In EM radiation, the magnetic field is $ 3*10^8$ times smaller than the electric field, but is it valid to say it's "weaker". These fields have different units, so I don't think you can compare them, but even so it seems like we only interact with the electric field of EM radiation, not the magnetic field. Why is this? 


Question: Opamp Voltage Doubler Unstable (After Extended Operation)
Answer: Your circuit should work, but there are some things that you should check:

First: Why is your regulator getting hot? Your OpAmp has a supply current of 3mA and the current into your pneumatic regulator should be less than 2mA. Even with your regulator dropping 12V at a worst case current of 10mA that only makes 0.12 Watt of dissipated power on the regulator. It should not get hot from this.

Are you driving any other things with it? 

If not, check why you have a higher current than expected. You'll likely find the culprit if you go down this road.

If you're driving other things with the regulator try a dedicated regulator for the OpAmp to see if the other loads influence the supply. You've mentioned a pneumatic regulator. Is this a inductive load, e.g. a motor of some sort? If so the inductance can do some crazy voltage swings when switched due to inductive kickback. This could be enough to kill the OpAmp over time due to high supply voltage spikes. A beefly flyback diode may be needed to suppress these voltage spikes.

Second: How far away from the OpAmp is the pneumatic regulator? If you have it connected with a long cable you may have a to high capacitive load at the output of your OpAmp. This can lead to instabilities of all sorts. 

Also long cables are excellent at picking up static electricity and may kill your OpAmp via ESD spikes into the output. 

You can prevent most of these problems by adding a series resistor with the output. A simple transistor driver that isolates the OpAmp output from the long cable may also help.