Two Dimensional Li Beam Imaging to Study the Magnetic Field Configuration Effects on Plasma Confinement in Spherical Tokamak CPD

Bhattacharyay, R.; Zushi, H.; Morisaki, T.; Kikukawa, Kiyoshi; Watanabe, Shinya; Inada, Yuki; Hasegawa, Makoto; Takahashi, Hayato; Sato, Kohnosuke; Nakamura, K.; Sakamoto, M.; Idei, H.; Sasaki, Kyuro; Xu, Handong; Wang, F.; Shoji, K.; Nakashima, Hideharu; Higashijima, A.

doi:10.1585/pfr.2.s1103

Cited by 2 publications

(2 citation statements)

References 5 publications

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“…A vertically extended slab image is observed at the low RF power (∼1.5 kW) phase, which indicates that an initial plasma is formed along the 1st resonance layer [4]. Furthermore, this image is found to be convexly curved, which agrees with the contour of the poloidal magnetic flux surfaces Φ(R, Z) without plasma current.…”

Section: Visualization Of Magnetic Surfaces During Current Ramp-up Phsupporting

confidence: 57%

“…However, the physics of current ramp-up mechanism, that is, magnetic reconnection, is still not clear. In CPD the sheet thermal Li beam and CCD imaging method have been used to get two dimensional density profile in the wide area [3][4][5]. This paper describes the first result of visualization of the topological change in magnetic configuration during the RF driven plasma current ramp-up by imaging technique.…”

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confidence: 99%

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Visualization of Magnetic Surfaces during Current Ramp-Up Phase Using Thermal Lithium Sheet Beam in CPD

Kikukawa

Zushi

Morisaki

et al. 2008

Plasma and Fusion Research

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Two dimensional electron density profile measurement has been performed in the spherical tokamak CPD (Compact PWI experimental Device) using Li sheet beam imaging technique. The topological change from the open magnetic field line configuration to the closed one is visualized by this technique. The plasma current can be driven by RF waves itself in a weak mirror configuration and a clear change is observed in plasma boundary as well as magnetic field topology associated with the transition of the current from low (∼1 kA) to high (∼3 kA) value. In CDX-U, DIII-D and LATE the electron cyclotron waves have been used to ramp-up the plasma current under open field configuration with the combination of the toroidal and vertical magnetic field lines [1,2]. However, the physics of current ramp-up mechanism, that is, magnetic reconnection, is still not clear. In CPD the sheet thermal Li beam and CCD imaging method have been used to get two dimensional density profile in the wide area [3][4][5]. This paper describes the first result of visualization of the topological change in magnetic configuration during the RF driven plasma current ramp-up by imaging technique.CPD is a spherical tokamak device whose diameter as well as height is ∼1.2 m as shown in Fig. 1. The diameter of the center stack is 0.255 m. The working gas is hydrogen and typical fuelling pressure is ∼1.0 × 10 −5 Torr.Four toroidal coils produce the magnetic field of 0.29 T at the major radius R ∼0.19 m. Three sets of poloidal field (PF) coils are used to create mirror configurations (decay index ∼ 0.046, B z ∼ 40 G at R = 0.2 m). In these experiments 1.5-60 kW of RF power (8.2 GHz) is injected from the lower field side of the CPD to initiate and sustain the plasma. The RF driven plasma current is measured with Rogowski coils installed inside the CPD chamber. The Li beam injector [3] is located at the bottom of the chamber and the beam is injected at an oblique angle of 18.18 degree with respect to the machine axis at R ∼ 0.29 m (see Fig. 1). The full width at half maximum of the sheet beam is 40 mm in the toroidal direction. The oven is heated up to a temperature of ∼900 K. The image of

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Section: Visualization Of Magnetic Surfaces During Current Ramp-up Phsupporting

confidence: 57%

mentioning

confidence: 99%

Visualization of Magnetic Surfaces during Current Ramp-Up Phase Using Thermal Lithium Sheet Beam in CPD

Kikukawa

Zushi

Morisaki

et al. 2008

Plasma and Fusion Research

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Study of magnetic configuration effects on plasma boundary and measurement of edge electron density in the spherical tokamak compact plasma wall interaction experimental device using Li sheet beam

et al. 2008

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Two-dimensional lithium beam imaging technique has been applied in the spherical tokamak CPD (compact plasma wall interaction experimental device) to study the effects of magnetic field configurations on rf plasma boundary in the absence of any plasma current, and also for the measurement of a two-dimensional edge electron density profile. With the present working condition of the diagnostics, the minimum measured electron density can be ∼1.0×1016m−3; this is considered to be the definition for the plasma boundary. The performance of the lithium sheet beam is absolutely calibrated using a quartz crystal monitor. Experimental results reveal that magnetic field configuration, either mirror or so-called null, critically affects the rf plasma boundary. A sharp lower boundary is found to exist in magnetic null configuration, which is quite different from that in the weak mirror configuration. Theoretical calculations of particle drift orbit and magnetic connection length (wall-to-wall) suggest that only mirror trapped particles are confined within a region where the magnetic connection length is ∼4.0m or more. A two-dimensional edge electron density profile is obtained from the observed LiI intensity profile. Overdense plasma formation is discussed from the viewpoint of mode conversion of rf wave into electron Bernstein wave and its dependence on the electron density profile.

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Two Dimensional Li Beam Imaging to Study the Magnetic Field Configuration Effects on Plasma Confinement in Spherical Tokamak CPD

Cited by 2 publications

References 5 publications

Visualization of Magnetic Surfaces during Current Ramp-Up Phase Using Thermal Lithium Sheet Beam in CPD

Visualization of Magnetic Surfaces during Current Ramp-Up Phase Using Thermal Lithium Sheet Beam in CPD

Study of magnetic configuration effects on plasma boundary and measurement of edge electron density in the spherical tokamak compact plasma wall interaction experimental device using Li sheet beam

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