Shafranov shift in the low aspect ratio heliotron/torsatron Compact Helical System

Yamada, H.; Ida, K.; Iguchi, H.; Morita, S.; Kaneko, O.; Arimoto, Hideki; Hosokawa, M.; Idei, H.; Kubo, S.; Matsuoka, K.; Nishimura, K.; Okamura, S.; Takeiri, Y.; Takita, Y.; Takahashi, C.; Hanatani, K.; Howe, H.C.; Hirshman, S. P.; Lee, D.K.

doi:10.1088/0029-5515/32/1/i03

Cited by 43 publications

(14 citation statements)

References 19 publications

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“…The location of the vertically viewing chords at the vertically elongated cross section is illustrated in Refs. [11] and [14]. At this location, the beam radius (half-width at half-maximum∼6 cm in the vertical direction) can be neglected compared with the plasma size in the vertical direction (minor radius of ∼30 cm).…”

Section: Charge Exchange Spectroscopic Measurementmentioning

confidence: 99%

“…Here, it should be noted that the Shafranov shifts in NBI heated plasmas in the CHS are often affected by fast-ion pressure. Therefore it is better to interpret shifts of measured tem-037-4 perature profiles as the actual Shafranov shifts [14]. Note, however, also that the shapes and positions of the flux surfaces near the outermost surface are insensitive to these finite beta effects, especially in inward shifted limiter configurations (using the vacuum vessel wall at the inboard side of the vertically elongated section as the limiter) in which the L/H transition has been observed [6,7].…”

Section: Charge Exchange Spectroscopic Measurementmentioning

confidence: 99%

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A Simultaneous Spectroscopic Measurement of the Global and Edge Local Structures in the Ion Temperature and Plasma Rotation Profiles in the Compact Helical System

Nishimura

Nagaoka

Yoshimura

et al. 2007

Plasma and Fusion Research

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In charge exchange spectroscopy (CXS), a simultaneous observation in different plasma toroidal cross sections and/or viewing ports is required to investigate radial distributions of ion temperatures T i (r), and poloidal rotation velocities V p (r) in magnetically confined toroidal plasmas. In recent studies of the edge transport barrier (ETB) in the Compact Helical System (CHS), a simultaneous viewing of the vertically elongated and the horizontally elongated plasma cross sections is used to improve the spatial resolution at the edge region. The 90 fibers used for this purpose are connected to one spectrometer, and a 256 × 243 pixel sampling CCD is used to detect the diffraction image. It is found that there is a localized edge ion temperature pedestal region with ∆T i ≈ 100 eV and ∆r/a ≈ 0.1, where r and a are flux surface averaged minor radii of measured surfaces and the outermost flux surface, respectively. The negative radial electric field at the edge is increased in the high confinement phase because of the increased ion pressure.

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Section: Charge Exchange Spectroscopic Measurementmentioning

confidence: 99%

Section: Charge Exchange Spectroscopic Measurementmentioning

confidence: 99%

A Simultaneous Spectroscopic Measurement of the Global and Edge Local Structures in the Ion Temperature and Plasma Rotation Profiles in the Compact Helical System

Nishimura

Nagaoka

Yoshimura

et al. 2007

Plasma and Fusion Research

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“…In neoclassical theories for stellarator/heliotron plasmas, [8][9][10] various integral theorems had been used for handling the 2-D real space of poloidal and toroidal angles in the coordinates systems, 11 such as Boozer and Hamada coordinates. However, it has been clarified in many experimental studies on the Shafranov shifts of the NBI heated plasmas 12,13 including resultant changes of the B-field strength modulation on the surfaces 14,15 that a modification of the Pfirsch-Schl€ uter current due to the large radial gradient of the fast ions' parallel pressure @p kf =@s is not negligible. The validity of the previously used theorems in these situations is explained in this section.…”

Section: Introductionmentioning

confidence: 99%

Parallel momentum input by tangential neutral beam injections in stellarator and heliotron plasmas

2015

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The configuration dependence of parallel momentum inputs to target plasma particle species by tangentially injected neutral beams is investigated in non-axisymmetric stellarator/heliotron model magnetic fields by assuming the existence of magnetic flux-surfaces. In parallel friction integrals of the full Rosenbluth-MacDonald-Judd collision operator in thermal particles' kinetic equations, numerically obtained eigenfunctions are used for excluding trapped fast ions that cannot contribute to the friction integrals. It is found that the momentum inputs to thermal ions strongly depend on magnetic field strength modulations on the flux-surfaces, while the input to electrons is insensitive to the modulation. In future plasma flow studies requiring flow calculations of all particle species in more general non-symmetric toroidal configurations, the eigenfunction method investigated here will be useful. V

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“…This is because the plasmas may have large Shafranov shifts due to the beam parallel pressure. 19 The region Ͻ0 denotes the inboard region and Ͼ0 denotes the outboard region. The background radiation, which is partially caused by the charge exchange with thermal neutrals, measured at the background viewing array is subtracted from the radiation observed at the beam charge exchange array.…”

mentioning

confidence: 99%

Inboard/outboard asymmetry of poloidal flow observed in the Compact Helical System

Nishimura¹,

Ida²,

Osakabe³

et al. 2000

Physics of Plasmas

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The poloidal flow velocity and the density of fully ionized carbon were measured in the Compact Helical System ͓K. Ida et al., Phys. Rev. Lett. 67, 58 ͑1991͔͒ using the charge exchange spectroscopy with the bidirectional viewing. The poloidal asymmetry of the poloidal flow velocity observed in the outward shifted plasma is due to the electrostatic potential being constant on the magnetic flux surfaces. The poloidal asymmetry of the ion density can be explained by the conservation of the poloidal ion flux under the strong toroidal viscosity. © 2000 American Institute of Physics. ͓S1070-664X͑00͒04002-7͔The spectroscopic measurements of plasma rotations are widely used to evaluate radial electric fields in magnetically confined toroidal plasmas. The rotation velocity is connected to the radial electric field and the ion pressure gradient by the radial force balance. In general, radial electric fields, ion pressure gradients, and rotation velocities are not constant on magnetic flux surfaces, since electrostatic potentials and ion pressures are considered to be constant on the magnetic flux surfaces. When the plasmas have toroidal curvatures ͑toroi-dal effects͒, the conservation of the poloidal plasma flux causes the difference of the poloidal rotation velocities between the inboard region of the magnetic axis (RϽR ax , where R ax is the major radius of the magnetic axis͒ and the outboard region (RϾR ax ). The standard neoclassical theory 1,2 predicts an inboard/outboard asymmetric parallel flow ͑a ''Pfirsch-Schlueter-like'' toroidal flow͒ to compensate for the unbalance of the perpendicular fluxes on the inboard and the outboard regions and to make the flow incompressible ("•vϭ0) in a steady state. In heliotron/ torsatron, 3-7 however, the strong toroidal viscosity due to helical ripples 3 damps this toroidal flow, as well as the net toroidal flows due to the radial electric field, the ion pressure gradient, and the toroidal momentum injection by neutral beams. This damping is strong in the peripheral region where the helical ripple is large. The poloidal rotation of impurity ions is also large in this peripheral region, since it is mainly driven by the radial electric field determined by the ambipolar condition of ripple diffusion fluxes.4-6 Therefore, the flow of impurity ions may not be incompressible as assumed in the neoclassical theory.The difference of poloidal rotation velocities and densities between the inboard and the outboard regions has not been studied in detail in either tokamaks or helical systems. In tokamaks, the poloidal rotation measurements are restricted in the outboard regions [8][9][10][11] because of the difficulty of installing chords viewing vertically the inboard regions where there are only very narrow spaces between toroidal and poloidal coils. In order to study the inboard/outboard asymmetry of poloidal flow, very precise measurements of Doppler shifts of impurity lines are required. The inboard/ outboard asymmetry has never been reported for lack of the accuracy of the absolute Doppl...

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Shafranov shift in the low aspect ratio heliotron/torsatron Compact Helical System

Cited by 43 publications

References 19 publications

A Simultaneous Spectroscopic Measurement of the Global and Edge Local Structures in the Ion Temperature and Plasma Rotation Profiles in the Compact Helical System

A Simultaneous Spectroscopic Measurement of the Global and Edge Local Structures in the Ion Temperature and Plasma Rotation Profiles in the Compact Helical System

Parallel momentum input by tangential neutral beam injections in stellarator and heliotron plasmas

Inboard/outboard asymmetry of poloidal flow observed in the Compact Helical System

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