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3 Main Linac 3.1 Introduction 3.2 Beam Dynamics
| Content Provider | Semantic Scholar |
|---|---|
| Abstract | In this chapter, we describe the layout and the properties of the main linacs, in which the electron and positron beams are accelerated from 5 to 250 GeV at a gradient of E acc =23.4 MV/m. The electron and positron linacs have a total length of 14.4 km each, including a ∼2 % overhead for energy management in case of klystron failures. The 10,296 9-cell cavities per linac are contained in cryomodules (12 cavities per module, see section 3.2.4), which also house the focusing quadrupoles, steering magnets, and beam position monitors (BPM). The radio frequency (RF) system (section 3.3) consists of 286 10 MW klystrons per linac (including overhead), which are installed in the tunnel and connected to the pulsed power supplies (modulators) in the external service halls by high voltage cables. The linac is operated at a pulse rate of 5 Hz, except for the first 3 km of the electron linac where the pulse rate is doubled to accelerate both the collider beam and the beam driving the X-ray Free Electron Laser (chapter 9). The flexibility of the RF control system allows independent adjustment of the accelerating gradient for the alternating collider and FEL beam pulses. The small design emittance requires careful control of the beam dynamics in the linac. This important issue is discussed in the following section. To achieve the desired high luminosity, long trains of bunches with small transverse emittances are required. In this section, emittance preservation during acceleration in the main linac is discussed. The primary sources of transverse emittance dilution in a high energy linear accelerator are the transverse wakefields excited in the accelerating sections in the presence of imperfections, and the dispersive errors caused by the focusing magnets. For TESLA, the low RF frequency and corresponding large irises of the accelerating structures result in much smaller wakefield kicks for a given mis-alignment than in higher frequency room-temperature designs. Furthermore, a given dispersion generates less emittance blow-up, because the beam energy spread is kept small along most of the accelerator. The small wakefields and low energy spread ultimately result in relatively relaxed alignment tolerances for the various components (focusing magnets, beam position monitors, accelerating structures), for which modern optical survey techniques in combination with the standard beam-based alignment |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://tesla.desy.de/new_pages/TDR_CD/PartII/chapter03/chapter03.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
