Question

I am taking some measurements concerning a vacuum based X-ray tube. One has to ramp up the voltage slowly in a process called conditioning of the tube. Without allowing a current to flow along the cathode filament, one observes nevertheless a (leak) current due to field emission (FE) and other processes due to (FE). The measurements I take are this current and the voltage. Along the voltage augmentation (in the order of some hundreds of kV) one observes regularly voltage breakdowns. It's ubiquitous that during such a breakdown the current increases and the voltage decreases rapidly. I need to show what these voltage breakdowns are due to. In particular, I need to show if the measurements are in line with the Fowler-Nordheim plot.What is the usual way to present the Fowler-Nordheim plot given the data I have? Which part of the data should I plot, i.e. only the voltage and current from the pre-breakdown to after breakdown for each such voltage breakdown or the whole data?How should the plot look like in order to claim that the voltage breakdown is due to FE as predicted by the Fowler-Nordheim? If it doesn't look as expected what should one conclude given what we know to date about FE in the regime of high voltage.One also observes frequently during a voltage breakdown that the current and the voltage start the rapid change at the same time point and thus different from what is described in the literature according to which the leak current announces the voltage breakdown so that the current starts changing prior to the voltage change. Does it make sense in that case to represent the Fowler-Nordheim plot?

Answer 1

To determine if voltage breakdowns in a vacuum-based X-ray tube are due to field emission as predicted by the Fowler-Nordheim plot, you would need to plot the current and voltage data for each breakdown. If the plot matches the expected behavior described by the theory, it suggests that field emission is the cause. However, if the plot deviates from the expected behavior, it may indicate other factors at play in the high voltage regime.

Step-by-step explanation:

In the context of a vacuum-based X-ray tube, voltage breakdowns occur when there is a rapid decrease in voltage and an increase in current.

These breakdowns are typically caused by phenomena such as field emission (FE).

To determine if the measurements are in line with the Fowler-Nordheim plot, you would need to plot the current and voltage data for each voltage breakdown.

The Fowler-Nordheim plot shows the relationship between the electric field and the tunneling current in a vacuum.

If the plot matches the expected behavior described by the Fowler-Nordheim theory, it would suggest that the voltage breakdown is indeed due to field emission.

However, if the plot does not match the expected behavior, it may indicate that there are other factors at play in the high voltage regime that are not well understood.

In the case where the current and voltage start changing at the same time during a voltage breakdown, contrary to what is described in the literature, it might be difficult to determine if field emission is the sole cause of the breakdown.

Therefore, representing the Fowler-Nordheim plot may not be as meaningful in that specific case.