SOLAR ELECTRON-BEAMS ASSOCIATED WITH RADIO TYPE-III BURSTS - PROPAGATION CHANNELS OBSERVED BY ULYSSES BETWEEN 1 AND 4 AU

Solar and interplanetary type III (TIII) radio bursts 1. are produced by solar electron beams of flare origin streaming away in the interpla netary medium. The radio emission process implies the excitation of La ngmuir waves by the electron beam which are converted by non linear pr ocesses into transverse electro-magnetic waves. The study of the beam properties reveals information about their propagation regime in the i nterplanetary medium. The local plasma condition observed in the vicin ity of the radio emission zone are important in understanding the Lang muir waves excitation process and their conversion into electromagneti c radiation as well as the propagation of the electron beams. Interpla netary TIII have therefore long been studied for either of theses aspe cts but only for few isolated cases could the three aspects of such ev ents be studied together. This paper presents for the first time a com plete study of the three aspects of nine interplanetary TIII events ob served by the radio, particle and plasma experiments aboard the Ulysse s spacecraft between 1.3 and 4.3 AU. The main result of this study is to establish that the interplanetary medium contains well beyond 1 AU 'propagation channels' previously identified around 1 AU. Those plasma structures an rooted in solar corona and seem to channel the propagat ion of solar electron beams. They have been identified in each of the nine events studied here; Langmuir waves and almost scatter-free propa gation of the solar electrons were observed while the spacecraft was c rossing these formations. Plasma properties of the 'propagation channe ls' have been studied: their main characteristic is a very low level o f magnetic field fluctuation. This property may be at the origin of a stabilization process of the plasma inside the channels explaining why they are maintained on such large distances as well as a key element in understanding the particle propagation regime and Langmuir waves ex citation observed inside. The implications on the medium distance (1-5 AU) heliosphere are also discussed.