S-P4-1
Project Summary for LHD Deuterium Experiment
ＬＨＤ重水素実験計画の概要
Yasuhiko Takeiri
竹入康彦
National Institute for Fusion Science322-6 Oroshi-Cho, Toki-City 509-5292, Japan
核融合科学研究所 〒509-5292 土岐市下石町322-6
The project of the deuterium experiment in the Large Helical Device is summarized. The main objective ofthe deuterium experiment is to investigate the reactor relevant plasmas by improving the plasma
performance. The isotope effect is highlighted as a physics issue to be identified for the burning plasmas.
Upgrade of the low-energy NBI systems is planned for enhancement of the ion heating power, and 10keVof the ion temperature is expected. The closed helical divertor is installed for efficient particle control. The
RF heating systems and the diagnostic systems are also upgraded for the deuterium experiment.

1. Objectives of LHD Deuterium Experiment
The Large Helical Device (LHD) has a plan ofthe deuterium experiment as the next step of theproject. The basic concept of the LHD project isto understand the reactor relevant plasma
performance in helical systems and to secure thedesign of a helical fusion reactor. To achieve it,the LHD plasmas should be also investigated withthe view of toroidal plasmas compatible withtokamak plasmas on a scientific base.
Considering the LHD project concept, theobjectives of the LHD deuterium experiment aresummarized as follows;
1. To realize high-performance plasmas byconfinement improvement and to provide awide range of plasma parameter space relevantto the reactor plasmas. As a consequence,scientific research area will be expanded withan increase in the variety of experiments.
2. To clarify the mass dependence (isotopeeffect) in the plasma confinement, leading toestablishment of a model for the burning
experiment using deuterium and tritium.
3. To demonstrate that the confinement
capability of high-energy ions is relevant tothe burning plasmas in helical systems.
2. Main
SubjectsinLHD
Deuterium
Experiment
The LHD Deuterium experiment should provide
a wide variety of research opportunities. Amongthem the following subjects are highlighted as main
subjects to achieve the objectives;(a) Confinement improvement and related physics
Research on the isotope effect in the plasma
confinement and the related confinement
improvement in the deuterium experiments,

toward systematic understanding of the toroidal
plasmas.
(b) Improvement of MHD stability and expansion ofhigh-β regime
Research on the MHD equilibrium and stability inhigh-β regime of collisionless plasmas realized by
the confinement improvement and the increase in
the heating power in the deuterium experiment.
(c) Confinement of high-energy ions
Research on the confinement of high-energy ions,such as ones accelerated by the ICRF D(H)heating scheme with a high-accuracy diagnostic.
(d) Optimization of divertor
Research on the particle and heat control in theperipheral plasma region with the closed helicaldivertor and improvement of the steady state
plasma performance.
(e) Plasma wall interaction
Research on the isotope effects in the plasma wallinteraction including the fuel recycling, tounderstand the behavior in the burning plasmas.
(f) Expansion of experimental approaches
Ion heating experiments by the ICRF heating
schemesof
H-minority/D-majorityand3
He-minority/D-majority.
3. Heating Scenario and Expected Plasma
Parameters
In the LHD experiments for over 10 years,
favorable compatibility of confinement and MHD
stability in the inner-shifted configuration of themagnetic axis is one of the most importantachievements. This should be applied to thehigh-energy ion confinement, and has resulted in
the success of the ICRF heating and theperpendicular NBI heating experiments. Therefore,
the upgrade of the low-energy perpendicular NBI isplanned so that intensive research on the iontransport should be possible by enhancement of theion heating power. Figure 1 shows a top view of theupgraded NBI systems for the LHD deuterium
experiment. Two positive-NBI systems of theperpendicular injection are upgraded to 9MW from
6MW of the injection power by raising the injectionenergy for the deuterium injection. Although threenegative-NBI systems of tangential injection areunchanged in the injection energy and power, theion heating ratio is improved for low density
plasmas by using the deuterium beams. The total
deuterium injection power planned is 32MW
(18MW of the positive-NBIs and 14MW of thenegative-NBIs).
Assuming the energy confinement time twice theISS95-scaling, the central ion temperature reaches
10keV at 2x1019m-3 with the above NBI heating. At
1x1020m-3, 3.8MJ of the plasma stored energy with5keV of the central plasma temperature and 3% of
the β value is also expected.
4. Device Development Program
The project of the LHD deuterium experimentwill start after concluding the Agreement with local
government bodies. The period of the deuterium
experiment is scheduled for 9 years following
around 3-year’s preparation, such as construction of
the tritium removal system, the neutron shieldingsystem, the radiation safety monitor system, and themanagement system for the radiation-controlledarea. In addition to the upgrade of the NBI systems,
various device developments are programmed forthe deuterium experiment.
4.1 Closed helical divertor
The active control of the peripheral plasmas byexhausting the fuel and impurity particles isplanned with the closed helical divertor. In all
inboard-side divertor area, closed-type helicaldivertors with baffle structure are installed,
equipped with a pumping system under the dome.
Figure 2 shows one section of the closed helicaldivertor. Improvement of the plasma performance is
expected by controlling and pumping the fuel andimpurity particles in the deuterium experiment.
4.2 RF heating system
For production of high-temperature plasmas andlocal control of the plasma potential and therotational transform by the ECCD, the ECH system
is upgraded to 6MW with 77 and 154GHz
gyrotrons. Steady state heating is also possible at1MW.
In the deuterium experiments, various ICRF

heating scenarios can be applied, such as the D(H)and D(3He) heating schemes, the second-harmonic
heating, and higher-harmonic heating in high-β
plasmas. The ICRF heating system is upgraded to6MW, which is available to steady-state heating
experiments with around 3MW.
4.3 Diagnostic system
Neutron diagnostic system is greatly important
not only for the measurement of plasma
performance, but also for the radiation safety
monitor. Fission chambers and scintillation
counters are installed with precise calibration.
High-energy particle diagnostics system is also
important to investigate the confinement capabilityof the high-energy ions in helical systems. The
collective Thomson Scattering system and the loss
ion probe system are planned.
Three-dimensional measurements are highlighted
for deep understanding of the LHD deuterium
plasma transport. The multi-channel ECE system isplanned, including the microwave reflectometry
and the BES system.

Fig.1. Top view of the upgraded NBI systems for theLHD deuterium experiment.

Fig.2. One section of the closed helical divertor.