Space Potential Distribution in the ISX-B Tokamak

The bifurcation nature of the electrostatic structure is studied in the toroidal helical plasma of the Compact Helical System ͑CHS͒ ͓K. Matsuoka et al., Proceedings of the 12th International Conference on Plasma Physics and Controlled Nuclear Fusion Research, Nice, 1988 ͑International Atomic Energy Agency, Vienna, 1989͒, Vol. 2, p. 411͔. Observation of bifurcation-related phenomena is introduced, such as characteristic patterns of discrete potential profiles, and various patterns of self-sustained oscillations termed electric pulsation. Some patterns of the electrostatic structure are found to be quite important for fusion application owing to their association with transport barrier formation. It is confirmed, as is shown in several tokamak experiments, that the thermal transport barrier is linked with electrostatic structure through the radial electric field shear that can reduce the fluctuation resulting in anomalous transport. This article describes in detail spatio-temporal evolution during self-sustained oscillation, together with correlation between the radial electric field and other plasma parameters. An experimental survey to find dependence of the temporal and spatial patterns on plasma parameters is performed in order to understand systematically the bifurcation property of the toroidal helical plasma. The experimental results are compared with the neoclassical bifurcation property that is believed to explain the observed bifurcation property of the CHS plasmas. The present results show that the electrostatic property plays an essential role in the structural formation of toroidal helical plasmas, and demonstrate that toroidal plasma is an open system with a strong nonlinearity to provide a new attractive problem to be studied.

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“…[42][43][44][45][46][47] The CHS device is equipped with an HIBP whose beam energy is up to 200 keV. The HIBP has a unique feature.…”

Section: Heavy Ion Beam Probementioning

confidence: 99%

Experimental study of the bifurcation nature of the electrostatic potential of a toroidal helical plasma

et al. 2000

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“…Although the E 3 B velocity shear due to the toroidal flow can be important in the plasma core [10], there have been few experiments that demonstrate a spontaneous toroidal flow not driven by NBI in tokamaks [11][12][13][14]. It is generally the case in tokamaks that the plasma rotates parallel (antiparallel) to the plasma current for the coinjected (counterinjected) NBI, which corresponds to a positive (negative) radial electric field ͑E r ͒ in L-mode plasmas [15]. However, when a negative E r is produced at the transport barrier, both localized toroidal flow in the counterdirection and localized poloidal flow in the electron diamagnetic direction are observed even for plasmas with coinjected NBI [5,16,17].…”

mentioning

confidence: 99%

Observation of Toroidal Flow Antiparallel to the〈Er×Bθ〉Drift Direction in the Hot Electron Mode Plasmas in the Compact

et al. 2001

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A toroidal flow antiparallel to the ͗E r 3 B u ͘ drift direction is observed in the hot electron mode plasmas when a large positive electric field and a sharp electron temperature gradient are sustained inside the internal transport barrier in the Compact Helical System. This toroidal flow reaches up to 5 3 10 4 m͞s at the plasma center, and it is large enough to reverse the toroidal flow driven by a tangentially injected neutral beam. These observations clearly show the plasma favors flow in the minimum =B direction at the transport barrier. DOI: 10.1103/PhysRevLett.86.3040 PACS numbers: 52.55.HcA spontaneous poloidal flow has been recognized to be important in the confinement of toroidal plasmas, since poloidal flow velocity and radial electric field shear were found to contribute an improvement of plasma confinement in H-mode plasmas [1,2]. The turbulence in the plasma is predicted to be suppressed by a E 3 B velocity shear through the mechanism of a nonlinear decorrelation [3,4]. It has been confirmed experimentally that the E 3 B shearing rate exceeds the growth rate of the turbulence at the transport barrier [5][6][7]. The toroidal flow has been considered to be determined by the radial transport of momentum driven by neutral beam injection (NBI) with anomalous shear viscosity [8,9]. Although the E 3 B velocity shear due to the toroidal flow can be important in the plasma core [10], there have been few experiments that demonstrate a spontaneous toroidal flow not driven by NBI in tokamaks [11][12][13][14]. It is generally the case in tokamaks that the plasma rotates parallel (antiparallel) to the plasma current for the coinjected (counterinjected) NBI, which corresponds to a positive (negative) radial electric field ͑E r ͒ in L-mode plasmas [15]. However, when a negative E r is produced at the transport barrier, both localized toroidal flow in the counterdirection and localized poloidal flow in the electron diamagnetic direction are observed even for plasmas with coinjected NBI [5,16,17]. These results show the need for detailed measurements of both toroidal and poloidal flow at the transport barrier, where the toroidal flow profile is not determined by the transport of momentum driven by NBI alone. Yet, despite the importance of the coupling between toroidal and poloidal flow, no studies until now have discussed the toroidal flow at the internal transport, where there is a large radial electric field.In a Heliotron/Torsatron device, there is no toroidal symmetry, and the minimum =B trace has a helical structure and helical flow along the minimum =B can be expected. The significant difference between tokamaks and Heliotron devices is the relationship between the poloidal field direction and the direction of dominant symmetry.The pitch angle of dominant symmetry is even larger than that of the averaged poloidal field in a Heliotron device, while it is zero due to the toroidal symmetry in tokamaks. This helical flow should change sign depending on the sign of E r or on the direction of the magnetic field. H...

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“…[2]. They include the Motional Stark Effect (MSE) [3,4], the Zeeman Effect in Lithium beam spectroscopy [5,6], the heavy-ion-beamprobe [7] and arrayed line-integrated Faraday-rotation measurements [8]. Tangential Soft X-Ray imaging was also used to constrain equilibrium reconstructions and infer the q profile [9].…”

Section: Introduction and Physical Principlementioning

confidence: 99%

A spinning mirror for fast angular scans of EBW emission for magnetic pitch profile measurements

Volpe

2010

Review of Scientific Instruments

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A tilted spinning mirror rapidly steers the line of sight of the electron Bernstein wave (EBW) emission radiometer at the Mega Amp Spherical Tokamak (MAST). In order to resist high mechanical stresses at rotation speeds of up to 12,000 rpm and to avoid eddy current induced magnetic braking, the mirror consists of a glass-reinforced nylon substrate of a special self-balanced design, coated with a reflecting layer. By completing an angular scan every 2.5-10ms, it allows one to characterize with good time resolution the Bernstein-extraordinary-ordinary mode-conversion efficiency as a function of the view angles. Angular maps of conversion efficiency are directly related to the magnetic pitch angle at the cutoff layer for the ordinary mode. Hence, measurements at various frequencies provide the safety factor profile at the plasma edge. Initial measurements and indications of the feasibility of the diagnostic are presented. Moreover, angular scans indicate the best launch conditions for EBW heating.

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Space Potential Distribution in the ISX-B Tokamak

Cited by 85 publications

References 10 publications

Experimental study of the bifurcation nature of the electrostatic potential of a toroidal helical plasma

Experimental study of the bifurcation nature of the electrostatic potential of a toroidal helical plasma

Observation of Toroidal Flow Antiparallel to the〈Er×Bθ〉Drift Direction in the Hot Electron Mode Plasmas in the Compact

A spinning mirror for fast angular scans of EBW emission for magnetic pitch profile measurements

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