Excitation of Fast Waves and Global Kink-Mode Oscillations from an Erupting Arched Laboratory Magnetoplasma

Abstract:

Arched magnetoplasma structures ubiquitously exist in the solar atmosphere and affect energetic phenomena such as flares and coronal mass ejections. In a laboratory setup, excitation of fast-waves (with characteristics of EUV/EIT waves on the Sun) and global kink-mode oscillations from an erupting arched magnetoplasma was recorded with an unprecedented detail by capturing spatio-temporal evolution of the three-dimensional magnetic-field and plasma density. Images of the arched magnetoplasma evolution were recorded using a fast-CCD camera. The global kink-mode oscillations were observed as transverse oscillations across the symmetry plane of the magnetoplasma. The arched magnetoplasma (plasma β ≈ 10^-3, Lundquist number ≈ 10²–10⁵, radius/ion-gyroradius ≈ 20, B ≈ 1000 Gauss at footpoints) was created using a lanthanum hexaboride (LaB₆) plasma source and it evolved in an ambient magnetoplasma produced by another LaB₆ source (See Ref. [2] for details). The experiment runs continuously with a 0.5 Hz repetition rate. Hence, plasma parameters were recorded with a good resolution (spatial-resolution/magnetoplasma-length ≈ 10^-2 – 10^-3, temporal-resolution/eruption-time ≈ 10^-3) using movable probes in three-dimensions. Mimicking the behavior of solar eruptions, a long pre-eruption phase (lasting up to 150 Alfvén transit times) was created in the laboratory by gradually increasing the electrical current. This leads to an impulsive eruption of the arched magnetoplasma within 4 Alfvén transit times. The relative magnitudes of the parameters of the arched and ambient magnetoplasma were varied to simulate a variety of conditions relevant to solar eruptions, examine the relevance of the existing models of the kink-mode oscillations, and investigate the dispersion characteristics of the fast wave.

References: (1) Tripathi and Gekelman, Phys. Rev. Lett. 105, 075005 (2010); (2) Tripathi and Gekelman, Solar Phys. 286, 479 (2013)

Figure Caption: Time-evolution of the density-profile of the magnetoplasma showing the pre-eruption, impulsive eruption, and post-eruption phases. The magnetoplasma expands along the negative x-axis. The kink-mode oscillations are indicated in the post-eruption phase.

(Work performed at Basic Plasma Science Facility, UCLA and supported by US DOE and NSF)