Beam lifetime in storage rings and colliders is affected by, among other effects, lattice nonlinearities. Their control is of great benefit to the dynamic aperture of an accelerator, whose ...enlargement leads in general to more efficient injection and longer lifetime. This article describes a procedure to evaluate and correct unwanted nonlinearities by using turn-by-turn beam position monitor data, which is an evolution of previous works on the resonance driving terms (RDTs). Effective normal and skew sextupole magnetic errors at the ESRF electron storage ring are evaluated and corrected (when possible) by using this technique. For the first time, also octupolar RDTs could be measured and used to define an octupolar model for the main quadrupoles. Most of the deviations from the model observed in the sextupolar RDTs of the ESRF storage ring turned out to be generated by focusing errors rather than by sextupole errors. These results could be achieved thanks to new analytical formulas describing the harmonic content of the nonlinear betatron motion to the second order. For the first time, linear combinations of RDTs have been also used for beam-based calibration of individual sextupole magnets. They also proved to be a powerful tool in predicting faulty magnets and in validating magnetic models. This technique also provides a figure of merit for a self-assessment of the reliability of the data analysis.
Full text
Available for:
CMK, CTK, FMFMET, IJS, NUK, PNG, UL, UM, UPUK
The scope of highly enantioselective and diastereoselective Michael additions of enolsilanes to unsaturated imide derivatives has been developed with use of Cu((S,S)-t-Bu-box)(SbF6)2 (1a) as a Lewis ...acid catalyst. The products of these additions are useful synthons that contain termini capable of differentiation under mild conditions. Michael acceptor π-facial selectivity is consistent with two-point binding of the imide substrate and can be viewed as an extension of substrate enantioselection in the corresponding Diels−Alder reactions. A model analogous to the one employed to describe the hetero Diels−Alder reaction is proposed to account for the observed relation between enolsilane geometry and product absolute diastereocontrol. Insights into modes of catalyst inactivation are given, including spectroscopic evidence for inhibition of the catalyst by a dihydropyran intermediate that evolves during the course of the reaction. A procedure is disclosed in which an alcohol additive is used to hydrolyze the inhibiting dihydropyran and afford the desilylated Michael adduct in significantly shortened reaction time.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
3.
Preparation of the EBS beam commissioning Liuzzo, S M; Carmignani, N; Franchi, A ...
Journal of physics. Conference series,
11/2019, Volume:
1350, Issue:
1
Journal Article
Peer reviewed
Open access
In 2020 the ESRF storage ring will be upgraded to a Hybrid Multi Bend Achromat (HMBA) lattice. The commissioning of the new ring will require dedicated tools, either updated from the existing ones or ...newly developed. Most of the software and procedures were tested on the existing storage ring before its decommissioning. In particular we present experiments on first-turn steering and beam accumulation, check of magnet polarity and calibration, and injection tuning. The use of a control-system simulator proved to be crucial for the debugging of the software and the development of the new control system, as far as beam measurements and manipulations are concerned.
The European Synchrotron Radiation Facility Extremely Brilliant Source (ESRF-EBS) is the first fourth generation 6 GeV storage ring (SR) light source making use of the hybrid multibend achromat ...lattice, reaching a natural horizontal emittance of 140 pm rad. Further, reducing the horizontal emittance would provide a more brilliant and a higher quality photon source for the EBS users. One way of achieving this is to operate the SR off-energy. The first approach reduces the electron beam energy by − 1 % , which gives a 121 pm rad natural horizontal emittance. To fulfill operation requirements, the full ring had to be rematched, including both the quadrupoles and the sextupoles in the linear optics correction. The off-energy settings are then tested in the SR in terms of lifetime, injection efficiency, and operability. Published by the American Physical Society 2024
Full text
Available for:
CMK, CTK, FMFMET, IJS, NUK, PNG, UL, UM, UPUK
In this paper the influence of betatron coupling on the transverse beam emittances is described using the resonance driving terms formalism. Betatron coupling and vertical dispersion generated by ...magnetic and installation errors are major sources of vertical emittance. A new scheme for minimizing the latter is presented here, together with results from measurements carried out in 2010 at the ESRF electron storage ring, which provided vertical emittance of about 4.4 pm, a record low for this machine. Two schemes for the automatic compensation of coupling introduced by insertion devices are also presented with results from the first implementation tests. This paper is also an attempt to clarify the various definitions and meanings of vertical emittance in the presence of coupling.
Full text
Available for:
CMK, CTK, FMFMET, IJS, NUK, PNG, UL, UM, UPUK
The general layout for Specialized Synchrotron Radiation Source 4th generation SSRS 4 is under development by leading of National Research Center "Kurchatov institute". In the framework of a ...collaborative project with European Synchrotron Radiation Facility (ESRF) supported by the Ministry of Education and Science of the Russian Federation, the applied research on determination of the configuration and key technical parameters for the control and beam diagnostic systems for 4th generation Specialized Synchrotron Radiation Source - SSRS- 4 is going on. The preliminary view of the proposed control and diagnostic system is presented and discussed. SSRS-4 inherits the experience of the scientific community including a great ESRF expertise in control system development (as founder of TANGO), robust diagnostics and long operational experience on ESRF's accelerator.
We have employed time-resolved X-ray diffraction with picosecond temporal resolution to measure the time-dependent rocking curves of laser-irradiated asymmetrically cut single InSb crystals. Coherent ...acoustic phonons were excited in the crystals by irradiation with 800-nm, 100-fs laser pulses at irradiances between 0.25 and 12 mJ/cm. The induced time-dependent strain profiles (corresponding to the coherent phonons) were monitored by diffracting collimated, monochromatic pulses of X-rays from the irradiated crystals. Recording of the diffracted radiation with a fast low-jitter X-ray streak camera resulted in an overall temporal resolution of better than 2 ps. The strain associated with the coherent phonons modifies the rocking curve of the crystal in a time-dependent manner, and the rocking curve is recorded by keeping the angle of incidence of the X-rays upon the crystal fixed, but varying the energy of the incident X-rays around a central energy of 8.453 keV (corresponding to the peak of the rocking curve of the unperturbed crystal). The observed time-dependent diffraction from the irradiated crystals is in reasonable agreement with simulations over a wide range of energies from the unperturbed rocking-curve peak.
Full text
Available for:
DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
A Low-Emittance Lattice for the ESRF Biasci, J.C.; Bouteille, J.F.; Carmignani, N. ...
Synchrotron radiation news,
11/2014, Volume:
27, Issue:
6
Journal Article
Peer reviewed
In the framework of its upgrade, the ESRF is designing a new lattice to replace the present double-bend achromat structure. This new lattice fulfills the following constraints and requirements: It ...fits in the present tunnel and keeps the insertion device source points at the same location; Its target horizontal emittance is around 150 pm; It keeps the electron energy at 6 GeV in order to preserve the spectral properties of the present beamlines; It minimizes the radiation losses and the magnet electrical consumption in order to decrease operating costs; The present injector complex is re-used with minor changes.
Full text
Available for:
BFBNIB, GIS, IJS, KISLJ, NUK, PNG, UL, UM, UPUK
10.
Synthesis of (−)-Epibatidine Evans, David A; Scheidt, Karl A; Downey, C. Wade
Organic letters,
09/2001, Volume:
3, Issue:
19
Journal Article
Peer reviewed
The synthesis of (−)-epibatidine has been accomplished utilizing a highly exo-selective asymmetric hetero Diels−Alder reaction. The key steps employed to transform the resulting bicycle into the ...natural product include a fluoride-promoted fragmentation and a Hofmann rearrangement.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
PDF
