Hydrodynamic Effects on Field-Generating Thermal Instability in Laser-Heated Plasma

Field Compressing Magnetothermal Instability in Laser Plasmas

“…∇n e = 0, precluding ∇T e × ∇n e field generation), nor hydrodynamic motion or anisotropic pressure. Thus, what we see is distinct from instabilities existing in the literature: such as those of Tidman-Shanny [12][13][14], for which ∇T e × ∇n e is necessarily non-zero; Weibel [15], where magnetic fields are not essential; Haines [16,17], which does not require either Righi-Leduc heat-flow or the Nernst effect; and Davies [18], where unstable filamentation arises from plasma motion.In our case, terms responsible for growth go as k 3 2 , where k is the wavenumber of a perturbation (not the more usual k), yielding traveling waves rather than purely growing perturbations. These, however, differ from the thermal-magnetic waves described by Pert [19] who neglected the Nernst effect.…”

Magnetothermal instability in laser plasmas including hydrodynamic effects

“…=3P e (where P e is the electron pressure) 2 and (ii) the Righi-Leduc heat-flow, the thermal flux deflected by fields acting on negatively charged, heat-carrying electrons. 1 Neither density gradients (which give rise to the field generating thermal instability), [15][16][17][18][19][20] large anisotropies (responsible for other heat-flux and Weibel-like instabilities), [21][22][23][24] nor hydrodynamic flow (necessary for interchange instabilities, such as the Rayleigh-Taylor instability and its analogues) [25][26][27] are required.…”

“…28 This is significant because coupling between the rT e  rn e effect and the Righi-Leduc heat-flow has long been known to drive a field generating thermal instability. [15][16][17][18][19] Nearly, all existing studies of the latter assume an unmagnetised plasma, meaning that our discussion also represents a generalised description of how the field generating instability functions in the presence of existing fields: indeed, only Fruchtman and Strauss 20 seem to have considered magnetised conditions; nevertheless, the absence of field gradients, damping terms (such as thermal diffusion), and important advective effects from their model render its verisimilitude somewhat questionable. The theory presented here is thus essential for understanding how the mechanisms behind the magnetothermal instability and the field generating thermal instability interact (Sec.…”

Nernst advection and the field-generating thermal instability revisited

“…These fields strongly affect electron transport by suppressing the cross-field thermal conductivity (Braginskii 1965) and are thus key to understanding a range of laser-plasma interactions, including ongoing efforts to achieve controlled inertial confinement fusion (Glenzer et al 1999;Lindl et al 2004;Nilson et al 2006;Froula et al 2007;Li et al 2007a,b;Schurtz et al 2007;Froula et al 2009;Li et al 2009Li et al , 2013. Of special importance in such contexts is the role transport effects might play in driving instabilities, especially given that such instabilities are themselves often candidate mechanisms for producing the self-generated field (Weibel 1959;Tidman & Shanny 1974;Bol'shov et al 1974;Ogasawara et al 1980;Haines 1981;Bissell et al 2010Bissell et al , 2012Gao et al 2012;Manuel et al 2013).…”

“…For this reason, our analysis followed in the tradition of previous work in its treatment of the Nernst advection terms (Brownell 1979;Hirao & Ogasawara 1981); however, we noted a curious feature of the Nernst mechanism in that it seems to predict peak instability growth-rates as the perturbation wave-number k vanishes. When trying to develop a mathematically consistent picture of the instability, this feature is problematic because analytical treatments typically assume some local conditions l n,T k 1 for the unstable modes, precluding k → 0 (Tidman & Shanny 1974;Bol'shov et al 1974;Ogasawara et al 1980;Brownell 1979;Hirao & Ogasawara 1981). Furthermore, the Nernst term (which compresses the field perturbations) does not couple to a corresponding term acting on thermal perturbations, meaning that mechanism (ii) does not account for unstable feedback in the usual way.…”