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Boyce D. McDaniel Professor of Physics
Lepton colliders; beam-beam interaction; particle beam optics; non-linear dynamics of particle beams; transverse coupling in beams; resonance phenomena; beam diagnostic instrumentation; RF superconductivity; circular colliders, electron cloud, low emittance tuning, collective effects, muon g-2, electric dipole moment of fundamental particles
- Cornell Laboratory for Accelerator-based Sciences and Education (CLASSE)
- Laboratory for Elementary-Particle Physics (LEPP)
- Superconducting Radio-Frequency (SRF)
Physics of ultra-low emittance particle beams:
The phase space density (emittance) of bunches of ultra-relativistic electrons and positrons circulating in a storage ring (like the Cornell Electron/Positron Storage Ring, CESR) is determined by the equilibrium of excitations - due to stochastic emission of photons, intra-beam scattering, electron cloud effects, interactions with residual gas and ions, and wake fields – and damping by synchrotron radiation. At the Wilson Laboratory we accelerate electrons and create positrons in our linear accelerator, boost their energy to anywhere from 1.5 to 5.3 GeV in the 768 m circumference synchrotron and then transfer them (positrons clockwise and electrons counterclockwise) to the storage ring CESR, where they circulate for many hours. The storage ring is instrumented with detectors to measure beam position, beam size, and bunch length, as well as the cloud of electrons that evolves around a positron beam and the ions trapped by an electron beam. CESR is the laboratory for the study of the physics that limits the particle density. We continue to develop instrumentation with better precision and higher bandwidth for monitoring beam properties. Our goal is to achieve the quantum limited emittance and to explore the particle dynamics in the ultra-low emittance regime.
Recent graduates Jim Shanks, Joe Calvey, and Mike Ehrlichman were involved in the development and study of low emittance tuning methods and instrumentation for measuring electron cloud density and energy spectrum, and intra-beam scattering,. Current graduate students Kelvin Blaser and Colin Clement are working to further reduce beam emittance and increase brightness, and to measure the interaction of the electron beam with ions.. David Sagan, Jim Crittenden, Yulin Li, Robert Meller, Kiran Sonnad, Dan Peterson, Walter Hartung, and Suntao Wang, are research associates and Mike Ehrlichman, Jim Shanks, and Joe Calvey postdocs in the CesrTA (CESR Test Accelerator) group. CesrTA is an international collaboration. Institutions from around the world, including KEK(Japan), SLAC(Stanford), LBNL(Berkeley), Fermi National Accelerator Lab, Brookhaven National Lab, Cockroft Institute (Great Britain), and CERN(Switzerland) are contributing equipment, numerical simulations and help with the experimental effort.
Muon g-2 experiment:
The goal of the new muon g-2 experiment at Fermi-Lab. is to measure the anomalous magnetic moment of the muon with 0.14ppm accuracy, corresponding to a 4-fold improvement over the existing best measurement. Meanwhile, there is a 3σ discrepancy between the measurement and the standard model calculation of the anomaly. The value of the anomaly arises from loops (radiative corrections) from virtual leptons, hadrons, and gauge bosons. The existing discrepancy between theory and measurement suggests the possibility of loops with new particles beyond the standard model. The new measurement will be sensitive to particles at the TeV scale, beyond the range accessible at the LHC. At present the uncertainties in the calculated and measured values of g-2 are comparable. The better measurement will motivate theorists to a better calculation. The experiment is planned to begin taking data in 2016. The experiment will also improve the upper limit on the muon electric dipole moment by a factor of nearly 100. The Cornell group is building the injection kicker for the muon storage ring and waveform digitizers for the calorimeters that detect the decay electrons.. Members of the Cornell g-2 group along with myself and Professor Lawrence Gibbons are graduate students Robin Bjorkquist and Andre Frankenthal, undergrads Jeffrey Bennett, He He, Thomas Rueter, Pratiti Deb, postdocs Nic Eggert and SeungCheon Kim, Senior Physicist Alexander Mikhailichenko. and engineer Nate Rider.
The Cornell Electron Storage Ring is the source of x-rays for CHESS, as well as for the CesrTA beam physics research program. The CESR /CHESS group is preparing a proposal to reconfigure the magnetic optics of the ring to reduce beam emittance by a factor of four. In order to make space for new undulator beam lines we plan to use magnets that combine focusing and bending into a single unit. The use of combined function magnets presents operational challenges that will require development of new algorithms for diagnosing and correcting machine errors. Postdocs Chris Mayes and Jim Shanks are leading the effort to design beam optics and magnets, to characterize the dynamics of the proposed machine, and develop commissioning strategies. Graduate student Colin Clement is experimenting with optimization algorithms for nonlinear lattice design. We expect to complete the upgrade and begin commissioning the new machine in 2017.