23P054-P
Edge Er structure in JT-60U H-mode having Type-I ELMs
JT-60UのType-I	 ELMy	 Hモードプラズマにおける周辺電場構造	 Kensaku Kamiya, Mitsuru Honda, Hajime Urano, Maiko Yoshida, Yoshiteru Sakamoto, et al.
神谷健作、本多充、浦野創、吉田麻衣子、坂本良照、宮戸直亮、仲野友英、松永剛、他Japan Atomic Energy Agency (JAEA), Naka
801-1 Mukouyama, Naka, Ibaraki, 311-0193 JAPAN
日本原子力研究開発機構	  〒311-0193	  茨城県 那珂市 向山 801-1
The first detailed measurements of radial electric field (Er) during NBI heated ELMy H-modes in the edgeof the JT-60U tokamak are reported. Depending on the direction of the external momentum input,
substantial changes in not only toroidal rotation but also poloidal rotation for the carbon impurity ions areobserved. The shear in the Er becomes wider in the co-NBI, while the Er-well becomes deeper in thecounter-NBI. The relationship between Er shear and pedestal structure at the onset of ELMs with variationin the direction of momentum input is investigated.

1. Introduction
In this study, we report the first detailed
measurements of radial electric field (Er) during
NBI heated ELMy H-modes in the edge of theJT-60U tokamak, investigating the relationshipbetween Er shear and pedestal structure in the ion
temperature at the onset of Type-I ELMs withvariation in the direction of momentum input.
The Er is determined from the radial force
balance equation for the carbon impurity ions, inwhich the diamagnetic, poloidal velocity, andtoroidal velocity terms are evaluated by means of
the upgraded CXRS diagnostic having fast time
resolution of up to 400 Hz with a better
signal-to-noise ratio [1-2]. It should be noted thatthe inferred poloidal rotation velocities are based on
carefulconsiderationoftheeffectiveenergy-dependent cross section and of thegyromotion of the ions, in which the apparent
rotations are corrected by using the Atomic Dataand Analysis Structure (ADAS) database for the C
VI (n=8→7) transition.
2. Results
2.1 Comparison of pedestal structures for co-,balanced-, and counter-NBI discharges at the onsetof Type-I ELM
As shown in Fig. 1, the shear in the edge Er
becomes wider in the co-NBI case than the ctr-NBI
case, while the edge Er-well becomes deeper in thecounter-NBI case than the co-NBI case (thebalanced case is roughly intermediate betweenthem). Comparing between co- and ctr-NBI cases,
the location of the Ti pedestal (shoulder) is inner inthe co-NBI case with the higher Ti value [3] (animportant caveat to this discussion is that thebalanced case is not intermediate between them.),
while the maximum |dTi/dr| values are almost

similar even though the Er structures are quite
different. On the contrary, the location of the ni
pedestal (shoulder) is slightly inner in the ctr-NBI
case with much higher ni value, while the maximum|dni/dr| values seem to be correlated with themaximum |Er| and/or |dEr/dr| values. It is noted thatthe locations of the maxium |dTi/dr| and |dni/dr| areclose to that of the maximum |dEr/dr|.

Fig.1. Profiles of (a) toroidal rotation, (b) ion
temperature, (c) impurity ion density, (d) radial electricfield, and (e)~(h) radial derivative of these profiles.	 
The solid, dashed, and dash dot curves represent theresults of fitting the data to a tanh-like function for co(red diamonds), ctr- (dark blue triangles), andbalanced-NBI (green squares) discharges, respectively.

2.2 Transient transport phenomenon during aninter-ELM phase
As shown in Fig. 2, quasi-coherent oscillations
measured by reflectometer (cut-off density;
1.4x1019 m−3) in a higher frequency range (100-200kHz, plus broad-band one) were observed at aroundthe Er shear region as that seen in a weak- Er phasesin the ELM-free H-phase. It is noted that No MHD
activity was seen during these frequency ranges, sothat are electro-static signals. Turbulence during
inter-ELM phase (~40-90% intervals of the ELMcycle) seems to be suppressed according to aformation of Er-shear. The most interesting point is
the later inter-ELM phase in the counter-NBI case,indicating an intermittent Dα drop and recovery,
which is similar to the complex multi-stage “Ertransition” seen in the ELM-free H-phase [1].
However, an important caveat to this discussion isthat no completely bifurcations in the edge Er
values and Da emission were observed during aninter ELM phase, so far. There is a special featureof the pedestal such as a higher density in theELMing phase than the ELM-free phase that can beassociated with different Er transition characteristics,
although the exact causality is still unclear.

accelerated toward the direction of the torque,
contributing to the different Er structures. As aresult, the shear in the edge Er becomes wider in theco-NBI case, while the edge Er-well becomesdeeper in the counter-NBI case. Thus, the Er shear
is enhanced in the co-NBI case after Er transition,
which occurs in a very narrow region at around
R-RSEP ~ -0.025m, while the onset condition for theEr transition may be more easy in the ctr-NBI, if theEr (or Poloidal Mach number, Up,m) value itself iscritical one.
Effect of other external momentum source on Erstructure (such as perpendicular NBI) is also
discussed. Applying the perpendicular injectedbeams, there could be a significant radial current
due to direct orbit (and/or ripple) losses of fast ions,which could lead to significant torque on theplasma edge region. Recently upgraded OFMC
(Orbit-Following Monte-Carlo) code, which iscapable of estimating both the jxB and collisional
torques [4], is a powerful tool to elucidate the originof the electric field in a plasma during the NBI
heating with various momentum sources, since
there are basically three “knobs” (diamagnetic drift,poloidal and toroidal rotations) affecting the radial
electric field. As a result, the jxB torque is found tocontribute to a negative Er structure at the plasmaedge region, depending on the momentum injection
angle. Some of the uncertainties in these results arealso discussed, and directions for future work toverify the paradigm of ExB shear suppression ofturbulence will be described.

Fig.2. Contour plot of the 34 GHz reflectometry complex
amplitude of the density flucutation in the ctr-NBI
discharge. The Da recycling signal (and itstime-expanded view) is also shown.

2.3 Er components
Depending on the direction of the external
tangential momentum input (co-, balanced-, andcounter-NBI), substantial changes in not only
toroidal but also poloidal flows for the carbon
impurity ions are observed at around the Er-wellregion near the bottom half of pedestal (at aroundR-RSEP ~ -0.04m), maintaining radial force balance.
It is noted that the poloidal flow for the carbon
impurity ions from the middle to the top of pedestal
seems to be damped, while the toroidal flow isFig.3. Radial profiles of the Er components. (a) toroidal
rotation term, (b) poloidal rotation term, (c) diamagnetic
term, and (d) total Er.
References[1] Kamiya K. et al 2010 Phys. Rev. Lett. 105045004.
[2] Kamiya K. et al 2011 Nucl. Fusion 51 053009.
[3] Urano H. et al 2007 Nucl. Fusion 47 706.
[4] Honda M. et al 2011 Nucl. Fusion 51 073018.