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

A 3-km long high-gradient W-band switched matrix linac may, in paralle l channels, accelerate multiple electron and positron bunches to an en ergy 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 acceler ator, whose length is restrained by eliminating chromatic correction. The interaction point (IP) spot size is limited by synchrotron radiati on in the last quadrupole (Oide effect). The energy loss due to beamst rahlung is optionally suppressed by combining bunches of opposite char ge and colliding the neutral beams. We present two different high-lumi nosity multiple-collision schemes, which can provide a luminosity of u p to 10(35) cm(-2) s(-1) with only about 1 MW average beam power. In t he first scheme, batches of equally-charged bunches are combined into superbunches which, possibly after charge compensation, are collided h ead-on with the opposing beam. In the second scheme, 25 charge-neutral electron-positron bunch pairs of one beam are each collided with 25 n eutral 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 channel s (e.g., a crystal) preserving the IP beam size between the collision points, a difficult if not impossible construct. We describe the chall enges posed by each approach.