Violation of quasi-neutrality for ion-neutral charge-exchange reactions in magnetized plasmas

Debye shielding is found not to be effective for the sudden change of ion trajectories induced by charge-exchange reactions with neutrals in typical tokamak plasmas. When the number of charge-exchange occurrences in Debye shielding is greater than unity, electrons are simultaneously engaged in the screening process for multiple point charges, which makes the shielding ineffective. The ion polarization drift is also found not to be applicable for the charge-exchange reactions because the individual particles experience an electric field that changes faster than particle’s cyclotron frequency and because the electron polarization drift is slower than the ion velocity responsible for the gyro-center shift current when the dimensionless number λ D / r x is greater than unity, which results in a violation of quasi-neutrality.