Dolgashev, V.A.

Paper	Title	Page
MOOCH03	Status of a Linac RF Unit Demonstration for the NLC/GLC X-band Linear Collider	42
	D.C. Schultz, C. Adolphsen, D.L. Burke, J. Chan, S. Doebert, V.A. Dolgashev, J.C. Frisch, R.K. Jobe, D.J. McCormick, C.D. Nantista, J. Nelson, M.C. Ross, T.J. Smith, S.G. Tantawi SLAC, Menlo Park, California D.P. Atkinson LLNL, Livermore, California Y.H. Chin, S. Kazakov, A. Lounine, T. Okugi, N. Toge KEK, Ibaraki
	Designs for a future TeV scale electron-positron X-band linear collider (NLC/GLC) require main linac units which produce and deliver 450 MW of rf power at 11.424 GHz to eight 60 cm accelerator structures. The design of this rf unit includes a SLED-II pulse compression system with a gain of approximately three at a compression ratio of four, followed by an overmoded transmission and distribution system. We have designed, constructed, and operated such a system as part of the 8-Pack project at SLAC. Four 50 MW X-band klystrons, running off a common 400 kV solid-state modulator, drive a dual-moded SLED-II pulse compression system. The compressed power is delivered to structures in the NLCTA beamline. Four 60 cm accelerator structures are currently installed and powered, with four additional structures and associated high power components available for installation late in 2004. We describe the layout of our system and the various high-power components which comprise it. We also present preliminary data on the processing and initial high-power operation of this system.
	Video of talk
	Transparencies
MOPLT133	Beam Loading and Higher-band Longitudinal Wakes in High Phase Advance Traveling Wave Accelerator Structures for the GLC/NLC	848
	R.M. Jones, V.A. Dolgashev, Z. Li, T.O. Raubenheimer SLAC, Menlo Park, California
	A multi-bunch beam traversing traveling wave accelerator structures, each with a 5pi/6 phase advance is accelerated at a frequency that is synchronous with the fundamental mode frequency. As per design, the main interaction occurs at the working frequency of 11.424 GHz. However, modes with frequencies surrounding the dominant accelerating mode are also excited and these give rise to additional modal components to the wakefield. Here, we consider the additional modes in the context of X-band accelerator structures for the GLC/NLC (Global Linear Collider/Next Linear Collider). Finite element simulations, mode-matching and circuit models are employed in order to calculate the wakefield.
TUPKF059	Simulation of Dark Currents in X-band Accelerator Structures	1081
	K.L.F. Bane, V.A. Dolgashev, G.V. Stupakov SLAC, Menlo Park, California
	In high gradient accelerator structures, such as those used in the main linac of the GLC/NLC, electrons are emitted spontaneously from the structure walls and then move under the influence of the rf fields. In this report we study the behavior of this "dark current" in X-band accelerator structures using a simple particle tracking program and also the particle-in-cell program MAGIC. We address questions such as what is the sensitivity to emission parameters, what fraction of dark current is trapped and reaches to the end of a structure, and what are the temporal, spatial, and spectral distributions of dark current as functions of accelerating gradient.
WEPLT155	Effect of Dark Currents on the Accelerated Beam in an X-band Linac	2200
	V.A. Dolgashev SLAC/ARDA, Menlo Park, California K.L.F. Bane, G.V. Stupakov, J. Wu SLAC, Menlo Park, California T.O. Raubenheimer SLAC/NLC, Menlo Park, California
	X-band accelerating structures operate at surface gradients up to 120-180 MV/m. At these gradients, electron currents are emitted spontaneously from the structure walls ("dark currents") and generate additional electromagnetic fields inside the structure. We estimate the effect of these fields on the accelerated beam in a linac using two methods: a particle-in-cell simulation code MAGIC and a particle tracking code. We use the Fowler-Nordheim dependence of the emitted current on surface electric field with field enhancement factor beta. In simulations we consider geometries of traveling wave structures that have actually been built for the Next Linear Collider project.