KEK, Ibaraki
The KEKB is a high luminosity accelerator which achieved the highest luminosity record of 2.1x1034. It requires the precise and stable beam control to keep its high luminosity continually. Slight change of the magnetic field may easily deteriorate the performance of the collisions of the very small and thin beams. The field measurement accuracy better than 10-4 has been already achieved. The resolution of the measurement has reached to a few 10-5. But it is known by the beam studies that the field change less than 10-4 may cause deterioration of the luminosity. The requirement on the stability of magnetic field will be stricter for future nano beam colliders. We have studied the effects of the following conditions on the magnetic field by using some KEKB magnets: changes of the magnetic field due to air or cooling water temperature, changes due to initialization conditions, field coupling between the adjacent magnets, effect of excitation of the adjacent magnet and behavior of the magnetic field under polarity change have been measured. These studies are not only useful for the existing KEKB but also important for future nano beam accelerators.
KEK, Ibaraki
A new set of magnets, skew sextupole magnets, were designed, manufactured, measured and installed during the winter shutdown of 2009. Twenty magnets were installed in the HER and eight magnets were installed in the LER. It was a challenging job for the magnet group to design, manufacture, measure the magnetic field and install them in the tunnel in just three months. Much effort to finish the installation in time and reduce the production cost was made at every step of the entire process. With these newly installed skew sextupole magnets, a significant luminosity boost was achieved. The production and installation of the skew sextupole magnets are described in this report.
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.
