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

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.