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 non-

inductive start-up and its maintenance.

R ： major radiusa ： minor radiusA ： aspect ratio

B ｔ： toroidal 　 magnetic fieldRF ： heating sourse

cross-sectional view of QUEST

Main purposes on QUEST are to research on non-inductive current start-up and current drive.

R[m] ～ 0.64a[m] ～ 0.36

A ～ 1.78Bt[T] ～ 0.25

 RF

2.45GHz8.2GHz28GHz

A purpose of newly installation of a 28GHz system

plasma current

Typical waveform of plasma current with 28GHz RF and plasma current

reached to more than 50kA.

28GHz RF

An experiment with 28GHz RF is started since 2013plasma current

increase28GHz

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 currentA frequency of the oscillation is from 20Hz to 30Hz.

Measurement of soft -ray (SXR) (Measurement of SXR has high

time and special resolutions ) A 2DSXR camera

An AXUV detector array

2 types of SXR diagnostics were used to investigate the phenomenon.

An AXUV detector array was firstly installed to measure SXR with wide

view. AXUV

Detector array

2.79m

2.75m

1m

0.44m

ch1 ch16

(b)

(a)

(b)

An energy sensitivity of the array is from 1.12eV visible light to 100keV SXR.

The array is covered with a SUS box

The array measures SXR from plasma through a pin hole of 7mm in

diameter.

(a)

The array can detect SXR emitted from approximately half of plasma in top view.

The array can detect SXR emitted from plasma with a wide view.

The array is composed of 16 ch and can cover most of plasma region in

the poloidal cross-sectional view.

AXUV detectorarray

CH1

CH16

cross-sectional view of dot-line

AXUV detectorarray

Top view of QUEST

A

A

A 2DSXR camera can detect SXR with high special resolution around core plasma

region.

A viewing area of the camera is a range of diameter 36 centi meter on

cross-sectional view of QUESTR=26cm

R=62cm

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.

The camera may break up by arc if the camera operates in high pressure

environment.

MCP must be provided high voltage

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.

The oscillation happened at combination of 28GHzRF

with 8.2GHzRF.

8.2GHz28GHz

It suggests the oscillation happens self-consistently.

Both poloidal coil currents and RF power are kept constant.

During the oscillation

CH1

CH16

The SXR oscillations are localized around the core plasma region.

The SXR oscillations with high amplitude appear in the range of ch4 to ch9.

The oscillation may be caused by the core plasma modification.

An oscillation range expected by next graph

AXUVDetector arrayCH9

CH9CH4

CH4

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.

1 2 3 4

5 6 7 1098 11

12 13 14

212019

18171615

22 23 24 25

Viewing area of the camera

The pictures measured every 1 ms.

The area with intense SXR signal repeats to expansion and shrink.

The intense SXR was emitted from 2nd ECR layer of 28GHz and spread with the expansion of LCFS.

18

26 32 　　 54 62

Z[cm]

R

18

-1826 32 　 54 62

Z1 21 2

R[cm] R

18

-1826 32 　 54 62

Z 33

• 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.

-18

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.

SXR is reduced during the oscillation even in LCFS, and

simultaneously increases outside.

SXR signals are different between inside and outside of core plasma.

2 3 6 74 51

• 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.