Impurity rotation in hydrogen and helium plasmas

Rowan, W. L.; Meigs, A.; Hickok, R. L.; Schoch, P. M.; Yang, Xiaodong; Zhang, B. Z.

doi:10.1063/1.860108

Cited by 17 publications

(6 citation statements)

References 14 publications

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“…The velocity of the impurity ions are assumed to be representative of the velocity of the main plasma ions. 19,20 The assumption is supported by the relatively high plasma density which has an ion collision time of approximately 200 ns. Doppler shifts are calculated by viewing the plasma through the oblique viewport with the ICCD spectrometer.…”

Section: B Evolution Of the Z-pinch Plasmamentioning

confidence: 99%

Sheared flow stabilization experiments in the ZaP flow Z pinch

et al. 2003

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The stabilizing effect of a sheared axial flow on the mϭ1 kink instability in Z pinches has been studied numerically with a linearized ideal magnetohydrodynamic model to reveal that a sheared axial flow stabilizes the kink mode when the shear exceeds a threshold. The sheared flow stabilizing effect is investigated with the ZaP ͑Z-Pinch͒ Flow Z-pinch experiment at the University of Washington. An axially flowing Z pinch is generated with a 1 m coaxial accelerator coupled to a pinch assembly chamber. The plasma assembles into a pinch 50 cm long with a radius of approximately 1 cm. An azimuthal array of surface mounted magnetic probes located at the midplane of the pinch measures the fluctuation levels of the azimuthal modes mϭ1, 2, and 3. After the pinch assembles a quiescent period is found where the mode activity is significantly reduced. Optical images from a fast framing camera and a ruby holographic interferometer indicate a stable, discrete pinch plasma during this time. Multichord Doppler shift measurements of impurity lines show a large, sheared flow during the quiescent period and low, uniform flow profiles during periods of high mode activity. Z-pinch plasmas have been produced that are globally stable for over 700 times the theoretically predicted growth time for the kink mode of a static Z pinch. The plasma has a sheared axial flow that exceeds the theoretical threshold for stability during the quiescent period and is lower than the threshold during periods of high mode activity.

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Section: B Evolution Of the Z-pinch Plasmamentioning

confidence: 99%

Sheared flow stabilization experiments in the ZaP flow Z pinch

et al. 2003

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“…Since the parallel impurity flows are determined by the balance between the impurity viscous force, the collisional friction with the bulk plasma condition [4,53].) This is because of loss mechanisms, that are not included in the neoclassical theory, such as charge-exchange momentum loss, play a role at the plasma edge [54].…”

Section: Plasma Potential Measurements With Heavy Ion Beam Probesmentioning

confidence: 99%

Experimental studies of the physical mechanism determining the radial electric field and its radial structure in a toroidal plasma

Ida

1998

Plasma Phys. Control. Fusion

183

164

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Experimental studies on radial structures of plasma rotation and radial electric field in toroidal plasmas are reviewed. In this context, the perpendicular and parallel viscosities that determine the toroidal/poloidal rotation velocity and radial electric field profiles are discussed. Experimental studies of parallel viscosity and the comparison with the neoclassical values in heliotron/torsatron and stellarator devices, are described. The anomalous perpendicular viscosity, which is dominant in dictating the toroidal rotation in tokamaks, is also discussed. Even without external momentum input, plasma rotation and radial electric field are sustained by non-ambipolar flux of off-diagonal terms of the transport matrix. The effects of radial electric field shear and the bulk rotation velocity shear on the improvement of particle, momentum and heat transport in bulk and edge plasma regimes are also discussed.

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“…The measurement also showed an appreciable difference in toroidal rotation between the main and the impurity ions in the edge region. Impurity rotation measurements have also been reported from the Texas Experimental Tokamak (TEXT) [6], where a comparison was made between hydrogen and helium fuelled discharges. In that paper, charge exchange collisions with cold neutral atoms in the plasma edge were proposed as a mechanism for the departure of experiment from the neoclassical prediction.…”

Section: Introductionmentioning

confidence: 99%

Effects of neutrals on plasma rotation in DIII-D

et al. 1997

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Friction due to charge exchange with cold neutral atoms in the edge is investigated as a candidate to govern the poloidal rotation in the edge of a tokamak plasma. The Hirshman and Sigmar neoclassical moment approach is used to determine the rotation velocities of the main plasma ions and of one impurity species, when charge exchange friction is included. It is found that the poloidal rotation of the main plasma ions is controlled by charge exchange friction with neutrals. The impurity ion poloidal rotation is governed by the balance between the impurity viscous force and the main-ion-impurity-ion friction force. The results of the calculation are compared with the measurements obtained in the edge of a DIII-D high (H) mode plasma, using charge exchange recombination (CER) spectroscopy. It is found that the measured main ion poloidal rotation can be accurately predicted by the neoclassical theory including the effect of neutrals, assuming a neutral density ⟨nn⟩ = 3 × 1017 m-3 at the separatrix, decreasing exponentially inside the plasma with an e-folding length of 0.012 m, and peaking near the X point region with a poloidal peaking parameter γ ≡ ⟨nn⟩⟨B2⟩/⟨nnB2⟩ = 1.5. However, for the impurity ions, the neoclassical theory including a single impurity charge state, and regardless of the effect of the neutrals, gives a prediction that has the correct sign, but whose value is a factor of 5 or 6 different from the experimental value

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Impurity rotation in hydrogen and helium plasmas

Cited by 17 publications

References 14 publications

Sheared flow stabilization experiments in the ZaP flow Z pinch

Sheared flow stabilization experiments in the ZaP flow Z pinch

Experimental studies of the physical mechanism determining the radial electric field and its radial structure in a toroidal plasma

Effects of neutrals on plasma rotation in DIII-D

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