26aD40P
核融合原型炉におけるプラズマ位置制御解析	 
Analysis of Plasma Position Control for DEMO Reactor
高瀬治彦1、宇藤裕康1、坂本宜照1、森一雄1、工藤辰哉1、日渡良爾1、飛田健次1、
原型炉設計合同特別チーム
1
Takase Haruhiko , Utoh Hiroyasu1, Sakamoto Yoshiteru1, Mori Kazuo1, Kudo Tatsuya1,
Hiwatari Ryoji1, Tobita Kenji1, Joint Special Design Team for Fusion Demo1

原子力機構
1
JAEA

Pre-conceptual designs of DEMO reactor haveproceeded under collaboration Japan and Europe(Broader Approach activities (BA)). While the plasma
elongation as high as possible is required for highplasma performance, the elongated tokamak plasma isunstable for the vertical motion in principle. Therefore,
it is necessary for the tokamak devices to provide theposition control system, which consists of passive
conducting shells and active feedback control coils for
positional stability. It is important for DEMO reactor totake into account the actual shape of vacuum vessel andin-vessel components since the design condition ofDEMO reactor is different from current tokamak devicesand ITER. There are several issues for the DEMO
plasma position control as described below:

detectors, respectively. The plasma position agrees verywell with the estimated value although there is the noisefrom the blanket modules.

1) More clearance between plasma surface and passive
conducting shells must be given to install thebreeding blanket modules.
2) Magnetic detectors to estimate the plasma position are
influenced by the noise generated from the eddy
currents in the breeding blanket modules.
3) The conducting shell must be divided for themaintenance in the case of DEMO reactor.
In this study, we focus the influence on the plasma
position control by the restriction as above.
The numerical model is assumed as follows: a) theplasma model is assumed as the rigid one which theplasma current density profile is taken into account, b)
the in-vessel components and the vacuum vessel areapproximated as 3-dimensional thin-layer structure, andc) the time evolution of eddy currents and coil currents isexpressed as circuit equations.
The main parameters of plasma used for numericalsimulation are the major radius Rp=8.2m, the minor
radius ap=2.57m, the plasma current Ip=14.6MA, theelongation κ95=1.65, the triangularity δ95=0.33, the safety
factor q95=4.2, the poloidal beta βp=1.8, the plasmainternal inductance li=0.9 and the decay-index n=-0.81.
According to results by power balance analysis, thefusion power output is 1.5GW. The conducting shells inthis study are separated into 48 parts (7.5 degree) intoroidal direction for feasibility of maintenance scheme.
Fig.1 shows the time evolution of the plasma positionin vertical and radial directions. The solid and dottedlines represent plasma position and estimated value by

Fig.1 Comparison between plasma position and estimation by detectors(flux loop coils)

0.10

0.010
Zplasma(m)0.005

Rplasma(m)Rdetector(m)Radial position(m)Vertical position(m)Zdetector(m)
0.05

0.00

0.000

-0.05

-0.005-0.10-0.010

0123Time (s)45The numerical simulation was carried out to evaluate
control coil power of DEMO reactor in the cases ofκ95=1.65 and βp=1.8/0.1. The Vertical Displacement
Events (VDE) and βP drop are adopted as the main
disturbance. Table 1 shows results of control coil power
and the maximum displacement from initial plasma
position using VDE.
Table 1. Simulation results by VDE
Minimum control coilpower (MW)Maximum
displacement (m)βP=1.86.1

0.061

βP=0.19.90.081

The control coil power is less than 10MW in Table1,
which is acceptable for DEMO reactor. The numericalresults in the case of βP drop are shown in Table 2.
Table 2. Simulation results by poloidal beta drop
Minimum control coilpower (MW)Maximum
displacement (m)βP=1.8 →1.732

0.034

βP=1.8 →1.6

1290.068

In the case of βP=1.8→1.6, it seems to be difficult tosupply the control coil power. Therefore, the large βPdrop needs some kind of countermeasure.