No abstract

No abstract

The high design luminosity of the SuperKEKB electron-positron collider is expected to result in challenging levels of beam-induced backgrounds in the interaction region. Properly simulating and mitigating these backgrounds is critical to the success of the Belle II experiment. We report on measurements performed with a suite of dedicated beam background detectors, collectively known as BEAST II, during the so-called Phase 1 commissioning run of SuperKEKB in 2016, which involved operation of both the high energy ring (HER) of 7 GeV electrons as well as the low energy ring (LER) of 4 GeV positrons. We describe the BEAST II detector systems, the simulation of beam backgrounds, and the measurements performed. The measurements include standard ones of dose rates versus accelerator conditions, and more novel investigations, such as bunch-by-bunch measurements of injection backgrounds and measurements sensitive to the energy spectrum and angular distribution of fast neutrons. We observe beam-gas, Touschek, beam-dust, and injection backgrounds. As there is no final focus of the beams in Phase 1, we do not observe significant synchrotron radiation, as expected. Measured LER beam-gas backgrounds and Touschek backgrounds in both rings are slightly elevated, on average three times larger than the levels predicted by simulation. HER beam-gas backgrounds are on on average two orders of magnitude larger than predicted. Systematic uncertainties and channel-to-channel variations are large, so that these excesses constitute only 1-2 sigma level effects. Neutron background rates are higher than predicted and should be studied further. We will measure the remaining beam background processes, due to colliding beams, in the imminent commissioning Phase 2. These backgrounds are expected to be the most critical for Belle II, to the point of necessitating replacement of detector components during the Phase 3 (full-luminosity) operation of SuperKEB.

No abstract

No abstract

No abstract

Kanazawa, K. 1995 11 30 How spatangoids produce their traces: relationship between burrowing mechanism and trace structure. Two spatangoid echinoids, Echinocardium cordatum and Lovenia elongata, were allowed to produce their traces in poorly and well‐sorted sediments in aquaria. In poorly sorted sediments they formed distinct traces, comparable to fossil traces. Sorting of sediment occurred during transportation by the lateroventral spines and brought about characteristic patterns in grain size at the bottoms of the burrows and in redeposited sediment, which made the traces visible. Differences in the burrowing mechanism between E. cordatum and L. elongata are reflected in their trace structures. E. cordatum formed a laminated backlill structure which resulted from periodic accumulation of excavated sediment behind it, while L. elongata simply pushed excavated sediment by compression to the posterior sides of the test, so that their traces lack a distinct laminated structure and the width of the trace becomes larger than that of the animal. In well‐sorted sediment, the echinoids burrowed in the same way as in poorly sorted sediment, but no visible trace was produced other than a drain tube. These observations reasonably explain some characteristic modes of occurrence of fossil spatangoid traces. Their different morphological expressions depend on sediment texture and the uneven lithification of traces. Spatangoids, trace, burrowing mechanism.

An upgrade plan of the KEK B-Factory (KEKB), Super KEKB (SKEKB) has been discussed in KEK. The R&D of main vacuum components for the SKEKB, such as beam ducts, bellows chambers and connection flanges etc., are now undergoing. Trial models of a beam duct with an antechamber and a bellows chamber with a comb-type RF shield were installed in the KEKB positron ring and tested with beam.Coatings with a low secondary electron yield were also investigated with the positron beam. A special connection flange with small impedance was examined in a test bench.