Aging Studies for the Large Honeycomb Drift Tube System of the Outer Tracker of HERA-B

TL;DR

This study investigates the aging effects on the HERA-B Outer Tracker's large honeycomb drift tubes, focusing on radiation damage, and presents modifications to improve durability in high-radiation environments.

Contribution

It introduces new design and operational strategies for drift tubes to withstand harsh radiation, validated through extensive testing and aging studies.

Findings

Radiation damage causes Malter currents and gain loss.

Surface conductivity and gas composition adjustments mitigate aging effects.

Operational tuning extends detector lifespan under high radiation.

Abstract

The HERA-B Outer Tracker consists of drift tubes folded from polycarbonate foil and is operated with Ar/CF4/CO2 as drift gas. The detector has to stand radiation levels which are similar to LHC conditions. The first prototypes exposed to radiation in HERA-B suffered severe radiation damage due to the development of self-sustaining currents (Malter effect). In a subsequent extended R&D program major changes to the original concept for the drift tubes (surface conductivity, drift gas, production materials) have been developed and validated for use in harsh radiation environments. In the test program various aging effects (like Malter currents, gain loss due to anode aging and etching of the anode gold surface) have been observed and cures by tuning of operation parameters have been developed.