Bane, K.L.F.

Paper	Title	Page
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.
WEYLH01	Emittance Control for Very Short Bunches	179
	K.L.F. Bane SLAC, Menlo Park, California
	Many recent accelerator projects call for the production of high energy bunches of electrons or positrons that are simultaneously short, intense, and have small emittances. Two examples of such projects are linear colliders, such as the GLC/NLC, and Self-Amplified Spontaneous Emission (SASE) FEL's, such as the Linac Coherent Light Source (LCLS). A major challenge in such projects is keeping in check forces that increase short bunch emittances in accelerator components, such as: wakefields of accelerator structures, collimators, and surface roughness, and coherent synchrotron radiation (CSR). We describe such forces and their control.
	Video of talk
	Transparencies
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.