Physics of auroral phenomena : proceedings of the 33rd Annual seminar, Apatity, 02 - 05 March, 2010 / [ed.: A.G. Yahnin, A. A. Mochalov]. - Апатиты : Издательство Кольского научного центра РАН, 2011. - 206 с. : ил.

*Physics of Auroral Phenomena", Proc. XXXIIIAnnual Seminar, Apatity, pp. 9 - 1 2 , 2011 / ' л Ч Polar ©Kola Science Centre, RussianAcademy of Science, 2011 \PZfl4 GeoPhVsical W у Institute INFLUENCE OF INTERMITTENСY ON PARTICLE ACCELERATION A.V. A rtem yev12, S.D. Rybalko13, L.M. Z elenyi1and A .A . Petrukovich1 1Space Research Institute (IKI), Moscow, Russia 2 Skobeltsyn Institute o fNuclear Physics o fMoscow State University 3Department o f Physics, Moscow State University Moscow, Russia Abstract. In this paper we constructed an analytical model reproducing the main characteristic of intermittent turbulent electromagnetic field. The comparison between the model and experimental data obtained in the Earth's magnetotail confirms that such model is capable to describe satisfactorily the main observational features of magnetotail turbulence. We investigate the dependence of particle acceleration on the level of intermittency. The obtained results indicate that the efficiency of particles energy gain increases with the growth of this parameter. Moreover, the efficiency of the spatial transport grows with intermittency level slower than efficiency of acceleration. As a result particles can gain more energy travelling the same distance in the intermittent turbulence. This result allows to explain charged particles acceleration up to very high energies in spatially localized areas of turbulent electromagnetic fields. Introduction The appearance of populations of high-energy particles in the Earth's magnetosphere is a common phenomenon [Vasyliunas, 1968; Sarris et al., 1976; Christon et al., 1989]. Along with the acceleration of particles in the vicinity of X-lines [Hoshino, 2005; Drake et al, 2006] and quasi-adiabatic acceleration [Lyons and Speiser, 1982] it is seems that another important mechanism of the formation of these populations is the turbulent acceleration [Zelenyi et al., 2008; Perri et al. 2009; Ono et al., 2009]. However, in the framework of existing models it is difficult to explain the acceleration of particles up to high energies in relatively small localized regions of space. In the model of electromagnetic clouds [Perri et al., 2009] the spatial diffusion is coupled with the diffusion in velocity space and the spatial one appears to be more reped. Similar result was obtained for the model of turbulent electromagnetic field constructed by an ensemble of plane travelling waves [Zelenyi et al., 2008]. Thus, if the turbulent electromagnetic field is localized in the small spatial region, then the particles can not gain sufficiently high energy before leaving this area. Consequently, the observation of particles with sufficiently high energies indicates that the turbulence might have quite different properties than those incorporated in existing models. On the other hand many satellite observations of the magnetic field in the Earth's magnetosphere indicate that it has an intermittent nature [Dudok de Wit and Krasnosel'skikh, 1996; Voros et al., 2004; Petrukovich, 2005]. This peculiarity of turbulence is associated with the presence o f certain regions with significantly different statistical properties in one-dimensional time-series of magnetic field B ftJ. In this paper will investigate the influence of the intermittent electromagnetic turbulence on transport of charched particles both in velocity (acceleration) and configurational space. We show that efficiency of particle acceleration grows with the level of intermittency faster than efficiently o f particle spatial transport. This result allows explaining the acceleration of particles up to high energies in the spatial localised regions with turbulence in the Earth's magnetosphere. Model In this paper we use simple 2D model of turbulent electromagnetic field: particles move in the neutral plane of the Earth magnetotail. Only single component of magnetic field Bz(x,y,t) is taken into account(here the GSM coordinate system is used). Particles move in the plane (x,y) and are accelerated by inductive electric fields Ex and Ey. The intermittency o f field B, can be characterized by means o f the structure function method [Frisch 1995]: S , = l | f i z (rn + A ) - B z ( O f (1) n Let us assume that we draw some straight line in the plane ( x, y ) and start to measure magnetic field along it. Then using the dependence Sp ~ one can plot the power law exponent £p as a function o f p. The difference between function and linear function ~ Cqp can be used to quantity degree of intermittency. Here we should notice that for the classic Kolmogorov turbulence t^p ~ Cop and C0 corresponds to the spatial dimension o f elements forming the turbulence [Frisch, 1995]. In our model field Bz(x,y, t ) is assumed to consist from the superposition of magnetic clouds [Perri et al., 2009] and an ensemble of plane magnetic waves [Zelenyi et a l, 2008].The magnetic cloud model is based on the assumption of the existence of the local structures with the intense magnetic fields. Pulsations o f these structures provide the inductive electric field. For geometry under consideration each magnetic cloud in the plane ( x, y) is defined by two components of vector potential: 9