Plasmamedizin at Universität Bochum

pulsed direct current

Circuit is mainly self-contained – target not main counterelectrode

-> Expect smaller (or zero) currents and electric fields at target

1. quasineutral

2. number of particles within Debye sphere >> 1

3. product of plasma frequency and time between collisions with neutrals >> 1 (-> electrostatic forces dominate over collisional interactions)

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- sphere, where potential energy≈ thermal energy, kT (thermal equilibrium with electric field)

- shielding effect -> electric potential decreases by magnitude of 1/e

- momentum transfer

- electronic excitation

- ionisation

- attachment

The medium to be treated is part of the electrical circuit of the plasma source –
target is counterelectrode

-> Expect larger currents and electric fields at target

Corona-, barrier-, radio-frequency-discharges

radio-frequency and glow discharges

Townsend breakdown
- Formation of homogeneous discharge in large volume

Streamer breakdown
- Formation of constricted discharge channels

- The conductive channel does not extend between the two electrodes

- The current from the power supply is limited

- Voltage pulses of ≤ 100s ns are used (precise value depends on conditions)

- Geometry of electrodes means that electric fields are inhomogenous and current
density at one electrode is too low to sustain spark formation i.e. One small
electrode, one large electrode -> corona discharge

- Electrical circuit design (resistance, inductance, capacitance)

- rotational excitation

- vibrational excitation

- dissociation

- dissociative attachment