Characterisation of the VELO High Voltage System

TL;DR

This paper evaluates the high voltage system of the LHCb VELO detector, ensuring its safety, stability, and performance through comprehensive testing of its hardware and operational modes.

Contribution

It provides a detailed characterization and validation of the VELO high voltage system, including safety features and failure mode behavior, enhancing confidence in its reliable operation.

Findings

High voltage modules behave reliably above 9V

Current ramping limits are effective for safety

System quickly cuts voltage during failures

Abstract

The high voltage system supplies the bias voltage to the 88 silicon sensors which comprise the LHCb Vertex Locator (VELO). This note describes the results of the tests which have been performed on the hardware of the high voltage system of the VELO. Each individual test detailed in this note corresponds to a specific requirement of the system. These requirements arise primarily from ensuring the safety of the silicon sensors and the quality of the data taken from the VELO modules. The tests performed are in four categories: normal operation of the high voltage system; verification of its stability under operation; discussion of its behaviour in failure modes; and details of operation at low voltage. Noteworthy issues, identified through the tests, include the behaviour of the high voltage modules at voltages below 9V, the current limit that can be applied during ramping of the voltage, and the speed with which the voltage is cut during failures of the system. The results of these tests provide high confidence that the high voltage system can be safely used and demonstrate that low noise is produced by the power supplies.