#### Daniel Kennedy Bhavin S Patel Colin M Roach

Microinstabilities often result in turbulence that influences energy confinement in tokamak discharges. One such microinstability, of particular importance to the design of next-generation spherical tokamaks (STs) such as STEP [1], is the microtearing mode (MTM), a tearing-parity mode centred on high-order rational surfaces. MTMs are short-wavel…

Preprint#### 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 Published#### 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 Published#### James Harrison RJ Akers SY Allan JS Allcock JO Allen L Appel M Barnes N Ben Ayed W Boeglin C Bowman J Bradley P Browning P Bryant M Carr M Cecconello CD Challis S Chapman IT Chapman GJ Colyer S Conroy NJ Conway M Cox G Cunningham RO Dendy W Dorland BD Dudson L Easy SD Elmore T Farley X Feng AR Field A Fil GM Fishpool M Fitzgerald

Recent results from MAST address key physics issues for ITER operations and the design of future devices, by advancing our understanding of through analysis of high-resolution data and numerical modelling. Modelling of the interaction between filaments with BOUT++ indicates filaments separated by more than 5x their width move independently, and …

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#### G. Merlo O. Sauter S. Brunner A. Burckel Y. Camenen F. Casson W.Dorland E. Fable T. Görler F. Jenko D. Told A. Peeters L. Villard

Verification is the fundamental step that any turbulence simulation code has to be submitted in order to assess the proper implementation of the underlying equations. We have carried out a cross comparison of three flux tube gyrokinetic codes, GENE [F. Jenko et al., Phys. Plasmas 7, 1904 (2000)], GKW [A. G. Peeters et al., Comput. Phys. Commun. 180…

Preprint Published#### E. G. Highcock A. A. Schekochihin S. C. Cowley M. Barnes F. I. Parra C. M. Roach W. Dorland

Sheared toroidal flows can cause bifurcations to zero-turbulent-transport states in tokamak plasmas. The maximum temperature gradients that can be reached are limited by subcritical turbulence driven by the parallel velocity gradient. Here it is shown that magnetic field pitch/inverse aspect ratio is a critical control parameter for sheared tokamak…

Published#### M.Barnes I.G.Abel W.Dorland T.Görler G.W.Hammett F.Jenko

Direct coupling between a transport solver and local, nonlinear gyrokinetic calculations using the multiscale gyrokinetic code TRINITY [M. Barnes, “TRINITY: A unified treatment of turbulence, transport, and heating in magnetized plasmas,” Ph.D. thesis, University of Maryland, (2008) eprint arXiv:0901.2868] is described. The coupling of the micr…

Published#### M.Barnes W.Dorland T.Tatsuno

Many plasmas of interest to the astrophysical and fusion communities are weakly collisional. In such plasmas, small scales can develop in the distribution of particle velocities, potentially affecting observable quantities such as turbulent fluxes. Consequently, it is necessary to monitor velocity space resolution in gyrokinetic simulations. In thi…

Published#### T. Tatsuno W. Dorland A. A. Schekochihin G. G. Plunk M. Barnes S. C. Cowley G. G. Howes

Electrostatic turbulence in weakly collisional, magnetized plasma can be interpreted as a cascade of entropy in phase space, which is proposed as a universal mechanism for dissipation of energy in magnetized plasma turbulence. When the nonlinear decorrelation time at the scale of the thermal Larmor radius is shorter than the collision time, a broad…

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