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Accelerator systems utilizing off-the-shelf, high-frequency thermionic cathode gridded electron guns are presently being commissioned. We have performed emittance measurements at voltage levels up to 32.5kV which indicate the beam transverse rms emittance is 8-10mm-mrad at 20kV, consistent with our gun simulations. The nominal system operating voltage will be 45kV. We have also studied the dependence of the extracted current as a function of RF power. After the initial transient phase, near linear behavior is observed. The maximum values achieved were 214mA at 32.5kV and ~100W input RF power, and 806mA at 23.2kV and ~200W input RF. We describe ongoing measurements at the Fritz Haber Institute THz FEL and compare these results to simulations. This relatively low-duty factor, S-band device utilizes low energy beam scraping after the gun to achieve the desired performance, which may not always be appropriate. The next step for such systems, which is ongoing, is to develop a lower frequency booster accelerator integrated with the gun, that raises the energy to greater than 1 MeV so that the performance of the concept can be evaluated without substantial beam spill.
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