Abstract
SuperKEKB is an asymmetric energy electron positrion collider currently under commissioning in Japan. It aims to achieve a record high luminosity of $8\ifmmode\times\else\texttimes\fi{}{10}^{35}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}2}\text{ }{\mathrm{s}}^{\ensuremath{-}1}$, for which accurate control of ${\ensuremath{\beta}}_{y}^{*}$ is needed. The advanced final focus system is also relevant for studies related to future linear colliders, which similarly need to achieve very small beam sizes. To work for SuperKEKB, the $K$ modulation technique is generalized to allow known quadrupole fields between the modulated magnets and the interaction point. Initial measurements taken in HER agree with simulations, and show that $K$ modulation is suitable for measuring the minimum of the $\ensuremath{\beta}$ function at the interaction point within 1%, however it is too uncertain to be used for measuring the displacement of the beam waist away from the interaction point. In addition, tune shift equations for a modulated quadrupole are derived without assuming a thin lens perturbation, giving a simple method to calculate the tune shift to second order in the quadrupole strength modulation.
Highlights
This article is based on results available in [1]
Initial measurements taken in High Energy Ring (HER) agree with simulations, and show that K modulation is suitable for measuring the minimum of the β function at the interaction point within 1%, it is too uncertain to be used for measuring the displacement of the beam waist away from the interaction point
Tune shift equations for a modulated quadrupole are derived without assuming a thin lens perturbation, giving a simple method to calculate the tune shift to second order in the quadrupole strength modulation
Summary
This article is based on results available in [1]. Currently under commissioning, SuperKEKB is an asymmetric energy electron positron collider at the High Energy Accelerator Research Organization in Japan (KEK) [2]. SuperKEKB and the upgraded Belle II aim at a luminosity of 8 × 1035 cm−2 s−1, surpassing the previous record by a factor 40 This will allow for an integrated luminosity of 50 ab−1, enabling precision measurements of rare events and testing of the Standard Model as well as potentially revealing hints about new physics [5]. This focusing system was tested at FFTB [15], but SuperKEKB will demonstrate the system at smaller IP beam sizes and initial studies have investigated the possibility of reducing βÃy by a factor 3 beyond the nominal value [16], which would give a further 40% reduction in the vertical beam size at the IP if chromaticity and nonlinear effects can be properly corrected Such dedicated studies of the final focus system would make it possible to compare.
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