A new regime of whistler waves in the laboratory

A new regime of whistler wave propagation in a large laboratory unbounded uniform plasma has been identified. The wave exhibits interesting topological characteristics, has an elongated structure and exhibits feeble resonance and almost no obliqueness [1]. Conventionally, whistler waves are known to exhibit complex three dimensional features with both parallel and oblique propagation. However, the waves excited here show no such feature. These characteristics are attributed to the electron inertia effects [2] that starts playing a significant role in a regime where typical antenna dimension is comparable to the electron skin depth ( de=c/ωpe), the characteristic spatial scale length of electron-magnetohydrodynamics (EMHD) of which whistler waves are the normal linear modes. Exact nonlinear solutions also exist in the form of structures called electron vortices, as shown by several theoretical and computational works [14]. Such solutions exist when spatial scale length λ ≤ de and structures propagate in the form of vortices uninhibited by the surrounding plasma. However, no experimental proof exists till date. Our results have revealed that the waves or structures excited indeed have spatial scale length limited to the electron skin depth when antenna dimension is of that order. A possible physical model describing the processes is also given. However, the parallel propagation is dominated by the guiding field and highly elongated. In the presence of feeble external guiding field or no field, the whistlerization does not occur, finite Larmor radius effects start playing a role and wave is guided along the resultant complex field [3]. The wave energy gets distributed due to the interplay between electron inertia and Larmor radius effects and the wave scatters. The results are very interesting because they have paved way for future work on the excitation of pure electron vortices and studies related to their relevance to plasma turbulence.