CLASSE, Ithaca, New York, USA
CalPoly, San Luis Obispo, California, USA
A fast beam profile monitor using visible synchrotron radiation (SR) has been constructed and installed in Cornell Electron Storage Ring. This monitor utilizes fast readout electronics based on the Hamamatsu H7260K multi-anode photomultiplier, which has a 32-channel linear array with 1mm channel pitch and sub-nanosecond rise time. In a low emittance lattice at 2 GeV, a double-slit interferometer is employed to measure the horizontal beam size. After careful calibration of the interference pattern, the horizontal beam size within a range of 100 to 500 microns can be measured with a precision of ±5 microns. Due to finite array size, the small vertical beam size is measured by imaging the pi-polarized component of the SR. The fast beam profile monitor is capable of measuring bunch-by-bunch turn-by-turn transverse beam sizes, which eliminates beam jitter inherent when imaging the average beam size with a CCD camera. Details of hardware and software controls are also discussed.
CLASSE, Ithaca, New York, USA
Manifestation of intrabeam scattering (IBS) in an electron/positron storage ring depends on the radiation damping time in two ways. First, the beam size is the equilibrium of the IBS growth rate in each of the three degrees of freedom and corresponding damping rates. Second, scattering events that occur less frequently than order once per damping time contribute to non-Gaussian tails that are invisible to our beam size monitors. The tail cut procedure excludes these relatively rare events in the calculation of equilibrium beam size. In machines with short damping times, the tail cut significantly reduces the effective IBS growth rate. At CesrTA, we measure the dependence of beam size on bunch charge in IBS-dominated beams. We vary the vertical emittance using a closed optics bump that increases the vertical dispersion and transverse coupling in the wiggler regions. Measurements are taken at both 2.1 and 2.3 GeV. Here we report the results of these experiments and compare those results to theory.
CLASSE, Ithaca, New York, USA
In storage rings, the presence of horizontal dispersion in the RF cavities introduces x-z coupling. The result is that the beam is skewed in the horizontal-longitudinal plane. The skew angle is proportional to the V15 term of the 6X6 coupling matrix which is proportional to the RF cavity voltage and the horizontal dispersion in the cavity. Here we report experiments at CesrTA where x-z coupling was explored using three distinct lattice configurations with different V15 coupling terms. We explore x-z coupling for each of these lattices by measuring the horizontal projection of the beam with a beam size monitor, as the RF voltage is varied. The first lattice has about 1 m dispersion in the RF cavities, resulting in a V15 term at the beam size monitor source point corresponding to 16 mrad x-z tilt. In the second, the V15 generated in one pair of cavities is compensated at the second pair by adjusting the horizontal betatron phase advance between the cavity pairs. In the third, the optics are adjusted so that the RF cavity region is dispersion-free, eliminating the coupling entirely. Additionally, intra-beam scattering is evident in our measurements of beam size vs. RF voltage.
CLASSE, Ithaca, New York, USA
The Cornell Electron Storage Ring is the laboratory for the CESR Test Accelerator damping ring R&D program, and the source of x-rays for CHESS. A peculiarity of the layout of the storage ring is that horizontal emittance is generated predominantly by the strong bends in the sextant of the ring that was designed with a long straight to accommodate the interaction region required for operation as an electron-positron collider. By reconfiguring that single sextant we reduce the emittance by 60% to 20 nm-rad at 5.3 GeV for x-ray production and with damping wigglers to 1.3 nm-rad at 2.1 GeV for investigations of low emittance phenomena. The 35 meter radius of curvature, 3.2 meter long dipoles are refitted as combined function (vertically focusing) magnets to create simple achromats. The layout can accommodate six, 3 meter long undulators, in addition to the six existing superconducting damping wigglers. With reduced horizontal emittance and energy spread, the reconfiguration enhances the sensitivity of CESR to the emittance diluting effects that are the subject of the CesrTA study. Capability of the x-ray source is significantly improved with six new undulator beam lines.