Search Results (4 total)

Sudden decreases in the beam lifetime, which are attributed to the dust trappings, sometimes occur at the electron storage ring Photon Factory Advanced Ring (PF-AR). Since these dust events cause difficulties in user operations, we have been carefully observing this phenomenon for many years. Our observations indicated that the dust trappings could be caused by electric discharges in vacuum ducts. In order to demonstrate this hypothesis experimentally, we designed a new vacuum device that intentionally generates electric discharges and installed it in PF-AR. Using this device, we could repeatedly induce sudden decreases in the beam lifetime because of the generated electric discharge. We also detected decreases in the beam lifetime caused by mechanical movement of the electrodes in the device. Moreover, we could visually observe the dust trapping phenomenon; the trapped dust particle was observed by two video cameras and appeared as a luminous body that resembled a shooting star. This was the first direct observation of a luminous dust particle trapped by the electron beam.

For many damped-accelerating cavities for high-intensity beams, classifications of eigenmodes according to azimuthal indices are generally insufficient due to a lack of their axial symmetry. To classify the eigenmodes in such cavities having general symmetry, the application of group theory is studied. By taking basis functions from a complete set of eigenmodes, one can form a representation of the symmetry group of the cavity. The eigenmodes can then be classified according to irreducible representations of the symmetry group. This method is particularly useful for classifying the eigenmodes in complicated cavities, and for understanding the effects of perturbations on the eigenmodes.

The frequencies (tunes) of transverse quadrupolar oscillations were measured in the 2.5-GeV Photon Factory storage ring at the High Energy Accelerator Research Organization (KEK). As a result, remarkable shifts in the quadrupolar frequencies with the bunch current were found; they were both positive and negative in the horizontal and vertical directions, respectively. This result can be explained by a focusing effect due to short-range wakefields containing a quadrupolar component.

In the 2.5-GeV Photon Factory storage ring at KEK, we have found that the beam lifetime can be improved by modulating the phase of an rf accelerating voltage at a frequency of 2 times the synchrotron oscillation frequency. By applying this phase modulation with a peak-to-peak amplitude of 3.2°, the beam lifetime could be improved, typically, from 22 to 36 h under a beam current of about 360 mA. At the same time, the longitudinal coupled-bunch instability could be considerably suppressed. The improvement in the beam lifetime can be explained as an improved Touschek lifetime, which was caused by a quadrupole-mode longitudinal oscillation of the stored bunches.