Spontaneous ion beam formation in the laboratory, space, and simulation

Abstract

We present experimental evidence for the spontaneous formation of multiple double layers within a single divergent magnetic field structure. Downstream of the divergent magnetic field, multiple accelerated ion populations are observed. The similarity of the accelerated ion populations observed in these laboratory experiments to ion populations observed in the magnetosphere and in numerical simulations suggests that the observation of a complex ion velocity distribution alone is insufficient to distinguish between simple plasma expansion and magnetic reconnection. Further, the effective temperature of the aggregate ion population is significantly larger than the temperatures of the individual ion population components, suggesting that insufficiently resolved measurements could misidentify multiple beam creation as ion heating. Ions accelerated in randomly oriented electric fields that mimic heating would have an ion heating rate dependent on the ion charge and mass that is qualitatively consistent with recent experimental observations of ion heating during magnetic reconnection. V C 2013 AIP Publishing LLC. [http://dx

Magnetospheric Multiscale observations of large‐amplitude, parallel, electrostatic waves associated with magnetic reconnection at the magnetopause

“…The 2‐D Vlasov simulation results indicate that a parallel potential acts to retard magnetosheath electrons from an in‐rush into the magnetosphere, preserving the quasi‐neutral plasma. Such parallel electric fields have been reported from laboratory experiments [e. g. Carr et al ., ] and from several simulations of magnetic reconnections [ Li et al ., ; Egedal et al ., ], albeit these simulations did not include a cold population. The same electric fields appear to accelerate cold electrons from the magnetosphere toward the reconnection site.…”

Experimental investigation of current free double layers in helicon plasmas

“…HELIX Experiments 7,13,15-17 have investigated the time development of the double layer as well as the effect of rf frequency using laser induced fluorescence (LIF) and energy analyzers. In the HELIX experiments, 15,17 which also contains observations of multiple beams, the strength of the DL was about 3k B T e /e, comparable to the DL formed in the free expansion Chi-Kung experiments 8 and slightly weaker than the DL formed in the Magnetic Nozzle Experiment (MNX) experiments 5,18 with a strong magnetic nozzle field. In these experiments, the DL appeared at neutrals pressures such that the ion-neutral collision length was comparable to the scale length of plasma density gradient.…”

“…However, it cannot assure the mechanism whether the presence of two distinguished populations of positive ions is the main cause for the formation of such DLs. Although in most of the cases, [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][20][21][22][23] similarities with the Hairapetian-Stenzel DL are clear there are still relevant differences. This may be described in the following way.…”

“…Some HPDs have recently reported CFDLs in plasmas expanding in a diverging magnetic field. [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] Ions pass through the potential structure of the DL and gain directed energy, and there has been interest in using this directed ion flux as a source of thrust. HELIX Experiments 7,13,15-17 have investigated the time development of the double layer as well as the effect of rf frequency using laser induced fluorescence (LIF) and energy analyzers.…”

Instability limits for spontaneous double layer formation

“…In hindsight, these IVDF measurements are actually the first observations of the spontaneous generation of multiple energy ion beams in an expanding plasma; a discovery our group recently reported in another manuscript. 32 For the same experimental configuration that results in the DL accelerated ion beam, five hundred averages of the power spectrum for the entire 100 ms time series from one tip of the electrostatic probe are shown in Fig. 7.…”