In 2009, when working on Beam Loss Monitor thresholds on triplet magnets in LHC, (see M. Sapinski, F. Certurri, B. Dehning, A. Ferrari, C. Hoa, A. Lechner, M. Mauri, A. Mereghetti ESTIMATION OF THRESHOLDS FOR THE SIGNALS OF THE BLMs AROUND THE LHC FINAL FOCUS TRIPLET MAGNETS, proceedings of IPAC12) we realised that in some simuations the current LHC Beam Loss Monitor system, with ionzation detectors installed on the cryostats of the superconducting magnets, cannot distinguish normal signal, for instance from collision debris, from potentially dangerous, quench-provoking beam loss. A few possible methods to overcome this problem have been identified but the most straightforward and the most challenging was to install ionization monitors close to superconducting coils of the magnets, in cryogenic conditions.

In 2010 Christoph Kurfuerst was appointed as a PhD student to investigate and test the possible technologies. During the Cryogenic BLM workshop in 2011 a accelerator community needs for such systems were discussed. High-power superconducting linacs turned out to be the main customer except of LHC, however radiation conditions in RF cavities is very different then the LHC magnet case. Some workers (in JLab and CEA) already tested the silicon diodes inside the cavities (see A. Palczewski, R. Geng, Evaluation Of Silicon Diodes As IN-SITU Cryogenic Field Emission Detectors For SRF Cavity Development or presentation of J. Marroncle at the workshop) but no experiment has been done yet to evaluate the radiation hardness.

In 2011 a close collaboration with Vladimir Eremin and colleagues from Ioffe Institute in St. Persburs and with Erich Griesmayer from CIVIDEC has started. During the years 2011 and 2012 Christoph Kurfuerst organized and performed the first cryogenic beam tests of Silicon and scCVD on T9 beamline in CERN East Hall. He made observed single particles crossing the detectors. He also developed a od Liquid Helium ionization chamber.

The most challenging was irradiation test of the detectors performed in the end of 2012 at T7 beamline. During more then one month of irradiation the degradation of the behaviour of the detectors with doses reaching several MGy was observed. Results of this test are published in Christoph's PhD thesis (and in conference papers as well as NIM paper in preparation). The main conclusion is that the diamond degrades slower and might have a significant advantage over Silicon for doses exceeding a few MGy.

The next step was installation of prototype detectors inside the LHC magnets during Long Shutdown 1 (LS1). It has been done in two locations: dispersion suppressors in IP7 and in IP5. The detecotrs were installed on the cold vessel, in the insulation vacuum in 2013 and 2014. They will be used as a long-time test detectors to observe system performance and potential other issues.

A the same time the next PhD student, Marcin Bartosik, prepares second irradiation test. Also the probing of the irradiated detectors using TCT method in cryogenic conditions continues. The goal is to understand the physics of the damage in cryogenic conditions and to prepare detecotrs to be installed in new triplet magnets in 2021.

mariusz.sapinski 2014