super dense core plasma due to internal diffusion barrier in lhd
DESCRIPTION
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), - PowerPoint PPT PresentationTRANSCRIPT
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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.