Plasma actuators are promising as active flow control devices due to their lack of mechanical parts, lightweight, and high response frequency. To carry out flow separation control in a hypersonic flow, the design and construction of a power supply to generate dielectric barrier discharges are necessary. This paper aims to construct and simulate the circuit topology to emulate the dielectric barrier discharge and study its various frequency responses. The high voltage generation circuit of 500W, which consists of two parts - an input power module and a resonance converter bridge, and is capable of producing voltages in the range of 10-25kV is designed. The filter circuit for the resonance converter is designed, and suitable off-the-shelf components are selected for the realization of the circuit in the lab. The range of operation of the resonant circuit is set between 10kHz to 50kHz. The high-frequency transformer is designed and fabricated. The entire circuit is powered from the AC mains, and the performance of the circuit is validated by comparison between the simulated and the laboratory results. The circuit has the capability to vary the nature and the frequency of the output waveforms, which facilitates the investigation of the discharges under different conditions. The closed-loop controller for the converter is designed and validated.

In the present work, different modeling approaches are applied for the numerical simulation of high-enthalpy flows under the assumption of local thermochemical equilibrium. The first approach uses Srinivasan curve fits for estimating thermodynamic and transport properties of air at high temperatures, whereas the second approach estimates the properties by computing the equilibrium composition at a given density and temperature. A two-dimensional finite volume solver has been developed and is validated for shock-wave-boundary-layer interaction over a compression corner. Comparison of the flow characteristics obtained for calorically perfect gas and equilibrium air assumptions are presented for different test cases of inviscid and viscous hypersonic flows. The effect of the presence of argon on the properties of high-enthalpy flows is also studied. The increase in argon concentration from 0 to 20% is found to result in less than 10% increase in the peak temperature in the flowfield and heat flux at the wall.

The ballooned nature of cross-field transport is shown to govern the steady state divertor imbalance of the energy flux leading to a factor 10 between the low field side and high field energy flux. An even stronger ratio is found for the divertor temperatures. Conversely the particle flux is expected to be a factor 10 larger on the high field side than on the low field side. The transition to detachment, close to divertor thermal collapse, exhibits several constraints to maintain steady state solutions. These constraints, related in particular to a large drop of the divertor density upon detachment, are shown to strongly correlate the pressure and particle flux variation along the field line and consequently the various loss channels. This delicate balance between different mechanisms is a possible understanding of the difficulty reported in detached plasma operation and simulation.

With a proper choice of a single dimensionless control parameter one describes the transition between subsonic and supersonic flows as a bifurcation. The bifurcation point is characterized by specific properties of the control parameter: the control parameter has a vanishing derivative in space and takes the maximum possible value equal to 1. This method is then applied to the sheath plasma with constant temperatures, allowing one to recover the Bohm boundary condition as well as the location of the point where the bifurcation takes place. This analysis is extended to fronts, rarefaction waves and divertor plasmas. Two cases are found, those where departure from quasineutrality is mandatory to generate a maximum in the variation of the control parameter (sheath and fronts) and those where the physics of the quasineutral plasma can generate such a maximum (rarefaction waves and supersonic flow in divertors). The conditions that are required to recover the Bohm condition, when modelling the wall using the penalization technique, are also addressed and generalized.

Plasma energy confinement in magnetically confined plasmas is governed by turbulent transport. Electric drift velocity that contributes to the plasma velocity fields depends on the electrostatic potential field, which is obtained from the charge balance equation for quasi–neutral plasmas [1, 2]. In gyrokinetic and fluid representations, extraction of the potential field from this equation is simplified by assuming that the background density gradient length scales are much larger than fluctuation scales, the so-called Boussinesq approximation. However, in practice there is no significant scale separation between the fluctuation and background gradient length–scales. It has been reported that the Boussinesq approximation results in reduced velocities for isolated mesoscale coherent structures evolving in a quiescent and uniform background plasma [3]. Such an idealized situation is not directly applicable to the turbulent scrape–off layer (SOL) where structures propagate through fluctuating fields of magnitudes comparable to that of the structure. A key point in the turbulent SOL is the competition between various time scales, that driving the density ballistic convection and that determining the evolution of the background electrostatic potential. Beginning with a simple linear analysis, we investigate simplified models to single out the role of the Boussinesq approximation on the characteristic time scale of the electrostatic potential. We use nonlinear simulations, using the fluid code TOKAM–2D [1], to investigate the effect of Boussiensq approximation on isolated coherent structures and on SOL turbulent transport. It is found that in most cases of interest the Boussinesq approximation has a relatively weak effect on the overall turbulence behaviour. However, when the contrast between the density in the blob structure and that of the background plasma is large, hence driving strong density gradients, one observes a slowing down of the electrostatic potential evolution, in agreement with our analytical predictions.

We present edge kinetic ion transport simulations of tokamak plasmas in magnetic divertor geometry using the fully nonlinear (full-f) continuum code TEMPEST. Besides neoclassical transport, a term for divergence of anomalous kinetic radial flux is added to mock up the effect of turbulent transport. To study the relative roles of neoclassical and anomalous transport, TEMPEST simulations were carried out for plasma transport and flow dynamics in a single-null tokamak geometry, including the pedestal region that extends across the separatrix into the scrape-off layer and private flux region. A series of TEMPEST simulations were conducted to investigate the transition of midplane pedestal heat flux and flow from the neoclassical to the turbulent limit and the transition of divertor heat flux and flow from the kinetic to the fluid regime via an anomalous transport scan and a density scan. The TEMPEST simulation results demonstrate that turbulent transport (as modelled by large diffusion) plays a similar role to collisional decorrelation of particle orbits and that the large turbulent transport (large diffusion) leads to an apparent Maxwellianization of the particle distribution. We also show the transition of parallel heat flux and flow at the entrance to the divertor plates from the fluid to the kinetic regime. For an absorbing divertor plate boundary condition, a non-half-Maxwellian is found due to the balance between upstream radial anomalous transport and energetic ion endloss.

We present edge gyrokinetic simulations of tokamak plasmas using the fully non-linear (full- f ) continuum code TEMPEST. A non-linear Boltzmann model is used for the electrons. The electric field is obtained by solving the 2D gyrokinetic Poisson equation. We demonstrate the following. (1) High harmonic resonances ( n > 2) significantly enhance geodesic-acoustic mode (GAM) damping at high q (tokamak safety factor), and are necessary to explain the damping observed in our TEMPEST q -scans and consistent with the experimental measurements of the scaling of the GAM amplitude with edge q 95 in the absence of obvious evidence that there is a strong q -dependence of the turbulent drive and damping of the GAM. (2) The kinetic GAM exists in the edge for steep density and temperature gradients in the form of outgoing waves, its radial scale is set by the ion temperature profile, and ion temperature inhomogeneity is necessary for GAM radial propagation. (3) The development of the neoclassical electric field evolves through different phases of relaxation, including GAMs, their radial propagation and their long-time collisional decay. (4) Natural consequences of orbits in the pedestal and scrape-off layer region in divertor geometry are substantial non-Maxwellian ion distributions and parallel flow characteristics qualitatively like those observed in experiments.

Convective blob propagation in the scrape-off-layer and/or limiter shadow region is analyzed analytically and numerically with emphasis on effects of a gradient in the equilibrium plasma density. The gradient of the equilibrium plasma density is taken into account beyond the Boussineque approximation. It is shown that the vorticity modification due to the plasma density gradient leads to the acceleration for the blobs propagating into the region of lower density and de-acceleration for the blobs propagating toward the regions of higher density. Analytical estimates are corroborated by direct numerical simulations.