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The passage of a multi-bunch beam through an X-band accelerator with cells and structures misaligned gives rise to wakefields which disrupt succeeding bunches. As a consequence, there is growth in the overall emittance of the final colliding bunches. Here we study this process in the context of a JLC-NLC which employs the recently developed RDDS (Rounded Damped Detuned Structures) accelerators with 120 s fill time and drives a 90 bunch, 250 ns bunch train. We investigate cumulative beam break-up (BBU) under various parameter regimes appropriate to the structure which is in the process of being fabricated by KEK and SLAC. We compute the resultant emittance growth by means of analytical expressions and find good agreement with the results we obtain from a particle tracking code. We set misalignment tolerances by specifying allowable emittance growth.

A linear collider is determined largely by the beamsstrahlung spectrum. The beammsstrahlung spectrum in turn is sensitive to the design parameters at the interaction point. In this paper we examine the optimization of the luminosity spectrum for discovery and detailed exploration of various physics processes of interest in the NLC, in particular, top and stop pair production, and a class of processes occurring via WW scattering.

We report progress on the design of the RF systems for the Next Linear Collider (NLC) damping rings. The 714 MHz RF system is a critical component of the damping ring complex, and must provide flexible operation with high-power systems generating 1.5 MV in the main damping rings and 2 MV in the positron pre-damping ring. Average beam currents are approximately 750 mA, and bunch trains are rapidly injected and extracted. A cavity design incorporating higher-order-mode (HOM) damping schemes to minimize beam impedance and maximize current thresholds for coupled-bunch instabilities will be presented. Cavity construction techniques are designed to reduce costs while providing a reliable system with excellent performance. Descriptions of feedback systems requirements will be presented, with particular attention to the klystron bandwidth requirement for feedback against transient beam loading. Flexible low-level controls and feedback loops will be described.

Several low-emittance damping rings are presently being designed to meet the requirements of future linear colliders. These rings tend to have relatively large circumferences /spl sim/300 m so that they can damp many trains of bunches at the same time. With the large circumference, the ring path length may become quite sensitive to thermal and ground motion effects.

We report progress on the design of the Next Linear Collider (NLC) damping rings complex (DRC). The purpose of the DRC is to provide 120 Hz, low emittance electron and positron bunch trains to the NLC linacs. It consists of two 1.98 GeV main damping rings, one positron pre-damping ring, two pairs of bunch length and energy compressor systems and interconnecting transport lines. The 2 main damping rings store up to 0.8 amp in 3 trains of 95 bunches each and have normalized extracted beam emittances /spl gamma//spl isin//sub x/=3 /spl mu/m-rad and /spl gamma//spl isin//sub y/=0.03 /spl mu/m-rad. The preliminary optical design, performance specifications and tolerances are given. Key subsystems include: 1) the 714 MHz RF system, 2) the 60 ns risetime injection/extraction pulsed kicker magnets, 3) the 44 m wiggler magnet system, 4) the arc and wiggler vacuum system, 5) the radiation management system, 6) the beam diagnostic instrumentation, 7) special systems used for downstream machine protection and 8) feedback-based stabilization systems.

The design of the NLC beam delivery system requires a firmer understanding of the effects of collimators on short, intense bunches than is presently available. We describe an experiment to directly measure these effects through use of a dedicated apparatus located at the 1.19 GeV point in the SLAC linac. The apparatus consists of an outer vacuum vessel and an interchangeable insertion containing up to 5 distinct collimator apertures. The insertion is capable of remote-controlled translation, allowing the collimator apertures to be misaligned relative to the electron beam without changing the incoming beam orbit; the wakefield deflection is then measured by observing the change in the outgoing orbit on 32 beam position monitors. The parameters of the apertures have been selected to allow confirmation of the scaling laws for collimator wakefields, and to strongly enhance either the geometric or resistive wall contribution of each aperture. Details of the apparatus design, the aperture parameters, and the experimental program are discussed.

The two main functions of the NLC extraction line include: 1) transmission of the outgoing disrupted beam and secondary particles to the dump with minimal losses; and 2) beam diagnostics and control. In this report, we describe the extraction line optics, present the results of tracking studies, and discuss the extraction line instrumentation., PAC99, 4 pages

At the present time, there are a number of future linear collider designs with a center-of-mass energy of 500 GeV or more that have luminosities in excess of 10/sup 34/ cm/sup -2/ s/sup -1/. Many of these designs are very advanced, however, to attain the high luminosity, the colliders require very small beam emittances, strong focusing, and very good stability. In this paper, some of the outstanding issues related to the small spot sizes are discussed. Although the different designs are based very different RF technologies, many of these problems are common to all designs.