Small-scale inhomogeneity effects on coherent solar radio emission��--- PIC simulations

1. Motivation

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• Setup

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• Results

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• Conclusion and Discussion

Outline

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• Incoherent emission [Aschwanden, 2002; Nindos, 2020; et al.]
• the total emission of a collection of elections == summing over the emission by single electron
• Types: e.g., synchrotron radiation, bremsstrahlung radiation
• brightness temperature T_B ~ 10⁶ K
• Coherent emission [Aschwanden, 2002; Melrose, 2017; et al.]
• involve some plasma instabilities _{(by non-Maxwellian velocity distributions of particles)},

collective (kinetic) plasma radiation

processes

• high brightness temperature T_B ~ 10⁸ K;
• short-eruptive time scale;
• narrow frequency bandwidth;
• strong polarization
• Types:
• plasma emission
• a nonlinear multi-stage process
• positive parallel velocity gradient u_//*df(u_//)/du_// > 0
• electron cyclotron maser （ECM） emission
• linear wave-electron resonance interaction
• positive perpendicular velocity gradient df(u_⊥)/du_⊥ > 0

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1. Motivation

[Benz, 2004]

1. Motivation --- PIC Simulation

PIC Code: the simulation domain is divided in a grid with many cells, filled with computational particles that can be everywhere.

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Collisionless ---- energy dissipation via wave-particle interactions

1. Motivation --- PIC Simulation + homogeneous Plasma

1. Motivation --- PIC Simulation + inhomogeneous Plasma

2. Setup --- inhomogeneously magnetized equilibrium plasma

2. Setup

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• Incoherent emission [Aschwanden, 2002; Nindos, 2020; et al.]
• the total emission of a collection of elections == summing over the emission by single electron
• Types: e.g., synchrotron radiation, bremsstrahlung radiation
• brightness temperature T_B ~ 10⁶ K
• Coherent emission [Aschwanden, 2002; Melrose, 2017; et al.]
• involve some plasma instabilities _{(by non-Maxwellian velocity distributions of particles)},

collective (kinetic) plasma radiation

processes

• high brightness temperature T_B ~ 10⁸ K;
• short-eruptive time scale;
• narrow frequency bandwidth;
• strong polarization
• Types:
• plasma emission
• a nonlinear multi-stage process
• positive parallel velocity gradient u_//*df(u_//)/du_// > 0
• electron cyclotron maser （ECM） emission
• linear wave-electron resonance interaction
• positive perpendicular velocity gradient df(u_⊥)/du_⊥ > 0

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1. Motivation

[Benz, 2004]

2. Setup

(Lee et al., 2011)

3. Results

Plasma Emission

ECM

3. Results --- electromagnetic waves

Doppler-shifted X1

Whistler

3. Results --- electromagnetic waves

O-mode

Z-mode

2nd harmonics

3. Results --- electromagnetic waves

3. Results --- electromagnetic waves

Zebra pattern structures on 2006 December 13 observed by SBRS/Huairou at 2.6–3.8 GHz and

the illustration of the processes of extracting the zebra pattern stripes (Yu, Nakariakov et al., 2013).

3. Results --- Application (zebra-pattern)

3. Results --- electrostatic waves

• Density gradient in plasma could lead to a wider frequency bandwidth in single harmonic stripe

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• Temperature of the background plasma does, however, not influence much on the excitation of the electromagnetic waves in the solar coronal plasmas.

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• The ECM emission processes are, hence, expected more for the generation of radio burst in the solar corona.

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• It still needs further investigations on whether the nonlinear wave-wave interactions in the the plasma emission mechanism occur to lead excitation of electromagnetic waves under the presence of the forward and backward Langmuir waves in these inhomogeneous plasmas.

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4. Conclusion and Discussion

Thanks for your attention