Vortices and flux ropes in Electron MHD plasmas I

Laboratory experiments are reviewed which demonstrate the existence and pro perties of three-dimensional vortices in Electron MHD (EMHD) plasmas. In th is parameter regime the electrons form a magnetized fluid which is charge-n eutralized by unmagnetized ions. The observed vortices am time-varying flow s in the electron fluid which produce currents and magnetic fields, the lat ter superimposed on a uniform de magnetic field B-0. The topology of the ti me-varying flows and fields can be described by linked toroidal and poloida l vector fields with amplitude distributions ranging from spherical to cyli ndrical shape. Vortices can be excited with pulsed currents to electrodes, pulsed currents in magnetic loop antennas, and heat pulses, The vortices pr opagate in the whistler mode along the mean held B-0. In the presence of di ssipation, magnetic self-helicity and energy decay at the same rate. Revers al of B-0 or propagation direction changes the sign of the helicity. Helici ty injection produces directional emission of vortices. Reflection of a vor tex violates helicity conservation and field-line tying. Part I of two comp anion papers reviews the linear vortex properties while the companion Part II describes nonlinear EMHD phenomena and instabilities.