The ALICE Inner Tracking System (ITS) detector is undergoing a major upgrade in order to cope with the increased data rates and to meet the requirements as set out by the physics goals of the experiment after the LHC Long Shutdown 2 (LS2). The new ITS will be completely made up of monolithic active pixel sensors (MAPS), called ALPIDE, based on the CMOS 180 nm process. A single sensor measures 30 mm × 15 mm and contains half a million pixels, with a pitch of 27 $\mathrm{\mu }\mathrm{m}\times 29$ $\mathrm{\mu }$m, distributed over 512 rows and 1024 columns. The ALPIDE sensors, thinned to 50 $\mathrm{\mu }$m and 100 $\mathrm{\mu }$m for the Inner and Outer Barrels, respectively, are mounted on ultra-lightweight carbon composite support structures with an embedded cooling system. This results in a considerable reduction of the material budget and a significant improvement of the impact parameter resolution and tracking efficiency for low-transverse momentum particles. The construction of the ITS detector has been completed and the commissioning on surface is ongoing. The detector will be installed in ALICE in 2020. This paper will give a brief overview of the motivation for the upgrade and will present the first results of the detector performance obtained during the commissioning.

ALICE内部跟踪系统（ITS）检测器正在进行重大升级，以应对增加的数据速率并满足LHC Long Shutdown 2（LS2）之后实验物理目标提出的要求。新的ITS将完全由基于CMOS 180 nm工艺的称为ALPIDE的单片有源像素传感器（MAPS）组成。单个传感器尺寸为30 mm×15 mm，包含五十万个像素，间距为27 $\mathrm{\mu }\mathrm{米}\times 29$ $\mathrm{\mu }$m，分布在512行和1024列中。ALPIDE传感器，薄至50 $\mathrm{\mu }$m和100 $\mathrm{\mu }$内桶和外桶的m分别安装在带有嵌入式冷却系统的超轻质碳复合材料支撑结构上。这大大降低了材料预算，并显着改善了低横向动量粒子的冲击参数分辨率和跟踪效率。ITS检测器的建设已完成，表面调试工作正在进行中。该探测器将在2020年安装在ALICE中。本文将简要介绍升级动机，并将介绍在调试过程中获得的探测器性能的初步结果。