Effects of electron mass on Alfven waves in a cylindrical plasma

Abstract

Effects of elecmn mass on A l f h waves in a cylindrical, inhomogeneous plasma are examined. in the cold plasma approximation, and in the frequency range from well below to several times the ion cyclotron frequency. oei. Both propagaling (k: > 0) and axially evanescent (k: c 0) modes are considered. It is shown how the cold plasma modes are coupled by a density gradient and how these modes are connected across the four domains bounded by kf = 0 and o = oci. Low-frequency surface-wave modes, predicted for a density step profile, lose their identity in a diffuse profile and merge with a discrete set of shear wave modes. High frequency surface modes survive in a diffuse profile. These, and other high frequency fast wave modes are axially evanescent at frequencies below ule k, = 0 cutdff fr&quency, and are Alfv6n-resonant if the cut& frequency is above the ion cyclotron frequency.

Observations of edge ICRF wave modes in the TORTUS tokamak

“…For the parameters chosen in the calculation of the curves in figure 1(a), l e is about 10 cm, but l e is typically about 30 cm in the low density edge regions of a tokamak plasma. A similar picture to that outlined above for evanescent and propagating shear modes also emerges in a bounded plasma [9], except that there is an increase in the complexity of the dispersion relations around = 1. This is illustrated in figure 2, where the dispersion relations have been calculated for a cylindrical plasma using the cold plasma equations (including finite electron mass) and a smooth density profile.…”

“…It is not possible to label intermediate k ⊥ modes unambiguously as either shear or fast. However, the k ⊥ > 50 m −1 curves can be labelled as shear since (i) the perpendicular component of the group velocity is much smaller than the parallel component, (ii) the dispersion relation is almost independent of k ⊥ , (iii) the k ⊥ = ∞ shear wave dispersion relation defines an Alfvén resonance surface in an inhomogeneous plasma with either < 1 and k 2 > 0 or > 1 and k 2 < 0 [9].…”

A minimal model of parallel electric field generation in a transversely inhomogeneous plasma

“…By using simpler, than kinetic [5,6,7,8], two-fluid, cold plasma linearised equa-tions, we show for the first time that E generation can be understood by an analytic equation that couples E to the transverse electric field. It should be noted that the generation of E is a generic feature of plasmas with the transverse density inhomogeneity and in a different context this was known for decades in the laboratory plasmas [13,14]. We prove that the minimal model required to reproduce the previous kinetic results of E generation is the two-fluid, cold plasma approximation in the linear regime.…”

“…The generation of E is a generic feature of plasmas with the transverse density inhomogeneity and in a different context this was known for decades in the laboratory plasmas Cross & Miljak(1993), Ross & et al(1982). Also, it should be emphasised that the two fluid description in the context of parallel electric field generation has been used before Goertz & Boswell(1979).…”

Shear Alfven wave excitation by direct antenna coupling and fast-wave resonant-mode conversion

“…This mode is referred to as the surface wave (SW) and is discussed in detail by Cross (1988a) for a slab plasma and ,by Cross (1988a) and Ballico and Cross (1989) for a cylindrical plasma. The effects of finite electron mass have been discussed by Cross and Miljak (1993). For a vacuum boundary, the surface wave satisfies the dispersion relation, U(: = kz, and an eigenmode G G 30rg resonance can be expected for antennae which possess this kz in their parallel wavenumber spectrum.…”