Thermal Mockup Studies of Belle $\text {II}$ Vertex Detector

Abstract

As the upgrade of the former KEKB collider, SuperKEKB, aims to increase the peaking luminosity by a factor of 40 to 8$\,\times \,$10$^{35}$ cm$^{-2}$s$^{-1}$. The Belle $\text {II}$ experiment is expected to accumulate a data set of 50 ab$^{-1}$ around 10 GeV in the next decade, to explore the new physics beyond the Standard Model at the intensity frontier. The Belle $\text {II}$ vertex detector (VXD) is upgraded with a new 2-layer DEPFET pixel detector (PXD) in the inner most part, surrounded by a 4-layer double-sided silicon strip detector. To achieve an accurate determination of decay vertex, the material budget in the detector acceptance is well optimised. The evaporative 2-phase $\text {CO}_2$ cooling is a newly developed low-mass cooling concept which is used in the tense VXD volume. The cooling system must be capable of removing a heat load of about 1 kW from the detectors. To verify and optimise the performance of the 2-phase $\text {CO}_2$ cooling system, a full-sized VXD thermal mockup is built at DESY. In this talk some aspects of mechanics design of Belle $\text {II}$ VXD are presented, as well as the thermal and mechanical measurements.