From: Mike Poulton
Subject: Re: Scary, high voltage power supplies. (7Kv, 50A, 50ns, 20Khz)
Date: 11 Nov 2002 01:46:33 GMT
Organization: MTP Technologies
On 09 Nov 2002, Chuck Simmons said:
> I suddenly thought of your 20kHz prf (pulse repetition frequency). You
> need to adjust that downward a lot for various reasons.
No can do. Copper halide lasers need a pair of pulses that close
together to ionize and subsequently excite the lasing medium. What can
be done is to use a pair of pulsing devices triggered 50us apart,
repeating at whatever rate you want. This keeps the rate down for each
individual device, makes cap charging easier, and decreases average
power. Many commercial laser do run at a full 20KHz or more, though,
and they do it with thyratrons. I'm not sure exactly how.
> You also have power constraints. Consider 7000 volt 50 amp pulses at
> 20kHz. With practical switches (other than hard tube) you will have a
> minimum pulse width of around 1 microsecond. This is 0.35 watts for
> 7000 volts and 50 amps averaged over 1 second. With a 20kHz prf, that
> is 7000 watts. I hope the microwave oven you took apart was made to
> cook whole cows in under two minutes! You wanna back that down to
> maybe 1kHz to get into reasonable power levels?
The initial voltage may be 7kV, but it is a capacitor discharge pulse
through a negative-resistance load. The actual current and voltage at
any point during the pulse would be very hard to estimate, and I'm not
sure where he's getting the 50A figure. In order to find the actual
average power, we need to know the capacitance he's using. Running a
copper halide laser at 20kHz is quire practical, and the average power
can be adjusted by changing the storage capacitance. Once commercial
unit uses an even higher rep rate and draws about 2kW.
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