Conductors in a Tube: High Resistance & Low Impedance

[atijaz]

Hi everybody,

I have an oscillating circuit that consist of a charged capacitor and two conductors connected that can be seen as the inductance. When I short the conductors at their ends an oscillation can be seen on the oscilloscope.
When I put an iron tube around each of the wires the damping of that oscillation is much higher. I measured the series resistance and the series impedance of both circuits. What can be seen ist that the resistance is much higher when the wires are in the tube. The impedance in that case is higher for low frequencies, too.
Is there any way to modify the tube so that we still have the high resistance but to keep the impedance low and stable?

Thank for your help,

atijaz

 

[Averagesupernova]

This is a bit confusing. Maybe a better description or drawing?