I am currently designing my own boost converter for a project that involves charging large capacitors, and I wanted it to convert 7.2V into about 400V. However, whenever I put all the components in place I only am able to attain about 120V. I have attached the circuit diagram and a picture of the breadboard setup. I am driving the mosfet in the boost converter with a 555 timer, and I know the mosfet is not suitable for the voltage that I want, but is that my only problem? All part specifications are in the image. I am still very new to the electronics engineering scene, so forgive me if I have made some crucial errors. Any help would be appreciated!

 

I know the mosfet is not suitable for the voltage that I want, but is that my only problem?

You are correct. It certainly is not suitable.
Don't know if that's you only problem, but that's likely one problem since the MOSFET is only rated for 100V max, so it's likely breaking down.
Why would you think that would work?

You need to fix that first before you can determine if there's another problem.

 

When the battery is +7.2V then the output pulses of an ordinary 555 go only to +6. But the IRF540 needs a gate voltage of 10V to fully turn on.
You should use a logic-level Mosfet that turns on well when its gate voltage is 4.5V.
Also I agree that you should use a high voltage Mosfet.