Electromagnetic heavy ion cyclotron instability: Anisotropy constraint in the solar corona

The electromagnetic proton cyclotron anisotropy instability is driven by T-perpendicular top/T-parallel top > 1 where p represents protons and the directional subscripts denote directions relative to the background magnetic field. Fluctuating field growth leads to wave-particle scattering, which in turn imposes an upper bound on the anisotropy of the form T-perpendicular top/T-parallel top - 1 = S-p/beta (alphap)(parallel top),where beta (parallel top) equivalent to 8 pin(p)k(B)T(parallel top)/B-0(2), and the fitting parameters S-p less than or similar to 1 and alpha (p) similar or equal to 0.4 Recent SOHO observations indicate that minority heavy ions are substantially hotter and more anisotropic than protons in the solar corona. Here linear theory and hybrid simulations have been carried out in a model of a homogeneous, magnetized, collisionless plasma with anisotropic minority oxygen ions (denoted by subscript O). These calculations show that the electromagnetic oxygen ion cyclotron anisotropy instability also leads to wave-particle scattering, which constrains that anisotropy by the form T-perpendicular toO/T-parallel toO - 1 = S-O/[(m(p)/m(O))<(<beta>)over bar>(parallel toO)](alphaO) where <(<beta>)over bar>(parallel toO) equivalent to 8 pin(e)k(B)T(parallel toO)/B-o(2), S-O similar to 10 and alpha (O) similar to 0.4. This constraint should be observable in the solar corona.