1. 49th ICFA Advanced Beam Dynamics Workshop. October 8–12, 2010 LEPP, the Cornell University Laboratory for Elementary-Particle Physics, has joined with CHESS to become the Cornell Laboratory for Accelerator-based Sciences and Education (CLASSE). LEPP's primary source of support is the National Science Foundation. Visit us on the web at: www.lepp.cornell.edu The rate of particle events in a collider depends upon the product of two quantities: * the interaction cross section of the reaction under study * the luminosity (interacting beam particle flux) Diluting the beam leads to reduction in luminosity. Electron clouds dilute positively charged beams. A simulation of a proton bunch in the Large Hadron Collider after 20 turns with electron cloud densities of 10 12 /m 3 (left), 10 13 /m 3 (middle), 10 14 /m 3 (right). Besides colliders, other applications such as spallation neutron sources and neutrino sources which use proton beams are also affected by electron clouds. The electrons are liberated from the surface through a variety of mechanisms They are attracted toward a positively charged beam, which then interfere with the motion of the beam particles throwing them off course. They are expected to pose a serious challenge to several future projects requiring high current beams. Examples are: Upgrade of the Large Hadron Collider, The ILC and CLIC damping rings, the high intensity neutrino (HINS) project at Fermilab, and the future B-factories KEK-B, Super-B. A simplified model used for simulating the interaction beam with an electron cloud. The spallation neutron source, located at Oak Ridge Tennessee is a facility for neutron scattering experiments, which help understand and improve the properties of materials that are part of our everyday lives. (left) Fermilab, in Batavia, Illinois is home to two experiments using neutrinos. These particles are highly elusive. Proton beams are used to produce neutrinos. Future upgrades and new experiments will require more intense beams, leading to increased electron cloud production (right) A picture of the beam pipe of the LHC at CERN in Geneva. It collides proton beams to investigate fundamental processes in hitherto unexplored kinematic domains. (left) Why Study Electron Clouds? Some Facilities Potentially Affected by Electron Clouds Methods and Tools to Study Electron Clouds Grooved chamber surfaces as a mechanism to mitigate electron cloud formation Mitigation Techniques Modeling Measurements The Large Hadron Collider A Discovery Machine The first publications are just now appearing! The International Linear Collider A PRECISION Machine S uch high-energy electron-positron collisions are feasibly only in a linear collider because the radiation in a ring would be too intense. Therefore, the beams must be made small BEFORE acceleration. The performance of the necessary damping rings will be limited by electron cloud buildup unless sufficient mitigation techniques are developed. Cornell Electron Storage Ring Test Accelerator CesrTA 2008-present Digitized oscilloscope traces from cloud electron detectors use witness bunches to measure cloud lifetime Worldwide effort: CERN, SLAC, LBNL, KEK, FNAL Retarding field analyzers for detecting cloud electron currents RFA segmented collectors TiN, a -C and NEG (activated) are all very effective in suppressing EC Precison measurements of electron cloud distortions of the guide fields Segmented RFA Data (Drift), taken with a 45 bunch train of positrons with 1 mA/bunch, at 5.3 GeV Dipole RFA Data, taken with a 45 bunch train of positrons with 1 mA/bunch, at 5.3 GeV April 2007 1.9 GeV 0.75 mA/bunch e+ and e- beams Field-free RegionMagnetic Dipole Region Modeling witness bunch cloud lifetime measurements to determine the elastic yield parameter. Pulsed high-voltage clearing electrodes Wide variety of custom vacuum chamber designs Titanium-nitride, a-carbon, NEG coatings Untreated alumimum chambers as control group Additional electron cloud detector ports such as those shown here for retarding field analyzers and shielded pickups VORPAL code package for modeling transmission of RF waves. The electron cloud causes phase shifts.