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Soft X-ray measurement in RF driven plasmas on QUEST

Soft X-ray measurement in RF driven plasmas on QUEST.

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Soft X-ray measurement in RF driven plasmas on QUEST

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  1. 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 TOGASHI6 • 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, Univof Hyogo7

  2. QUEST is a medium size of spherical tokamak, which aims to realize non-inductive start-up and its maintenance. Main purposes on QUEST are to research on non-inductive current start-up and current drive. 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 plasma current cross-sectionalview of QUEST

  3. 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 plasma current increase 28GHz RF 28GHz Plasma current reached to more than50kA. The 28GHz RF injected into the plasma from 1.8 to 3.46 sec.

  4. 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

  5. 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. Measurement of soft -ray (SXR) (Measurement of SXR has high time and special resolutions ) An AXUV detector array Slow oscillation of plasma current A frequency of the oscillation is from 20Hz to 30Hz. A 2DSXR camera 2 types of SXR diagnostics were used toinvestigate the phenomenon.

  6. An AXUV detector array was firstly installed to measure SXR with wide view. An energy sensitivity of the array is from 1.12eV visible light to 100keV SXR. 2.75m (b) AXUV Detector array (a) 1m (b) 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.

  7. The array can detect SXR emitted from plasma with a wide view. AXUVdetector array AXUVdetector array CH16 A CH1 A cross-sectionalview of dot-line Top view of QUEST The array is composed of 16 ch and can cover most of plasma region in the poloidal cross-sectional view. The array can detect SXR emitted from approximately half of plasma in top view.

  8. A 2DSXR camera can detect SXR with high special resolution around core plasma region. An energy sensitivity of the camera is from 10eVto 10keV SXR MCP must be provided high voltage A 2DSXR camera + + phospher Al filter MCP The camera may break up by arc if the camera operates in high pressure environment. The operation of the camera needs to install an orifice and should take a distance between plasma and MCP. R=62cm A viewing area of the camera is a range of diameter 36 centi meter on cross-sectionalview of QUEST R=26cm The camera is useful to measure SXR from core plasma in detail.

  9. 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.

  10. The SXR oscillations are localized around the core plasma region. An oscillation range expected by next graph AXUV Detector array CH16 CH9 CH4 CH9 CH1 The SXR oscillations with high amplitude appear in the range of ch4 to ch9. CH4 The oscillation may be caused by the core plasma modification.

  11. 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. 4 3 2 1 7 8 6 5 11 9 10 The pictures measured every 1 ms. 18 12 13 16 15 17 14 25 21 20 23 22 19 24

  12. The intense SXR was emitted from 2nd ECR layer of 28GHz and spread with the expansion of LCFS. Z Z Z[cm] 18 18 18 1 3 2 1 2 3 R R R [cm] -18 -18 26 32 54 62 -18 263254 62 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 • 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. Yellow lines illustrate a location of LCFS at the time.

  13. SXR is reduced during the oscillation even in LCFS, and simultaneously increases outside. SXR signalsare different between inside and outside of core plasma. 7 1 2 3 4 5 6 • 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.

  14. 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.

  15. 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.

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