A general kinetic mirror instability criterion for space applications

Suprathermal particle populations and loss‐cone structures are the most common characteristics of ion and electron velocity distributions observed in space plasmas. We introduce a significant generalization of the family of kappa distributions to a suprathermal loss‐cone distribution, applicable to a variety of space plasma modeling. On the basis of this concept a general mirror instability threshold criterion is derived from an energy principle for collisionless plasmas, covering the full range from two‐temperature Maxwellians to complex loss‐cone conditions occupied by high‐energy ion species. We demonstrate that nonthermal plasma characteristics are the source of significant mirror instability threshold reduction where the specific structure of the velocity‐space distribution dominates as a regulating mechanism for wave mode excitation.