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Exploring streamer variability in experiments

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. Contents. Experimental setup Streamer start and propagation Positive and negative streamers

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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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