Spectra of Magnetic Turbulence in a Relativistic Plasma

Abstract

We present a phenomenological and numerical study of strong Alfvénic turbulence in a magnetically dominated collisionless relativistic plasma with a strong background magnetic field. In contrast with the nonrelativistic case, the energy in such turbulence is contained in magnetic and electric fluctuations. We argue that such turbulence is analogous to turbulence in a strongly magnetized nonrelativistic plasma in the regime of broken quasi-neutrality. Our 2D particle-in-cell numerical simulations of turbulence in a relativistic pair plasma find that the spectrum of the total energy has the scaling k −3/2, while the difference between the magnetic and electric energies, the so-called residual energy, has the scaling k −2.4. The electric and magnetic fluctuations at scale ℓ exhibit dynamic alignment with the alignment angle scaling close to cos ϕ ℓ ∝ ℓ 1 / 4 . At scales smaller than the (relativistic) plasma inertial scale, the energy spectrum of relativistic inertial Alfvén turbulence steepens to k −3.5.

MHD turbulence: a biased review

“…Of this, relativistic turbulence has indeed been found guilty, provided it was stirred up with δB ∼ B 0 (Zhdankin et al 2017;Comisso & Sironi 2018). The most recent spate of papers on this topic, which represent the state of the art and from which the historical paper trail can be followed, are Comisso & Sironi (2021), Vega et al (2022b); Vega, Boldyrev & Roytershteyn (2022a), Hankla et al (2022) (imbalanced turbulence), Nättilä & Beloborodov (2022) (small δB/B 0 , no non-thermal acceleration), Zhdankin, Uzdensky & Kunz (2021) (non-unity mass ratio, ion vs. electron heating), and Chernoglazov, Ripperda & Philippov (2021) (alignment and current sheets in fluid but relativistic MHD turbulence). It is interesting that in this context again, reconnecting structures spontaneously generated by turbulence appear to play a prominent rolethis time as sites of particle acceleration.…”

“…The most recent spate of papers on this topic, which represent the state of the art and from which the historical paper trail can be followed, are Comisso & Sironi (2021), Vega et al. (2022 b ); Vega, Boldyrev & Roytershteyn (2022 a ), Hankla et al. (2022) (imbalanced turbulence), Nättilä & Beloborodov (2022) (small , no non-thermal acceleration), Zhdankin, Uzdensky & Kunz (2021) (non-unity mass ratio, ion vs. electron heating), and Chernoglazov, Ripperda & Philippov (2021) (alignment and current sheets in fluid but relativistic MHD turbulence).…”

Turbulence and Particle Acceleration in a Relativistic Plasma

“…Recently, attention has been drawn to particle acceleration by turbulence and specifically, magnetically dominated turbulence, which may provide a complementary or alternative mechanism to previously studied acceleration processes (Zhdankin et al 2017(Zhdankin et al , 2018a(Zhdankin et al ,b, 2019(Zhdankin et al , 2021Comisso & Sironi 2018, 2021, 2022Wong et al 2020;Nättilä & Beloborodov 2021, 2022Trotta et al 2020;Vega et al 2022a;Bresci et al 2022). Kinetic numerical simulations indicate that turbulence accelerates particles to ultra-relativistic energies, with powerlaw energy distribution functions.…”

Spatial Intermittency of Particle Distribution in Relativistic Plasma Turbulence

“…Recently, attention has been drawn to particle acceleration by turbulence and specifically, magnetically dominated turbulence, which may provide a complementary or alternative mechanism to previously studied acceleration processes (Zhdankin et al 2017(Zhdankin et al , 2018a(Zhdankin et al , 2018bComisso & Sironi 2018Zhdankin et al 2019;Trotta et al 2020;Wong et al 2020;Comisso & Sironi 2021;Nättilä & Beloborodov 2021;Zhdankin et al 2021;Vega et al 2022a;Comisso & Sironi 2022;Bresci et al 2022;Nättilä & Beloborodov 2022). Kinetic numerical simulations indicate that turbulence accelerates particles to ultrarelativistic energies, with power-law energy distribution functions.…”