NON-MONOTONIC DISTRIBUTIONS OF EXCITED ATOMS INPOSITIVE COLUMN OF He DISCHARGES: DYNAMIC PLASMA

DOE Plasma Science CenterControl of Plasma Kinetics

HIGHLIGHT

Radial distribution of excited atoms for different pressure and time during the current pulse.

Simulation: Different Stages of Positive Column in Pulsed Current Regimes

· Nonmonotonic radial distributions of excited helium have been experimentally observed in a pulsed positive column using laser induced fluorescence. Simulations indicate a “dynamic discharge” regime with peculiar properties.

r/r0

-0.5 0.0 0.5

Exc

ited s

tate

de

nsi

ty

0.0

0.2

0.4

0.6

0.8

1.0

11.2 Torr-cm 10 Torr-cm

5.6 Torr-cm 5 Torr-cm

2.3 Torr-cm 1 Torr-cm

Early

Later

Measured 23P Simulated 23S

Cu

rre

nt (A

)

0.0

0.5

1.0

E (

V/c

m)

0

5

10

Time (s)

-50 0 50 100 150 200

kTe (

eV

)

0123

3 Torr-cm, 0.3 Amp10 Torr-cm, 1 Amp

E0

kTe0

(1) (2) (3) (4)

I0

QUASI-PERIODIC MODE HOPPING INCOMPETING IONIZATION WAVES

DOE Plasma Science CenterControl of Plasma KineticsPLSC_0213 HIGHLIGHT

· Neon-ionization-wave normal modes compete as coupled spatiotemporal oscillators modulated by resonant laser light chopped almost synchronously with the subdominant wave mode resulting in indefinite mode hopping.

· The mode-amplitude normalization of the driving term in the differential equations, inherent in driven-oscillator phenomena and responsible for quasi-periodic mode hopping, is validated by experimental observations.

· Amount that spatiotemporal driving-force amplitude MST exceeds temporal driving-force amplitude MT increases as the spatiotemporal entrainment threshold is approached.