Tests for an advanced slow stochastic extraction (SSE) scheme have been performed successfully at the U70, the 70 GeV proton synchrotron at the Institute for High Energy Physics (IHEP), Protvino, in the Moscow region. A holder of the record for highest-energy accelerator during the late 1960s, the U70 is still in operation today, and the feasibility tests in November and December 2004 may offer an interesting option for future beams.
The SSE concept was pioneered in 1978 by Simon van der Meer at CERN as a spin-off from his work on stochastic cooling, which led to the conversion of CERN’s Super Proton Synchrotron to a proton-antiproton collider, and a share of the 1984 Nobel Prize in physics for van der Meer. This technique, yielding long and uniform spills, was later successfully used at CERN in the Low Energy Antiproton Ring (LEAR), achieving extraction times of several hours.
Stochastic extraction is a modification of resonant extraction in which particles are moved to the extraction resonance by random kicks from a noisy radiofrequency system. It has the advantage of being immune to unavoidable ripples in the magnetic optics that deteriorate the spill under resonant extraction. This might prove especially useful to a venerable machine like the U70.
The SSE tests were performed on an ejection plateau at 60 GeV in the U70, with recorded beam and extraction currents as shown in the figure in blue together with the fitted curves in red.
About 90% of the spill is extracted in 0.8 s. The extracted current is not free from AC ripple, but the IHEP engineers are hopeful that they can suppress this in future. The design goal is to obtain ripple-free flat-topped spills lasting 2-3 s or longer.
The tests have been deemed a success and the feasibility of SSE at the U70 has been confirmed by the beam measurements. The scheme promises smoother and longer spills, which will improve the machine’s functionality.
