FINAL-FOCUS SYSTEM AND COLLISION SCHEMES FOR A 5-TeV W-BAND LINEAR COLLIDER

Abstract

A 3-km long high-gradient W-band switched matrix linac may, in parallel channels, accelerate multiple electron and positron bunches to an energy of 2.5 TeV, with a tight control on the intra-bunch energy spread. In this report, we describe a final-focus system for such an accelerator, whose length is restrained by eliminating chromatic correction. The interaction point (IP) spot size is limited by synchrotron radiation in the last quadrupole (Oide effect). The energy loss due to beamstrahlung is optionally suppressed by combining bunches of opposite charge and colliding the neutral beams. We present two different high-luminosity multiple-collision schemes, which can provide a luminosity of up to 1035 cm -2 s -1, with only about 1 MW average beam power. In the first scheme, batches of equally-charged bunches are combined into superbunches which, possibly after charge compensation, are collided head-on with the opposing beam. In the second scheme, 25 charge-neutral electron-positron bunch pairs of one beam are each collided with 25 neutral bunch pairs of the other beam. These multiplexed collisions are facilitated by a crossing angle and by crab cavities upstream of the electron-positron combiner; however they also require focusing channels (e.g., a crystal) preserving IP beam size between the collision points, a difficult if not impossible construct. We describe the challenges posed by each approach.