Lecture 2 - Collisional processes Flashcards
Kinetic temperature is when…
…the elastic scattering rates are fast enough to ensure that the velocity distribution function for particles will be close to a Maxwellian Distribution
When is the three-body collisional rate important?
For population of the high-n levels of atomic hydrogen
When is the impact approximation valid?
When the interaction is weak enough to produce only a small deflection (which is often true)
Interaction energy in collisional processes
Z_1Z_2e^2/b_min
What is the Debye Length
Screening length in plasmas and other conductors
Is the relaxation time for an electron scattered by a proton proportional to that of the same scattered by an electron?
Yes, they are proportional
When are inverse square law forces at play?
When the particles in the interactions both have charges
When are short range forces at play?
When the none of the particles in the interaction is charged (neutral-neutral)
Cross section of hard-sphere scattering (short range force) is on the order of
10^-15 cm^2
Is the rate coefficient for an Ion-Neutral Collision temperature dependent?
No, no temperature dependence is present there.
What’s an Orbiting Trajectory?
A trajectory from an Ion-Neutral process where b < b_0
Why is Ion-Neutral collision rates different from Neutral-Neutral collision rates?
Because the ion polarizes the neutral
Saha’s equation is based on an equation from statistical mechanics. What?
The Law of Mass Action
Saha’s equation assumes
Thermodynamic equilibrium for both collisions and radiation (low temperatures)
