Chapter 1: Introduction

What is plasma?
- ionized gas (~~short but incomplete~~)
- solid/liquid/gas + energy \(\rightarrow\) PLASMA
- PLASMA
  - fully ionized: 100% of atoms are ionized
    - only consist ions & electrons
  - partially ionized: fraction of atoms are ionized
    - consist ions & Electrons & neutral atoms and molecules
Examples of plasmas
- sun, interstellar medium, lightning ......
Plasma temperature
- most behave classically \(\rightarrow\) Boltzmann statistics
  - distribution of particle speed follows Maxwell-Boltzmann distribution
    - \(f(v)=4\pi v^2 n(\frac{m}{2\pi k_B T})^{\frac{3}{2}}\exp(-\frac{mv^2}{2k_B T})\)
    - \(v_p=(\frac{2k_B T}{m})^{\frac{1}{2}}\) (speed at the peak)
    - \(v_{rms}=(\overline{v^2})^{\frac{1}{2}}=(\frac{3k_B T}{m})^{\frac{1}{2}}\) (root mean square speed)
- convert temperature \(K\) into \(eV\):
  - \(=\frac{k_B T}{e}\)
  - \(1.0eV=1.16\times 10^4 K\)
Debye Shielding
- changed spheres electrostatically shielded
- shielding incomplete because charge particles in the high energy tail of the Maxwellian can escape
- Debye Length: \(\lambda_D=(\frac{\epsilon_0 k_B T}{ne^2})^{1/2}\)
  - \(n\) is the density at distance \(>>\lambda_D\)
Plasma Criteria
- macrosopic charge neutrality(quasineutrality)
  - total postive charge = total negative charge
- must show collective behaviour
  - electomagnetic forces dominate over normal hydrodynamics
- to quantify:
  - \(L>>\lambda_D\)
    - \(L\) is plasma dimension
  - the number in a Debye sphere more than 1
    - \(N_D=\frac{4}{3}\pi \lambda_D^3 n_e>>1\)