A series of plasma diagnostic have been carried out in our large area plasma processing system which is based on a modulated electron-beam produced plasma. These discharges were created in both electrically conducting and insulated vacuum chambers operated in 30-120 mTorr of pure gases (argon, oxygen, and nitrogen). Langmuir probes, microwave transmission, mass spectrometry, and external current sensors show robust discharges were made over fairly wide parameter ranges resulting in plasma densities of 1-4 x 10(11) cm(-3) and temperature ranging from 0.2 eV for the molecular gases and 1.4 eV for argon. The effects of various experimental techniques, parameters, and contamination issues are discussed in detail.