Investigations of enhanced emission regions in a dusty plasma H. Tawidian, T. Lecas, T. Gibert, M. Mikikian GREMI, UMR7344 CNRS/Université d’Orléans, 14 rue d’Issoudun, BP6744, 45067 Orléans Cedex 2, FRANCE Plasma regions with an enhanced light emission are easily found in dusty plasmas. They can appear during some instabilities induced by the presence of a high dust particle density, or in the plasma center. In this last case, this region corresponds to the "void" that is a dust-free region. In this paper, experimental characterizations of these two kinds of regions are presented. Experiments are performed in the PKE-Nefedov reactor where Ar or Kr plasmas are produced by a capacitively-coupled radio-frequency discharge with a typical power of about 3 W at a pressure around 1.6 mbar. Dust particles are grown by sputtering a polymer layer previously deposited on the electrodes [1]. Regions of enhanced light emission during dusty plasma instabilities When a high density of dust particles is grown in a plasma, the plasma equilibrium is dras- tically disturbed. Indeed, dust particles attach many plasma free electrons that are no more available to sustain the discharge. In these conditions, the plasma enters in an unstable state characterized by many different types of low-frequency instabilities. Their shape and frequency evolve as dust particles are growing and they can be evidenced on all the plasma or discharge parameters. These instabilities have been observed in several experiments where they are char- acterized by the filamentary or great void modes [2], or they are called dust particle growth instabilities (DPGI) [3, 4]. During DPGI, a particular behavior has been observed that consists of plasma spheroids appearing close to the electrodes [5, 6] or in the plasma bulk. In this paper, a special attention is paid to the plasma spheroids in the plasma bulk. These delimited regions of enhanced light emission have a size of a few mm and appear stochastically in between the elec- trodes. They have been recently observed in a Kr plasma as shown in Fig. 1 presenting images taken with a high-speed camera at 16000 frames per second. The electrodes (separated by about 3 cm) correspond to the dark regions on the top and bottom of each frame. The plasma spheroids are the bright plasma regions appearing in between the electrodes. They are often observed by pair, and they have a comet-like shape as well-evidenced in image 150. These spheroids are observed during dust particle growth and the question of their composition is posed: they can contain just plasma (like the "void") or plasma and dust particles. At the moment, no clear ex- perimental indication allows to select one of these possibilities. In Fig. 1, small spheroids are also observed very close to the electrodes [5, 6] but will not be discussed in this paper. 39 th EPS Conference & 16 th Int. Congress on Plasma Physics O2.304