Papers by T. Raubenheimer
Presented at the 4th …, 1994
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A small transverse slice emittance at the undulator entrance is essential for high performance of... more A small transverse slice emittance at the undulator entrance is essential for high performance of the free electron laser. To achieve this, preservation of the phase space density of the electron bunch during acceleration and compression is absolutely necessary. The LCLS-II-HE is designed to transport a 100 pC bunch with an emittance of ~0.3 mm-mrad with minimal emittance dilution. However, in simulations starting from a normalized emittance on the order of 0.1 mm-mrad, the emittance growth is significant. In this paper, the sources of emittance growth are studied along the accelerator, in particular, around the laser-heater, the two bunch compressors. We have investigated mechanisms of emittance growth such as space charge, coherent synchrotron radiation, chromatic aberration, and spurious dispersion. Due to the extremely small emittance from the injector, 3-D space charge effect is important to determine the space charge dominated region and emittance dominated region. With this u...
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In order to prevent electrical breakdown occurring in the JLC/NLC (Japanese Linear Collider/Next ... more In order to prevent electrical breakdown occurring in the JLC/NLC (Japanese Linear Collider/Next Linear Collider) X-band structures several new structures are under investigation. These accelerating structures represent an evolutionary design of the DDS series of structures [1]. The phase advance per cell has been varied and the detailed elliptical shape of the cell has been varied in order to simultaneously minimize the group velocity, the surface electromagnetic fields and the pulse temperature rise on the copper surface [2]. It is also important to ensure that the wakefield induced by multiple bunches traversing the accelerating structures does not disrupt trailing bunches. The wakefield must be damped adequately in order to prevent a BBU (Beam Break Up) instability occurring and to ensure that emittance dilution due to the higher order modes is kept to acceptable levels. The long-range wakefield is forced to de-cohere by detuning all of the frequencies such that the mode density...
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The ions in a linac with high repetition rate, such as ERL, draw more attention recently. LCLS-II... more The ions in a linac with high repetition rate, such as ERL, draw more attention recently. LCLS-II has a long linac with 1 MHz repetition rate. The ions, in general, are not deeply trapped due to the long bunch spacing. The effect of ion thermal energy becomes important in this regime. The beam dynamics with ions are studied both theoretically and numerically. There is a linear growth in amplitude, instead of exponential growth as traditional fast ion instability. This linear growth set a maximum bunch-train length to limit the beam amplitude to fractional beam sigma. We also extend our works to different regimes where the motions of ions from stable to partially stable.
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The LCLS-II will be a CW X-ray FEL upgrade to the existing LCLS X-ray FEL at the SLAC National Ac... more The LCLS-II will be a CW X-ray FEL upgrade to the existing LCLS X-ray FEL at the SLAC National Accelerator Laboratory (SLAC). This paper will describe the overall layout and performance goals of the upgrade project.
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Linear accelerators are the central components of the proposed next generation of linear collider... more Linear accelerators are the central components of the proposed next generation of linear colliders. They need to provide acceleration of up to 750 GeV per beam while maintaining very small normalized emittances. Standard simulation programs, mainly developed for storage rings, do not meet the specific requirements for high energy linear accelerators. The authors present a new program LIAR (LInear Accelerator Research code) that includes wakefield effects, a 4D coupled beam description, specific optimization algorithms and other advanced features. Its modular structure allows to use and to extend it easily for different purposes. They present examples of simulations for SLC and NLC.
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In this paper, we will first review the status of the Stanford Linear Collider (SLC). In particul... more In this paper, we will first review the status of the Stanford Linear Collider (SLC). In particular, we will discuss the luminosity and performance issues and the accelerator studies that relate to future linear colliders. Next, we will describe the present state of the Next Linear Collider (NLC) design and the ongoing RD detailed descriptions of the NLC design can be found in Refs. [1, 2, 3].
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AIP Conference Proceedings, 1997
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Proceedings Particle Accelerator Conference
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Beam instability caused by the electron cloud has been observed in positron and proton storage ri... more Beam instability caused by the electron cloud has been observed in positron and proton storage rings, and it is expected to be a limiting factor in the performance of future colliders [1-3]. The effect is expected to be particularly severe in magnetic field regions. To test possible mitigation methods in magnetic fields, we have installed a new 4-dipole chicane experiment
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Proceedings Particle Accelerator Conference
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Proceedings Particle Accelerator Conference
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Proceedings of International Conference on Particle Accelerators
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Physical Review Special Topics - Accelerators and Beams, 2000
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Papers by T. Raubenheimer