Copper Pipe in Solenoid Center

[n1caboose]

I wanted to know how the magnetic field of a solenoid would be affected if a copper/iron pipe section was put into its center. In other words, what would the resulting magnetic field be if I simply wrapped a coil around a metal pipe section without removing the pipe afterward?

Will there be a stronger field? I was wondering as I came across a copper pipe with a 1cm diameter and am working on a low-power coilgun.

Thank you.

 

[Bob S]

The copper pipe will have absolutely no effect on a dc solenoid. It will have a very serious attenuating effect on an ac or pulsed solenoid.

Bob S

 

[n1caboose]

Okay, thanks. Why exactly would the magnetic field strength be diminished so dramatically?

Also, is there a method to amplify the magnetic of a pulsed solenoid without increasing the input current or changing the coil's wrap density?

 

[Bob S]

From Faraday's law;

V_tube = -d/dt[∫B·ndA] = -A dB/dt, where A is the cross-sectional area of the tube, and V is the induced voltage around the circumference.

Because the copper tube is an electrical short circuit, there is a very large azimuthal induced current in the copper tube that opposes any change in the magnetic flux inside. (Lenz's Law).

High frequency ferrite will help. Also small-diameter coated soft iron wire, like inside the old style automotive cylindrical ignition coils.

[Added note] If you cut a narrow slit along one side of the copper tube for the entire tube length, this will eliminate the induced azimuthal (Lenz's Law) current which opposes the pulsed magnetic field inside the tube.There could still be small higher-order effects though.

Bob S

 

[pmacias]

I can tell you that inserting a copper/iron pipe into the center of a solenoid will definitely affect the magnetic field. The presence of a conductive material, such as copper, within the solenoid will cause a change in the distribution of the magnetic field lines. This is because the moving electrical charges in the copper will create their own magnetic fields, which will interact with the magnetic field of the solenoid.

The resulting magnetic field will depend on the size and position of the copper pipe within the solenoid, as well as the strength and configuration of the solenoid itself. In general, the presence of the copper pipe will likely cause the magnetic field to become more concentrated and stronger in the area where the pipe is located.

However, it is important to note that the addition of the copper pipe will also introduce some resistance to the flow of electricity in the solenoid, which could potentially affect the overall performance of your coilgun. This is something that you will need to take into consideration and possibly adjust for in your design.

Overall, I would recommend conducting experiments to determine the exact effects of inserting a copper pipe into a solenoid for your specific coilgun design. This will give you a better understanding of how the presence of the pipe will impact the magnetic field and allow you to make any necessary adjustments for optimal performance.