S. Buontempo

Nanoscale TiO 2 -coated LPGs as radiation-tolerant humidity sensors for high-energy physics applications

This Letter deals with a feasibility analysis for the development of radiation-tolerant fiber-optic humidity sensors based on long-period grating (LPG) technology to be applied in high-energy physics (HEP) experiments currently running at the European Organization for Nuclear Research (CERN). In particular, here we propose a high-sensitivity LPG sensor coated with a finely tuned titanium dioxide (TiO₂) thin layer (~100 nm thick) through the solgel deposition method. Relative humidity (RH) monitoring in the range 0%-75% and at four different temperatures (in the range -10°C-25°C) was carried out to assess sensor performance in real operative conditions required in typical experiments running at CERN. Experimental results demonstrate the very high RH sensitivities of the proposed device (up to 1.4 nm/% RH in correspondence to very low humidity levels), which turned out to be from one to three orders of magnitude higher than those exhibited by fiber Bragg grating sensors coated with micrometer-thin polyimide overlays. The radiation tolerance capability of the TiO₂-coated LPG sensor is also investigated by comparing the sensing performance before and after its exposure to a 1 Mrad dose of γ-ionizing radiation. Overall, the results collected demonstrate the strong potential of the proposed technology with regard to its future exploitation in HEP applications as a robust and valid alternative to the commercial (polymer-based) hygrometers currently used.

Radiation hard polyimide-coated FBG optical sensors for relative humidity monitoring in the CMS experiment at CERN

This work investigates the performance and the radiation hardness capability of optical thermo-hygrometers based on Fibre Bragg Gratings (FBG) for humidity monitoring in the Compact Muon Solenoid (CMS), one of the four experiments running at CERN in Geneva. A thorough campaign of characterization was performed on 80 specially produced Polyimide-coated RH FBG sensors and 80 commercial temperature FBG sensors. Sensitivity, repeatability and accuracy were studied on the whole batch, putting in evidence the limits of the sensors, but also showing that they can be used in very dry conditions. In order to extract the humidity measurements from the sensor readings, commercial temperature FBG sensors were characterized in the range of interest. Irradiation campaigns with ionizing radiation (γ-rays from a Co60 source) at incremental absorbed doses (up to 210 kGy for the T sensors and up to 90 kGy for the RH sensors) were performed on sample of T and RH-Sensors. The results show that the sensitivity of the sensors is unchanged up to the level attained of the absorbed dose, while the natural wavelength peak of each sensor exhibits a radiation-induced shift (signal offset). The saturation properties of this shift are discussed.

A Comparative Study of Radiation-Tolerant Fiber Optic Sensors for Relative Humidity Monitoring in High-Radiation Environments at CERN

In this paper, we report a comparative study of fiber optic sensors for applications of relative humidity (RH) monitoring in high-radiation environments. In particular, we present investigations carried out since 2011 by our multidisciplinary research group, in collaboration with the European Organization for Nuclear Research (CERN) in Geneva. Our research has been first focused on the development of polyimide-coated fiber Bragg grating (FBG) sensors, and recently, it has been extended to nanoscale metal oxide-coated long-period gratings (LPGs). Experimental tests in the [0-70] %RH range at different temperatures, before and after γ-ionizing radiation exposures, have been carried out to assess the sensors performances in conditions required in experiments running at CERN. The advantages and disadvantages of the two proposed technologies are discussed in this paper in light of their possible application in high-energy physics environments. In particular, reported results suggest that LPG-based sensors can be preferred in some applications (particularly in presence of very low humidity levels) mainly because they are able to provide very high RH sensitivity (up to 1.4 nm/% RH), which is up to three orders of magnitude higher than that exhibited by FBG-based hygrometers. On the other side, compared with FBGs, LPGs are more difficult to multiplex due to limitations in terms of available bandwidth.

Long-Term Temperature Monitoring in CMS Using Fiber Optic Sensors

In this paper, the results of the long-term temperature monitoring of the compact muon solenoid experiment (CMS) at CERN are shown. The measurements were carried out by means of a system based on fiber Bragg grating (FBG) sensors in wavelength-division multiplexing (WDM). Due to the harsh working conditions at the CMS, the FBG sensor represents the ideal candidate to realize a reliable and accurate sensing system. The sensing principles of the FBG sensor and its temperature characteristics are introduced. A temperature monitoring system based on FBG for high-energy physics applications is designed and installed. The sensing system was used successfully last year in monitoring the temperature of CMS bulkhead. The reported results show good reliability and high accuracy of the FBG sensing system during the long-time working stage.

Radiation hard humidity sensors for high energy physics applications using polymide-coated Fiber Bragg Gratings sensors

This work is devoted to a feasibility analysis for the development of fiber optic humidity sensors to be applied in high-energy physics applications and in particular in the experiments actually running at the European Organization for Nuclear Research (CERN). On this line of argument, due to the wide investigations carried out in the last years aimed to assess the radiation hardness capability of fiber optic technology in high energy physics environments, our multidisciplinary research group has been recently engaged in the development and assessment of fiber optic sensors based on polyimide-coated Fiber Bragg Gratings (FBGs) to perform relative humidity (RH) monitoring at temperatures below 0°C as well as in presence of strong ionizing radiations. Data here reported, obtained during a deep experimental campaign carried out in the laboratories of CERN, demonstrate the amazing RH sensing properties of such sensors in the temperature range −15–20°C as well as their radiation hardness capability up to (at least) 10kGy dose of ionizing radiations.

Fiber Optic Sensors for CMS-CERN

In this paper we present the activity that our research group is making on Fiber Optic Sensors (FOS) applications to monitor high-energy physics (HEP) experiments. Starting from the consideration that Fiber Optic radiation hardness has been widely proven, we have applied the technology of Fiber Optic Sensors to this very relevant field of interest. Here, we give the experimental evidences of the possibility to use such a class of sensors also in these very complex environmental side conditions. In particular, regarding the Compact Muon Solenoid (CMS) experiment at the CERN, we have monitored temperatures and strains in different locations by using Bragg Grating sensors, and we are now starting the development of a new class of Relative Humidity sensor based on Fiber Optic technology. Preliminary results are very encouraging, letting us consider the use of FOS technique as a robust and effective solution for monitoring requirements in HEP detectors for other physical and environmental parameters.

One year of FBG-based thermo-hygrometers in operation in the CMS experiment at CERN

In this contribution we present results concerning the very first application of fiber optic sensors (FOSs) for relative humidity (RH) monitoring in high radiations environments. After a few years of investigations at CERN in Geneva, since December 2013 our multidisciplinary research group has successfully installed 72 thermo-hygrometers based on Fiber Bragg Grating (FBG) technology, organized in multi-points arrays, in cold areas of the Tracker Bulkhead of the Compact Muon Solenoid (CMS) experiment, where hundreds of electrical connectors are housed and thousands of services, including many cold pipes, cross the volumes through them. In such a complicated environment, a constant hygrometric monitoring is vital, in order to avoid dangerous phenomena of condensation. The collected results in the last year of operation of the proposed sensors are effective and reliable, with temperature, relative humidity and dew point temperature measurements from the FBG-based devices in full agreement with the readings of conventional sensors, temporarily present in the detector. However, experience in operation has shown some limitations of this technology, which are fully detailed in the last section of the paper.

High-sensitivity metal oxides-coated long-period fiber grating sensors for humidity monitoring in high-energy physics applications

This contribution deals with a feasibility analysis for the development of radiation tolerant fiber optic humidity sensors based on long period grating (LPG) technology to be applied in high-energy physics (HEP) experiments currently running at the European Organization for Nuclear Research (CERN). In particular, here we propose a high-sensitivity LPG sensor coated with a finely tuned titanium dioxide (TiO2) thin layer (~100 nm thick) through the sol gel deposition method. The sensor characterization in the relative humidity (RH) range [0-75] % at four different temperatures (in the range -10°C - 25°C) was carried out to assess sensor performances in real operative conditions required in typical experiments running at CERN. Experimental results demonstrate the very high RH sensitivities of the proposed device (up to 1.4 nm/%RH in correspondence of very low humidity levels), which turned out to be from one to three orders of magnitudes higher than those exhibited by fiber Bragg grating (FBG) sensors coated with micrometer thin polyimide overlays. The radiation tolerance capability of the TiO2-coated LPG sensor is also investigated by comparing the sensing performances before and after its exposure to 1Mrad dose of γ-ionizing radiation. Collected results demonstrate the strong potentialities of the proposed technology in light of its future exploitation in HEP applications as robust and valid alternative to currently used commercial hygrometers.

Radiation hard humidity sensors based on polyimide-coated fiber Bragg gratings

We report on a feasibility analysis for the development of fiber optic humidity sensors to be applied in high-energy physics applications and in particular in experiments actually running at the European Organization for Nuclear Research (CERN). Due to the stringent sensors requirements concerning radiation hardness capability and low temperature operation, we focus our attention on the investigation of fiber optic humidity sensors based on polyimmide (PI)-coated Fiber Bragg Gratings (FBGs). Data here reported, obtained during a wide experimental campaign carried out in the laboratories of CERN, demonstrate that the selected technological platform is able to perform relative humidity (RH) measurements with percent resolution in the temperature range -15-20°C as well as in presence of ionizing radiations up to 10KGray, largely outperforming conventional humidity sensors, currently employed within CERN environment.

Effect of the anisotropic magnetostriction on Terfenol-D based fiber bragg grating magnetic sensors

In this work, we study the effect of anisotropic magnetostriction on Terfenol-D based fiber Bragg grating magnetic sensors under different types of magneto-mechanical loading. We demonstrate that a Terfenol-D rod is subjected to axial strain also when the magnetic field is perpendicular to the rod axis and as consequence we question the hypothesis of uniaxial behavior that is normally found in the literature for these sensors. In order to address this issue, we propose a calibration model that introduces transverse sensitivity coefficients that take into account the effect of the transverse magnetic field.