We present an analysis of the energy partitioning in the magnetotail during a substorm at 03:58:00 UT on 7 February 2009. The analysis employs a multiscale approach where we use a state from a global magnetohydrodynamics (MHD) model to spawn a kinetic particle‐in‐cell (PIC) simulation of a large portion of the tail. We directly investigate the energy fluxes resulting from magnetic reconnection. The kinetic run provides information on the additional processes absent in the MHD description. The ion bulk energy and enthalpy fluxes carry the greatest energy, but the Poynting flux and electron enthalpy flux also carry a significant portion. The other fluxes (e.g., heat flux) are relatively small but are especially important because they allow us to identify the extra processes present only in the kinetic description. The energy fluxes present in the MHD approximation (Poynting flux, enthalpy flux, and bulk energy flux) are quantitatively accurate, and the kinetic correction does not greatly alter the MHD picture. However, there are two unique effects resulting from the kinetic physics. First, the formation of a rarefaction of the plasma flow into the reconnection site leads to a progressive decline in time of the particle energy fluxes with respect to the Poynting flux. Second, we observe that the instabilities developing in the kinetic reconnection outflows form structures absent from the MHD description. These structures reveal themselves as fluctuations within the energy fluxes. Especially notable are regions of inverted heat flux, where the heat flux is in the opposite direction to the total energy and mass flow.
Using incoherent Thomson scattering, electron heating and acceleration at the electron velocity distribution function (EVDF) level are investigated during electron-only reconnection in the PHAse Space MApping (PHASMA) facility. Reconnection arises during the merger of two kink-free flux ropes. Both push and pull type reconnection occur in a single discharge. Electron heating is localized around the separatrix, and the electron temperature increases continuously along the separatrix with distance from the X-line. The local measured gain in enthalpy flux is up to 70% of the incoming Poynting flux. Notably, non-Maxwellian EVDFs comprised of a warm bulk population and a cold beam are directly measured during the electron-only reconnection. The electron beam velocity is comparable to, and scales with, electron Alfvén speed, revealing the signature of electron acceleration caused by electron-only reconnection. The observation of oppositely directed electron beams on either side of the X-point provides “smoking-gun” evidence of the occurrence of electron-only reconnection in PHASMA. 2D particle-in-cell simulations agree well with the laboratory measurements. The measured conversion of Poynting flux into electron enthalpy is consistent with recent observations of electron-only reconnection in the magnetosheath [Phan et al., Nature 557, 202 (2018)] at similar dimensionless parameters as in the experiments. The laboratory measurements go beyond the magnetosheath observations by directly resolving the electron temperature gain.
more » « less- NSF-PAR ID:
- 10363359
- Publisher / Repository:
- American Institute of Physics
- Date Published:
- Journal Name:
- Physics of Plasmas
- Volume:
- 29
- Issue:
- 3
- ISSN:
- 1070-664X
- Page Range / eLocation ID:
- Article No. 032101
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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