Stabilizing effect of ionized background on trans-Alfvenic expansion of exploding plasmas

Summary form only given. Recently a lot of theoretical and numerical calculations have been performed for the study of the large-larmor-flute instability (LLFI). Such instability was discovered initially in the laboratory and later in active experiments (AMPTE, CRRES) on expansion of a quasispherical plasma cloud (with velocity v/sub 0/ and energy E/sub 0/) in a "vacuum" magnetic field B/sub 0/ (i.e. in the sub-Alfvenic regime M/sub A/=v/sub 0//spl radic/(4/spl pi/n/sub */m/sub */)/B/sub 0//spl Lt/1). In our laser-produced plasma experiments at "KI-1" facility it was established for the first time, that such nonMHD instability and LHD-instability of the skin-layer may effectively be suppressed by ionized background at high-Alfven Mach numbers as well as in a transient regime. In the present paper on the basis of laboratory and computer simulation the value of M/sub A/ was defined more exactly and other similarity parameters characterizing the development of LLFI was founded. The laser experiments were realized in hydrogen and argon background plasmas. The computer simulations were carried out with 2D electromagnetic hybrid code (particle ions, fluid electrons). It was exposed the transition from flute increase to decrease one when M/sub A/ changed from M/sub A/=1 to M/sub A/=3.