Electron beam sizes and lifetimes at MAX II and MAX III

The MAX II and MAX III synchrotron light sources at MAX-lab provide synchrotron radiation for experiments in a wide variety of research fields. The synchrotron radiation is emitted by ultra-relativistic electrons circulating in electron storage rings. In this thesis the transverse and longitudinal electron beam sizes and the electron beam lifetime limitations in electron storage rings are discussed and the methods used at MAX-lab to measure them are described. The thesis describes how measurements of the electron beam sizes and lifetimes were used to investigate and improve the performance of MAX III and to evaluate a change in the MAX II vacuum system. MAX II was the first synchrotron light source to install nonevaporable getter (NEG)-coated dipole vacuum chambers. They were installed in order to test the feasibility of the MAX IV 3 GeV storage ring vacuum design, where NEG-coated dipole chambers are an integral part of the design. From measurements of the lifetime limitations in MAX II it was concluded that NEG-coated dipole vacuum chambers do not appear to have any negative impact on the performance and operation of a synchrotron light source. A diagnostic beam line was designed and installed in MAX III in order to determine the transverse electron beam profile. The performance of the beam line was investigated by conducting a series of measurements at different beam line settings. There was good agreement between the determined beam sizes for the different settings. The diagnostic beam line was used to determine the horizontal and vertical dispersion and emittance in MAX III at low currents, and an increase in the momentum spread from longitudinal instabilities at higher currents. By adding a second passive Landau cavity to the MAX III radio frequency (RF) system the instabilities were damped in the main window of operation. Measurements of the longitudinal beam size and the induced voltages in the passive cavities agreed well with computer simulations of the triple RF system of MAX III. At high Landau cavity voltages a stable overstretched bunch shape with two regions of phase stability was observed. The lifetime limitations and acceptances in MAX III were determined and the location of a horizontal aperture restriction was identified. Removing the aperture restriction increased the lifetime in MAX III by a factor of two

Transverse electron beam imaging system using visible synchrotron radiation at MAX III

The diagnostic beam line at the MAX III synchrotron light source utilizes the synchrotron radiation (SR) in the visible to ultraviolet range to form images of the transverse electron beam profile. The emission and subsequent propagation and focusing of the SR is modeled, taking into account effects such as diffraction and the longitudinally distributed SR generation. A detailed description of the setup of the beam line and method used to determine the transverse beam profile is given in the paper. In order to investigate the imaging method, a series of measurements were performed where the beam line configuration was varied to utilize different wavelengths and polarizations of the SR and different horizontal opening angles of the measurement system. A suggestion is made how to measure future small horizontal beam sizes. (C) 2011 Elsevier B.V. All rights reserved

Equilibrium bunch density distribution with passive harmonic cavities in a storage ring

The MAX IV storage rings, currently under construction in Lund, Sweden, will use third harmonic cavities operated passively to lengthen the bunches and alleviate collective instabilities. These cavities are an essential ingredient in the MAX IV design concept and are required for achieving the final design goals in terms of stored current, beam emittance, and beam lifetime-such performance challenges are in fact common to all recent ultralow emittance storage ring designs and harmonic cavities are currently under consideration in several laboratories. In this paper, we report on parametric studies comparing different harmonic cavity settings in terms of the resulting bunch length, peak bunch density, and incoherent synchrotron frequency spread for the MAX IV 3 GeV ring. The equilibrium longitudinal bunch density distribution was calculated by establishing a self-consistent equation for the bunch form factor, describing the bunch shape. The calculations are fully self-consistent in the sense that not only the amplitude but also the phase of the waves excited by the beam in the harmonic cavity were assumed to be a function of the bunch shape, which allowed us to explore a wide parameter range not restricted to the region close to the conditions for which the first and second derivatives of the total rf voltage are zero at the synchronous phase. Our results indicate that up to a factor 5 increase in rms bunch length is achievable with a purely passive system for the MAX IV 3 GeV ring while keeping a relatively large harmonic cavity detuning, thus limiting the unavoidable Robinson antidamping rate from the fundamental mode of a passively operated harmonic cavity to values below the synchrotron radiation damping rate. The paper is complemented by results of measurements performed in the MAX III storage ring, which showed good agreement with calculations following the fully self-consistent approach

Experiences from nonevaporable getter-coated vacuum chambers at the MAX II synchrotron light source

Vacuum chambers coated with nonevaporable getter (NEG) materials have been used in straight sections of synchrotron light sources for the past 10 years. The MAX II storage ring, where four NEG-coated insertion device vacuum chambers and three NEG-coated dipole vacuum chambers have been installed, is the first synchrotron light source to also use NEG-coated dipole vacuum chambers. In connection with the installation of the latest two NEG-coated dipole chambers in April 2009, the evolution of the pressure and lifetime-limiting effects in MAX II has been determined from measurements with movable scrapers. The results have been compared with results from scraper measurements done in 2003, before any NEG-coated vacuum chambers were installed in the storage ring. Less than three months after the installation of the latest dipole chambers the vacuum system in MAX II was performing well with a pressure already lower than the pressure measured in 2003. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3281432

Using Multi-Bend Achromats in Synchrotron Radiation Sources

Multi-bend achromats offer small electron beam emittance, large energy acceptance and a good dynamic aperture. Two examples are discussed below, each using 7-bend achromats; a 12 achromat lattice and a 20 achromat one. Some possible technical solutions associated with the dense lattices are discussed: magnet technology, vacuum system and RF system. Some characteristics of the two rings are also presented; effects of Intra Beam Scattering, Touschek life-time and the electron beam parameter values

BioMAX the first macromolecular crystallography beamline at MAX IV Laboratory

BioMAX is the first macromolecular crystallography beamline at the MAX IV Laboratory 3 GeV storage ring, which is the first operational multi-bend achromat storage ring. Due to the low-emittance storage ring, BioMAX has a parallel, high-intensity X-ray beam, even when focused down to 20 μm × 5 μm using the bendable focusing mirrors. The beam is tunable in the energy range 5-25 keV using the in-vacuum undulator and the horizontally deflecting double-crystal monochromator. BioMAX is equipped with an MD3 diffractometer, an ISARA high-capacity sample changer and an EIGER 16M hybrid pixel detector. Data collection at BioMAX is controlled using the newly developed MXCuBE3 graphical user interface, and sample tracking is handled by ISPyB. The computing infrastructure includes data storage and processing both at MAX IV and the Lund University supercomputing center LUNARC. With state-of-the-art instrumentation, a high degree of automation, a user-friendly control system interface and remote operation, BioMAX provides an excellent facility for most macromolecular crystallography experiments. Serial crystallography using either a high-viscosity extruder injector or the MD3 as a fixed-target scanner is already implemented. The serial crystallography activities at MAX IV Laboratory will be further developed at the microfocus beamline MicroMAX, when it comes into operation in 2022. MicroMAX will have a 1 μm × 1 μm beam focus and a flux up to 1015 photons s with main applications in serial crystallography, room-temperature structure determinations and time-resolved experiments

Long-term effects of restriction of intravenous fluid in adult ICU patients with septic shock

PURPOSE To assess long-term outcomes of restrictive versus standard intravenous (IV) fluid therapy in adult intensive care unit (ICU) patients with septic shock included in the European Conservative versus Liberal Approach to Fluid Therapy in Septic Shock in Intensive Care (CLASSIC) trial. METHODS We conducted the pre-planned analyses of mortality, health-related quality of life (HRQoL) using EuroQol (EQ)-5D-5L index values and EQ visual analogue scale (VAS), and cognitive function using Mini Montreal Cognitive Assessment (Mini MoCA) test at 1 year. Deceased patients were assigned numerical zero for HRQoL as a state equal to death and zero for cognitive function outcomes as worst possible score, and we used multiple imputation for missing data on HRQoL and cognitive function. RESULTS Among 1554 randomized patients, we obtained 1-year data on mortality in 97.9% of patients, HRQoL in 91.3%, and cognitive function in 86.3%. One-year mortality was 385/746 (51.3%) in the restrictive-fluid group versus 383/767 (49.9%) in the standard-fluid group, absolute risk difference 1.5%-points [99% confidence interval (CI) - 4.8 to 7.8]. Mean differences were 0.00 (99% CI - 0.06 to 0.05) for EQ-5D-5L index values, - 0.65 for EQ VAS (- 5.40 to 4.08), and - 0.14 for Mini MoCA (- 1.59 to 1.14) for the restrictive-fluid group versus the standard-fluid group. The results for survivors only were similar in both groups. CONCLUSIONS Among adult ICU patients with septic shock, restrictive versus standard IV fluid therapy resulted in similar survival, HRQoL, and cognitive function at 1 year, but clinically important differences could not be ruled out

Pantoprazole in Patients at Risk for Gastrointestinal Bleeding in the ICU

BACKGROUND Prophylaxis for gastrointestinal stress ulceration is frequently given to patients in the intensive care unit (ICU), but its risks and benefits are unclear. METHODS In this European, multicenter, parallel-group, blinded trial, we randomly assigned adults who had been admitted to the ICU for an acute condition (i.e., an unplanned admission) and who were at risk for gastrointestinal bleeding to receive 40 mg of intravenous pantoprazole (a proton-pump inhibitor) or placebo daily during the ICU stay. The primary outcome was death by 90 days after randomization. RESULTS A total of 3298 patients were enrolled; 1645 were randomly assigned to the pantoprazole group and 1653 to the placebo group. Data on the primary outcome were available for 3282 patients (99.5%). At 90 days, 510 patients (31.1%) in the pantoprazole group and 499 (30.4%) in the placebo group had died (relative risk, 1.02; 95% confidence interval [CI], 0.91 to 1.13; P=0.76). During the ICU stay, at least one clinically important event (a composite of clinically important gastrointestinal bleeding, pneumonia, Clostridium difficile infection, or myocardial ischemia) had occurred in 21.9% of patients assigned to pantoprazole and 22.6% of those assigned to placebo (relative risk, 0.96; 95% CI, 0.83 to 1.11). In the pantoprazole group, 2.5% of patients had clinically important gastrointestinal bleeding, as compared with 4.2% in the placebo group. The number of patients with infections or serious adverse reactions and the percentage of days alive without life support within 90 days were similar in the two groups. CONCLUSIONS Among adult patients in the ICU who were at risk for gastrointestinal bleeding, mortality at 90 days and the number of clinically important events were similar in those assigned to pantoprazole and those assigned to placebo. (Funded by Innovation Fund Denmark and others; SUP-ICU ClinicalTrials.gov number, NCT02467621 .)