Turbulent momentum transport due to the beating between different tokamak flux surface shaping effects

Introducing up-down asymmetry into the tokamak magnetic equilibria appears to be a feasible method to drive fast intrinsic toroidal rotation in future large devices. In this paper we investigate how the intrinsic momentum transport generated by up-down asymmetric shaping scales with the mode number of the shaping effects. Making use the gyrokinetic tilting symmetry (Ball et al (2016) Plasma Phys. Control. Fusion 58 045023), we study the effect of envelopes created by the beating of different high-order shaping effects. This reveals that the presence of an envelope can change the scaling of the momentum flux from exponentially small in the limit of large shaping mode number to just polynomially small. This enhancement of the momentum transport requires the envelope to be both up-down asymmetric and have a spatial scale on the order of the minor radius.

Comments: 20 pages, 5 figures

Similar Publications

The anti-Stokes scattering and Stokes scattering in stimulated Brillouin scattering (SBS) cascade have been researched by the Vlasov-Maxwell simulation. In the high-intensity laser-plasmas interaction, the stimulated anti-Stokes Brillouin scattering (SABS) will occur after the second stage SBS rescattering. The mechanism of SABS has been put forward to explain this phenomenon. Read More


In this work, we study the outward propagation of temperature perturbations. For this purpose, we apply an advanced analysis technique, the Transfer Entropy, to ECE measurements performed in ECR heated discharges at the low-shear stellarator TJ-II. We observe that the propagation of these perturbations is not smooth, but is slowed down at specific radial positions, near 'trapping zones' characterized by long time lags with respect to the perturbation origin. Read More


We discuss the dynamics of seeded large amplitude plasma blobs and depletions in an (effective) gravitational field. If the flows are incompressible, the radial center of mass velocity of blobs and depletions is proportional to the square root of their initial cross-field size and amplitude. For compressible flows this scaling holds only for ratios of amplitude to size larger than a critical value. Read More


The nonlinear thin-shell instability (NTSI) may explain some of the turbulent hydrodynamic structures that are observed close to the collision boundary of energetic astrophysical outflows. It develops in nonplanar shells that are bounded on either side by a hydrodynamic shock, provided that the amplitude of the seed oscillations is sufficiently large. The hydrodynamic NTSI has a microscopic counterpart in collisionless plasma. Read More


A scheme with gold cone-capillary is proposed to improve the protons acceleration and involved problems are investigated by using the two-dimensional particle-in-cell simulations. It is demonstrated that the cone-capillary can efficiently guide and collimate the protons to a longer distance and lead to a better beam quality with a dense density $\geq10n_c$, monoenergetic peak energy $E_k \sim 1.51~\mathrm{GeV}$, spatial emittance $\sim0. Read More


A recently proposed technique correlating electric fields and particle velocity distributions is applied to single-point time series extracted from linearly unstable, electrostatic numerical simulations. The form of the correlation, which measures the transfer of phase-space energy density between the electric field and plasma distributions and had previously been applied to damped electrostatic systems, is modified to include the effects of drifting equilibrium distributions of the type that drive counter-streaming and bump-on-tail instabilities. By using single-point time series, the correlation is ideal for diagnosing dynamics in systems where access to integrated quantities, such as energy, is observationally infeasible. Read More


Using two-dimensional hybrid expanding box simulations we study the competition between the continuously driven parallel proton temperature anisotropy and fire hose instabilities in collisionless homogeneous plasmas. For quasi radial ambient magnetic field the expansion drives $T_{\mathrm{p}\|}>T_{\mathrm{p}\perp}$ and the system becomes eventually unstable with respect to the dominant parallel fire hose instability. This instability is generally unable to counteract the induced anisotropization and the system typically becomes unstable with respect to the oblique fire hose instability later on. Read More


From numerical simulations, we show that non-rotating magnetohydrodynamic shear flows are unstable to finite amplitude velocity perturbations and become turbulent, leading to the growth and sustenance of magnetic energy, including large scale fields. This supports the concept that sustained magnetic energy from turbulence is independent of the driving mechanism for large enough magnetic Reynolds numbers. Read More


We present a 2.5-dimensional charge-conservative electromagnetic particle-in-cell (EM-PIC) algorithm optimized for the analysis of vacuum electronic devices (VED) with cylindrical symmetry (axisymmetry). We explore the axisymmetry present in the device geometry, fields, and sources to reduce the dimensionality of the problem from 3D to 2D. Read More


The pilot system development in metre-scale negative laboratory discharges is studied with ns-fast photography. The systems appear as bipolar structures in the vicinity of the negative high-voltage electrode. They appear as a result of a single negative streamer propagation and determine further discharge development. Read More