New micromegas for axion searches in CAST

Micromegas detectors have been taking data in the CAST experiment since 2002, occupying one opening (out of the two looking for sunrise axions) of the magnet and showing good performance and stability. Currently, three of the four X-ray detectors used in the experiment are micromegas. The new detectors are of the Microbulk technology, which have attracted a lot of attention because of the advantages they present, among them the low-material construction, high radiopurity and good energy resolution. Here, their performance during the last year will be commented. In particular, the low background levels reached in some detectors have triggered a set of studies in order to understand the effect.