| Paper | Title | Page |
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| TUPCH056 | A Simpler Method for SR Interferometer Calibration | 1136 |
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| Previous methods of performing absolute calibration of the SR interferometer used at KEKB (measuring mirror distortion with a pinhole mask, virtual beam broadening via local bumps, physical beam broadening via dispersion bumps) are very time-consuming, and require dedicated machine time to take the necessary data. We report on a new, simpler method we have developed, wherein we create small local bumps at the SR source point and observe the resulting shifts in the phase of the interference fringes. From these data we can calibrate the total magnification of the system, including the effects of mirror distortion. The calibration data can be taken in a very small amount of time (tens of minutes), and in parallel with physics running, without stopping the beam-size measurement system or interfering with its use for luminosity tuning. By taking the calibration data at different beam currents and correlating the magnification at each current with the appropriate interference pattern fit parameters, we can also obtain the parameters needed for real-time mirror distortion correction. | ||
| TUPCH057 | A Diagnostic System for Beam Abort at KEKB | 1139 |
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| A controlled beam abort system has been installed at KEKB for the protection of the hardware components of the accelerator and detector from damage by ampere-class beam currents. In order to identify the reason for each abort and optimize the abort system to handle each type of problem as well as improve machine operation, a diagnostic system has been developed. Fast signals, such as beam currents, accelerating voltages of the RF cavities and beam loss monitor signals from PIN photo-diodes are recorded and analyzed by a data logger system with a high sampling rate at the moment of each abort. Beam oscillations, radiation dose at the detector and vacuum pressure are also examined to classify the reasons for beam loss and aborts. Statistics and typical examples of these aborts will be discussed. | ||
| WEOFI01 | Beam Dynamics Measurements in the Vicinity of a Half-integer Resonance | 1902 |
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| The operating point of the betatron tune set near a half-integer is a crucial parameter to make high luminosity in electron/positron ring colliders. Dynamic beam-beam effects would change the optics parameters of the colliders, depending on the betatron tune and the beam-beam parameter. On the other hand, existence of the half-integer stopband makes the beam unstable. Therefore, beam behavior near a half-integer might provide interesting issues from the viewpoint of beam dynamics. We measured a frequency response of the beam across a half-integer for measuring the betatron tune at KEKB. A sharp spike just at a half-integer was observed in the tune spectrum. We believe that the spectrum would be a nonlinear resonance caused by some off-momentum particles in a bunch, not by a coherent motion of a whole bunch. The horizontal beam size measured using a synchrotron radiation monitor indicated a slight increase when the tune approached a half-integer. The variations in the beam size are discussed, considering both dynamic beam-beam effects and a beta beat due to the half-integer stopband. | ||
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Transparencies | |
| THPCH050 | Further Studies on Betatron Sidebands due to Electron Clouds | 2898 |
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We have observed vertical betatron sidebands in the transverse beam spectra of positron bunches at the KEKB LER which are associated with the presence of electron clouds in single-beam studies*, and which are also associated with a loss of luminosity when the KEKB beams are in collision**. The sidebands may be signals of a fast head-tail instability due to short-range wakes within the electron cloud, providing a diagnostic for exploring the mechanism for transverse beam blow-up due to electron clouds. We report here on further studies on the behavior of the sidebands under varying beam conditions, including varying initial beam size below the beam blow-up threshold, chromaticity, RF voltage and fill pattern.
*J. W. Flanagan et al. PRL 94, 054801 (2005).**J. W. Flanagan et al. Proc. PAC05, p. 680 (2005). |
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| THPCH051 | The Effect of the Solenoid Field in Quadrupole Magnets on the Electron Cloud Instability in the KEKB LER | 2901 |
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| The electron cloud instability which causes vertical beam blowup in the KEKB LER is largely suppressed by applying a weak solenoid field to vacuum chambers in the drift region. However the blowup is still observed when the bunch spacing is reduced to 3.27 rf buckets or shorter. A question is where the remaining electron clouds are. To investigate the electron clouds in the quadrupole magnets, solenoids made of flat cables were developed and installed in 88 quadrupole magnets. The field strength of the solenoid is 17 Gauss. The effect of the solenoid field on the blowup is now under beam study. So far no clear effect of the solenoids on the luminosity and the sideband accompanied by the blowup is found. We report on the solenoid system, the results of the experiments and comparison of the experimental results with simulations. | ||
| THPCH103 | Design and Testing of Gproto Bunch-by-bunch Signal Processor | 3038 |
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| A prototype programmable bunch-by-bunch signal acquisition and processing channel with multiple applications in storage rings has been developed at SLAC. The processing channel supports up to 5120 bunches with bunch spacings as close as 1.9 ns. The prototype has been tested and operated in five storage rings: SPEAR-3, DAFNE, PEP-II, KEKB, and ATF damping ring. The testing included such applications as transverse and longitudinal coupled-bunch instability control, bunch-by-bunch luminosity monitoring, and injection diagnostic. In this contribution the prototype design will be described and its operation will be illustrated with the data measured at the abovementioned accelerators. |