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Lecture 2: Physical Processes In Astrophysical and Laboratory Plasmas

Lecture 2: Physical Processes In Astrophysical and Laboratory Plasmas. Lecture 1: Temperature-Density regime Many physical processes Focus on Atomic+Plasma interactions Atomic properties are intrinsic , independent of external factors (temp, den, etc.)

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Lecture 2: Physical Processes In Astrophysical and Laboratory Plasmas

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  1. Lecture 2: Physical Processes InAstrophysical and Laboratory Plasmas • Lecture 1: Temperature-Density regime • Many physical processes • Focus on Atomic+Plasma interactions • Atomic properties are intrinsic, independent of external factors (temp, den, etc.) • Plasma interactions are treated as extrinsic • Approximation:  Isolated atoms perturbed by environment

  2. Quantum Statistical Equilibrium • Division between atomic and plasma physics • Calculation of individualatomic parameters – Chs. 2-7  Hartree-Fock, Close-Coupling (R-Matrix), etc.  Radiative and collisional properties  Transition probabilities and cross sections • External statistical equilibrium of particles • Local-Thermodynamic-Equilibrium (LTE)  characterized by local temperature-density  Saha ionization balance, Boltzmann level population  Boltzmann-Saha distribution • Non-LTE requires explicit particle-radiation coupling  Collisional-Radiative model (simple) – Ch. 8: Emission lines  Multi-level radiative transfer model (complex) – Ch. 9: Absorption

  3. Collisional-Radiative(CR) Models • Section 8.2 and Fig. 8.7 • Need excitation and radiative parameters, viz.  Electron impact cross sections (E): Ch. 5 – EIE  Maxwellian averaged rate coefficients (T)  Eq. (5.31)  A-values and oscillator strengths  Ch. 4 – Radiative Transitions • Other processes such as fluorescent excitation by background radiation field may be included

  4. Coupled CR Rate Equations • Level Populations, emissivity, line ratios  Section 8.1.3 • Examples: [O II], [S II] forbidden lines • He-like X-ray lines: Section 8.4, Fig. 8.7 • General time-dependent rate equation  Eq. (8.41) • Transient emission spectra (e.g. black-hole accretion disk x-ray flares): Fig. 8.13

  5. Non-LTE Radiative Transfer Models • Ch. 9: Absorption lines and radiative transfer • Consider radiation-matter coupling explicitly • For each photon frequency, specify monochromatic source function S  monochromatic opacity and emissivity • Section 9.4: Radiative transfer

  6. Optical Depth • Definition: Fig. 9.9 and Eq. (9.118) • Basic radiative transfer equation: Eq. (9.119) • Absorption and emissivity coefficients • Source function: Eq. (9.126) • S  Einstein A,B coefficients

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