Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
LBNL, Berkeley, California, USA
The electron cloud (EC) density in accelerator beam-pipe has been measured using resonant microwaves. The resonances are produced by changes in beam-pipe geometry that generate reflections and standing waves, with typical behavior being similar to a section of waveguide with shorted ends. The technique uses fact that the EC density will shift the resonant frequencies. In previous analysis, we have made the simplifying approximation that the standing waves are multiples of a half-wavelength and that the magnitude of the electric field is symmetric about the longitudinal center of the resonance. In this paper we show that some changes in beam-pipe geometry will result in asymmetric electric field magnitudes along the resonant length. When this is combined with an EC density that varies along this length, the magnitude of the frequency shift will be altered. We present our initial attempt to correct for this effect by modeling the existing beam-pipe using CST Microwave Studio(R) to obtain a more realistic electric field distribution. This correction is then applied to data taken with beam at several resonant frequencies. The measurements were made at the Cornell Electron Storage Ring (CESR), which has been reconfigured as a test accelerator (CesrTA) providing electron or positron beams ranging in energy from 2 to 5 GeV.
* http://dx.doi.org/10.1016/j.nima.2014.03.063
SLAC, Menlo Park, California, USA
LBNL, Berkeley, California, USA
CERN, Geneva, Switzerland
We present experimental measurements taken from CERN SPS machine development studies with a wideband intra-bunch feedback channel prototype. The demonstration system is a digital processing system with recently installed wideband kicker and amplifier components. This new hardware extends the bandwidth up to 1GHz and allows driving and controlling multiple vertical transverse modes in the bunch. The studies are focused on both driving the bunch with spectrally controlled signals to identify a reduced model of the bunch dynamics and testing model-based feedback controllers to stabilize the bunch dynamics. The measurements are structured to validate reduced MIMO models and macro-particle simulation codes, including the dynamics and limits of the feedback channel. Noise effects and uncertainties in the model are evaluated via SPS measurements to quantify the limits of control techniques applied to stabilize the intrabunch dynamics. The design of controllers for Q26 and Q20 optics are illustrated and future control developments are described.
LBNL, Berkeley, California, USA
Improvements in brightness and coherent flux of about two orders of magnitude over operational storage ring based light sources are possible using multi bend achromat lattice designs. These improvements can be implemented as upgrades of existing facilities, like the proposed upgrade of the Advanced Light Source, making use of the existing infrastructure, thereby reducing cost and time needed to reach full scientific productivity on a large number of beamlines. An R&D program funded by internal laboratory funds was started at LBNL to further develop the technologies necessary for diffraction-limited storage rings (DLSR). It initially involves five areas, and focuses on the specific needs of soft x-ray facilities: vacuum system/NEG coating of small chambers, injection/pulsed magnets, RF systems/bunch lengthening, magnets/radiation production with advanced radiation devices, and beam physics design optimization. Some hardware prototypes have been built. The work will expand in the future to demonstrate necessary key technologies at the subsystem level or in beam tests and include new areas like photon beamline optics.
LBNL, Berkeley, California, USA
The ALS upgrade proposal (ALS-U) requires lengthening the bunch by a factor of at least four in order to increase the beam lifetime to acceptable values. Due to the presence of gaps in the fill pattern, required by the injection/extraction kicker system, the beam-induced voltage in the passive, normal-conducting, cavities which we plan to use is not constant over the length of a bunch train. We present our result on the optimal tuning of the harmonic cavities to obtain the best lifetime increase, including the effects of strongly non-gaussian bunch shapes and wakefield distortions of the potential well.