Download Streamer discharges in High magnetic fields F. Manders 1 , P

Streamer discharges in High magnetic fields
F.
1
Manders ,
P.
2
Christianen ,
J.
2
Maan
1: Philips Lighting B.V., Advanced Development Lighting, P.O. Box 80020, 5600 JM Eindhoven, The Netherlands
2: University of Nijmegen, high field magnet laboratory, Toernooiveld 7, 6525 ED Nijmegen, The Netherlands
Point to plate measurements in nitrogen with –40 kV
Introduction
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
The calculated paths for a streamer for
different QH and the measured path
Experimental results
• Changing magnetic field direction,
chances the direction of the curvature
400 Torr -40 kV magnetic fields different direction • 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
T
400 Torr positive voltage 40 kV
T
Conclusions
•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