TPS exceeds design goal of 500 mA stored current

18 March 2016

In December last year, the 3 GeV Taiwan Photon Source (TPS) of the National Synchrotron Radiation Research Center (NSRRC) stored 520 mA of electron current in its storage ring, and gave the world a bright synchrotron light as the International Year of Light 2015 came to an end. This is the second phase of commissioning conducted after the five-month preparation work set to bring the electron current of TPS to its design value of 500 mA (CERN Courier June 2010 p16 and April 2015 p22).

After the first light of TPS shone on 31 December 2014, the beam injection stored an electron current greater than 100 mA with the efficiency of the booster to storage ring exceeding 75% using Petra cavities. To overcome the instability of the electron beam, high chromaticity and a vertical feedback system were applied to damp the vertical instability at a high current, in this case close to 100 mA, whereas the longitudinal instability appeared when the beam current reached around 85 mA. Subsequently, the dynamic pressure of the vacuum conditioning reached 10–7 Pa at 100 mA after feeding 35 amps-per-hour beam dose. At this stage, the TPS was ready for the upgrade implementation scheduled for the remainder of 2015.

Several new components were installed during this phase, including new undulators and superconducting cavities, while the cryogenic and control systems were completed.

The upgrade activities also involved the injection system and the transfer line between booster and storage, to improve the injection efficiency and the stability of the system. In addition, 96 fast-feedback corrector magnets were placed at both ends of the straight sections, as well as upstream of the dipole magnets.

After several test runs in the fourth quarter of 2015, an unusual and unfamiliar phenomenon began to emerge, preventing the electron current from progressing beyond 230 mA. The pressure of the vacuum chamber located in the first dipole of the second arc section in the storage ring repeatedly surged to more than 300 times the normal value of 10 × 10–9 Pa when the beam current increased to 190 mA. A small metal–plastic pellet that contaminated the vacuum environment was removed and the staff performed flange welding on the spot.

After the vacuum problem had been solved, commissioning of TPS went smoothly, ramping from 0 to 520 mA in 11 minutes on 12 December.

While the TPS was ramping up to its stored-current target value, two beamlines – the protein microcrystallography beamline (TPS-05) and the temporally coherent X-ray diffraction beamline (TPS-09) – were in the commissioning phase. The TPS beamlines will be open for use in 2016.

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