Funneling experience at Los Alamos: Experiments and designs

Modern linacs are capable of accelerating high-current low-emittance beams input above a minimum energy. However, the ability of ion sources to produce such beams and the ability of low energy structures to accelerate high currents to this minimum energy is lacking. Funneling is a method of combining two or more beams to overcome this limitation. It is very important to note that the phase space of the two beams to be combined is not merged, in violation of Liouville's theorem. Instead beam micropulses from two sources are interleaved in time. It is also important to note that the micropulse frequency has doubled over that of the separate sources and must be accommodated by the linac following the funnel. Thus if the two funneled beams were accelerated by 400 MHz linacs, further acceleration must be done by an 800 MHz (or higher) linac. Other concepts are possible, but the authors concentrate on the one presented as the most feasible. The presence of both longitudinal and transverse focusing elements are crucial to device performance, as are adequate diagnostic elements. To attain the high peak currents needed for Los Alamos projects, such as the Ground Test Accelerator (GTA), Accelerator Production of Tritium (APT),more » Accelerator Transmutation of Waste (ATW), or the 5 MW upgrade to the National Center for Neutron Research (NCNR), a funneling scheme is needed. In these projects the authors consider funneling of two beams with peak currents of up to 100 mA and transverse emittances of the order of 0.02[pi] cm mrad, rms normalized. This article discusses a funneling experiment done at Los Alamos and briefly mentions a program at another institution that has demonstrated the concept. The authors will also discuss the funnel design for APT, now undergoing conceptual design.« less