In 2008 the Cornell Electron Storage Ring (CESR) will end nearly three decades of providing electron-positron collisions for the CLEO experiment. At that time it will be possible to reconfigure CESR as a test accelerator, CesrTA, for important accelerator R&D work directed to high intensity beam development and the International Linear Collider (ILC) project. CESR offers a unique opportunity with which to investigate beam physics and instrumentation critical to the design and operation of the ILC component known as "damping rings" that are perhaps the most challenging accelerator system in the ILC and other possible projects.. The changes required to make CESR available as a test accelerator are modest so that research results will be available in a timely fashion.
The scientific broader impacts of this work are significant. The use of real time measurements for the optimization of beam performance via interactive algorithms has applications in several other areas of research of high complexity. The fast x-ray profile monitors being developed here and the other instrumentation developed for CesrTA will be very useful for synchrotron radiation research and other accelerator applications. Of primary importance for the broader impact of this work is the hands-on training of accelerator and x-ray beam line scientists that serve around the world as principals and staff of laboratories for nuclear and particle physics and x-ray science.
Further, faculty, staff and students participate in a broad gauged program of outreach and education involving graduate and undergraduate students and the general public with special emphasis on K-12. The laboratory's intellectual and physical resources are used to promote the adventure of science directly to young people as well as to provide workshops and direct support for teachers of science in their own classrooms and in group settings on campus. In addition, the Lab has been collaborating with underrepresented populations in both urban settings of New York City and rural areas here on the edge of Appalachia. Creation of materials for the classroom is also an important part of this work in helping teachers in New York State deal with changing science curricula.
The International Linear Collider (ILC) is a proposed particle accelerator that would complement the Large Hadron Collider (LHC) at CERN, to unlock some of the deepest mysteries of the universe, including the origin of mass, and the nature of dark matter and dark energy. The machine would consist of two superconducting linear particle accelerators that face each other, one for electrons and the other for positrons (anti-electrons). The electron and positron beams, each accelerated to an energy of over a hundred billion electron volts, would be brought into head on collision in a central detector. In order to obtain useful collision rates, bunches of electrons and positrons, each containing twenty billion particles, must be compressed to a cross section of a few nanometers high by a few hundred nanometers wide. (A nanometer is a billionth of a meter.) In order to prepare these ultra high density bunches of particles, they are cooled in damping rings prior to acceleration to high energy. The damping rings take the high emittance (large cross section) bunches that are delivered from the electron and positron sources, and through the process of radiation damping, squeeze them into ultra low emittance (small cross section) bunches in preparation for their journey to high energy in the linear accelerators. In the damping ring, a number of effects can interfere with preparation of the intense beams that are required. The ring in which the particles circulate is an evacuated metal tube in the shape of a bicycle inner tube. Magnets guide the particles in circles along the center of the tube. As the particles speed around the tube, they emit x-rays that can strike the inner surface of the tube and knock electrons off of its surface and into the path of the particle beam. In the positron ring, these knock off electrons accumulate and form an electron cloud, which then interacts directly with the circulating positrons. Indeed the build-up of the electron cloud, and the subsequent interaction of the cloud with the positron beam in the damping ring, was identified as a major risk for the successful construction of a linear collider. In order to investigate the physics of the electron cloud in a damping ring with very small, high density bunches of positrons, the Cornell Electron/positron Storage Ring (CESR) was converted to operate like such a damping ring. It was instrumented to measure the growth of the electron cloud and its subsequent effect on the positron beam, and to test techniques and equipment for suppressing the cloud. We refer to the reconfigured machine as the CESR Test Accelerator (CESRTA). We have learned through our investigations that there is a maximum tolerable electron cloud density, beyond which the very small positron bunches will begin to grow bigger due to their interaction with the cloud. We discovered that by applying special mechanical and chemical treatments to the surface of the vacuum tube through which the positrons circulate, that the growth of the cloud can be suppressed. These discoveries depended on our invention of specialized detectors for measuring the electron cloud and its effect on the positron beam. Along the way we developed instruments and a methodology for routinely compressing the positron bunches to very small dimensions and correspondingly very high intensities. On the basis of our findings we have designed a damping ring for the linear collider that we are confident can deliver the intense bunches required for the pursuit of those deep mysteries of the universe we referred to above. The CESRTA collaboration includes scientific staff and students from Cornell University’s Laboratory for Elementary-Particle Physics as well as more than 50 senior staff members from over a dozen accelerator laboratories and universities around the world.
