger. It means that perpendicular temperature is much higher at ω/Ωc0 < 1 case.

New Operation Regime

•Preionization with no puffing in central cell produces high density plasmas

•The usual transition to low density plasmas at low fields is not observed as low as 104%

100 102 104 106 108 110 112 1140.00E+000

2.00E+013

4.00E+013

6.00E+013

8.00E+013

1.00E+014

1.20E+014

1.40E+014

nel (

cm-2)

magnetic field (%)

ICRH=250 kW2004.10.19CC preionizationprefill-no puff

ICRH=200 kW2004.6.30CC preionizationprefill-no puff

ICRH=200 kW2001.5.25No preionizationHigh pressure puffing

0.0 0.1 0.2 0.3 0.40.0

2.0x1013

4.0x1013

6.0x1013

ne

Pneu

time[s]

line

dens

ity[c

m-2]

0.0

1.0x10-5

2.0x10-5

3.0x10-5 neutral pressure[Torr]

0.0 0.1 0.2 0.3 0.40.0

5.0x1012

1.0x1013

1.5x1013

2.0x1013

ne

Pneu

time[s]

line

dens

ity[c

m-2]

0.0

2.0x10-4

4.0x10-4

6.0x10-4 neutral pressure[Torr]low gas pre-puff, 150kw rf

high gas pre-puff, 150kw rf

/ 0.96ciω ω =

/ 1.33ciω ω =

Discharge Simulation-Radial Transport Model

Ion continuity

Ion temperature

Electron temperature

Neutral continuity

Quasi-neutrality

( ) ( ) ( )

( )

( ) ( ) ( )

( )

rT

mTnq

rT

mTnq

nEPn

TTn

P

rqrrn

rVrr

TVTrt

T

nEkNnn

TTn

P

rqrrn

rVrr

TVTrt

Tr

Ern

mTn

rTeE

m

nn

nsrt

n

NSrt

N

e

ee

eee

i

ii

iii

ce

eleinel

eie

ei

e

eabs

ee

ee

e

ci

ili

exiiii

ieie

ie

e

iabs

ie

ii

i

i

ii

ii

i

iii

iie

ilii

ii

klkk

kk

∂∂

−=∂∂

−=

⎟⎟⎠

⎞⎜⎜⎝

⎛+−

−+=

∂∂

+∂∂

−∂∂

+∂

∂

⎟⎟⎠

⎞⎜⎜⎝

⎛+∑−

−+=

∂∂

+∂∂

−∂∂

+∂∂

∂∂

−=∂∂

−⎟⎠⎞

⎜⎝⎛

∂∂

−=Γ

=

−=∂Γ∂

+∂∂

−=∂Γ∂

+∂

∂

∑

**

,

,

**

2 ,7.432

32

32

3

32

32

32

3

,1

νν

ττ

τε

τ

φνν

ν

ν

Heat flux

Drift-diffusion

ce

e

ci

i

i

nnττ

=∑ ambipolarity

0 5 10 15 20 250.0

0.5

1.0

1.5

2.0

2.5

Plas

ma

Den

sity

(1012

cm-3)

r (cm)

0 5 10 15 20 250

20

40

60

80

100

120

Electron

Ion

Tem

pera

ture

(eV

)

r (cm)

Temperature Profile

Plasma Density Profile

Simulation results for plasma density and temperature at 1.6x10-5 Torr . Solid lines and circles represent simulation result and Langmuir probe measurementdata, respectively. Square represents ion temperature estimated by semi-empirical method.

Simulation Results - DEGAS2

low gas puff, 150kw ICRH

/ 1.0ciω ω =

low gas puff, 150kw ICRH

/ 0.96ciω ω =

Calculated radial profiles

Loss power calculations Particle balance and recycling coeff.

Neutral hydrogen density

The reconstruction is performed for a square region of 32 cm 32cm, which is divided into 30 30 equally spaced pixels about 1.1cm in length.

Emissivity profiles (#19937)

T = 5.513 sec T = 5.516 sec

T = 5.52 sec T = 5.76 sec

Bayesian Probability Theory (BPT) withMaxEnt method

Neutral hydrogen density profiles (#19937)

-0.15

-0.1

-0.05

0

0.05

0.1

0.15

0.15 -0.1 -0.05 0 0.05 0.1 0.150.15 -0.1 -0.05 0 0.05 0.1 0.15

5.73E+165.54E+165.35E+165.16E+164.97E+164.78E+164.59E+164.39E+164.20E+164.01E+163.82E+163.63E+163.44E+163.25E+163.06E+162.87E+162.67E+162.48E+162.29E+162.10E+161.91E+161.72E+161.53E+161.34E+161.15E+169.55E+157.64E+155.73E+153.82E+151.91E+15

Vert

ical

rad

ius

[m]

Horizontal radius [m]

Summary

RF has significant effects on mirror MHD phenomena

Theories indicate that HANBIT experiments are in the range where sideband coupling effects are dominant over ponderomotive force effects.

Various methods for stabilization have been tried

A hot-electron ring has been created in the plug section of Hanbit. The β is not large enough to permit stabilization of the central cell plasma. The kinetic stabilizer is being under test. Other options are also being considered.

Low pressure helps increase temperature

Low pressure discharge is now available with pre-ionization. Order of magnitude reduction of the initial pressure reduces the charge exchange loss substantially.

Plasma modeling and neutral transport studies help characterize HANBIT plasmas

A heuristic plasma model based on Degas2 and 1-D plasma transport is developed and it reproduces the experimental plasma quite reliably.(accurate measurement of Te and ne profiles are essential)

For ion heated plasma, Ti is limited mainly by high wall recycling rate due to excessive charge-exchange process