Computing tensor ponderomotive force terms in Vorpal for use in BOUT++

A literature survey across numerous references discussing ponderomotive force leads us to a single consolidated formulation, utilizing the fluid force equation and separation of time-scales. We present analytical case studies from various scenarios of the formulation where ponderomotive forces can occur. Of significance is that this work includes the presence of collisions with neutral gas (RF drag and absorption) in the far-SOL and partial ionization regions. The formulation includes a classical term with ∇|V_RF|², thus permitting force in non-drift directions. Other terms include cyclotron motion and neutral gas collisions, and have gradients of plasma and neutral gas density, and thus can be significant in the steep density gradients. We implement diagnostic calculation of these ponderomotive forces in the Vorpal time-domain plasma model, and starting from the description of the BOUT equations in Reference [1], we formulate the computed ponderomotive forces terms needed for use in the BOUT++ code. We also set up simple launcher geometries, and visualize the analytical case studies in higher dimensions.

[1] Umansky et al., Computer Physics Communications 180 (2009) 887.