1: You can pass current from your source through a wire and check the direction of the magnetic field with a compass.
But, then, a compass is a meter also.
2: Make a circuit by connecting in series a battery, your source and a resistor. The configuration that dissipates more heat on the resistor (use your finger as a heat probe) is when DC source and battery are placed with the same polarity ( +DC- +BATT- R ).
If there is no effect from the setup itself, this sounds like an effect of the ionized air to me.
In a corona discharge, the electric field is high enough to ionize the air, making it a conductor and creating light.
If the voltage is switched off, there are still all the ionized atoms around the wire, and it takes time for them to recombine with electrons. This time typically is in the order of milliseconds. This explains why you can see an effect when both pulses are generated within nanoseconds, and not, when they are generated within milliseconds.
I'm not sure why the current of the second pulse is lower, one could also imagine a higher current, since there are already ions around. It is possible that the ions already act as conductor before the voltage is high enough for a corona discharge, which means the effective diameter of the conductor (the wire) increases. This lowers the field strength and so the rate of ionization and the current flow.
Think about: 100A is really lots of current, and I can't imagine a corona discharge with a constant current of 100A in a smaller setup. This rather seems to be an inrush current.
Is it possible to generate a constant 16kV with a short leading edge? I guess you'll see a high current peak falling to a much lower constant value.
But as said, also check your equipment and make sure it doesn't affect your measurement. (For example, use a much thicker central wire to prevent corona discharge and compare)
Best Answer
The part you are missing is that what looks like uninsulated wire actually isn't. A lot of enamel coated or "magnet wire" can look like bare copper at first glance, but the wire is actually coated with a thin semi-transparent insulation layer. The reason for using thin insulation is so that lots of turns of the coil can fit into the tightest possible space.
Electrically, a coil of wire is quite different from a cylinder. To make a magnetic field, you need current flowing around where you want the field. Think of a cylinder of current surrounding the area. The magnetic field is proportional to the total current in the cylinder.
A coil is sortof a cheat on that. The same current is re-used each turn to add to the apparent cylinder current. Let's say you have a coil with 100 turns. If you run 1 A thru it, each of those turns contributes 1 A to the overall cylinder current. You get the same magnetic field as if it were a solid cylinder with 100 A running around it.