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　 Super dense core plasma due to Internal Diffusion Barrier in LHD

N. Ohyabu 1), T. Morisaki 1), S. Masuzaki 1), R. Sakamoto 1), M. Kobayashi 1),J. Miyazawa 1), M. Shoji 1), T. Akiyama 1), N. Ashikawa 1), M. Emoto 1), H .Funaba 1), P. Goncharov 1), M. Goto 1), J.H. Harris 2), Y. Hirooka 1), K.Ichiguchi 1) T. Ido 1), K. Itoh 1), H. Igami 1), K. Ikeda 1), S. Inagaki 1), H .Kasahara 1), T. Kobuchi 1), S. Kubo 1), R. Kumazawa 1), S. Morita 1) S. Muto 1), K. Nagaoka 1), N. Nakajima 1), Y. Nakamura 1), H. Nakanishi 1), K. Narihara 1) Y. Narushima 1), M. Nishiura 1), T. Notake 1), S. Ohdachi 1), N. Ohno 1), Y. Oka 1), M. Osakabe 1), T. Ozaki 1), B.J. Peterson 1), K. Saito 1), S. Sakakibara 1), R. Sanchez 2), H. Sanuki 1), K. Sato 1), T. Seki 1), A. Shimizu 1), H. Sugama 1), C. Suzuki 1), Y. Suzuki 1), Y. Takeiri 1), K. Tanaka 1), N. Tamura 1), K. Toi 1), T. Tokuzawa 1), S. Toda 1), K. Tsumori 1) I. Yamada 1), O. Yamagishi 1), M.Yokoyama 1), S. Yoshimura 1), Y. Yoshimura 1), M. Yoshinuma 1), K. Ida 1), T. Shimozuma 1), K.Y. Watanabe 1), Y. Nagayama 1), O. Kaneko 1), T. Mutoh 1), K. Kawahata 1), H. Yamada 1), A. Komori 1), S. Sudo 1), O. Motojima 1)1) National Institute for Fusion Science, Toki, Gifu-ken, Japan

presented by N. Ohyabu for LHD team

at 21st IAEA Fusion Energy Conference 16-21 October 2006, Chengdu China

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Contents1) A brief description of LHD, LID

2) Observation of Internal Diffusion Barrier （ IDB) in the LID divertor Discharge

Features of IDB mode Time Evolution of IDB LID divertor function+ Pellet injection Location of IDB Foot High (o) plasma at high B Steady State operation of IDB mode

3) Summary

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• LHD picture

LHD A super conducting large helical device (l=2, M=10)

Rax = 3.5-3.9 m, a 0.5-0.6 m, B = 3T

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Objectives i) to develop island divertor concept.Of LID experiment ii) to study island related physics iii) to explore confinement enhancement

mode.

Local Island Divertor

Pumping Duct

Vacuum Pump

Main Plasma

Island

Divertor Chamber

Pellet

LID Head

A closed divertor with high pumping efficiency

Pellet core fueling

Powerful particle control

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Internal Diffusion Barrier (IDB)

n(0) = 4.6 1020m-3, 　　　　 T(0) = 0.85 keV,

Wp = 1.1 MJ 　 at P = 10 MW,

noETo = 0.44 1020m-3keVm-3s

(0) = 4.4 % at B = 2.64 T 　　

Outer region (Mantle)

Pellet

Island Separatrix

IDB

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Time evolution of IDB

Time constant of n(0) decay is 1sec.

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Confinement Improvement Mechanismsin IDB discharges

SDC IDB Mantle

High n

High T

Low n

Low TT

n

Edge Density limit

Dense core plasma

Low mantle density High T in the mantle High core temperature

　　　　　　　　　　　　　　　　　　　 　　　　　　　　 Avoidance of radiative collapse

High confinement

Pumping

IDB + Pellet injection

IDB discharge: high core density + low mantle densityGas puff discharge : flat n profile

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In the outer region (mantle), T increases with P/nedge

q = - n T

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0

1.0

2.0

3.0

4.0

-1.2 -0.8 -0.4 0 0.4 0.8 1.2

sh57645-936-r375q100b105a8020

Te

ne

Te

(k

eV

)

0

1000

2000

3000

4000

-1.2 -0.8 -0.4 0 0.4 0.8 1.2

sh55603-1536-rho-47

Te(eV)

n

0

1000

2000

3000

4000

ne (1

020m

-3 )

Inward shifted configuration (Rax=3.65m).

Small, but clear core

Standard configuration (Rax=3.75m)

Optimum core

Dense core expands with beta and Rax.

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Dense core expands up to LCFS for outward shifted configuration (Rax = 3.85m).

<> = 1.38 %

<> = 0.63 %

LCFS

Dense core expands with beta and Rax.

n

n 1x 1020m-3

1x 1020m-3

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“Reheat” raises the core beta up to 5.1 %

(B=1.5T)

Large Shafranov shift. n profiles before and during “reheat”

“Reheat” starts

Te n

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* Pumping of the recycled particles low nmantle

* With intensive wall conditioning, IDB is maintained by wall pumping (without LID).

* For longer pulsed operation, divertor pumping is essential.

Pumping Duct

Vacuum Pump

Main Plasma

Island

Divertor Chamber

Pellet

LID Head

Role of LID

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Quasi-steady state operation of IDB mode has been demonstrated.

Pellet injection tends to fuel the particle in the region with high n.

Continuous pellet injectionno

= 2.0E20m-3

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Summary

• We have discovered Internal Diffusion Barrier which maintains a 　 high density core plasma (n(0) = 4.6 1020m-3, T(0)=0.85 keV, (0)=4.4 in the LHD divertor discharge fueled by pellets.

• Radial location of IDB foot increases with beta and magnetic axis.

• Function of the LID is pumping of the recycled particles. This leads to low density in the outer region and hence increase in temperature there.

• We propose a novel ignition scenario at high density and relatively low temperature in the helical device.

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End

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Particle Balance

core

mantle

n- profileCore pellet = nc Vc / c c = 0.4 s　　　　　　　 nc = 3.3 x 1020m-3

pellet = 0.5 x 1022s-1

　　　　　　 Vc = 6 m3

Mantle pump = <nouter> V / p*

p* = 0.5 s, <nouter> = 8.3 x 1019m-3

pellet

recycled

pump

Role of LID

* Pumping of the recycled particles low p* low nmantle

* With intensive wall conditioning, IDB is maintained by wall pumping (without LID).

* For longer pulsed operation, divertor pumping is essential.

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A New Ignition Scenario

(SDC reactor design) no = 5-7 1020m-3, To = 7-9 keV

(Conventional reactor) no = 1.5 1020m-3, To = 30 keV

• Internal Diffusion Barrier +Pellet maintain

high density core.

• Achievement of ignition with core temperature

as low as possible.