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Unbalanced forces in a mercury arc?

     The oscillograph below shows a sample run of 1 second. Actual experimental runs varied but were on the order of 10 seconds. The graphs were in all other respects identical so just the calibration run is shown to clarify the pulse sequence and demonstrate the veracity of the circuit.

     On relay closure total voltage rises to 25 volts. 1/10 of a second later the ignitron circuit is strobed and the voltage drops to about 22 volts. The current sense resistor shows peak pulse current to be 136 amps with a few percent variation at the leading edge of the pulse.

Fred Sparber provided the following estimate of the predicted force.

     At 145 amperes and 11.0 volts cathode fall potential an Hg+ ion has a velocity,

v = [2*11.0*1.6E-19/(1.66E-27*200)]^1/2 = 3.256E-3 meters/second

thus a momentum,

mv = 1.66E-27*200*3.256E-3 = 1.08E-21 kg-meters/sec.

For 145 amperes:

F_ ion+ = 1.08E-21*145*6.25E18 = 0.98 newtons

F_electron- = 0.98/600 = 0.0016 newtons

     The experiment was done first with the clip in place, which raised the current somewhat due to the lack of an arc drop. No force was initially noted using 10 sec pulses but some force developed (~1gram) after several shots. This seemed to be due to the shorting wire which got VERY hot as you can imagine. This would not affect the experimental run as the bulk of the ignitron limits temperature rise greatly.

     A second calibration test was performed using a penny. I dropped the penny onto the scale portion of the finished apparatus and noted the scale deflect both in quantity and time until settled. Removing the penny returned the scale to tare, showing that the flexible leads were not suffering from hysteresis. The time to settle was typically between 1 and 2 seconds, due mostly to the digital scale, so 10 sec runs were done for the final live experiment.

     I then removed the shorting wire and allowed the ignitron to carry the discharge current. After a few shots with nothing exploding ( surplus ignitrons being what they are ), I felt confident enough to stick my head around the corner and observe the scale. No unbalanced force was noted to within 1 gram, or about .01 newton. I conclude that if the force is manifesting itself in the arc regime of a mercury tube that a counter force develops on the anode to cancel it to within 1%. Newton would be pleased; Fred however was less than sanguine.

     This experiment should be repeated in the glow and pulsed anomalous glow regimes, as other researchers have suggested that the second regime would be more likely to produce an anomalous force.

     The next page shows some more details of the apparatus.

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