Nuclear Fusion Research and Development

Intrinsic Rotation Due to Plasma Pressure Discovered–Toward the Understanding of High Pressure / Highly SelfRegulating Plasma–(a) Rotation
Mechanism Pressure?
edge core edge

NB injection

pressuregradient

Neutral beam (NB)
injection can change
the plasma rotation

Transport
Understoodby the original
experimentedge core edge

Plasmarotation

Pressure
gradient

Plasma rotationedge core edge

Current(b)

(c)

(d)

Intrinsic rotation (km/s)

3-2Intrinsic rotation

Final rotation profile
Intrinsic rotation grows
with pressure gradient

Pressure gradient (104Pa/m)
Fig.3-4(a) Schematic view of self-regulating high pressureplasmaThe plasma pressure, rotation, and electric current profiles
are strongly linked to each other.
(b) Schematic drawing of JT-60 plasma
JT-60 has various neutral beams (NB) with different injection
angles, which can change the direction of the plasma rotationand the rotation profile flexibly.

Fig.3-5(c) Formation mechanism of the rotation profile
The rotation profile is determined by the external momentum
input by NBs, momentum transport, and the intrinsic rotation
caused by the plasma itself. Using an original experimentand analysis method, we have separately evaluated theexternally induced rotation and the intrinsic rotation.
(d) Relation between the intrinsic rotation and thepressure gradient
The intrinsic rotation increases with increasing pressure
gradient. The difference in color corresponds to the different
NB power and torque.

Burning plasmas for nuclear fusion reactors are highly selfregulating, governed by strong linkage among plasma pressure,electric current, and rotation profiles as shown in Fig.3-4(a).
To construct fusion reactors, it is essential to understand andcontrol this self-regulating system. However, it has been an
open critical issue for nuclear fusion research worldwide tounderstand the formation mechanism of the rotation profileand the relation between the rotation and pressure profiles.
The rotation profiles are determined by various mechanisms:(1) the external torque input by neutral beams (NBs), (2) themomentum transport, and (3) the intrinsic rotation. However,these terms cannot be evaluated separately by the conventionalsteady-state-experiment and analysis.
In order to address this issue, we newly developed andapplied an experimental method utilizing the modulation of apart of the NBs, and as a result we evaluated the momentum

transport correctly. At low plasma pressure, it was found that therotation profiles are determined by the external torque appliedby the NBs and the momentum transport. At higher plasmapressures, the self-regulation appeared. In this case, we foundthat the measured rotation profiles cannot be explained merely
by the momentum transport and the external momentum input
from the NBs, and the intrinsic rotation becomes dominant.
The relation found between the plasma pressure gradient andthe intrinsic rotation in various confinement modes is shownin Fig.3-5(c). It was experimentally found for the first timethat the intrinsic rotation grows with increase in the pressure
gradient in all cases. This study enables us to understand themechanism of the intrinsic rotation in high pressure and highly
self-regulating plasmas, and gives important information about
the prediction and operation of the self-regulation plasmas inITER and other future fusion reactors.

ReferenceYoshida, M. et al., Role of Pressure Gradient on Intrinsic Toroidal Rotation in Tokamak Plasmas, Physical Review Letters, vol.100, 2008,
p.105002-1-105002-4.

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JAEA R&D Review 2008