As the featured discharge pattern and widely present in lightning discharge channels, leader corona system is crucial for continuous leader propagations in long air gap discharges and natural lightning, which had attracted numerous studies experimentally or theoretically. In the simulation of discharge process and lightning attachment calculations, the vertex angle of streamer zone ahead of leader channel is the crucial parameter, which could only be obtained by discharge experiments. As a result, morphological researches on leader corona system gave an intuitive insight on the streamer zone ahead of the leader channel and helped comprehensive theoretical modeling studies especially in the calculation of electric field. In order to obtain the accurate shape features and provide the calculation parameter for model modification, in this paper, experiments of 4-m long air gap discharges were carried out based on a four-frame PCO.dicam C4 ICCD camera. Clear images of leader corona were observed. Results showed that the corona zone was assumed as conical and the average angle at the vertex was 75.2° which was less than the first corona during the stable leader propagation stage. Influences of exposure time and leader branching phenomenon were investigated in this paper. It was concluded that the competitive relationship of the branched leaders shrank the vertex angle of the conical corona zone. Results in this paper could instruct the future theoretical model researches on leader corona system and help to modify the existing lightning attachment models like SLIM or leader process model.

Jianwei Gu, Shengxin Huang, Yufei Fu, Weidong Shi, Weijiang Chen. ICCD Images of Leader Corona in a 4 m Rod-Plane Gap Discharge. Academic Journal of Engineering and Technology Science (2022) Vol. 5, Issue 3: 27-32. https://doi.org/10.25236/AJETS.2022.050305.

[1] Arevalo L, Cooray V, Wu D. Laboratory long gaps simulation considering a variable corona region [C] 2010 30th International Conference on Lightning Protection (ICLP), 2010: 1159-1-7.

[2] Gallimberti I. The mechanism of the long spark formation[J]. Le Journal de Physique Colloques, 1979, 40(C7): C7-193-C7-250.

[3] Les Renardières Group. Research on long air gap discharges at Les Renardieres[J]. Electra, Paris, 1972 (23): 53-157.

[4] Gallimberti I, Bacchiega G, Bondiou-Clergerie A, Lalande P. Fundamental processes in long air gap discharges[J]. Comptes Rendus Physique, 2002, 3(10): 1335-1359.

[5] Lebedev V, Feldman G, Gorin B, Shcherbakov Y, Syssoev V, Rakov V. Features of application of image converter cameras for research on lightning and discharges in long air gaps[C]. 26th International Congress on High-Speed Photography and Photonics. 2005, 5580: 887-897.

[6] Chen W J, Zeng R, He H X. Research progress of long air gap discharges[J]. High Voltage Engineering, 2013, 39(6): 1281-1295.

[7] Gu S, Chen W, Chen J, He H, Qian G. Observation of the streamer–leader propagation processes of long air-gap positive discharges[J]. IEEE transactions on plasma science, 2009, 38(2): 214-217.

[8] Zeng R, Chen S. The dynamic velocity of long positive streamers observed using a multi-frame ICCD camera in a 57 cm air gap[J]. Journal of Physics D: Applied Physics, 2013, 46(48): 485201.

[9] Arevalo L, Cooray V, Wu D, Jacobson B. A new static calculation of the streamer region for long spark gaps[J]. Journal of electrostatics, 2012, 70(1): 15-19.

[10] Bondiou A, Gallimberti I. Theoretical modelling of the development of the positive spark in long gaps[J]. Journal of Physics D: Applied Physics, 1994, 27(6): 1252.

[11] Goelian N, Lalande P, Bondiou-Clergerie A,Bacchiega G, Gazzani A, Gallimberti I. A simplified model for the simulation of positive-spark development in long air gaps[J]. Journal of Physics D: Applied Physics, 1997, 30(17): 2441.

[12] Becerra M, Cooray V. A simplified physical model to determine the lightning upward connecting leader inception[J]. IEEE Transactions on Power Delivery, 2006, 21(2): 897-908.