Published by Fusion Energy Division, Oak Ridge National Laboratory
Building 5700 P.O. Box 2008 Oak Ridge, TN 37831 -6169, USA
Editor: James A. Rome Issue 113
E-Mail: jar@ornl.gov Phone (865) 482-5643
On the Web at http://www.ornl.gov/sci/fed/stelnews
February 2008
High ion temperature plasma
production in LHD
Ion temperature Tx has been successfully increased in the
Large Helical Device (LHD) in Toki, Japan. In FY 2006
(the 10th experimental campaign), 7j exceeded 5 keV at an
average plasma density nt of 1.2 x 1019m~3, and it has
exceeded 6 keV at ne ~ 2 x 1019m~3 in FY 2007 (the 11th
campaign). These achievements have demonstrated the
capability of high-Ji plasma confinement in helical
devices, which leads towards a helical fusion reactor. In
this report, we summarize the highlights of high-Tj plasma
production experiments in FY 2006. Further progress in
FY 2007 will be reported somewhere in the near future.
The Setup for Ion Heating Experiments in LHD
The most powerful heating system in LHD is negativeion-
based neutral beam injection (NBI), provided by three
tangential injectors with nominal hydrogen injection
energy of 180 keV [1]. The total injection power from tangential
NBI has reached about 14 MW. One injector (#2)
has the opposite injection direction to the other two injectors
(#1 and #3). A low-energy positive NBI system (#4)
with perpendicular injection became operational in FY
2005, and it achieved 40-keV 7-MW injection in FY 2006.
To demonstrate high-7^ plasma confinement capability in
LHD, high-Z (such as Ne and Ar) plasmas with low ion
density (in the range of 1017 m~3) were previously used as
targets when only tangential NBIs were available, to effectively
increase the absorption power per ion. With this
approach 7- of about 13.5 keV was successfully demonstrated
[2]. This successful proof-of-principle experiment
for high-rj plasma confinement has led to the installation/
power increase of a low-energy NBI system to directly
increase the ion heating power. As noted earlier, beam #4
is perpendicularly injected, enabling charge-exchange
recombination spectroscopy (CXS) measurement with a
toroidal line of sight for radial profiles of Tx and toroidal
rotation velocity (Vt), even in cases in which impurity content
(utilized for measurement) has a hollow density profile.
A schematic view of the NBI configuration and CXS
system is provided in Ref. [3]. Information on the Tx and
Vj. profiles enhances the physics understanding of the confinement
characteristics of helical plasmas.
Heating in the ion cyclotron range of frequency (ICRF) [4]
can also be utilized because the target plasmas for high-7^
experiments in LHD are now the lighter ion species, such
as hydrogen and/or helium. A total ion cyclotron heating
(ICH) power of about 2 MW (38.47 MHz) was injected
through four antennas using the minority-ion heating
mode.
In addition, electron cyclotron heating (ECH) has been
recognized as an effective way to improve ion confinement
in the core region through the appearance of the electron-
root radial electric field (Er) [2]. This effect was
clearly recognized at ne ~ 0.3 x 1019 m~3 in high-Z plasmas.
Since the target density for the high-7- hydrogen
plasma production experiments described in this report is
above 1019 m~3, clear effects of ECH on ion energy confinement
have not yet been observed, although an increase
In this issue...
High ion temperature plasma production in LHD
Ion temperature (7j) has been successfully increased
in the Large Helical Device (LHD) in Toki, Japan. In
FY 2006 (the 10th experimental campaign), 7^
exceeded 5 keV at an average plasma density (ne) of
1.2 x 1019m~3, and it has exceeded 6 keV at ne ~ 2 x
1019m"3 in FY 2007 (the 11th campaign). These
achievements have demonstrated the capability of
high-7^ plasma confinement in helical devices, which
leads towards a helical fusion reactor. In this report,
we summarize the highlights of high-7*j plasma production
experiments in FY 2006. Further progress
achieved in FY 2007 will be reported in the near
future 1
Changes in the ORNL Stellarator Program
James Lyon retired at the end of January. His role is
being assumed by Jeffrey Harris 5
All opinions expressed herein are those of the authors and should not be reproduced, quoted in publications, or
used as a reference without the author's consent.
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