Intrinsic suppression of turbulence in linear plasma devices

Abstract

Plasma turbulence is the dominant transport mechanism for heat and particles in magnetized plasmas in linear devices and tokamaks, so the study of turbulence is important in limiting and controlling this transport. Linear devices provide an axial magnetic field that serves to confine a plasma in cylindrical geometry as it travels along the magnetic field from the source to the strike point. Due to perpendicular transport, the plasma density and temperature have a roughly Gaussian radial profile with gradients that drive instabilities, such as resistive drift-waves and Kelvin-Helmholtz. If unstable, these instabilities cause perturbations to grow resulting in saturated turbulence, increasing the cross-field transport of heat and particles. When the plasma emerges from the source, there is a time, τ , that describes the lifetime of the plasma based on parallel velocity and length of the device. As the plasma moves down the device, it also moves azimuthally according to E × B and diamagnetic velocities. There is a balance point in these parallel and perpendicular times that sets the stabilisation threshold. We simulate plasmas with a variety of parallel lengths and magnetic fields to vary the parallel and perpendicular lifetimes, respectively, and find that there is a clear correlation between the saturated RMS density perturbation level and the balance between these lifetimes. The threshold of marginal stability is seen to exist where τ ≈ 11τ ⊥ . This is also associated with the product τ γ * , where γ * is the drift-wave linear growth rate, indicating that the instability must exist for roughly 100 times the growth time for the instability to enter the non-linear growth phase. We explore the root of this correlation and the implications for linear device design.

Edge turbulence in ISTTOK: a multi-code fluid validation

“…Hermes [12] is a 3D, five-field (cold-ion) model based on the Simakov-Catto drift-reduced equations [29], and solved using the BOUT++ framework [13,30] in curvilinear coordinates. Hermes has been applied to turbulence in linear devices [31] including the interaction between plasma and neutral gas [32], limiter and diverted tokamaks [12]. For simulations of the poloidally-limited ISTTOK device, the geometry includes both open and closed field-line regions, and the coordinate system uses the poloidal plane as the drift plane (X-Z in BOUT++ coordinates).…”

Simulations of Argon plasmas in the linear plasma device GyM with the SOLPS-ITER code

“…Effects of pumping efficiency and radial transport coefficients were studied [20] and a quantitative analysis of the importance of transport and atomic processes, based on the two-point model [21,22], was performed. Alongside the efforts to adapt tokamak mean-field edge codes to LPDs, some attempts were also made to develop codes which implement plasma transport models in cylindrical geometry, both considering mean-field transport questions [23][24][25][26][27] and a consistent treatment of turbulence [28][29][30][31][32]. While this approach allows simplifications in the transport equations due to a simpler geometry, these codes are presently limited due to the absence or the highly simplified treatment of neutral species and their interactions with the background plasma.…”

New low temperature multidipole plasma device with a magnetic X-point and its properties

“…A common feature of these linear devices is that they all have axial magnetic fields in cylindrical geometry. In addition, linear plasma devices utilizing hot DC cathodes for producing plasmas have allowed many researchers to investigate various fascinating subjects such as waves [7][8][9][10][11], turbulence [12][13][14][15][16][17] and transports [18][19][20][21] of magnetized plasmas owing to the fact that such devices have easy access to monitor and control plasmas while plasmas are steady-state and/or reproducible.…”