Plasmoid instability in the semi-collisional regime

Dataset · Thu Jan 10 00:00:00 EST 2019

DOI:https://doi.org/10.7910/DVN/3MVSWV· OSTI ID:1880638

Bhat, Pallavi; Loureiro, Nuno F.

We investigate analytically and numerically the semi-collisional regime of the plasmoid instability, defined by the inequality δSP ≫ ρs ≫ δin, where δSP is the width of a Sweet-Parker current sheet, ρs is the ion sound Larmor radius, and δin is width of boundary layer that arises in the plasmoid instability analysis. Theoretically, this regime is predicted to exist if the Lundquist number S and the length of the current sheet L are such that (L/ρs ) 14/9 < S < (L/ρs ) 2 (for a sinusoidal-like magnetic configuration; for a Harris-type sheet the lower bound is replaced with (L/ρs ) 8/5 ). These bounds are validated numerically by means of simulations using a reduced gyrokinetic model (Zocco & Schekochihin, Physics of Plasmas 18, 2011) conducted with the code Viriato. Importantly, this regime is conjectured to allow for plasmoid formation at relatively low, experimentally accessible, values of the Lundquist number. Our simulations obtain plasmoid instability at values of S as low as ∼ 250. The simulations do not prescribe a Sweet-Parker sheet; rather, one is formed self-consistenly during the nonlinear evolution of the initial tearing mode configuration. This proves that this regime of the plasmoid instability is realizable, at least at the relatively low values of the Lundquist number that are accessible to current dedicated experiments.

• Research Organization: Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Plasma Science and Fusion Center
• Sponsoring Organization: USDOE Office of Science (SC), Fusion Energy Sciences (FES)
• DOE Contract Number: SC0016215; FG02-91ER54109
• OSTI ID: 1880638
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY