50 research outputs found
Hermes-3: Multi-component plasma simulations with BOUT++
A new open source tool for fluid simulation of multi-component plasmas is
presented, based on a flexible software design that is applicable to scientific
simulations in a wide range of fields. This design enables the same code to be
configured at run-time to solve systems of partial differential equations in
1D, 2D or 3D, either for transport (steady-state) or turbulent (time-evolving)
problems, with an arbitrary number of ion and neutral species. To demonstrate
the capabilities of this tool, applications relevant to the boundary of tokamak
plasmas are presented: 1D simulations of diveror plasmas evolving equations for
all charge states of neon and deuterium; 2D transport simulations of tokamak
equilibria in single-null X-point geometry with plasma ion and neutral atom
species; and simulations of the time-dependent propagation of plasma filaments
(blobs). Hermes-3 is publicly available on Github under the GPL-3 open source
license. The repository includes documentation and a suite of unit, integrated
and convergence tests.Comment: Submitted to Computer Physics Communication
The role of particle, energy and momentum losses in 1D simulations of divertor detachment
A new 1D divertor plasma code, SD1D, has been used to examine the role of recombination, radiation, and momentum exchange in detachment. Neither momentum or power losses by themselves are found to be sufficient to produce a reduction in target ion flux in detachment (flux rollover); radiative power losses are required to a) limit and reduce the ionization source and b) access low-target temperature, T_target, conditions for volumetric momentum losses. Recombination is found to play little role at flux rollover, but as T_target drops to temperatures around 1eV, it becomes a strong ion sink. In the case where radiative losses are dominated by hydrogen, the detachment threshold is identified as a minimum gradient of the energy cost per ionisation with respect to T_target. This is also linked to thresholds in T_target and in the ratio of upstream pressure to power flux. A system of determining the detached condition is developed such that the divertor solution at a given T_target (or lack of one) is determined by the simultaneous solution of two equations for target ion current - one dependent on power losses and the other on momentum. Depending on the detailed momentum and power loss dependence on temperature there are regions of T_target where there is no solution and the plasma 'jumps' from high to low T_target states. The novel analysis methods developed here provide an intuitive way to understand complex detachment phenomena, and can potentially be used to predict how changes in the seeding impurity used or recycling aspects of the divertor can be utilised to modify the development of detachment
The role of particle, energy and momentum losses in 1D simulations of divertor detachment
A new 1D divertor plasma code, SD1D, has been used to examine the role of recombination, radiation, and momentum exchange in detachment. Neither momentum or power losses by themselves are found to be sufficient to produce a reduction in target ion flux in detachment (flux rollover); radiative power losses are required to a) limit and reduce the ionization source and b) access low-target temperature, T_target, conditions for volumetric momentum losses. Recombination is found to play little role at flux rollover, but as T_target drops to temperatures around 1eV, it becomes a strong ion sink. In the case where radiative losses are dominated by hydrogen, the detachment threshold is identified as a minimum gradient of the energy cost per ionisation with respect to T_target. This is also linked to thresholds in T_target and in the ratio of upstream pressure to power flux. A system of determining the detached condition is developed such that the divertor solution at a given T_target (or lack of one) is determined by the simultaneous solution of two equations for target ion current - one dependent on power losses and the other on momentum. Depending on the detailed momentum and power loss dependence on temperature there are regions of T_target where there is no solution and the plasma 'jumps' from high to low T_target states. The novel analysis methods developed here provide an intuitive way to understand complex detachment phenomena, and can potentially be used to predict how changes in the seeding impurity used or recycling aspects of the divertor can be utilised to modify the development of detachment
The effects of non-uniform drive on plasma filaments
Wendelstein 7-X core fueling is primarily achieved through pellet injection. The trajectory of plasmoids from an ablating pellet is an ongoing research question, which is complicated by the complex magnetic geometry of W7-X; curvature drive varies significantly toroidally, including a change in the drift drive direction. Here we use the Hermes model in BOUT++ to simulate cold plasma filaments in slab geometries where the magnetic drift drive is non-uniform along the field line. It is shown that if the field-line-averaged curvature drive is non-zero, a filament will propagate coherently in the direction of average drive. It is also shown that a non-uniform drive will provide a non-uniform propagation; an effect which is reduced at higher temperatures due to an increased sound speed along the field line. Finally, simulations with curvature similar to that found in Wendelstein 7-X are performed which indicate a slow radial propagation of plasma filaments despite a highly non-uniform drive profile
Ion temperature measurements of L-mode filaments in MAST by retarding field energy analyser
Influence of plasma turbulence on microwave propagation
It is not fully understood how electromagnetic waves propagate through plasma
density fluctuations when the size of the fluctuations is comparable with the
wavelength of the incident radiation. In this paper, the perturbing effect of a
turbulent plasma density layer on a traversing microwave beam is simulated with
full-wave simulations. The deterioration of the microwave beam is calculated as
a function of the characteristic turbulence structure size, the turbulence
amplitude, the depth of the interaction zone and the size of the waist of the
incident beam. The maximum scattering is observed for a structure size on the
order of half the vacuum wavelength. The scattering and beam broadening was
found to increase linearly with the depth of the turbulence layer and
quadratically with the fluctuation strength. Consequences for experiments and
3D effects are considered.Comment: 16 pages, 13 figures. This is an author-created, un-copyedited
version of an article submitted for publication in Plasma Physics and
Controlled Fusion. IoP Publishing Ltd is not responsible for any errors or
omissions in this version of the manuscript or any version derived from i