Ion hole one-dimensional equilibrium and stability

Ion holes are electrostatic solitary waves with negative potential,

now frequently observed in space plasmas. This new theoretical work[1],

using a generalization of the treatment recently developed for slow

electron holes[2], shows that an often-cited criterion for ion hole

existence is mistaken and they can in fact exist for a wide range of

ion to electron temperature ratios. Shifts of the hole velocity $v_h$

relative to the ion distributions systematically decrease the

permitted hole depths, which become extremely small by $v_h/v_{ti}sim

2$. Ion holes are usually unstably accelerated by electron reflection

forces which are calculated numerically and analytically for the

resulting asymmetric potential structure. The timescale of this

acceleration is proportional to the ion plasma period, and generally

longer than the ion bounce time in the potential well. Thus, ion holes

behave like approximately rigid entities and even when unstable can

survive much longer than the typical transit time of a satellite, so

as to be observable.

[1] I H Hutchinson, Phys. Plasmas 30, 032107 (2023)

[2] I H Hutchinson, Phys. Rev. E 104, 055207 (2021)