1. Why Study Electron Clouds? Methods and Tools to Study Electron Clouds
49th ICFA Advanced Beam Dynamics Workshop. October 8–12, 2010
Why Study Electron Clouds?
Methods and Tools to Study Electron Clouds
Some Facilities Potentially Affected by Electron Clouds
Mitigation Techniques
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)
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.
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)
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
Grooved chamber surfaces
as a mechanism to mitigate
electron cloud formation
Besides colliders, other applications such as spallation neutron
sources and neutrino sources which use proton beams are also
affected by electron clouds.
Pulsed high-voltage clearing electrodes
Measurements
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)
Worldwide effort: CERN (Switzerland) , SLAC & LBNL (California), KEK (Japan), FNAL & ANL (Chicago), many more !
TiN, a-C and NEG (activated) are all very effective in suppressing EC
Retarding field analyzers for detecting cloud electron currents
Cornell Electron Storage Ring Test Accelerator
CesrTA
2008-present
A simulation of a proton bunch in the Large Hadron Collider after 20 turns with electron cloud
densities of 1012/m3 (left), 1013/m3(middle), 1014/m3 (right).
The Large Hadron Collider
A Discovery Machine
The first publications are just now appearing!
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.
Precison measurements of electron cloud distortions of the guide fields
Digitized oscilloscope traces from cloud electron detectors use witness bunches to measure cloud lifetime
RFA segmented collectors
The International Linear Collider
A PRECISION Machine
Such 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.
Modeling
Field-free Region
Magnetic Dipole Region
A simplified model used
for simulating the interaction beam with an electron cloud.
Segmented RFA Data (Drift), taken with a 45 bunch train of positrons with 1 mA/bunch, at 5.3 GeV
VORPAL code package for modeling transmission of RF waves. The electron cloud causes phase shifts.
Modeling witness bunch cloud
lifetime measurements to
determine the elastic yield
parameter.
Dipole RFA Data, taken with a 45 bunch train of positrons with 1 mA/bunch, at 5.3 GeV
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:
April 2007
1.9 GeV
0.75 mA/bunch
e+ and e- beams