Soft X-ray measurement in RF
driven plasmas on QUEST
Hiroki MIURA1 , Kazuaki HANADA2 , Hideki ZUSHI2 ， Kazuo NAKAMURA2 ,
Akihide FUJISAWA2 , Hiroshi IDEI12 , Yoshihiko NAGASHIMA2 , Makoto
HASEGAWA2 , Hisatoshi NAKASHIMA2 , Shoji KAWASAKI2 , Aki
HIGASHIJIMA2 , Osamu MITARAI3 , Takashi MAEKAWA4 , Atsushi
FUKUYAMA5 , Yuichi TAKASE6 , Akira EJIRI6 , Naoyuki FUKUMOTO7 ,
Takashi YAMAGUCHI6 , Hiro TOGASHI 6
IGSES Kyushu Univ. 1 , RIAM, Kyushu Univ.2 , Tokai Univ3 , Department of
Nuclear Engineering Kyoto Univ. 4 , Kyoto Univ5 ,
Graduate School of Frontier Science Univ. of Tokyo6 , Univ of Hyogo7
QUEST is a medium size of spherical
tokamak, which aims to realize noninductive start-up and its maintenance.
Main purposes on QUEST are to research on
non-inductive current start-up and current drive.
R[m]
a[m]
A
Bt[T]
RF
～0.64
～0.36
～1.78
～0.25
2.45GHz
8.2GHz
28GHz
R：major radius
a：minor radius
A：aspect ratio
Bｔ：toroidal
magnetic field
RF：heating sourse
A purpose of newly installation of
a 28GHz system
cross-sectional view of QUEST
plasma current
Typical waveform of plasma current
with 28GHz RF and plasma current
reached to more than 50kA.
An experiment with 28GHz RF is started since 2013
28GHz RF
plasma current
increase
28GHz
Plasma current reached
to more than 50kA.
The 28GHz RF injected
into the plasma from
1.8 to 3.46 sec.
Plasma current frequently degrades
with additional 8.2GHz RF power.
Plasma current frequently degrades
with additional 8.2GHz RF power.
The reason is still not understood
There is something to be an
interesting phenomenon
between 28GHz and
8.2GHz plasma
Slow oscillation of plasma current sometimes
happens in 28GHz and 8.2GHz plasmas.
There is an interesting phenomenon at
combination of 28GHz and 8.2GHz.
Slow oscillation of plasma current
A frequency of the oscillation is from 20Hz to 30Hz.
2 types of SXR diagnostics were used to investigate the phenomenon.
Measurement of soft -ray (SXR)
(Measurement of SXR has high
time and special resolutions )
An AXUV detector array
A 2DSXR camera
An AXUV detector array was firstly
installed to measure SXR with wide view.
2.75m
An energy sensitivity of the array is from
1.12eV visible light to 100keV SXR.
AXUV
Detector array
1m
(a)
2.79m
(a)
0.44m
ch1
ch16
The array is covered with a SUS box
The array measures SXR from plasma
through a pin hole of 7mm in diameter.
(b)
(b)
The array can detect SXR emitted from
plasma with a wide view.
AXUV detector
array
AXUV detector
CH16
array
A
CH1
Top view of QUEST
The array can detect SXR
emitted from approximately
half of plasma in top view.
cross-sectional view of dot-line A
The array is composed of 16 ch and
can cover most of plasma region in
the poloidal cross-sectional view.
A 2DSXR camera can detect SXR with high
special resolution around core plasma region.
An energy sensitivity of the camera is from 10eV to 10keV SXR
A 2DSXR camera
Al filter + MCP
+ phospher
The operation of the camera needs to
install an orifice and should take a
distance between plasma and MCP.
A viewing area of the camera is a
range of diameter 36 centi meter on
cross-sectional view of QUEST
MCP must be provided high voltage
The camera may break up by arc if the
camera operates in high pressure
environment.
R=62cm
R=26cm
The camera is useful to measure
SXR from core plasma in detail.
Typical waveforms of a slow oscillation
from 20 to 30 Hz are illustrated.
8.2GHz
28GHz
The oscillation happened at
combination of 28GHzRF
with 8.2GHzRF.
During the oscillation
Both poloidal coil currents and
RF power are kept constant.
It suggests the oscillation
happens self-consistently.
The SXR oscillations are localized
around the core plasma region.
An oscillation range
expected by next graph
CH16
CH9
CH4
The SXR oscillations with high amplitude
appear in the range of ch4 to ch9.
CH9
CH1
CH4
The oscillation may be caused by
the core plasma modification.
AXUV
Detector array
The SXR oscillation around core plasma
can be detected by the 2DSXR camera.
Camera’s results are used to investigate
core plasma behavior in detail.
Viewing area of
the camera
The area
with intense
SXR signal
repeats to
expansion
and shrink.
The pictures
measured
every 1 ms.
1
2
3
9
10
5
6
7
8
12
13
14
15
20
21
22
19
16
23
17
24
4
11
18
25
The intense SXR was emitted from 2nd ECR layer
of 28GHz and spread with the expansion of LCFS.
1
18 Z[cm] 1
2
18
3
R
[cm]
-18
-18
26 32
54 62
Two green lines show a location of a
second harmonic resonance layer of
28GHz at R=32cm and a fundamental
resonance layer of 8.2GHz at R=54cm
Yellow lines illustrate a location of
LCFS at the time.
Z
26 32
2
Z
18
3
R
-18
54 62
26 32
R
54 62
• The intense SXR was emitted
from 2nd ECR layer of 28GHz
and spread with the expansion of
last-closed flux surface.
• The SXR oscillation can be
partially explained by the
modification of LCFS.
SXR is reduced during the
oscillation even in LCFS, and
simultaneously increases outside.
SXR signals are
different between
inside and outside
of core plasma.
1 2 3 4 5 6 7
• The reduction of SXR
signal takes place even
inside LCFS and takes
a rise outside LCFS.
• This means particles
and/or energy flow out
from LCFS.
Particles of core plasma are exhausted
from LCFS during the oscillation.
The oscillation with the same frequency is also observed in
line integrated density measured through the mid-plane.
It suggests particles of core plasma are exhausted
from LCFS during the oscillation.
Summary
 The slow oscillation with 20-30Hz in plasma current was
observed in 28GHz + 8.2GHz non-inductive plasmas.
 The slow oscillation can be detected by SXR
measurement and is localized around the core plasma.
 The oscillation can be monitored in a 2D SXR camera.
The intense SXR area spread with expansion of LCFS.
The reduction of SXR was observed even inside LCFS
during the oscillation and the increase simultaneously
happened outside LCFS. This means particles and/or
energy flow out from LCFS.
 The oscillation with the same frequency was observed in
line integrated density and this means at least particles
flow out from LCFS during the oscillation.