ANL, Argonne, USA
Insertion devices (IDs) in light sources generally produce small dipole perturbations on the stored beam of a storage ring light source, which is usually compensated by orbit correction. Tougher orbit stability requirements for the Advanced Photon Source Upgrade have led us to revisit the requirements of these magnetic-field errors. When including the effect of orbit correction (including fast orbit feedback), we realized that the field-error requirements change from a limit in absolute values of magnetic-field error integrals to that of rates of change in magnetic-field error integrals. Some modeling of the combined effect of ramping the strength of an ID with orbit correction will be presented. This new thinking has the potential of greatly alleviating the tuning requirements of insertion devices of all types.
ANL, Argonne, USA
Sextupole offset plays a large role in modern storage ring coupling control. Due to the non-linear field, the beam-based alignment of sextupoles becomes more difficult and often requires a sophisticated post-data process. A simple method had been developed at the APS that measures the vertical orbit variation (orbit change at BPM with variation of sextupole strength) versus beam trajectory through a sextupole in one plane while keeping the trajectory in other plane fixed. This method converts the non-linear problem into a linear one, and experiment results show very good reproducibility and accuracy.
ANL, Argonne, USA
Purdue University, West Lafayette, Indiana, USA
The first prototype superconducting undulator (SCU0) was successfully installed and commissioned at the Advanced Photon Source (APS) and is delivering photons for user science. All the requirements before operating the SCU0 in the storage ring were satisfied during a short but detailed beam commissioning. The cryogenic system performed very well in the presence of the beam. The total beam-induced heat load on the SCU0 agreed well with the predictions, and the SCU0 is protected from excessive heat loads through a combination of orbit control and SCU0 alignment. When powered, the field integral measured with the beam agreed well with the magnet measurements. An induced quench caused very little beam motion, and did not cause loss of the beam. The device was found to quench during unintentional beam dumps, but quench recovery is transparent to storage ring operation. There were no beam chamber vacuum pressure issues and no negative effect observed on the beam. Finally, the SCU0 was operated well beyond its design requirements, and no significant issues were identified. The beam commissioning results are described in this paper.
ANL, Argonne, USA
Purdue University, West Lafayette, Indiana, USA
The first prototype superconducting undulator (SCU0) was successfully installed and commissioned at the Advanced Photon Source (APS) and is delivering photons for user science. The magnet cores are mounted on but thermally isolated from the beam vacuum chamber. Protecting the SCU0 from high beam-induced heat loads was an important requirement before operating the SCU0 in the storage ring. Precise alignment of the beam vacuum chamber with respect to both the electron beam orbit as well as the synchrotron radiation generated in the upstream dipole magnet was therefore extremely important. The beam vacuum chamber was instrumented with nine thermal sensors. Using the sensors, the chamber alignment was determined with a 100-micron precision. This precision is more than 10 times higher than in a standard aperture scan. Other advantages of the thermal sensor-based alignment method include isolating the SCU0 alignment from other components in the orbit bump and providing good longitudinal spatial resolution. The chamber temperatures agreed well the predicted heat load and dependence on steering. This novel beam-based alignment method and results will be presented.
ANL, Argonne, USA
Development of a new fast-switching Electromagnetic Variably Polarizing Undulator (EMVPU) is underway at the Advanced Photon Source (APS). The EMVPU can produce x-rays with left- and right-handed circular polarizations and horizontal and vertical linear polarizations in the energy range 400-2000 eV. The undulator will be able to switch between left- and right-handed circular polarization at 10 Hz, fast enough to allow for magnetic circular dichroism studies that rely on lock-in amplifier techniques. The handedness switch will be accomplished by switching only the vertical component of the field while the horizontal component stays constant. Details of the EMVPU and its initial experimental test models are presented.
ANL, Argonne, USA
An electromagnetic variably polarizing quasi-periodic undulator was installed in the Advanced Photon Source (APS) storage ring in April 2012 and has been successfully commissioned with stored beam. This device is identified as the Intermediate Energy X-ray (IEX) undulator. The IEX undulator takes its name from the IEX beamline where it is installed. The IEX undulator is able to produce a variety of polarizations: linear vertical, linear horizontal, and right- or left-handed elliptical or circular. Ten pairs of poles, distributed quasi-periodically along the undulator length, are powered separately, allowing the field strength of the quasi-periodic poles to be adjusted. This adjustability allows the user to seek a balance between the suppression of the higher harmonics and the loss of flux in the fundamental that best suits the measurement being made. The IEX undulator has a 12.5-cm period and can achieve photon energies as low as 250 eV in horizontal polarization and 440 eV in vertical polarization. A description of the IEX undulator will be presented.
ANL, Argonne, USA
Strong beam perturbation from the intermediate-energy x-ray (IEX) undulator operation has been expected from the beginning. This paper describes our efforts including the initial magnet design, field measurements and compensation, special considerations of power supplies and the control system, and the final commissioning results with beam. Perturbations are well within the specified limits, and the IEX was made ready for user operation in less than six months.
ANL, Argonne, USA
The APS Upgrade project includes adding more insertion devices (IDs) to the APS storage ring. Perturbations from IDs have been reviewed, and the most significant sources are coming from the IDs that generate circular polarized light. To address this issue, we measured non-linear effects from the existing circular polarized undulator (CPU) and intermediate-energy x-ray (IEX). Measurement results have been compared with the simulation work. Correction schemes have been proposed and tested through experiments.
ANL, Argonne, USA
An ultra-low-emittance light source generally manifests very strong non-linear effects due to the significant focusing force applied and the resultant strong sextupoles. As one of the consequences, the dynamic aperture becomes very small, and only on-axis "swap-out" beam injection is workable. Another consequence is that the intra-beam scattering (IBS) effect and beam instability are much more severe, which limits the maximum achievable single-bunch intensity. As a result, multiple bunches with tight bunch spacing are required to reach high average beam current, which requires injection to be finished in a very short period, e.g., during the interval between bunches. Using a multi-bend-achromat (MBA) lattice designed for the Advanced Photon Source (APS) storage ring as an example, this paper presents an on-axis injection scheme based on the fast stripline technique together with discussions on how the scheme works with different parameter settings.