#### Alessandro Geraldini Felix Parra Fulvio Militello

Using a kinetic model for the ions and adiabatic electrons, we solve a steady state, electron-repelling magnetic presheath in which a uniform magnetic field makes a small angle α

Preprint Published#### P. Helander F.I. Parra S.L. Newton

The bootstrap current and flow velocity of a low-collisionality stellarator plasma are calculated. As far as possible, the analysis is carried out in a uniform way across all low-collisionality regimes in general stellarator geometry, assuming only that the confinement is good enough that the plasma is approximately in local thermodynamic equilibri…

Preprint Published#### G. J. Colyer A. A. Schekochihin F. I. Parra C. M. Roach M. A. Barnes Y. C. Ghim W. Dorland

In electrostatic simulations of MAST plasma at electron-gyroradius scales, using the local flux-tube gyrokinetic code GS2 with adiabatic ions, we find that the longtime saturated electron heat flux (the level most relevant to energy transport) decreases as the electron collisionality decreases. At early simulation times, the heat flux quasisatura…

Preprint Published#### A. Geraldini F. I. Parra F. Militello

We develop a gyrokinetic treatment for ions in the magnetic presheath, close to the plasma-wall boundary. We focus on magnetic presheaths with a small magnetic field to wall angle, a << 1 (in radians). Characteristic lengths perpendicular to the wall in such a magnetic presheath scale with the typical ion Larmor orbit size, r

Preprint Published#### J. Ball F. I. Parra

Breaking the up-down symmetry of tokamaks removes a constraint limiting intrinsic momentum transport, and hence toroidal rotation, to be small. Using gyrokinetic theory, we study the effect of different up-down asymmetric flux surface shapes on the turbulent transport of momentum. This is done by perturbatively expanding the gyrokinetic equation in…

Preprint Published#### J. Ball F. I. Parra M. Barnes

A poloidal tilting symmetry of the local nonlinear _f gyrokinetic model is demonstrated analytically and verified numerically. This symmetry shows that poloidally rotating all the flux surface shaping effects with large poloidal mode number by a single tilt angle has an exponentially small effect on the transport properties of a tokamak. This is sh…

Preprint Published#### F. I. Parra M. Barnes

A set of flux tube gyrokinetic equations that includes the effect of the spatial variation of the density, temperature and rotation gradients on the turbulence is derived. This new set of equations uses periodic boundary conditions. In the limit l?/L « 1, where l? is the characteristic perpendicular length of turbulent structures and L is the char…

Preprint Published#### J. Ball F. I. Parra

Using analytic calculations, the effects of the edge ux surface shape and the toroidal current profile on the penetration of ux surface shaping are investigated in a tokamak. It is shown that the penetration of shaping is determined by the poloidal variation of the poloidal magnetic field on the surface. This fact is used to investigate how differe…

Preprint Published#### F. I. Parra M. Barnes

Self-consistent equations for intrinsic rotation in tokamaks with small poloidal magnetic field Bp compared to the total magnetic field B are derived. The model gives the momentum redistribution due to turbulence, collisional transport and energy injection. Intrinsic rotation is determined by the balance between the momentum redistribution and the …

Preprint Published#### J.C. Hillesheim F.I. Parra M. Barnes N.A. Crocker H. Meyer W.A. Peebles R. Scannell A. Thornton The MAST Team

Tokamak plasmas rotate even without external injection of momentum. A Doppler backscattering system installed at MAST has allowed this intrinsic rotation to be studied in Ohmic L-mode and Hmode plasmas, including the first observation of intrinsic rotation reversals in a spherical tokamak. Experimental results are compared to a novel 1D model, whic…

Preprint Published