Dex Dexter wrote:
You need to get a copy of Bazelyan and Raizer, "Spark Discharge", published by CRC Press. It covers most of what you want to know. Perhaps requesting it with interlibrary loan at your local public library would do?Hi, Thanks for the answer. I'm not interested in losses as already said. Neither I'm interested in low repetition rate operation. I'm interested in a VERY high repetition rates with fixed primary energy what (roughly) gives fixed output voltage. If necessary ,4500 pps to be used with 100 khz solid state system. To clarify,you basically say that with generated ~100 kV secondary peaks it's not possible to get more than 5 feet discharge no matter what you do? What would be aproximate maximum for ~200 kV?Dex
First, all the usual breakdown tables and equations only apply to certain special conditions: sphere gaps, rod gaps, uniform fields, etc.
A long spark is none of those. It usually starts with a highly non-uniform field, and continues by propagating that highly non-uniform field as if it were a ever growing wire a few mm in diameter.
The limiting factor on spark growth is getting the new charge to the end of the growing leader fast enough. While the charge is moving (i.e. current flowing in the spark channel), the channel is kept hot by ohmic loss. Eventually enough charge is at the end of the channel that the field at the head of the leader is high enough to exceed the breakdown of air.. the leader jumps forward some amount (determined by the charge it pulls out of the channel behind it), and the process restarts. The TC topload has to have enough charge stored on it to keep feeding the leader at the tail end.
There's a whole lot of limitations on the process that boil down to the power and energy available, which, in turn is determined by the voltage and size of the system.
The speed at which charge can propagate down the leader is determined by the inductance and capacitance of the leader. More current makes a fatter leader, which has less inductance, so the charge can move faster. (because, remember, the spark channel is always cooling, so you have to keep charge flowing in it to keep it hot, if you get behind, the spark dies out)
The energy available to feed the leader is determined by the capacitance of the electrode from which the spark starts and its voltage. A bigger electrode has both more C and more V (because the radius of curvature determines the maximum voltage on the topload). If you try and make a physically large topload, but keep the voltage low, then you run up against the inductance of the topload itself (i.e. the charge can't move from the far side of the topload to the base of the spark fast enough to keep up).
If you had a magic power supply with zero inductance that could feed your electrode at 100kV, you could probably keep the spark growing quite a while, but such power supplies do not exist.
The advantage of higher voltages is that the energy storage goes up as the square, for the same topload. It's even better in real life, because the topload size sets the max voltage before the spark starts.. Double the size of the topload and you have twice the voltage, so you have 8 times the energy stored. yes, the inductance has doubled also, but still, the power (amount of energy the top load can deliver to the growing spark per unit time) is bigger by a factor of 4, which is a "good thing".
_______________________________________________ Tesla mailing list Tesla@xxxxxxxxxxxxxx http://www.pupman.com/mailman/listinfo/tesla