KEK, Ibaraki
CLASSE, Ithaca, New York
Cornell University, Ithaca, New York
UH, Honolulu, HI
An x-ray beam size monitor based on coded aperture imaging* has been developed at CesrTA, for the purpose of making bunch-by-bunch, turn-by-turn measurements of low emittance beams. Using low-emittance beam (~44 pm, or 16 microns at the x-ray source point) we have been able to make detailed comparisons between the measured mask response and that predicted by theory, validating our simulations of the mask response. In turn, we demonstrate the ability to measure both integrated and single-bunch turn-by-turn beam sizes and positions for monitoring the progress of the low-emittance tuning of the machine, and for electron-cloud instability-related beam dynamics studies.
* J.W. Flanagan et al., EPAC08, 1029 (2008).
KEK, Ibaraki
Crab cavities were installed in the KEKB rings in order to increase the luminosity. We measured the tilt of the bunches in the x-z plane using streak cameras. In a previous report*, the measured tilt in the HER was 2 times smaller than the expected crabbing angle, while the LER measurement was consistent with that expected. After the streak camera's vertical sweep speed was calibrated, the results were consistent with the expected crabbing angle in both rings.
* H. Ikeda et al., PAC07, 4018.
KEK, Ibaraki
SLAC, Menlo Park, California
Coherent synchrotron radiation (CSR) is generated when a bunched beam traverses a dipole magnet or a wiggler/undulator. It can degrade the beam quality in both storage rings and linacs through enhancing the beam energy spread and lengthening the bunch length, even cause single-bunch microwave instabilities. Using several methods, CSR impedances in the positron damping ring (DR) of the SuperKEKB which is under design were calculated. From the impedances due to CSR, resistive wall and various vacuum components, quasi-Green function wake potentials were constructed and used in simulations of Particle-In-Cell (PIC) tracking. We present the CSR related results in this paper.
KEK, Ibaraki
Super-KEKB, an upgrade plan of the present KEKB collider, has recently changed its scheme from 'high current' option to 'nano-beam' scheme. In the latter the current is relatively low(4A/2.3A for LER/HER ring) compared to that of the high-current option(9.4A/4.1A), while the vertical beam size is squeezed to 60 nm at the interaction point to get the high luminosity. The emittance of the injected beam should be low and, since the Tousheck lifetime is very short(600 sec), the intensity of the positron beam is as high as 8 nC/pulse. For the electron beam a low-emittance high-intensity RF gun is adopted. For the positron beam a damping ring has been proposed. The design of the damping ring has been performed for the high-current option*. In this paper an updated design for the nano-beam scheme is presented.
* Nucl. Instr. Meth. A 556 (2006) 13-19
KEK, Ibaraki
KEKB is an e-/e+ collider for the study of B physics and is also used for machine studies for future machines. The peak luminosity of KEKB, which is the world-highest value, has been still increasing. This report summarizes recent progress at KEKB.
