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A new remote-controllable sensing system for a laser-based alignment system is in development to measure slow dynamic displacements of the tunnel floor in real time at the KEKB injector linac. Although the injector linac had initially been aligned with a laser-based alignment system, we have found that, based on recent real-time observations, the transverse displacements of the tunnel floor to the laser axis caused by dynamic ground motion are not negligibly small compared with the required alignment tolerance, in terms of the straightness of the beam line. Based on spatial and temporal cross-correlation analyses performed using displacement vectors from data recorded during a nearly eight-month period, it was found that the tunnel floor moves coherently in space and time domains over the entire length of the linac on average over long periods of time, while the cross-correlation function varies irregularly and complexly over shorter periods of time. This report describes in detail the basic design, experimental results, and present status of the new remote-sensing system for real-time alignment observations at the KEKB injector linac.

A new tungsten single-crystal target has been successfully employed at the positron source of the KEKB injector linac. The crystal thickness was determined to be 10.5 mm based on previous systematic measurements of the positron-production efficiency. The crystal axis, ⟨111⟩, was precisely aligned to the direction of the 4-GeV primary electron beam. The positron yield increased by ∼25% compared to that for a conventional tungsten plate with a thickness of 14 mm. On the contrary, the steady-state heat load on the crystal target decreased by ∼20%. After a two-month operation, no degradation of the positron-production efficiency was observed, and the crystal target has been stably operating at the KEK B factory.

A new energy-spread feedback control system using nondestructive energy-spread monitors has been developed in order to control and stabilize the energy spreads of single-bunch electron and positron beams in the KEKB injector linac. A well-controlled feedback system has been successfully working in daily operation not only for keeping the injection rate higher along with the beam-orbit and energy-feedback control system, but also for reducing the background level to the KEKB collider experiment. The energy spreads of the injection beams have been well stabilized within 0.33±0.01% and 0.50±0.02% (0.55±0.06%) for the electron beam and the first (second) bunch of the high-current primary electron beam for positron production at the 180° arc, respectively, and within 0.39±0.01% (0.36±0.03%) for the first (second) bunch of the positron beam at the end of the injector linac through the energy-spread feedback control system under the nominal operation condition. In this report we describe in detail the energy-spread feedback control system using nondestructive energy-spread monitors with multi–strip-line electrodes and their performance in KEKB operation.

A nondestructive beam energy-spread monitor using multi-strip-line electrodes has been newly developed in order to measure and control the energy spread of a single-bunch electron beam at an 180° arc with a beam energy of 1.7 GeV in the KEKB injector linac. The detection principle is described based on a multipole-moment analysis of an electromagnetic field generated by a charged beam. A proof-of-principle experiment was performed to verify the analysis. The result shows that taking into account the second-order moment derived from the multipole-moment analysis, the analyzed transverse beamwidths are consistent with those measured by a screen monitor, and the energy spreads are estimated to be 0.150%±0.007% and 0.264%±0.004% for electron beams with charges of 0.9 and 8 nC/bunch at the rf phase of the energy-spread minimum, respectively. In this report we describe in detail the experimental result using the beam energy-spread monitor along with a theoretical multipole-moment analysis.