Building the impedance model of a real machine

A reliable impedance model of a particle accelerator can be built by combining the beam coupling impedances of all the components. This is a necessary step to be able to evaluate the machine performance limitations, identify the main contributors in case an impedance reduction is required, and study the interaction with other mechanisms such as optics nonlinearities, transverse damper, noise, space charge, electron cloud, beam-beam (in a collider). The main phases to create a realistic impedance model, and verify it experimentally, will be reviewed, highlighting the main challenges. Some examples will be presented revealing the levels of precision of machine impedance models that have been achieved

A primary electron beam facility at CERN -- eSPS Conceptual design report

The design of a primary electron beam facility at CERN is described. The study has been carried out within the framework of the wider Physics Beyond Colliders study. It re-enables the Super Proton Synchrotron (SPS) as an electron accelerator, and leverages the development invested in Compact Linear Collider (CLIC) technology for its injector and as an accelerator research and development infrastructure. The facility would be relevant for several of the key priorities in the 2020 update of the European Strategy for Particle Physics, such as an electron-positron Higgs factory, accelerator R\&D, dark sector physics, and neutrino physics. In addition, it could serve experiments in nuclear physics. The electron beam delivered by this facility would provide access to light dark matter production significantly beyond the targets predicted by a thermal dark matter origin, and for natures of dark matter particles that are not accessible by direct detection experiments. It would also enable electro-nuclear measurements crucial for precise modelling the energy dependence of neutrino-nucleus interactions, which is needed to precisely measure neutrino oscillations as a function of energy. The implementation of the facility is the natural next step in the development of X-band high-gradient acceleration technology, a key technology for compact and cost-effective electron/positron linacs. It would also become the only facility with multi-GeV drive bunches and truly independent electron witness bunches for plasma wakefield acceleration. A second phase capable to deliver positron witness bunches would make it a complete facility for plasma wakefield collider studies. [...

The ESSnuSB design study: overview and future prospects

ESSnuSB is a design study for an experiment to measure the CP violation in the leptonic sector at the second neutrino oscillation maximum using a neutrino beam driven by the uniquely powerful ESS linear accelerator. The reduced impact of systematic errors on sensitivity at the second maximum allows for a very precise measurement of the CP violating parameter. This review describes the fundamental advantages of measurement at the 2nd maximum, the necessary upgrades to the ESS linac in order to produce a neutrino beam, the near and far detector complexes, the expected physics reach of the proposed ESSnuSB experiment, concluding with the near future developments aimed at the project realization.Comment: 19 pages, 11 figures; Corrected minor error in alphabetical ordering of the authors: the author list is now fully alphabetical w.r.t. author surnames as was intended. Corrected an incorrect affiliation for two authors per their reques

Examining the operational effectiveness and accountability of federal agencies as indicated in the performance and accountability reports required by the Government Performance And Results Act of 1993

MBA Professional ReportThe Government Performance and Results Act of 1993 (GPRA) was enacted to improve the confidence of the American people in the capability of the federal government and to initiate program performance improvement. The purpose of this project was to determine if GPRA initiatives have lead to indications of material performance improvements within three specific executive agencies. The agencies chosen were performing at different levels of effectiveness, according to the performance and accountability scorecard produced by the Mercatus Center at George Mason University, a non-governmental citizen advocacy center. The analysis examined performance plans, performance reports and strategic plans from the previous five years. The intent was to determine if the reports indicated improvements in program effectiveness and accountability over the five year evaluation period. An evaluation tool was constructed to create a performance matrix based on the raw data in the agencies' annual performance and accountability reports. Four customized measures were used to evaluate the agencies' performance from year to year. The results of the analysis indicated material performance improvements in one of the three agencies. Analysis revealed the other two agencies did not clearly indicate improvement in performance effectiveness. Evidence of improved program effectiveness and accountability inferred that these improvements may relate to the transparency and accountability requirements of GPRA.http://archive.org/details/examiningoperati1094510188Outstanding ThesisApproved for public release; distribution is unlimited

Beam Dynamics in the ESS Linac under the Influence of Monopole and Dipole HOMs

The European Spallation Source (ESS), planned to be operational in 2019, is anticipated to be the worlds most intense neutron source. The total beam power will be 5 MW. We focus on the impact of manufacturing errors on the beam quality. In particular we assess the emittance dilution which occurs due to Higher Order Modes (HOMs) excited at a harmonic of the bunch frequency. We also discuss some alignment issues pertaining to the cavities

Synchronous phase shift measurements for evaluation of the longitudinal impedance model at the CERN SPS

The High Luminosity LHC (HL-LHC) requires 2.3 × 1011 protons per bunch (ppb) at LHC injection. For the SPS, the injector to the LHC, this goal requires a doubling of the injected intensity to 2.6 × 1011 ppb. Longitudinal instabilities were observed in the SPS for intensities below the required 2.6 × 1011 ppb. Identifying, and ultimately mitigating, the impedance sources driving the instabilities requires an accurate impedance model. Here, we report on measurements of the synchronous phase shift with intensity and corresponding energy loss at the SPS injection. Using the loss factor to compute the energy loss from the measured bunch spectrum and the SPS impedance model leads to significant disagreements with measurements. This issue is investigated for the simplified case of a single resonator. However, simulating matched bunches using the SPS impedance model yields better agreement with measurements

Final Acceptance Testing of the CERN SPS Electrostatic Septa

In the framework of the LHC Injector Upgrade (LIU) project, the high field electrostatic septa (so-called ZS) have been upgraded to comply with the new requirements. Prior to their installation in the SPS accelerator in 2020, the septa were tested to verify their final performance. This report summarises the results of these final acceptance tests, covering the vacuum acceptance test, the HV conditioning, the final beam impedance measurements together with the ZS interconnects and validation of the upgraded ion trap system

Needs and Solutions for Machine Impedance Reduction

Particle beams with highest possible beam intensities are requested nowadays, hence in modern circular accelerators, the consideration of beam coupling impedance issues is of increasing relevance. Classical sources of beam coupling impedance are RF-systems, injection and extraction kickers, but also beam diagnostic elements such as wire scanners where the object itself forms an undesired cavity, and beam pipe transitions, namely tapers or steps. Optimally, for any machine, impedance mitigation shall take place already during the design phase. However, for older existing machines, often considerable hardware changes would be required to obtain a significant impedance reduction. In these cases, the required geometry changes for reducing beam coupling impedance are costly to be carried out, hence retro-fitted solutions such as impedance shields or damping mechanisms are required. For both approaches, different impedance mitigation strategies are available and their selection also depends on the needs, i.e., the type of problem that is arising. Single bunch instabilities, for example, require an optimization of the object geometry with the goal to reduce R/Q, whereas multi bunch instabilities or heating will ask for different measures. In this presentation, we will explain about typical sources of beam coupling impedances and how they could be circumvented. Possibilities to reduce beam coupling impedance in existing machine elements are included and applied solutions, such as impedance shields or HOM dampers will be presented as well