C. Steier - Academia.edu (original) (raw)

Papers by C. Steier

IEEE Transactions on Applied Superconductivity, 2012

Forty-eight harmonic sextupole magnets with integrated dipole correctors and skew quadrupole coil... more Forty-eight harmonic sextupole magnets with integrated dipole correctors and skew quadrupole coils will be introduced in the Advanced Light Source Storage Ring. These new magnets are required to allow the ALS to provide the 40 beamline users with higher photon beam brightness (factor of 2 or 3). Introducing new combined-function magnets in an existing storage ring is a challenge due to the limited space available and a balance had to be found between magnet performance and spatial constraints. Consequently four different magnet designs were required. The calculation and simulation results obtained for each design as well as the impact of the different design choices on the magnetic performance are developed in this paper.

The Advanced Light Source is one of the earliest 3rd generation light sources. With an active upg... more The Advanced Light Source is one of the earliest 3rd generation light sources. With an active upgrade program it has remained competitive over the years. The latest in a series of upgrades is a lattice upgrade project that was started in 2009. When it will be completed, the ALS will operate with a horizontal emittance of 2.2 nm and an effective emittance of 2.6 nm. Combined with the high current of 500 mA and the small vertical emittance the ALS already operates at this upgrade will keep it competitive for years to come. The presentation will present the status of the upgrade, including beam dynamics studies and lattice optimizations as well as the magnet design and status.

The beam energy at the Advanced Light Source (ALS) at Lawrence Berkeley National Laboratory was m... more The beam energy at the Advanced Light Source (ALS) at Lawrence Berkeley National Laboratory was measured with high precision using resonant depolarization. In a storage ring where the beam lifetime is dominated by largeangle intrabeam (Touschek) scattering, the relative beam polarization can be measured by relative changes in the beam lifetime because of the dependence of the Moller scattering rate on the polarization. In the fully Touschekdominated regime, the change in lifetime at the ALS due to a complete depolarization is larger than 10%. The energy calibration has been used at the ALS to perform high precision measurements of the machine stability, machine reproducibility and the momentum compaction factor.

Proceedings Particle Accelerator Conference, 1995

To expand the capabilities of the Advanced Light Source (ALS) and to satisfy the demand for high ... more To expand the capabilities of the Advanced Light Source (ALS) and to satisfy the demand for high energy x-ray sources with high brightness, three 1.3 T normal conducting bending magnets were replaced with three 5 T superconducting magnets (Superbends) in 2001. The new magnets will ultimately provide 12 new beam lines for users. The x-ray brightness and flux of the Superbends at 12 keV is more than one order of magnitude higher than the one of the conventional magnets they replaced. The Superbend project was a major upgrade of the ALS since the 3 Superbends are an integral part of the machine lattice and perturb its original 12-fold symmetry. This paper describes the successful (and quick) commissioning period and the accelerator physics issues associated with the Superbend upgrade (especially the off-energy single particle dynamics).

PACS2001. Proceedings of the 2001 Particle Accelerator Conference (Cat. No.01CH37268)

To satisfy the demand for more high energy, high brightness x-ray sources at the Advanced Light S... more To satisfy the demand for more high energy, high brightness x-ray sources at the Advanced Light Source (ALS), a plan is in place to replace three 1.3 Tesla normal conducting bending magnets with three 5 Tesla superconducting magnets (Superbends) in the year 2001. This will result in 12 new x-ray beam lines (four from each superbend) for users. The Superbend sources will be an order of magnitude higher in x-ray brightness and flux at 12 keV than the conventional 1.3 Tesla bending magnets. The Superbend project is a major upgrade to the ALS where the 3 superconducting magnets will be an integral part of the machine lattice. In this paper we discuss the current status of the Superbend projectas well as precomissioning studies prior to the 2001 installation for users.

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2005

The Advanced Light Source (ALS) is a third generation synchrotron light source located at Lawrenc... more The Advanced Light Source (ALS) is a third generation synchrotron light source located at Lawrence Berkeley National Laboratory (LBNL). There was an increasing demand at the ALS for additional high brightness hard x-ray beamlines in the 7 to 40 keV range. In response to that demand, the ALS storage ring was modified in

IEEE Transactions on Applied Superconductivity, 2014

The Advanced Light Source (ALS) is a third-generation light source in operation since 1993. This ... more The Advanced Light Source (ALS) is a third-generation light source in operation since 1993. This light source is providing state-of-the-art performance to more than 40 beamlines and their users, due to the upgrades that have been completed over the last few years. The storage ring upgrade project that is developed here will allow the ALS to provide the 40 beamline users with higher photon beam brightness (factor of 2 or 3) by having its storage ring lattice modified. Forty-eight harmonic sextupole magnets with integrated dipole correctors and skew quadrupole coils will be introduced, which will require a level of installation activity not seen at the ALS since its original construction in 1991. Introducing new combined-function magnets in an existing storage ring is a challenge due to the limited space available and a balance had to be found between magnet performance and spatial constraints. After an introduction reviewing the characteristics of the three design families of the 48 combined-function magnets, the magnet fabrication and installation are developed along with analyses based on the magnetic measurements and the ALS storage ring commissioning results.

To understand the dynamics in an accelerator it is essential to have a good model representing it... more To understand the dynamics in an accelerator it is essential to have a good model representing its realistic lattice. One method used at the ALS to calibrate the linear (coupled) accelerator model is the analysis of orbit response matrices. Recently this method has been combined with frequency map techniques, both in tracking and experiment at the accelerator. Comparing the results of simulated and measured frequency maps shows how accurately the accelerator model describes the nonlinear beam dynamics. In addition measured frequency maps can serve as a model independent tool to evaluate the quality of a lattice. The measurements at the ALS clearly show the network of coupling resonances and the agreement with the simulation using the calibrated model is very good whereas the disagreement is large when using an ideal accelerator model.

The Advanced Light Source (ALS) at Berkeley Lab while one of the earliest 3rd generation light so... more The Advanced Light Source (ALS) at Berkeley Lab while one of the earliest 3rd generation light sources remains one of the brightest sources for soft x-rays worldwide. A multiyear upgrade of the ALS is currently under way, which includes new and replacement x-ray beamlines, a replacement of many of the original insertion devices and many upgrades to the accelerator. The accelerator upgrade that affects the ALS performance most directly is the ALS brightness upgrade, which will reduce the horizontal emittance from 6.3 to 2.2 nm (2.6 nm effective). This will result in a brightness increase by a factor of three for bendmagnet beamlines and at least a factor of two for insertion device beamlines. Magnets for this upgrade are currently in production and will be installed starting later this year.

Proceedings of the 2005 Particle Accelerator Conference

A scheme is proposed for producing ps length pulses of xray radiation from the Advanced Light Sou... more A scheme is proposed for producing ps length pulses of xray radiation from the Advanced Light Source (ALS) using two RF deflecting cavities. The cavities create vertical displacements of electrons correlated with their longitudinal position in the bunch. The two cavities separated by 180 degrees of vertical phase advance. This allows the vertical kick from one cavity to be compensated by the vertical kick of the other. The location of the cavities corresponds to the end of one straight section and the beginning of the following straight section. Halfway between the cavities a bending magnet source is located. The radiation from the bend can be compressed to ~1 ps in duration.

Proceedings of the 2003 Particle Accelerator Conference, 2003

For synchrotron light sources and for damping rings of linear colliders it is important to be abl... more For synchrotron light sources and for damping rings of linear colliders it is important to be able to minimze the vertical emittance and to correct the spurious vertical dispersion. This allows one to maximize the brightness and/or the luminosity. A commonly used tool to measure the skew error distribution is the analysis of orbit response matrices using codes like LOCO. Using the new Matlab version of LOCO and 18 newly installed power supplies for individual skew quadrupoles at the ALS the emittance ratio could be reduced below 0.1% at 1.9 GeV yielding a vertical emittance of about 5 pm. At those very low emittances, additional effects like intra beam scattering become more important, potentially limiting the minimum emittance for machine like the damping rings of linear colliders.

Journal of Physics: Conference Series, 2018

The ALS upgrade into a diffraction-limited soft X-rays light source requires a small emittance, w... more The ALS upgrade into a diffraction-limited soft X-rays light source requires a small emittance, which is achieved by much stronger focusing than in the present ALS. Very strong focusing elements and a relatively small vacuum chamber make the required rapid commissioning a significant challenge. This paper will describe the progress towards a startto-end simulation of the machine commissioning and present first simulation results.

The beam emittance at the interaction point of linear colliders is expected to be strongly influe... more The beam emittance at the interaction point of linear colliders is expected to be strongly influenced by the emittance of the beams extracted from the damping rings. Intra-beam scattering (IBS) potentially limits the minimum emittance of low-energy storage rings, and this effect strongly influences the choice of energy of damping rings [1]. Theoretical analysis suggests that the NLC damping rings will experience modest emittance growth at 1.98 GeV, however there is little experimental data of IBS effects for very low-emittance machines in the energy regime of interest. The Advanced Light Source (ALS) at Lawrence Berkeley National Laboratory is a third-generation synchrotron light source operating with high-intensity, low-emittance beams at energies of approximately 1- 2 GeV, and with emittance coupling capability of 1 % or less. We present measurements of the beam growth in three dimensions as a function of current, for normalized natural horizontal emittance of approximately 1- 10 ...

Elliptically Polarizing Undulators [1] that provide full photon polarization control also have fa... more Elliptically Polarizing Undulators [1] that provide full photon polarization control also have fast, intrinsic trans-verse roll-off of the magnetic field. The roll-off is espe-cially fast for vertical polarization settings, and can have big detrimental effects on the nonlinear single particle dy-namics. Particularly low and medium energy light sources and long period EPUs are prone to those effects. The three existing 50 mm period EPUs at the ALS have been retrofitted with shims to correct for these dynamic multi-pole effects and a new 90 mm period device which other-wise would have caused a huge reduction in dynamic aper-ture has been shimmed before installation. Beam dynamics measurements on all devices show that the shimming works very well and user operation with the long period EPU has begun.

The ALS-U project consists in the upgrade of the existing Advanced Light Source at LBNL to a new ... more The ALS-U project consists in the upgrade of the existing Advanced Light Source at LBNL to a new ultra-low emittance lattice for production of diffraction-limited soft x-rays. In order to compensate for the reduced beam lifetime we intend to operate the machine in continuous topoff mode, where one of several bunch trains is extracted every 30-60 seconds and swapped with a fresh train from the accumulator ring, which is injected on axis without perturbing the circulating beam. In this paper we present our design for the injection/extraction kicker based on matched stripline electrodes. Such kicker has to provide the necessary deflection for simultaneously extracting a bunch train and injecting on-axis a fresh one from the accumulator ring. Rise and fall times must fit in the gap between bunch trains so that the injection/extraction process does not affect the remaining bunches. The main parameters of such a kicker are discussed with particular emphasis on the minimum gap length betwe...

The Advanced Light Source (ALS) is a third generation synchrotron light source that has been oper... more The Advanced Light Source (ALS) is a third generation synchrotron light source that has been operating since 1993 at Berkeley Lab. A few years ago, the ALS was upgraded to achieve Top-Off Mode, which required replacing the booster dipole and quadrupole magnet power supplies to increase the peak booster beam energy from 1.5GeV to 1.9GeV. The original analog controller for each power supply has been replaced by a digital power supply controller (DPSC) to improve stability and resolution and provide a remote interface

Beam stability is one of the most important properties for the users of a synchrotron light sourc... more Beam stability is one of the most important properties for the users of a synchrotron light source. Beam stability includes the stability of orbit, beamsize, current (lifetime), energy, and energy spread. As light sources are generating higher brightnesses, adding fast switching variable polarization devices, and and producing smaller source sizes, there is a necessity for continuous improvements in beam stability. In this talk an overview of the state of the art in beam stabilization and remaining challenges for beam stability are presented. CONTRIBUTION NOT RECEIVED MO3PBI03 Proceedings of PAC09, Vancouver, BC, Canada 54 Light Sources and FELs A05 Synchrotron Radiation Facilities

In 2006, the 30mm period In-Vacuum Insertion Device (IVID) was operational for the femtosecond ph... more In 2006, the 30mm period In-Vacuum Insertion Device (IVID) was operational for the femtosecond phenomena beamline at the Advanced Light Source (ALS) of Lawrence Berkeley National Laboratory. Since routine operation began a series of partial or total beam losses as well as coincident sudden pressure increases within the IVID vacuum system have occurred while changing the IVID gap. This paper reports these observations and describes the investigations and the repair attempt performed on this insertion device.