Quasineutral plasma models

The quasineutral plasma model proposed by Langmuir more than 75 years ago is still widely used today and is based on two approximations: charge neutrality and the Boltzmann relationship for electrons. However, the Boltzmann relationship is unnecessary and is not always justified. Moreover, because the Boltzmann relationship is fluid based, it compromises kinetic treatments and gives rise to troublesome singularities in the Bohm condition. To overcome these limitations, more general quasineutral models are developed. Two of the models are fluid based while the third is fully kinetic. The kinetic model and one of the fluid models lead directly to the Bohm condition, but without the singularities seen earlier. Fluid simulations are presented to test and compare the various approaches.