05aE13P
LHD における重イオンビームプローブ(HIBP)による電位の二次元構造の計測

Two-Dimensional Measurement of Electric Potential by Heavy Ion Beam Probe(HIBP) in LHD
倉地正也, 清水昭博 a), 井戸毅 a), 西浦正樹 a), 加藤眞治 a)
Kurachi Masaya, Shimizu Akihumi a), Ido Takeshi a), Nishiura Masaki, Katou Shinji a)
名大 エネルギー理工, 核融合科学研究所a)

Nagoya Univ, NIFS a)with β of 0.69% are also shown. The potential profile
in Fig.2 seems to be on non-uniform on the magnetic
surfaces. One of the reasons is that finite β effect isnot taken into account when the measurement
positions are projected on a poloidal plane. The effectwill shift the measurement positions in Fig.2
downward, qualitatively. The validation of themeasurement with the automatic optimization system
will be discussed in the presentation.
0.6
0.4

Bt = 1.375T, Rax = 3.75m,
Bq = 100%, γ = 1.254

 = 18deg.

Z (m)

0.2
0.882MeV
0.966MeV
1.134MeV
1.302MeV
1.470MeV
1.639MeV
1.807MeV
1.975MeV

0.0

-0.2
-0.4
-0.6

3.0

3.5

R (m)

4.0

4.5

Fig.1. The Observable regions of LHD-HIBP in Bt =1.375T, Rax = 3.75m, Bq = 100%, γ = 1.254. The
measurement position traces a marked curve during an
injection-angle-sweep of the probe beam for each Eb.
0.60.4

ECH (4.55s - 4.65s)
Bt = 1.375T, Rax = 3.75m,
Bq = 100%, γ = 1.254

 = 18deg.

4.0

3.5

Z (m)

0.2

3.0

0.0

2.5

-0.2

2.0

#117653_-0.4 1.302MeV

1.5#117647_1.134MeV #117652_0.966MeV
-0.6

3.0

3.5

R (m)

4.0

Potential [kV]

Heavy ion beam probes (HIBPs) are uniquediagnostic tools for directly measuring the profile ofthe electrostatic potential and its temporal evolution in
high-temperature magnetically confined plasmas. In
the Large Helical Device (LHD), a HIBP has beendeveloped to study confinement physics related toelectrostatic potential [1]. Recently, two-dimensional
measurement is tried to study detail of transportphysics related to magnetic islands, spatial structures,
fluctuation profiles and so on.
The observation point of LHD-HIBP can be changed
one-dimensionally by sweeping an injection angle ofprobe beam. The two-dimensional potential profile
can be obtained by changing the probe beam energy(Eb) as shown in Fig.1, where the each measurement
position is projected on the poloidal cross section by
tracing the vacuum magnetic field line from the actual
observation point. However, it is difficult to change Ebpractically because it spends much time (about 30minutes) to optimize the beam trajectory by adjusting
more than 20 control parameters after changing the Eb.
Now, we have been developing a PC-based fast
automatic trajectory optimization system, and apply itto measure the two-dimensional potential profiles on apoloidal plain on shot-to-shot basis in the LHD.
In the optimization process, the deviation of theprobe beam from the center of beam-transport line isadjusted to be 0 by controlling voltage of steerer
electrodes installed in the beam-transport system.
The beam deviation is measured by rotating wire
called Beam Profile Monitors (BPMs) at five positionsin the beam-transport line, and measured in the two
axis perpendicular to the beam line by each BPM.
The applied voltages on the steerers are automatically
optimized, using deviations measured by BPMs. The
matrix of conversion factor from the deviations to therequired voltages has been calibrated in advance.
In the 2013 campaign on LHD, the automaticoptimization system has been applied on LHD-HIBP.
As a result, the optimization of beam trajectory has
been completed within 30 seconds on average, whichis shorter than the interval between discharges (3minutes). Figure 2 shows the two-dimensional
potential profile measured by HIBP using theautomatic optimization system. The magnetic surfaces

1.0

4.5

Fig.2. Two-dimensional potential profile measured
with HIBP by applying automatic optimization system.
Magnetic surfaces are plotted under β = 0.69%, φ =18deg. Bt = 1.375T, Rax = 3.75m, Bq = 100%, γ =1.254.
[1] Ido,T.,Shimizu,A.,Nishiura,M.: Journal ofPlasma and Fusion Research Vol86, No9(2010)507-516