Showing 1 - 10 of 25 Journals Results

2021

UKAEA-CCFE-PR(21)61

#### V. H. Hall-Chen F. I. Parra J. C. Hillesheim

#### We use beam tracing — implemented with a newly-written code, Scotty — and the reciprocity theorem to derive a model for the linear backscattered power of the Doppler Backscattering (DBS) diagnostic. Our model works for both the O-mode and X-mode in tokamak geometry (and certain regimes of stellarators). We present the analytical derivation of o…

Preprint2020

UKAEA-CCFE-PR(20)21

#### J F Parisi F I Parra C M Roach C Giroud W Dorland D R Hatch M Barnes J C Hillesheim N Aiba J R Ball P G Ivanov

#### Local linear gyrokinetic simulations show that electron temperature gradient (ETG) instabilities are the fastest growing modes for kyρi >~ 0.1 in the steep gradient region for a JET pedestal discharge (92174) where the electron temperature gradient is steeper than the ion temperature gradient. Here, ky is the wa…

Preprint Published2020

UKAEA-CCFE-PR(20)20

#### P G Ivanov A A Schekochihin W Dorland A R Field F I Parra

#### The saturated state of turbulence driven by the ion-temperature-gradient instability is investigated using a two-dimensional long-wavelength fluid model that describes the perturbed electrostatic potential and perturbed ion temperature in a magnetic field with constant curvature (a Z-pinch) and an equilibrium temperature gradient. Numerical simulat…

Preprint Published2018

UKAEA-CCFE-PR(19)13

#### M. R. Hardman M. Barnes C. M. Roach F. I. Parra

#### Multiple space and time scales arise in plasma turbulence in magnetic confinement fusion devices because of the smallness of the square root of the electron-to-ion mass ratio and the consequent disparity of the ion and electron thermal gyroradii and thermal speeds. Direct simulations of this turbulence that include both ion and electron space-ti…

Preprint Published2018

UKAEA-CCFE-PR(18)58

#### 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 Published2016

CCFE-PR(16)68

#### 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 Published2016

CCFE-PR(16)48

#### 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 Published2016

CCFE-PR(16)50

#### 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 Published2016

CCFE-PR(16)29

#### 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 Published2016

CCFE-PR(16)28