Vibrational Stability of Glc/nlc Linear Collider: Status and R&d Plans*

Multiple feedback systems are foreseen to ensure stable luminosity for the X-band linear collider. Beam-based train-by-train steering feedbacks will be used in the linac and at the IP. Active stabilization of the final doublet is being developed to counteract the possibility of excessive vibration from the detector. Another option is fast intratrain feedback that could recover a major part of the luminosity while other systems are being commissioned. An important part of the strategy is to limit vibration of collider components and their contribution to beam jitter. STABILITY OF GLC/NLC Several conditions contribute to luminosity stability of the GLC/NLC X-band linear collider. First, the site should be sufficiently stable. Fig.1 shows an example of the integrated spectrum measured at one of the California sites studied. The vibration tolerance of the GLC/NLC linac quadrupoles is approximately 12 nm above several Hz. The measured motion shown in Fig.1 for this site or even the intermediate noise model are several times better than the stability requirements. Figure 1: Integrated spectrum measured at one of the representative sites in California compared with low noise (LEP), intermediate noise (SLAC) and high noise (HERA) models. Given a site that meets the stability requirements, one must then ensure a) that noise sources on the linac girder are minimized and decoupled from the quadrupoles, and b) noise produced in the utility tunnel is mitigated. The first issue was addressed in ref. [1] which showed that vibration of the accelerating structure induced by cooling water is decoupled from the linac quadrupoles. This paper will concentrate on describing the approach to minimizing utility tunnel noise. Figure 2: Layout of GLC/NLC beam and utility tunnels and schematic of equipment located in the utility tunnel. A possible layout and cross-section of the GLC/NLC tunnels is shown in Fig.2. Most of the equipment that could produce vibration is located in the utility tunnel. Among the possible vibration sources in the utility tunnel are the klystron modulators and the equipment which provides cooling water. Figure 3: Vibration measured directly on the modulator (top plot), and on the floor near the modulator (bottom). The 60 Hz harmonics are removed for clarity. Vibration produced by the modulator has been studied at NLCTA, with the IGBT modulator operating at a _________________________________________ *Supported by Department of Energy contract DE–AC03–76SF00515 [email protected] Stanford Linear Accelerator Center, Stanford University, Stanford, CA 94309 Presented at the 9th European Particle Accelerator Conference (EPAC 2004), 7/5/2004 7/9/2004, Lucerne, Switzerland July 2004 SLAC-PUB-10555