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| MOCLA02 | Design of a Compact L-band Transverse Deflecting Cavity with Arbitrary Polarisations for the SACLA Injector | 22 |
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We are planning to install a transverse deflecting cavity (TCAV) in the injector of the X-ray free electron laser (XFEL) facility, SACLA [*], in order to measure longitudinal bunch profiles after a velocity bunching process. This is because the longitudinal bunch profile in the injector is critically important for reproducing the XFEL performance [**]. The TCAV will be installed at the end of the velocity bunching section, where the bunch length ranges from 10 ps to several 100 ps, the kinetic energy of the beam is approximately 1 MeV, and the transverse beam motion is rotated by solenoid lenses. Considering these conditions, we designed a compact L-band (1428 MHz) TM110-mode pillbox-shape TCAV (~300 mm-diameter and ~100 mm-long) with two input ports intersecting at a right angle. One of the advantages of this TCAV is that the polarisation of a deflecting rf field can be freely chosen, e.g. linear or circular, by changing the amplitude and phase at each rf port. We can select the linear polarisation for linear streaking with an arbitrary direction, or the circular one for axially symmetric deflection to reduce transverse mixing due to a solenoid B-field, depending on the situation.
[*] T. Ishikawa, et al., Nature Photonics 6, 540-544 (2012). [**] T. Asaka, et al., Proceedings of LINAC2012, 486-488, TUPB006, (2012). |
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Slides MOCLA02 [11.996 MB] | |
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| TUPB020 | Long-Term Stability of the Beam Position Monitors at SPring-8 | 359 |
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At the SPring-8 storage ring, the renewal of BPM electronics in 2006 has improved orbit feedback resolution *. However, a stability issue of the whole BPM system, including the buttons, the cables and the electronics, remains to be settled for long-term stability of the beam orbit. The BPM in the present SPring-8 has gain imbalances among 4 electrode channels, which result in large offsets (~1 mm). The imbalances are routinely corrected in accordance with a beam-based measurement **. But, the offset error increases close to 100 um during the operation, because of the imbalance fluctuations. Major origin of the imbalances is standing waves caused by reflections in BPM cables. As a countermeasure for the imbalance issue, isolators to mitigate the standing waves were equipped. They significantly reduced the imbalances, but not sufficient to completely suppress the imbalance fluctuations. The requirement of stability for the BPM system for the upgrade plan of SPring-8 is going to be more stringent. We started extensive survey to find the sources of fluctuations of the gain imbalances in order to achieve long-term stability of the BPM system applicable to the planned SPring-8 upgrade.
* S. Sasaki, T. Fujita et al., Proc. of the DIAPC 2007, Venice, Italy, (2007) p. 114 ** M. Masaki et al., Proc. of the 11th Symp. on Accel. Sci. and Technol., (1997), p.83. |
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