The RASNIK Real-Time Relative Alignment Monitor for the CDF Inner Tracking Detectors

TL;DR

This paper presents the design, implementation, and two-year operational experience of a low-cost, high-precision optical alignment system for the CDF inner tracking detectors, enabling continuous real-time monitoring in a radiation environment.

Contribution

It introduces a modified two-element RASNIK system for improved ambiguity reduction and radiation hardness, along with a robust data-acquisition setup for continuous detector alignment monitoring.

Findings

Achieved submicron precision in real-time alignment monitoring.

Identified sources of detector motion over two years of operation.

Demonstrated system reliability in a high-radiation environment.

Abstract

We describe the design and operation of the RASNIK optical relative alignment system designed for and installed on the CDF inner tracking detectors. The system provides low-cost minute-by-minute alignment monitoring with submicron precision. To reduce ambiguities, we modified the original three-element rasnik design to a two-element one. Since the RASNIKs are located within 10--40 cm of the beamline, the systems were built from low-mass and radiation-hard components and are operated in a mode which reduces damage from radiation. We describe the data-acquisition system, which has been running without interruption since before the CDF detector was rolled into its collision hall in March 2001. We evaluate what has been learned about sources of detector motion from almost two years of RASNIK data and discuss possible improvements to the system.