model

1. Introduction Point to plate measurements in nitrogen with –40 kV All experiments are done in a nitrogen atmosphere with a point to plate geometry. The distance between the point and plate is 15 mm. We used a ICCD camera which has a gate time of 5 nsec. and it can only take one image per discharge. With a good timing it is possible to gate the camera in such a way that we can see the starting of the discharge and by changing the delay time follow the whole development of the discharge as can be seen in figure to the left side. Results without magnetic field • The higher the pressure the slower the discharge • The higher the pressure the more branching • The lower the pressure the more diffuse the streamer tip is (see the figure on the left side at 200 Torr) • Negative streamers branch more then positive streamers The calculated paths for a streamer for different QH and the measured path model 200 Torr , -40 kV different magnetic fields • There is a Lorentz force on a charged particle • F = q(E + v x B) • constant drift, perpendicular to B and E • The drift motion for particle with a collision time t: • mv = -eE – ev x B – mv/t • rewriting to: • tanqH = eBt/m • In a pure radial electric field a particle always makes the same Hall angle with the local, radial directed electric field qH The calculated paths for a streamer for different QH and the measured path qH Experimental results qH • Changing magnetic field direction, chances the direction of the curvature • Changing direction of the electric field, has no influence • Amplitude of the electric field has no influence on the curvature • It is possible to simulated the streamer path by calculating the direction of the electric field in every point and adding qH 400 Torr -40 kV magnetic fields different direction T Conclusions 400 Torr positive voltage 40 kV • The path of a streamer in magnetic field can be described by a particle which always makes the same Hall angle with the local, radial directed electric field • Field enhancement after streamer formation indeed leads to a new propagation direction • Photoionization does not play a mayor role in the direction where the discharge is growing, otherwise the discharge would go straight ahead in a magnetic field (magnetic field does not have any influences on Photons) • More details see: http://webdoc.ubn.kun.nl/mono/m/manders_g/condtoint.pdf T