From: Bert Hickman
Date: Thu, 28 Jun 2001 07:49:30 -0500
Subject: Re: [TSSP] Toroid breakdown voltage indirect meas.
Malcolm and Paul, >From one of the other postings: The color of the streamers is indeed bright blue - this is apparently from vibrationally excited nitrogen molecules (created by collisions with free electrons during the avalanche process). As these return to the ground state they emit the characteristic bright blue color. This posting: What happens as the terminal voltage rises is a function of how fast the voltage is replenished and how fast it subsequently rises. Some thoughts on the behavior: 1. If the terminal dv/dt is too slow, we have insufficient displacement current through the leader channel to maintain sufficient leader conductivity, and the e-field at the leader tips collapses below the point where additional streamers can form, and we get no further propagation. This would be the case of an underpowered coil, or one just barely able to break out its top terminal. However, the breakout voltage at the NEXT bang will be lower in the residual heated channel so we might see further leader propagation during the NEXT bang. 2. If dv/dt is optimal: Displacement current through the channel is sufficient to maintain leader conductivity, e-field increases at the leader tip(s), new streamers form, and the leader propagates in another one or more additional "jumps". This process can continue indefinitely with optimal dv/dt... until we finally run out of voltage. 3. If dv/dt is too fast (i.e., resonator can overpower both the topload as well as the capacitive loading from the initial leader): In addition to the original leader, new streamers and leaders may form in other locations around the terminal where the local space charge distribution presents favorable E-field stress. Suspect this is why we get multiple breakout points when we have a topload that's too small, or one that has too small a ROC in a system capable of delivering sufficient power. Ultimately, as the bang energy is diverted/shared amongst multiple leaders, individual leader length is constrained to be significantly less than the optimal case above. This may also be why it's more difficult to get multiple leaders to coalesce in higher frequency systems. I suspect Paul is correct - the capability of the resonator to deliver additional charge and to replenish Vtop is also critical to optimal performance. Best regards, -- Bert -- -- Bert Hickman Stoneridge Engineering Email: bert.hickman@aquila.net Web Site: http://www.teslamania.com Paul wrote: > > I wrote: > > > > What happens when the voltage is raised above the breakout > > > threshold, do you get longer streamers, or just more of them, > > > or both? > > Malcolm Watts wrote: > > > A bit of both. More seems to be the preference though. > > Perhaps that is because the top voltage is being more or less > clamped at the breakout threshold. Further increase of Vpri > is then serving simply to supply more charge, hence generally > more and brighter streamers, rather than longer. The top volts > measurements, when we can do them, will tell. If it turns out > to be the case, then we would have confirmation that coil stored > charge is just as important as topload stored charge in determining > streamer capability. > > Cheers, > -- > Paul Nicholson, > Manchester, UK. > --
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.