Rarefied Populations of Heavy Nuclei and Associated Transport*

Plasmas in which low density populations of heavier nuclei than those of the main population are a frequent occurrence [1] and an important case is that of “impurities” whose cyclotron frequencies, Ω_I  , differ from that, Ωi , of the main population. “Ω_I − frequency” modes are found to be sustained by the impurity density gradient. In the limit of “short” transverse wavelengths    (k² d_i² >1 , where d_i = c/ω_pi ) these modes are nearly electrostatic while in the relatively long wavelength limit (k² d_i² <<1) they involve significant magnetic field fluctuations [2]. The relevant transverse phase velocities are in the direction of the local impurity diamagnetic velocity and produce a transport of this population across the magnetic field. Growth rates are found which depend on pre-existing thermal energy transport processes for the same population such as those associated with the excitation of the lower frequency “impurity drift modes” introduced in Ref. [3]. A programmed immission of non-reacting minority populations is suggested in order to increase the total reactivity of a fusion burning plasma column, for instance, by conditioning the spatial density profiles [1] of the reacting populations.

1. C. Mazzotta, et al., Paper IAEA-CN-899 MFE, Fusion Energy Conference (I.A.E.A., Vienna, 2021).

2. B. Coppi, S. Cowley, et al., Phys. Fluids 29, 4060 (1986).

3. B. Coppi, H. Furth, M. Rosenbluth and R. Sagdeev, Phys. Rev. Lett. 17, 377 (1966).