**4. Beam hash and instability: the limit to analyzed beam current**

It had been found early on in the Calutrons that there was a practical limit to the high beam currents that could be reliably analyzed, due to a phenomenon referred to as 'hash' on the beam—this was quasi-random high-frequency noise of several hundred kHz, which disrupted the space-charge neutralization of the ion beam, resulting in a loss of mass resolution and an inability to transmit higher currents [1, 2]. This phenomenon was not fully understood, but I had observed it when attempting to increase the transmitted current of arsenic beams above the specification. The beam could clearly be observed to blow up, and to exhibit hysteresis as certain source parameters were tuned. I later observed a similar phenomenon on a test stand I was working on in 1990 and 1991, where I had developed a PIG ion source delivering significantly more low-energy current than prior sources in a low-emittance ribbon
