Stochastic Acceleration of Electrons and Protons. I. Acceleration by Parallel-Propagating Waves

By V. Petrosian, Siming Liu. 2004

190 citations recorded by the source corpus.

Stochastic acceleration of electrons and protons by waves propagating parallel to the large-scale magnetic fields of magnetized plasmas is studied with emphasis on the feasibility of accelerating particles from a thermal background to relativistic energies and with the aim of determining the relative acceleration of the two species in one source. In general, the stochastic acceleration by these waves results in two distinct components in the particle distributions, a quasi-thermal and a hard nonthermal, with the nonthermal one being more prominent in hotter plasmas and/or with higher level turbulence. This can explain many of the observed features of solar flares. Regarding the proton-to-electron ratio, we find that in a pure hydrogen plasma the dominance of the wave-proton interaction by the resonant Alfvén mode reduces the acceleration rate of protons in the intermediate energy range significantly, while the electron-cyclotron and Whistler waves are very efficient in accelerating electrons from a few keV to MeV energies. The presence of such an acceleration barrier prohibits the proton acceleration under solar flare conditions. This difficulty is alleviated when we include the effects of 4He in the dispersion relation and the damping of the turbulent waves by the thermal background plasma. The additional 4He cyclotron branch of the turbulent plasma waves suppresses the proton acceleration barrier significantly, and the steep turbulence spectrum in the dissipation range makes the nonthermal component have a near power-law shape. The relative acceleration of protons and electrons is very sensitive to a plasma parameter α = ωpe/Ωe, where ωpe and Ωe are the electron plasma frequency and gyrofrequency, respectively. Protons are preferentially accelerated in weakly magnetized plasmas (large α). The formalism developed here is applicable to the acceleration of other ion species and to other astrophysical systems.

Subfields: Astronomy and Astrophysics, Atomic and Molecular Physics, and Optics

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Citations in the corpus

Space weather: the solar perspective (2021, background): “Figure 4 sketches three different time steps in the evolution of an eruptive flare event, causing a CME and SEPs, as a consequence of magnetic reconnection (see Petrosian and Liu 2004; Lin and Forbes 2000; Mikić and Lee 2006).”
On the Momentum Diffusion of Radiating Ultrarelativistic Electrons in a Turbulent Magnetic Field (2008, background): “…integrated (over the turbulent region) one-dimensional particle momentum distribution, n( p; t) 4 p2h f ( p; t)i, is obtained from (see, e.g., Petrosian & Liu 2004) @n( p; t) @t ¼ @ @p D( p) @n( p; t) @p @ @p 2D( p) p þ h ṗi n( p; t) n( p; t) tesc þ Q̃( p; t): ð2Þ Let us further assume the…”
A UNIFIED COMPUTATIONAL MODEL FOR SOLAR AND STELLAR FLARES (2015, background): “Even though direct evidence of their presence is scarce, models of particle acceleration predict that lower energy ions ( 1 MeV) will be accelerated –albeit on longer time scales than electrons (Petrosian & Liu 2004).”
An Observational Overview of Solar Flares (2011, background): “Other than high density and magnetic trapping, turbulence or plasma waves (e.g., Benz 1977; Miller et al. 1996; Petrosian & Liu 2004), generated as a consequence of magnetic reconnection, provide an alternative mechanism that could accelerate electrons and, at the same time, confine them to the…”
Hard X-ray emission from the solar corona (2008, methodology): “For closed coronal regions, possible processes include stochastic acceleration by MHD turbulence, either fast or Alfvénic: (e.g., Miller and Ramaty 1987; Miller and Roberts 1995; Miller 1997; Hamilton and Petrosian 1992; Petrosian and Liu 2004) or stochastic current sheets (Turkmani et al 2005, 200”
Double Coronal Hard and Soft X-Ray Source Observed by RHESSI: Evidence for Magnetic Reconnection and Particle Acceleration in Solar Flares (2007, methodology): “This observation, in the framework of the stochastic acceleration model developed by Hamilton & Petrosian (1992) and Petrosian & Liu (2004), supports the scenario (Figure 9) that a higher turbulence level and thus more acceleration and less heating are located closer to the reconnection site.”
Recent Advances in Understanding Particle Acceleration Processes in Solar Flares (2011, background): “Some of the high-energy particles may be trapped in the corona by plasma turbulence (e.g., Petrosian & Liu 2004) and/or by magnetic mirroring (e.g., Melrose & White 1979; Leach 1984;Somov & Kosugi 1997), to produce hard X-ray (HXR) looptop sources (e.g., Masuda et al. 1994; Petrosian et al. 2002;…”
Stochastic Acceleration by Turbulence (2012, unknown): “On the middle panel we show variation of R1 (from Petrosian & Liu, 2004, PL04) with energy for several values of µ for both electrons and protons interacting with parallel propagating plasma waves.”
Impulsive Phase Flare Energy Transport by Large-Scale Alfvén Waves and the Electron Acceleration Problem (2007, background): “> i (e.g., Miller & Ramaty 1987; Hamilton & Petrosian 1992; Yan & Lazarian 2002; Petrosian & Liu 2004).”
Ion heating resulting from pickup in magnetic reconnection exhausts (2009, background): “D [Onofri et al., 2006] and with magnetohydrodynamic waves [Miller, 1998; Petrosian and Liu, 2004] have been proposed.”
A study of solar energetic particle events of 1997–2006: Their composition and associations (2010, background): “Petrosian and Liu [2004] suggested that proton acceleration might be more efficient in the later phases of flares because of a higher gas density in the coronal flare loops.”
PLASMOID EJECTIONS AND LOOP CONTRACTIONS IN AN ERUPTIVE M7.7 SOLAR FLARE: EVIDENCE OF PARTICLE ACCELERATION AND HEATING IN MAGNETIC RECONNECTION OUTFLOWS (2013, background): “…the gyro-radii of background particles) at some distance from the reconnection site, turbulence can accelerate the particles and heat the plasma (Hamilton & Petrosian 1992; Miller et al. 1996; Chandran 2003; Petrosian & Liu 2004; Petrosian et al. 2006; Jiang et al. 2009; Fleishman & Toptygin 2013).”
A MAGNETIC RECONNECTION MECHANISM FOR ION ACCELERATION AND ABUNDANCE ENHANCEMENTS IN IMPULSIVE FLARES (2009, background): “…unknown although models based on particle interaction with multiple magnetic islands in two dimension (Matthaeus et al. 1984; Kliem 1994; Shibata & Tanuma 2001) and three dimension (Onofri et al. 2006) and with magnetohydrodynamic waves (Miller 1998; Petrosian & Liu 2004) have been proposed.”
Cosmic-Ray Propagation: Nonlinear Diffusion Parallel and Perpendicular to Mean Magnetic Field (2007, background): “In addition, stochastic acceleration by the MHD turbulence is a promising mechanism for generating high energy particles during solar flares (see, e.g., Petrosian & Liu 2004, and references therein).”
Compressible turbulence in galaxy clusters: physics and stochastic particle re-acceleration (2007, background): “…acceleration of particles in many astrophysical environments, e.g. Solar wind, Solar flares, ICM, gamma-ray bursts (see Schlickeiser & Miller 1998; Chandran 2003; Brunetti et al. 2004; Petrosian & Liu 2004; Cho & Lazarian 2006; Petrosian et al. 2006; Becker, Le & Dermer 2006; Dogiel et al. 2007).”