First Observations of a "Fast Beam-Ion Instability"

We report the results of experiments on a "fast beam-ion instability" at the Advanced Light Source (ALS). This ion instability, which can arise even where the ions are not trapped over multiple beam passages, will likely be important for many future accelerators. In our experiments, we filled the ALS storage ring with helium gas, raising the pressure approximately two orders of magnitude above the nominal value. With gaps in the bunch train large enough to avoid conventional (multi-turn) ion trapping, we observed a factor of 2-3 increase in the vertical beam size along with coherent beam oscillations. The single-pass nature of this instability was demonstrated

Measurement with beam of the deflecting higher order modes in the TTF superconducting cavities

This paper reports on recent beam measurements of higher order modes in the TESLA Test Facility (TTF) accelerating modules. Using bunch trains of about 0.5 ms with 54MHz bunch repetition and up to 90% modulated intensity, transverse higher order modes are resonantly excited when the beam is offset and their frequency on resonance with the modulation frequency. With this method, the trapped modes can be excited and their counteraction on the beam observed on a wide-band BPM downstream of the module. Scanning the modulation frequency from 0 to 27MHz allows a systematic investigation of all possible dangerous modes in the modules

Proof-of-Principle Experiment for FEL-Based Coherent Electron Cooling,”

Abstract Coherent electron cooling (CEC) has a potential to significantly boost luminosity of high-energy, highintensity hadron-hadron and electron-hadron colliders. In a CEC system, a hadron beam interacts with a cooling electron beam. A perturbation of the electron density caused by ions is amplified and fed back to the ions to reduce the energy spread and the emittance of the ion beam. To demonstrate the feasibility of CEC we propose a proof-of-principle experiment at RHIC using SRF linac. In this paper, we describe the setup for CeC installed into one of RHIC's interaction regions. We present results of analytical estimates and results of initial simulations of cooling a gold-ion beam at 40 GeV/u energy via CeC

HERA Performance Upgrade: Achievements and Plans for the Future

With the design luminosity already surpassed in 1997, an ambitious upgrade of the HERA proton-lepton collider was installed in 2000/2001 to provide higher luminosity and longitudinally polarized lepton beams in the colliding beam experiments, H1 and ZEUS. Initially, experimental backgrounds limited the total beam currents. After completion of the HERA-B experiment in 2003, the number of colliding bunches was reduced while maintaining the same total beam currents to increase the single-bunch beam currents. With pre-upgrade bunch currents the specific luminosity was measured to be 3 times higher with the upgrade. Following modifications which helped to alleviate the detector backgrounds in 2003 and an extended period of steady operation, HERA is now operating with the design number of bunches while the total beam currents Ip×Ie are being steadily increased. With less than 60% of the total design current, peak luminosities of 3.5×1031 cm$^{-2}$s$^{-1}$ have been demonstrated with a longitudinal polarization at the interaction points exceeding 50%. In this presentation experience with the luminosity upgrade and future plans will be described

Measurement and Control of Charged Particle Beams

This advanced textbook and reference is the first comprehensive and systematic review of all methods used for the measurement, correction, and control of the beam dynamics of modern particle accelerators. Based on material presented in several lectures at the US Particle Accelerator School, the text is intended for graduate students starting research or work in the field of beam physics. Relativistic beams in linear accelerators and storage rings provide the focus. After a review of linear optics, the text addresses basic and advanced techniques for beam control, plus a variety of methods for the manipulation of particle-beam properties. In each case, specific procedures are illustrated by examples from operational accelerators, e.g., CERN, DESY, SLAC, KEK, LBNL, and FNAL. The book also treats special topics such as injection and extraction methods, beam cooling, spin transport, and polarization. Problems and solutions enhance the book’s usefulness in graduate courses