Prospects for Very High Gradient Linac-Colliders

The energy realistically attainable by an electron-positron storage ring is limited by the RF voltage and power requirements imposed by synchrotron radiation to about 100 GeV. To reach energies of 300 × 300 GeV and higher in a colliding beam machine of reasonable dimensions, we must look to the linac-collider operating at an energy gradient on the order of 100 MV/m. Proper choice of an RF structure for such a collider can minimize the total RF power requirement and the effects of longitudinal and transverse single-bunch beam loading. For an operating frequency in the range 4-6 GHz, the total RF power requirement for a 300 × 300 GeV collider with a luminosity of 1032 cm-2s-1 accelerating 1011 particles per bunch is on the order of 50 MW. To drive this collider, RF power sources are needed having a peak output power in the range 1-2 GW. Possibilities for attaining these peak power levels by direct generation and by energy storage and fast switching are discussed.