MHD development

MHD Development Agenda

List of Potential Topics

• Pre-Release Points: Need a publishable version of MHD
  • Con2Prim failures
    • Save initial state in all Con2Prim routines, check results before overwriting
    • Pass ideal & acceptable tolerances, have end C2P tolerance GF
• Paper updates and progress
• Issues with current MHD methods
  • Divergence cleaning and mesh refinement
  • Combining constraint transport and divergence cleaning
• New methods
  • Con2Prim Inversion -- Force-free
  • Vector Potential implementation

Con2Prim Inverter

• add code to transition into force-free inversion (no force free evolution) if magnetic pressure starts to dominate gas pressure (done in SpEC, seems robust)

Vector Potential

Evolving the vector potential allows for better control of the B-field divergence and better behavior around a puncture. Evolving the vector potential is also better behaved surrounding puncture BHs.

Current State

This was partially implemented in the last development workshop, but removed again within the last year. We had agreed to implement the algebraic gauge first with a view towards the Lorenz gauge. Initial implementation had been of cell-centered vector potential, though we should now be able to support staggered grid vector potential.

Matters to Discuss

• Staggered vs unstaggered A^i
• Prolongation operators given the location on the cell ( for staggered A only )
• Scheduling for reconstructing B from the vector potential

Coding Tasks

As this workshop will take place during the pre-release phase, this development should take place in Zelmani.

• Storage and evolution (simpler now that E^i has been implemented and tested for the constraint transport)
• B-field construction from A^mu
• Initial Prim2Con support for A^mu
• Reconstruction support for A^mu
• Riemannsolver support for A^mu
• Recovery point-wise support for A^mu