Laboratory demonstration of slow rise to fast acceleration of arched magnetic flux ropes

Abstract

We demonstrate the slow rise to fast acceleration of an arched plasma‐filled magnetic flux rope. The flux rope expansion is inhibited by an externally applied customizable strapping field. When the strapping field is not too strong and not too weak, expansion forces build up while the flux rope is in the strapping field region. When the flux rope moves to a critical height beyond the peak strapping field region, the plasma accelerates quickly corresponding to the observed slow rise to fast acceleration of solar eruptions. This behavior is in agreement with the predictions of the torus instability.

Apex Dips of Experimental Flux Ropes: Helix or Cusp?

“…However, a particular feature common to several of these experiments (Hansen & Bellan 2001;Stenson & Bellan 2012;Tenfelde et al 2014;Ha & Bellan 2016) has not been well understood. This feature is a downward dip present at the loop apex as shown in Figure 1(a).…”

“…Third, kink modes should grow but the dip remains a constant size. Lastly, the dip feature only appears in certain experiments (Hansen & Bellan 2001;Arnold et al 2008;Stenson & Bellan 2012;Ha & Bellan 2016), but not in others with similar physics (Tripathi & Gekelman 2013;Myers et al 2016). An alternative to the helical interpretation is that the dip is a sharp downward cusp, but this interpretation has no obvious formation mechanism and has consequently not been considered until now.…”

“…Experiments are relevant because the MHD equations have no intrinsic length scale and can be expressed in a nondimensional fashion. Many mechanisms for flux rope stability (Hansen & Bellan 2001;Ha & Bellan 2016;Myers et al 2016), formation (Bellan 2003;Stenson & Bellan 2012;Tripathi & Gekelman 2013), particle acceleration (Tripathi et al 2007), and reconnection (Hansen et al 2004) have been discovered and tested in these experiments.…”

“…Several experiments (Hansen & Bellan 2001;Hansen et al 2004;Stenson & Bellan 2012;Tripathi & Gekelman 2013;Tenfelde et al 2014;Ha & Bellan 2016;Myers et al 2016) have sought to improve the understanding of solar flux ropes by recreating scale models in the laboratory. Experiments are relevant because the MHD equations have no intrinsic length scale and can be expressed in a nondimensional fashion.…”

“…and are especially relevant to the morphology of solar eruptions. Furthermore, other plasma experiments that use FGVs (Hansen & Bellan 2001;Milanese et al 2006;Stenson & Bellan 2012;Suzuki-Vidal et al 2013;Onchi et al 2014;Raman et al 2014;Tenfelde et al 2014;Loebner et al 2015;Ha & Bellan 2016) should be aware of the potential for nonlinear interaction between multiple gas valves.…”