Aleksey Kuritsyn

Electromagnetic Fluctuations during Fast Reconnection in a Laboratory Plasma

Experimental evidence for a positive correlation is established between the magnitude of electromagnetic fluctuations up to the lower-hybrid frequency range and enhancement of reconnection rates in a well-controlled laboratory plasma. The fluctuations belong to the right-hand polarized whistler wave branch, propagating obliquely to the reconnecting magnetic field, with a phase velocity comparable to the relative drift velocity between electrons and ions. The measured short coherence lengths indicate their strongly nonlinear nature.

Experimental study of two-fluid effects on magnetic reconnection in a laboratory plasma with variable collisionality

This article describes the recent findings on two-fluid effects on magnetic reconnection in plasmas with variable collisionality in the magnetic reconnection experiment (MRX) [M. Yamada et al., Phys. Plasmas 4, 1936 (1997)]. The MRX device has been upgraded to accommodate a variety of reconnection operation modes and high energy density experiments by increasing its capacitor bank energy and extending the discharge duration. As our experimental operation regime has moved from the collisional to the collision-free, two-fluid effects have become more evident. It is observed that the two-dimensional profile of the neutral sheet is changed significantly from the rectangular shape of the familiar Sweet-Parker type to a double wedge shape as the collisionality is reduced and the reconnection rate increases. The recent evolution of our experimental research from the magnetohydrodynamics (MHD) to the two-fluid analysis is presented to illuminate the physics of Hall MHD in a collision-free reconnection layer. In p...

Measurements of the parallel and transverse Spitzer resistivities during collisional magnetic reconnection

Plasma resistivity has been studied experimentally in a reconnecting current sheet. Resistivities during collisional reconnection, when the electron mean free path is much shorter than the current sheet thickness, in the presence and absence of the guide field are found to be in a good agreement with the parallel and transverse Spitzer values, respectively.

Equilibrium and stability studies of oblate field-reversed configurations in the Magnetic Reconnection Experiment

The equilibrium and stability of oblate field-reversed configurations (FRCs) have been studied in the Magnetic Reconnection Experiment [M. Yamada et al., Phys. Plasmas 4, 1936 (1997)]. In the absence of a passive stabilization, tilt and shift instabilities often become unstable, with the tilt in particular limiting the plasma lifetime. The tilt instability can be mitigated by either including a passive stabilizing conductor, or by forming very oblate plasmas. Large perturbations (n=2 and 3) may still remain after passive stabilization is applied. These perturbations have the characteristics of co-interchange modes, which have never been observed, and can lead to the early termination of the plasma. The co-interchange modes can be minimized through the formation of plasmas with a very oblate shape, leading to the maximum FRC lifetime. A code has been developed to calculate equilibria for these plasmas. A rigid-body model explains the improved stability of oblate plasmas to n=1 tilt modes. Numerical calcula...

Measurements of Magnetic Fluctuations in Magnetic Reconnection Experiment

Magnetic reconnection plays an important role in determining the evolution of magnetic topology in laboratory and astrophysical plasmas. A central question concerns why the observed reconnection rates are much faster than predictions made by classical theories, such as the Sweet‐Parker model based on MHD with classical Spitzer resistivity. Often, the local resistivity is conjectured to be enhanced by micro‐instabilities to accelerate reconnection rates either in the context of the Sweet‐Parker model or by facilitating setup of the Pestchek model. Although it is commonly believed that there is plenty of free energy available at the reconnection region to destabilize some sort of micro‐instability, a clear identification of this instability and its exact role in reconnection has never been established experimentally. We report the first such experimental evidence of a clear and positive correlation between magnetic fluctuations in the lower‐hybrid frequency range and resistivity enhancement during fast reco...

Development of the Megahertz Planar Laser-induced Fluorescence Diagnostic for Plasma Turbulence Visualization

A megahertz LIF-based diagnostic system for measuring ion density fluctuations in two spatial dimensions is described. Well resolved spatial and temporal 2D images of turbulent structures will be useful in understanding ion turbulence in magnetically confined plasmas which is a key factor in the performance of fusion experimental devices. A sheet beam of a megahertz repetition rate tunable Alexandrite laser is used to excite ion emission from argon plasma. The fluorescence emitted from the plane of the laser beam is detected with a narrow band interference filter and intensified ultra-fast CCD camera providing 2D images of relative ion density fluctuations every microsecond. It is expected that the edge plasma on fusion devices will be accessible to this technique.

Experimental Verification of the Hall Effect during Magnetic Reconnection in a Laboratory Plasma

In this letter we report a clear and unambiguous observation of the out-of-plane quadrupole magnetic field suggested by numerical simulations in the reconnecting current sheet in the Magnetic Reconnection Experiment (MRX). Measurements show that the Hall effect is large in collisionless regime and becomes small as the collisionality increases, indicating that the Hall effect plays an important role in collisionless reconnection.

Study of Magnetic Reconnection in a Laboratory Experiment

This paper reviews the most recent findings of the laboratory experiment which address the local physics of magnetic reconnection, and related physics issues. In particular, physics analysis of the experimental data from Magnetic Reconnection Experiment (MRX) based on the one‐fluid MHD and the two‐fluid MHD formulations are comparatively highlighted. Major results are: (1) Reduced magnetic reconnection rate measured with externally applied guide field, (2) Experimental verification of Hall MHD effects in the Harris‐type neutral sheet, with the width comparable to the ion skin depth, during magnetic reconnection, (3) Recognition of correlation between magnetic turbulence and reconnection rate, and (4) Discussions with regard to scalings for magnetic reconnection observed in MRX, particularly on the transition from the collisional to the collisionless regime. This paper also briefly discusses the basic goals and approaches of the new initiatives to study magnetic reconnection as a part of magnetic self‐orga...