Recent Development ofLHD ExperimentO.Motojima

for the LHD teamNational Institute for Fusion Science4521

1

Primary goal of LHD project
1.5

3. Fundamental research for steadystate operation with employing divertor.
4. Confinement studies on high energetic
particles and simulation experimentsof alpha particles
5. Complimentary study to tokamaks
leading to comprehensive understandingof toroidal plasmas.

/2. MHD studies beyond b of 5%.

i (=1/q)

1. Transport studies in sufficiently highntET regime relevant to reactor condition.

1.0W7-X
Standard Tokamak

LHD

0.500Reversed Shear Tokamak
0.2 0.4 0.6 0.8 1.0r

6. Reactor technology, in particular,
superconducting system, high heat flux
components, and structural material.

Heliotron configuration with employing
4521
full superconducting manget system.

2

Large Helical Device (LHD)
Dimension R/a = 3.9/0.6 m
Magnetic field 2.9T
Þ Exploration of Low r* and n*, and High b plasmas
Þ New perspective of attractive fusion reactor
by net current-free plasmas
Maximum achieved parameters
Line-averaged density
1.5´1020m-3
Energy confinement time tE
0.36 sPlasma stored energy
Wp1.03 MJElectron temperature
Te(0) 10 keV
Ion temperatureTi(0) 3.9 keVVolume-average beta
<b>
3.0 %
Discharge duration
127 s4521

3Present experimental specifications of LHD
Major radius
Poloidal coils
VacuumChamber
3.4 ~ 4.1 m
Helical coils
PlasmaMinor radius~ 0.63 m (at Rax=3.6m)
Plasma Volume~ 30 m3 (at Rax=3.6m)
Magnetic field
2.98 T (at Rax=3.5m)
Heating power
ECH (84 /168 GHz)
Divertor
1.7 MW
N-NBI (<170keV, H ) Leg
7.0 MW
ICRF ( 25-100MHz)
Cryostatvessel
2.7 MW4521

4

LHD main experimental hall

4521

5

Steady Progress of Plasma Performance (I)Stored energy exceeds 1MJ.

First plasma

Beta reaches 3%

Present plasma

4521

Progress of experimental
condition has been enhancing
performance of plasmas. 6

Progress of LHD experiment(2)LHD(NIFS,Japan)
JET(EU)ASDEX-U(FRG)
DIII-D(USA)Stored energy (J)

107

RS

JT-60U(JAERI,Japan)
ASDEX(FRG)
JFT-2M(JAERI,Japan)
RS

106

105

104
100

LHD is entering theoperational regimeof large tokamaks.

101
102
Plasma volume(m3)106107Heating power (W)Tokamak data extracted fromITER H-mode DB.

4521

7

Electron temperature has reached 10 keV

Te (106 degree C)

10 #26943

Thomson Scat.
ECE
X-ray PHA

864Experimental conditions
ECRH 1.2 MW
B
2.976 T
3.5 m
Rax

20

Achieved parameters
10 keV
Te(0)
Ti(0)
2 keV
<ne> 5x1018 m-3
tE
0.05 sDischarge duration 0.4s

3.0

3.5

4.0

4.5

R (m)
4521

8

4521

9

LHD is extending the frontieronsteady-state plasmas
102 Ignition

Commercial Reactor

JT-60U
Q=1ITERJET
10LHD 2nd target
JT-60U
DIII-DJET
100
LHD 1st target

n0Ti0tE (1020m-3 keV s)

Fusion triple product

110-1

LHD

10-2

Tokamaks

10-3
10-4

Preceding
Helical Dev.

min. hour

TRIAM-1Mdaymonth

10-5
10-1 100 101 102 103 104 105 106 107
4521

Operated Duration (s)10Accumulation of Database for Stellarators (1)Heliotron E (Kyoto Univ.)
ATF (ORNL)
W7-AS (IPP Garching)
CHS (NIFS)
R/a<2.2m/0.28m

LHD 1999 ⇒in plan
W7-X 2006(IPP Greifswald)
R/a=5.5m/0.53m
B=3T4521

NCSX 2007(PPPL)
R/a=1.42m/0.33m
B>2T11

Accumulation of Database for Stellarators (2)International stellarator database
Nucl. Fusion 36 (1996) 1063

• Description and format in conformity of ITER DB.
• Scalar data onlyInternational Stellarator Scaling 95 (ISS95)
95
0.80 -0.59 0.51 0.65 2.21 -0.40
tISS
=0.
26
B
P ne R a q2 / 3E

W7-AS
ATF
CHS
H-E
W7-A

010

µ tBr*-0.71b-0.16n*-0.04

LHD R3.75
LHD R3.6Mid.Tokamaks
AUG
DIII-D
JT-60
JET-310-310-2-11010010

Extract q dependenceèComparison withELMy H-mode

exp-210IPB 98 ( y , 2 )t scl(q / 5) 0.93
E = tE

ISS95(s)Et0Tokamaks(s)1010-110-2

q=3q=5104521

LHDtEtEexp (s)

-1

10-2

10-1

tEscl (s)10120Performance of LHD plasma depends on
the position of magnetic axis
Orbit of deeply trapped particle

3.4

3.6

3.75

3.9

Magnetic Axis Position (m)Good particle orbit
Magnetic well
Magnetic hill

Good stability
4521

13New finding of breakthroughs on confinement
Successful suppression of neoclassical helical ripple transport
by geometrical optimizationISS95 tEexp/tEISS95 ~1.5 isrobust towards b of 3% in
Rax=3.6m

ç Keep good confinement down
to nb* of 0.05 by inward shift ofmagnetic axis
tEexp/tEISS95

100tEexp / tEISS95

100

Rax=3.6m
Rax=3.65m
Rax=3.75m

10-1

10-1

Rax=3.6m
Time trace of discharge
reaching to 3%012

3<b> (%)

Rax=3.9m

10-1

100

n*101

Good confining property observed in4521 Unfavorable configuration from 14
linear theory on MHD instabilities

Information from Pressure
gradient and MHD activities
in high b discharge( around i =/ 0.5 )• Observed pressure gradient at
r=0.5 is predicted to be Mercier
unstable even from low beta valueof 0.5%. However, the pressure
gradient increases as beta.
•It is suggested that the plasma
enters the second stability region
over <bdia>〜2.3% by beta effect(forming magnetic well).

•

n/m=1/2 mode appears from 0.3%
to 2.3% where the region is Mercier
unstable, and it disappears when
the plasma enters the secondstability.

4521

15

Observation of Internal Transport Barrier in LHD
10transition
with ITNB

no ITB6Bifurcation phenomenaInternal Transport Barrier (ITB) appears when
the ECH power exceeds the threshold

4eT (0) [keV]

8Electron root plasmaCentral ECH is applied to NBI plasma with low
collisionality in the electron root

192n =0.3x10 m-3

e

00200

8400
PECH (kW)with ITB(358kW)-1[d(lnT )/dt] =228mse1
with ITB
0.828ms
0.6

ln[Te(0)]6no ITB
4 (253kW)eT [keV]600

Confinement improvement
Slow decay of Te after ECH turned-off shows
the lower ce inside the ITB

0.4296ms
no ITB

0-1-0.50r

0.514521

0.202040 60
Time [ms]8010016

Long pulse discharge is quite stable.
Plasma heated by NBI◎ Plasma discharges havebeen prolonged to 80 s by
NBI(0.5 MW) and 120 s by
ICRF(0.8 MW) .
◎ Temperature, density,radiation, and emission from
impurities are almost constantduring a discharge.
Plasma heated by ICRF
◎ Carbon divertor plates
have enabled us high density
operation.
◎ Next goal
104 sec Steady state operationby ICRH
4521

17

LHD 5th Campaign

4521

18

Plan in 5th Experimental Campaign(Sep.2001-Feb.2002)
Major objectives
Production of high-temperature& high-b plasmas
Clarification of confinement physics
Targets (Achievements)
Plasma performance
Temperature 100 million゜C(120 million゜C)
Stored energy 1.5 MJ (1.03 MJ)
Heating power
NBI
9 MW (7 MW)
ECH
1.5 MW (1.7 MW)
ICH
3 MW (2.7 MW)
Magnetic field
2.976 T @ Rax=3.5 m

4521

Research subjects
Confinement
Scaling law
Transport barrier
Role of electric field
Magnetic island effect
MHD in high-b regime
Equilibrium
StabilityLong pulse discharge
Particle control
Real-time control of magnetic
field
Density control
Pellet injection
Density limit
Radiation collapse
Impurity effect
19
Edge plasmas & Divertor

Summary
1. LHD is opening new perspective towards attractive fusion reactor bynet current-free plasmas.
2. Complementary role to tokamaks
Major physics should be common for toroidal plasmas.
• No net currents, Reversed shearè Intrinsic suppression of neoclassical tearing mode
• Density limit• No disruption
3. New findings as well as performance improvement have extended
frontiers.
4. More than one minute long operation with maintaining performanceis easy (10000-s demonstration in plan)è Unique contribution to steady-state related issues.
Near term plan (2001-2002)• Increase heating resources• Active particle control by Local Island Divertor

Long term plan : Second experimental phase (2008-)• Deuterium operation• Magnetic field of 4 T by superfluid He cooling4521• Closed divertor system

20

Contributions to ITC-12/APFA’01
from the LHD Team
1. Invited Talks(1) Impact of energetic-ion-driven global modes on toroidal plasma
confinements
by K.Toi on Wed.
(2) Role of radial electric field shear at the magnetic island in thetransport of plasmas
by K.Ida on Thu.
(3) Study of time evolution of toroidal current in LHD
by K.Y.Watanabe on Fri.
2. Posters on Tue. & Wed.
Plasma experiment
TheoryEngineering/Technology

25 papers
6 papers
4 papers

3. NIFS TourIn the afternoon on Thursday (Dec.13)
4521

21