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Exploring streamer variability in experiments

This workshop presentation by T.M.P. Briels et al. details experimental findings on the variability of streamers in gaseous media, particularly focusing on the characteristics of positive and negative streamers. Key aspects include experimental setups examining diameter, velocity, and energy dissipation under various pressures and voltage conditions. Findings reveal that positive streamers are generally thicker and faster than negative ones, especially at higher voltages, and present scaling behaviors with pressure. The work culminates in conclusions about streamer evolution, structure, and energetic profiles.

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Exploring streamer variability in experiments

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  1. Exploring streamer variability in experiments T.M.P. Briels, S. Nijdam, G.J.J. Winands, E.M. van Veldhuizen, U. Ebert [T.M.P. Briels, Ph.D. thesis, Dec. 2007] Workshop Leiden, 8-12 October 2007

  2. Contents • Experimental setup • Streamer start and propagation • Positive and negative streamers - diameter - velocity - energy • Scaling with pressure (pos. str.) • diameter • branching structure • Conclusions

  3. Experimental setup New parameter ranges: • Gap: 10-160 mm • Voltage: 5-96 kV • Rise time: 15-150 ns • Pressure: 13-1000 mbar • Pos. and neg. streamers • Point-plane • Air

  4. Time resolved photographs 30 kV, air [Ebert et al, PSST, 15 (2006) S118] needle Exposure: 300 ns 50 ns 10 ns 2 ns (0 < t < 300 ns) (50 < t < 100 ns) (50 < t < 60 ns) (46 < t < 48 ns) 40 mm plate

  5. Streamer start from needle electrode 99.8% N2 : 0.2% O2, 15 mbar, 16 cm gap, 5 kV [0,0.2] [0.2,0.4] tє[0,70 us] [0.4,0.6] [0.6,0.8] E/p = 21 kV/(cm*bar) [0.4,0.7] [0.3,0.7]

  6. Start and propagation • E/p = 16 kV/(cm*bar):40 mm gap, 400 mbar, 25 kV, air, Trise = 25ns • E/p = 22 kV/(cm*bar):30 mm, 613 mbar, 40 kV, synt. air, Trise = 12ns, MIPT tє[0,50 ns] [50,100 ns] [125,175 ns] [125,175 ns] tє[5,10 ns] [10,15 ns] [20,25 ns] [80,85 ns]

  7. Positive and negative streamers air, 1 bar, 40 mm gap, texp = 160 ns positive negative Observations: • Channels form - pos: V Vinception - neg: V Vdc-breakdown • Stability field (= voltage/streamer length) - pos: ~5 kV/cm - neg: ~15 kV/cm 20 kV 20 kV 46 kV 47 kV 83 kV 77 kV

  8. Diameter and velocity needle à • Diameter: dx - FWHM - single streamer - in focus - no return stroke • Velocity: dy/dtexp - dtexp large and small enough dx 40 mm dy plate à R2 = 0, R3 = 4 kOhm, Vp=54 kV, Ip=8 A, texp= 2 ns 050815:43

  9. Positive and negative diameter air, 1 bar, 40 mm gap • Positive 10% thicker than negative but within error margins • For V > 25 kV and short rise times ( 30 ns) streamers become fat(factor 10!) ~ factor 10 ~ factor 2

  10. Positive diameter d and v vary factor 10 in one discharge! • Type 1: d ~ 2.5 mm, v > 1 mm/ns, I ~ 12 A. • Type 2: d ~ 1.2 mm, v ~ 0.5 mm/ns, I ~ 1 A. • Type 3: d ~ 0.2 mm, v ~ 0.1 mm/ns, I ~ 10 mA • Thin: - V ~ Vinception - via branching - seriesresistance [Briels et al, J. Phys. D.: Appl. Phys. 39 (2006) 5201] air, 1 bar, 60 kV

  11. 40 mm Positive and negative velocity air, 1 bar, 40 mm gap • Positive 20% faster than negative ~ factor 8 ~ factor 2

  12. Diameter and velocity • v ~ 0.5*d2 (d varies with applied voltage)

  13. Positive and negative dissipated electrical energy air, 1 bar, 40 mm gap • Energy: • Total: positive more energetic than negative • Primary: equally energetic

  14. Scaling with pressure air, 40 mm gap, 10 kV • Scaling away from electrode [preliminary results: Briels et al, IEEE, 33 (2005) 264]

  15. Scaling of diameter 13-1000 mbar, 10-160 mm gap • air: p*d = 0.20 ± 0.02 mm*bar for thinnest (type 3) streamers

  16. Scaling of branching structure 40 mm gap • Air: D/dmin = 11.6 ± 1.5 D d

  17. Conclusions on streamers in air • Evolution of streamers out of initial cloud • Positive and negative streamers become more alike at higher voltages • For 25 < V < 55 kV and short rise times ( 30 ns) streamers become fat(factor 10) and fast (factor 8). • Scaling minimal streamers: (p*d)/T = 0.2 mm*bar/293K

  18. N2 (99.9%), 40 mm gap, 400 mbar, 16 kV

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