Thermal disequilibration of ions and electrons by collisionless plasma turbulence

Kawazura, Y; Barnes, M; Schekochihin, A

Journal article

Thermal disequilibration of ions and electrons by collisionless plasma turbulence

Abstract:: Does overall thermal equilibrium exist between ions and electrons in a weakly collisional, magnetized, turbulent plasma? And, if not, how is thermal energy partitioned between ions and electrons? This is a fundamental question in plasma physics, the answer to which is also crucial for predicting the properties of far-distant astronomical objects such as accretion disks around black holes. In the context of disks, this question was posed nearly two decades ago and has since generated a sizeable literature. Here we provide the answer for the case in which energy is injected into the plasma via Alfvénic turbulence: Collisionless turbulent heating typically acts to disequilibrate the ion and electron temperatures. Numerical simulations using a hybrid fluid-gyrokinetic model indicate that the ion–electron heating-rate ratio is an increasing function of the thermal-to-magnetic energy ratio, βi: It ranges from ∼0.05 at βi=0.1 to at least 30 for βi≳10. This energy partition is approximately insensitive to the ion-to-electron temperature ratio Ti/Te. Thus, in the absence of other equilibrating mechanisms, a collisionless plasma system heated via Alfvénic turbulence will tend toward a nonequilibrium state in which one of the species is significantly hotter than the other, i.e., hotter ions at high βi and hotter electrons at low βi. Spectra of electromagnetic fields and the ion distribution function in 5D phase space exhibit an interesting new magnetically dominated regime at high βi and a tendency for the ion heating to be mediated by nonlinear phase mixing (“entropy cascade”) when βi≲1 and by linear phase mixing (Landau damping) when βi≫1.

Publication status:: Published

Peer review status:: Peer reviewed

Actions

Email

Email this record

Send the bibliographic details of this record to your email address.

Your Email
Please enter the email address that the record information will be sent to.

-
Your message (optional)
Please add any additional information to be included within the email.
Cite

Cite this record

APA Style

Kawazura, Y., Barnes, M., & Schekochihin, A. (2018). Thermal disequilibration of ions and electrons by collisionless plasma turbulence. Proceedings of the National Academy of Sciences, 116(3), 771–776.

MLA Style

Kawazura, Y., et al. “Thermal Disequilibration of Ions and Electrons by Collisionless Plasma Turbulence.” Proceedings of the National Academy of Sciences, vol. 116, no. 3, National Academy of Sciences, 2018, pp. 771–76.

Chicago Style

Kawazura, Y, M Barnes, and A Schekochihin. 2018. “Thermal Disequilibration of Ions and Electrons by Collisionless Plasma Turbulence.” Proceedings of the National Academy of Sciences 116 (3): 771–76.
Share
Print