THE EXCITATION OF LOWER-HYBRID WAVES DRIVEN BY THE DEL-B EFFECT IN THE CURRENT SHEET

We have investigated the excitation of electrostatic and electromagnet ic lower hybrid waves in the magnetic field reversal region of the pla sma sheet using a two-fluid approach. We consider a two-dimensional ta il configuration that includes the B-x and B-z magnetic field componen ts and examine the nonlocal properties of lower hybrid modes near the weak field region, where the field B-x(z) reverses sign. We have shown that an electrostatic lower hybrid mode is excited by the magnetic fi eld gradient while electromagnetic modes are driven unstable by the co mbined effects of the magnetic field gradient and the electron fluid d rift across the B-x field. We have shown that the electrostatic and el ectromagnetic lower hybrid modes grow in a few milliseconds and a few tens of milliseconds, respectively, the former for wavelengths shorter than the current sheet width (that is, for k(y) lambda greater than o r equal to 1 where lambda is the current sheet width) and the latter f or long wavelengths (k(y) lambda much less than 1).