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We present new results of multi-scale simulations of Langmuir turbulence during heating experiments where a powerful electromagnetic wave is injected into the overhead ionosphere where it excites parametric instabilities leading to turbulence on multiple spatial and temporal scales. The simulations are carried out using a generalized Zakharov model [1, 2] in which the complex phase and...
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Ion-gyroradius-scale microinstabilities typically have a frequency comparable to the ion transit frequency. Due to the small electron-to-ion mass ratio and the large electron transit frequency, it is conventionally assumed that passing electrons respond adiabatically in ion-gyroradius-scale modes. However, in gyrokinetic simulations of ion-gyroradius-scale modes in axisymmetric toroidal...
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A new quasilinear saturation model SAT3 has been developed for the purpose of calculating radial turbulent fluxes in the core of tokamak plasmas. The new model is shown to be able to better recreate the isotope mass dependence of nonlinear gyrokinetic fluxes compared to contemporary quasilinear models, including SAT2 (Staebler et al 2021 Nucl. Fusion 61 116007), while performing at least as...
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To be economically competitive, spherical tokamak (ST) power plant designs require a high beta (plasma pressure/magnetic pressure) and sufficiently low turbulent transport to enable steady-state operation. A novel approach to tokamak optimisation is for the plasma to have negative triangularity, with experimental results indicating this reduces transport. However, negative triangularity is...
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The steep plasma pressure gradient that forms at the edge of the high confinement, H-mode regime of tokamak operation provides free energy to drive electromagnetic micro-instabilities that are widely believed to influence the transport processes in this so-called pedestal region. This high pressure gradient also provides a high current density (bootstrap current), known to influence ballooning...
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The analytical theory describing the resonant excitation and coupling of volume and surface fields on the surface of two-dimensional complex electrodynamic structures is presented. The theoretical analysis is valid over a broad frequency spectrum from mm-wave frequencies through THz and even optical frequencies. An experimental study of planar periodic structures has been carried out using a...
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Spherical tokamaks (STs) have been shown to possess properties desirable for a fusion power plant such as achieving high plasma β and having increased vertical stability. To understand the confinement properties that might be expected in the conceptual design for a high β ST fusion reactor, a 1 GW ST plasma equilibrium was analysed using local linear gyrokinetics to determine the type of...
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High-power microwave sources are typically relativistic in nature, employing multi-kilo-ampere electron beams that require significant magnetic confinement for efficient operation. As the desired output power increases, so does the complexity, and overall energy requirements, of the source. It can, therefore, be advantageous to consider the use of several, moderate-power, sources operating as...
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Stimulated Brillouin scattering experiments in the ionospheric plasma using a single electromagnetic pump wave have previously been observed to generate an electromagnetic sideband wave, emitted by the plasma, together with an ion- acoustic wave. Here we report results of a controlled, pump and probe beat-wave driven Brillouin scattering experiment, in which an ion-acoustic wave generated by...
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The azimuthally rippled cavity for a large-orbit, coharmonic gyro-multiplier, designed to operate at the second and fourth harmonics, at frequencies of 37.5 and 75 GHz, respectively, has been numerically and experimentally confirmed to be insensitive to the polarization of quadrupole, \textTE_2,n -like modes, including the second-harmonic operating mode of the multiplier, a cylindrical...
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The performance of spherical tokamak reactors depends on plasma β, and an upper limit is set by long-wavelength kinetic ballooning modes (KBMs). We examine how these modes become unstable in spherical-tokamak reactor relevant plasmas, which may contain significant fast-ion pressure. In a series of numerically generated equilibria of increasing β, the KBM becomes unstable at sufficiently high...
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A new algorithm for toroidal flow shear in a linearly implicit, local δfδf\delta f gyrokinetic code is described. Unlike the current approach followed by a number of codes, it treats flow shear continuously in time. In the linear gyrokinetic equation, time-dependences arising from the presence of flow shear are decomposed in such a way that they can be treated explicitly in time with no...
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We perform a study of system-scale to gyro-radius scale electromagnetic modes in a pedestal-like equilibrium using a gyrokinetic code ORB5, along with a comparison to the results of wimulations in a local gyrokinetic code, GS2, and an MHD energy principle code, MISHKA. In the relevant large-system, short wavelength regime, good agreement between the gyrokinetic codes is found. For global-scale...
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The electromagnetic effect is studied on the short wavelength branch of the ion temperature gradient mode in the linear regime for the first time using a global gyrokinetic model. The short wavelength ion temperature gradient mode growth rate is found to be reduced in the presence of electromagnetic perturbations at finite plasma β. The effect on real frequency is found to be weak. The...
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Magnetic reconnection is a process that contributes significantly to plasma dynamics and energy transfer in a wide range of plasma and magnetic field regimes, including inertial confinement fusion experiments, stellar coronae, and compact, highly magnetized objects like neutron stars. Laboratory experiments in different regimes can help refine, expand, and test the applicability of theoretical...
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