Transverse coherent transition radiation for diagnosis of modulated proton bunches

Transverse coherent transition radiation (TCTR) emitted by a relativistic particle bunch traversing a conducting surface is analyzed. The bunch emits dipolelike radiation in the direction transverse to the bunch axis when the beam radius is smaller than the radiation wavelength. The radiation wavelength is defined by the longitudinal structure of the particle bunch. The particular case of proton bunches modified by propagation in plasma, but still carrying an unmodulated current, is considered. Radius-modulated bunches with a constant current emit axially symmetric radiation. Hosed bunches emit antisymmetric radiation in the plane of hosing. The TCTR field amplitude may reach $100\text{ }\text{ }\mathrm{kV}/\mathrm{m}$ for the existing proton bunches.