Experimental evidence of space charge driven resonances in high intensity linear accelerators

In the construction of high intensity accelerators, it is the utmost goal to minimize the beam loss by avoiding or minimizing contributions of various halo formation mechanisms. As a halo formation mechanism, space charge driven resonances are well known for circular accelerators. However, the recent finding showed that even in linear accelerators the space charge potential can excite the 4 sigma = 360 degrees fourth order resonance [D. Jeon et al., Phys. Rev. ST Accel. Beams 12, 054204 (2009)]. This study increased the interests in space charge driven resonances of linear accelerators. Experimental studies of the space charge driven resonances of high intensity linear accelerators are rare as opposed to the multitude of simulation studies. This paper presents an experimental evidence of the space charge driven 4 sigma = 360 degrees resonance and the 2 sigma(x(y)) - 2 sigma(z) = 0 resonance of a high intensity linear accelerator through beam profile measurements from multiple wire-scanners. Measured beam profiles agree well with the characteristics of the space charge driven 4 sigma = 360 degrees resonance and the 2 sigma(x(y)) - 2 sigma(z) = 0 resonance that are predicted by the simulation.