Betatron coupling measurement and optimization in Indus-2 storage ring.

Brightness is an important parameter for any synchrotron radiation source. Correcting the emittance coupling is one of the ways to increase photon beam brightness in the operational storage ring. The main source of this effect is betatron coupling, resulting from the skew quadrupolar errors. Tune split and Linear Optics from Closed Orbit (LOCO) techniques are used to measure the betatron coupling. We discuss the measurement result of betatron coupling and its correction in the Indus-2 storage ring using available four power supplies, as the knobs, driving the skew quadrupole windings located on sextupoles. The measured coupling ratio of ∼0.8% closely matches with the coupling ratio obtained from the LOCO fit model. Based on LOCO correction, the coupling ratio can be reduced to ∼0.4%, which is limited by the degrees of freedom and not by the field strengths. To achieve a smaller and controlled value of coupling, simulation studies based on the LOCO fit model and using the multi-objective differential evolution algorithm with more skew quadrupole power supplies are performed in Indus-2. With sixteen independent power supplies, the emittance ratio can be reduced to <0.04% and the brightness enhances by an order of magnitude. Besides, the optimization method used provides quantitative trade-offs between coupling related parameters such as beam tilt angle, emittance ratio, vertical emittance, and vertical beam size, and desired values can be chosen from the Pareto optimal front.

Beam based alignment and its relevance in Indus-2.

Initially in the Indus-2 storage ring, the closed orbit distortion (COD) could be best corrected to 1.3 mm rms in the horizontal and 0.43 mm rms in the vertical plane. The strength of the corrector magnets required high values for COD correction. This revealed that offsets in COD readout by the beam position monitors (BPMs) played a role in not achieving a rms COD lower than the above value. Thus, the offset between the electrical center of BPMs and the magnetic center of the nearest quadrupole magnet could be estimated using the beam based alignment (BBA) method. It prefers that the quadrupole magnet is able to be controlled individually and active shunt power supply (ASPS) system was designed for this purpose that works efficiently. This paper describes the methodology of BBA, topology of ASPS and its performance, and COD minimization using the measured BPM offsets. After BBA, the COD could be reduced to 0.45 mm rms and 0.2 mm rms in horizontal and vertical planes, respectively.

Measurement of parameters in Indus-2 synchrotron radiation source.

The paper presents the measurement of optics parameters in Indus-2 synchrotron radiation source, which include betatron tune, beta function, dispersion function, natural chromaticity, corrected chromaticity, central RF frequency, momentum compaction factor, and linear betatron coupling. Two methods were used for beta function measurement; a conventional quadrupole scan method and a method using the fitting of the orbit response matrix. A robust Levenberg-Marquardt algorithm was used for nonlinear least square fitting of the orbit response matrix. In this paper, detailed methods for the parameter measurements are described. The measured results are discussed and compared with the theoretical values obtained using accelerator simulation code Accelerator Toolbox in MATLAB.