1. 11th IAEA Technical Meeting on H-mode Physics and Transport Barriers" 26 - 28, September, 2007
Tsukuba International Congress Center "EPOCHAL Tsukuba", Tsukuba, Japan
Effects of low central fuelling on density and ion temperature profiles in reversed shear plasmas on JT-60U
H. Takenaga, S. Ide, Y. Sakamoto, T. Fujita Japan Atomic Energy Agency, Naka Ibaraki , Japan
OUTLINE
Introduction
NBI and ECH in JT-60U
Effects of low central fuelling after strong ITB formation
Introduction
NBI and ECH system in JT-60U
Effects of low central fuelling after strong ITB formation
Effects of low central fuelling during ITB formation
Relation between density ITB and ion temperature ITB
Summary
Reversed shear plasmas in JT-60U
P-NBI  central fuelling & ion dominant heating
N-NBI & ECH  low/no central fuelling & electron dominant
heating (reactor relevant condition)
Peaked density profile
It is possible to achieve high fusion output with relatively low edge density (<nGW).
Suppression effects on ITG instability
Impurity accumulation is one of the largest concerns.
but, when impurity accumulation level is smaler than neoclassical prediction, peaked density profile is acceptable.
The central ECH was applied from t = 5.6 s after the strong ITB was formed using P-NB and the P-NB heating power was reduced at t = 5.8 s.
E041738, BT=3.7T
The electron heating power is higher by a factor of 1.6 than the ion heating power at t = 6.5 s.
HHy2~2 is achieved with Te(0) > Ti(0).
Strong ne and Ti ITBs were maintained with low central fuelling under dominant electron heating.
PNB
PEC
P-NB : keV, MW/unit
perp. 7 units (1 unit for CXRS)
co 2 units
ctr 2 units (1 or 0.5 unit for MSE)
N-NB : keV, MW/unit
Summary
QgasD2 ne W
QgasHe
Effects of low central fuelling on density and ion temperature profiles have been investigated using N-NBI and ECH in reversed shear plasmas of JT-60U.
Strong density and ion temperature ITBs were maintained when central fuelling was decreased after the strong ITB formation.
Similar density and ion temperature ITBs were formed both in low and high central fuelling cases.
Strong correlation between density gradient and ion temperature gradient was observed.
Particle transport and ion heat transport are strongly coupled or density gradient assists the ion temperature ITB formation through ITG mode suppression.
These results indicated that effects of low central fuelling on density and ion temperature profiles are not strong. Thus, it is possible to obtain density ITB in a fusion reactor.
Calculation :
ASSTR-2 : Ip=12MA, BT=11T,
Rp=6.2m, a=1.5m, Impurity=Ar
Fusion output ~4GW,
Pradmain~400MW,
Aux. heating=60MW A B
Ti(0)
Te(0)
ASSTR-2
tE = W / (Paux. + Pa - Prad(r/a<0.9))
Experiment : Impurity accumulation is smaller than neoclassical prediction.
high p H-mode plasma (weak shear)
nAr(0)/nAr(ITB-foot)~2xne(0)/ne(ITB-foot)
RS plasma
High confinement is demonstrated with high radiation loss in the main plasma. (Pradmain/Pnet~0.8).
Deff is smaller in the low central fuelling case.
DHe/DHeNC in the low central fuelling case is similar to or even larger than that in the high central fuelling case at the same i/iNC.
DHe : He gas-puffing modulation exp.
ECH
Gyrotron
4 units
110GHz
≤1MW/unit
Transmission line
~60m
70-80% transmitted
Antenna
A : fixed for co-ECCD
B : steerable for co-/ctr-ECCD or ECH
It is important to characterize density and ion temperature ITBs under condition of low central fuelling.
Effects of low central fuelling during ITB
Relation between density ITB and ion temperature formation
ne gradient near the qmin location was attempted to increase by gas-puffing stop/decrease and to decrease by LH transition.
E046144:
After gas-puffing was stopped at t = 4.4 s,
The edge ne decreased just after gas-puffing was stopped, while the central ne continued to increase, resulting formation of ITB like structure in the ne profile.
At the same time, the central Ti largely increased.
ne and Ti ITBs were formed simultaneously.
E046146:
After the LH transition at t ~ 5.0 s,
The edge ne increased and the ne gradient decreased.
Increase in the central Ti seems to be prevented.
Decrease in gas-puffing rate
The central Ti restarted to increase together with increase in the ne gradient.
ITB formation with low central fuelling and dominant electron heating at Ip=1 MA and BT=3.7 T.
During Ip ramp-up,
Low central fuelling case
EC+N-NB+P-NB (1u perp.+0.5u ctr.)
High central fuelling case
P-NB (4u perp.+0.5u ctr.)
Time evolutions of ne and Ti in the low central fuelling case are similar to those in the high central fuelling case, although time evolution of Te is quite different for two cases.
Gas-puffing rate necessary for ne feedback control is slightly higher in the low central fuelling case than in the high central fuelling case.
The ne and Ti ITBs are formed in the region of r/a = even in the low central fuelling case, which are similar to those in the high central fuelling case.
In the low central fuelling case, wide current hole (CH) was produced due to higher Te, thus, Ti profile in the central region is flat in the low central fuelling case.
Te profile is different for two cases.
ne raise by gas-puffing
E046146
Gas-puffing stop/decrease
LH transition
E046144
E046146
Particle flux in the core
Increase in edge density
Increase in ne gradient
Decrease in density gradient in the core
similar effect to central fuelling
Low central fuelling
High central fuelling
(a) E046209
(b) E046220
E046144 Ip
E046146 EC
N-NB
P-NB
Ip (MA)x10
Pinj (MW) 12
P-NB
P-NB
N-NB EC EC
ne (1019 m-3)
Qgas (10 Pam3/s) 3
Qgas
Profiles in the low & high central fuelling cases ne 3
IDouter divertor
(1019 ph/m2 sr s) 2 1 CH
r/a=0.4
r/a=0.4 3
The ne and Ti gradients are strongly linked.
Particle transport and ion heat transport simultaneously decrease ?
ne ITB assists formation of Ti ITB ?
Time delay of the increase in Ti gradient from the increase in ne gradient was not obvious.
 The fast CXRS system is being developed in JT-60U.
r/a=0.6
r/a=0.6 2
ne (1019 m-3)
r/a=0.4 1
r/a=0.4 4
r/a=0.6 3
r/a=0.6
Ti (keV) 2
r/a=0.4
r/a=0.4 1
r/a=0.6
r/a=0.6 3 4 5 6 7 3 4 5 6 7
Time (s)
Time (s)