Long-term operation of the multi-wire-proportional-chambers of the LHCb muon system

Abstract

The muon detector of LHCb, which comprises 1368 multi-wire-proportional-chambers (MWPC) for a total area of 435 m 2 , is the largest instrument of its kind exposed to such a high-radiation environment. In nine years of operation, from 2010 until 2018, we did not observe appreciable signs of ageing of the detector in terms of reduced performance. However, during such a long period, many chamber gas gaps suffered from HV trips. Most of the trips were due to Malter-like effects, characterised by the appearance of local self-sustained high currents, presumably originating from impurities induced during chamber production. Very effective, though long, recovery procedures were implemented with a HV training of the gaps in situ while taking data. The training allowed most of the affected chambers to be returned to their full functionality and the muon detector efficiency to be kept close to 100%. The possibility of making the recovery faster and even more effective by adding a small percentage of oxygen in the gas mixture has been studied and successfully tested.

Proposal on application of the multi-wire proportional chambers of the LHCb MUON Detector at very high rates for the future upgrades

“…During this period, the MUON MWPCs did not show any gain reduction or other apparent symptoms of reduced performance in terms of efficiency or time resolution [5,7]. A very limited fraction of gaps, affected with high currents due to Malter-like effect [8] are well under control, with a developed and successfully applied method of treatment in situ and did not show yet any visible impact on efficiency of the MD [9]. The absence of aging phenomena in the MD is a key argument for a possible massive reuse of the present MWPCs as a scenario at U2.…”

The LHCb Upgrade I

“…The findings of these systematic studies, described in details in ref. [156], are summarised in this section.…”

Исследование Радиационной Эрозии В Газоразрядном Детекторе С Помощью Атомно-Силовой Микроскопии

“…Это связано с планируемым на 2025-й год почти десятикратным увеличением светимости БАК и, как следствие, с необходимостью обеспечить радиационную стойкость детекторов на последующие 10 лет работы. Важной мотивацией выполненной работы стало периодическое появление в пропорциональных камерах спонтанных самоподдерживающихся токов (мальтеровский эффект (МЭ)) [3], которые в десятки раз превышают ток ионизации в эксперименте. Спонтанные токи до 30−40 µA вызывают ложные срабатывания детекторов и ускоренное старение анодных проволочек в области генерации МЭ.…”