Protons are created by ionizing hydrogen gas. Hydrogen is fed from a 56L pressurized lecture bottle. H2 output is controlled by a 2 stage regulator, with 2nd stage output set to 10 PSIG. The tank mates to the regulators with a 170 CGA connection. The 2nd stage output is 1/8” FNPT. This is connected to 1/4" ACR copper tubing. The tank is mounted to the front bottom of the cart with 2” PVC pipe. The copper tubing extends up to the chamber area, An inline Parker needle metering valve is used to reduce the H2 pressure even further. This is connected to the copper tubing and the chamber with ¼” Swagelok fittings. The metering valve has a 10 turn knob. Flow coefficient at 9 turns is 0.030; at 1 turn the coefficient is 0.0025. In practice, the knob is usually advanced at most 1/4 turn. This increases the vacuum to around 5E-4 torr from a baseline of 1E-5 torr or below.