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

Collective Effects Associated With Ultra-High Beam Intensities in Factories

The beam currents at the new $e^+e^−$ factories exceed those of conventional colliders by more than an order of magnitude. To achieve high luminosities the multi-bunch, highcurrent beams must be both longitudinally and transversely stable. Commissioning of the $e^+e^−$ factories has provided a wealth of new experimental data on beam stability in the regime of extremely high beam intensities. Many high-current effects have been studied including ion and dust trapping, issues relating to heavy beam loading, and positron beam emittance dilutions due to electron cloud instabilities arising from photoelectrons and/or multipacting inside the vacuum chamber. This paper will review the new experimental data on high intensity issues with emphasis on new effects

Emittance Preservation in Linear Accelerators (only abstract)

Preservation of the phase space density of charged particles during the acceleration to high energies is essential for achieving high luminosities in linear colliders. Precise knowledge of the electromagnetic fields which govern the beam transport is very important. Inaccurate knowledge of these parameters, which may come about in practice, may be overcome using powerful methods which exploit measurements of the beam behavior. In this report preservation of the single-bunch beam emittances using such methods in linear colliders will be reviewed with experimental results from the electron-positron linear collider at Stanford