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Report of the CISC Review CommitteeSeptember 3, 2019Review Committee : David Montanari, Gina Rameika (Chair), Filippo Resnati, Ruben SaakyanExecutive SummaryThe DUNE Cryogenic Instrumentation and Slow Controls (CISC) Consortia is a joint consortia covering both the Single Phase and Dual Phase far detectors. A scope review of CISC was held at CERN on June 19, 2019. The review was focused on instrumentation. Slow Controls were not covered. Presentations were given on the Temperature Monitors (Static and Dynamic), Purity Monitors and Cameras. Temperature profilers and level meters installed in the ProtoDUNE Dual Phase were also presented.The strategy of the CISC Consortia is to validate the designs of all systems and test them in the ProtoDUNEs, both the on-going runs and in the up-coming opportunity in ProtoDUNE –II.The committee felt that the presentations were complete and addressed the questions that were given.The committee agreed that all of the proposed instruments were useful devices, albeit to different degrees and at different moments in time. The committee encourages the Consortia to develop clear plans for deployment of the new instrumentation in ProtoDUNE-II. This should be done as soon as possible to ensure that the necessary resources can be put into place.The final definition of the instrumentation scope for DUNE can be developed over time, however all issues related to interfacing with other detector systems needs to be addressed promptly, in particular any interfaces with the APAs. In this report we summarize the presentations and discussions which took place at the review in the form of Findings, Comments and Recommendations.A follow-up review on the time frame of about six months would be helpful to discuss progress on the analysis of temperature and purity monitors, and to clearly define the scope of instrumentation that will be deployed in ProtoDUNE-II.FindingsThe current number of purity monitors in a DUNE-FD module is 8 total, 6 inside the cryostat and 2 external inline.?Of the 6 inside, 4 will be standard length (25 cm) and two will be long (100 cm). The longer monitors should increase the range of measured lifetime. Improvements to the light source are also planned. The new designs will be tested in ProtoDUNE-II. The external monitors will be standard length.Purity monitors are used to measure electron lifetime, measure purity stratification and verify the computational fluid dynamics (CFD) model.The current systematic uncertainty on e-lifetime for the ProtoDUNE-SP purity monitors range from 5% to 13% (top to bottom). ProtoDUNE-SP deployed three different styles of temperature sensors : a Static T-Gradient Monitor which is a vertical array with laboratory calibration, a Dynamic T-Gradient Monitor vertical array with in-situ calibration and individual sensors along the roof, walls, floor and the ullage.The Static and Dynamic T-Gradient monitors are sensitive in the milli-Kelvin (mK) range. Most of the individual sensors (12 at the bottom and 8 at the top) are also high precision sensors. In addition, individual sensors are epoxied to the floor (12) and walls (5) which are sensitive in the tens of mK. In addition to checking the proper functioning of the cryogenics system, data from the temperature sensors is used to validate the CFD models of the liquid argon flow, as well as provide input for determining the electron lifetime. Analysis was presented that showed a direct relation between temperature measurements and the electron lifetime in the 35ton prototype.The in-situ calibration of the Dynamic T-Gradient sensors has been demonstrated in ProtoDUNE –SP. If such a monitor were to be deployed in DUNE several design changes are necessary including segmentation of the pieces due to limited overhead installation space and a re-designed viewport in light of the failure of the initial one installed.ProtoDUNE Dual Phase contains approximately 150 temperature sensors (plus sensors on the electronics) serving different purposes including monitoring the liquid level, vapor temperature, evaluation of the roof heat input, evaluation of the CRP deformation and performance of the cryostat insulation.It was stated that the cost of the temperature sensor system for a 10-kt module would be less than $300K (M&S).ProtoDUNE Dual Phase also contains 18 capacitive level meters to follow the liquid argon filling, monitor and adjust the liquid level with respect to the cryostat, adjust the position of the CRPs and to evaluate the CRP deformation. Proto-DUNE SP deployed 11 cameras, of three different designs, 2 designs were cold and 1 was warm.ProtoDUNE –DP has 11 cold cameras. No warm cameras were deployed.Twelve cold, fixed location cameras are proposed for each 10 kT far detector. Three warm, moveable cameras which are deployed into instrumentation ports are also proposed.There are a limited number of ports available on top of the ProtoDUNE-SP cryostat which must be shared between CISC and mentsThe purity monitors in ProtoDUNE-SP played important roles in several occasions.They were crucial during filling, when they first observed a degradation of the purity, that was afterwards associated to the early saturation of the purification cartridges. On this occasion the prompt reaction of the purity monitors limited the consequences.The ProtoDUNE purity monitors also observed degradation of the purity due to unforeseen stops of the liquid argon pump. Again the quick reaction to the purity monitor data minimized the impact of the pump stops. The continuous monitoring of the liquid argon purity during operation is a fast and effective way to ensure the basic quality of the data.It is clear that purity monitors are a necessary tool for filling and commissioning DUNE cryostats with LAr. It is also very useful and an essential tool for routine data taking over the entire period of DUNE running. If purity monitors inside the cryostat are to be used to spot problems and quickly react to them (e.g. a drop in purity due to a crack in a window) the question of the operational duty cycle (e.g. should they be run daily, hourly etc.) needs to be addressed. This is connected to the question of ageing and photocathode degradation (see later).?In order to keep the uncertainty on dE/dx due to e-lifetime at 1% level the purity monitor uncertainty should be improved to 4.5%. There are also unanswered questions on how the purity measurements by monitors outside the TPC can be reliably translated to the purity levels inside the TPC.?Given the current systematic uncertainties with the purity monitor results and (much bigger) uncertainties with purity results from TPC (cosmic ray runs) the purity stratification claim appears to be inconclusive.?Purity monitors are most useful during the commissioning and early data taking. Their long term operation is more difficult to guarantee. This is certainly an issue for those that are inside the cryostats as they cannot be easily accessed and replaced. Available data on possible photocathode ageing as it is exposed to UV light and dirtier LAr appear to be inconclusive.?The committee endorses the inclusion of the external purity monitors, but notes that the cryogenic team will monitor the filtration system and perform the regeneration well before it is needed (e.g. before the filters saturate). Under normal conditions they are not expecting to use the purity monitors ?to gauge when the filters need regeneration. Note after the review : That being said, there has been an incident in the protoDUNE operations where prompt results from inline monitors would have been able to catch a failure in the system which caused severe degradation of the argon purity.The temperature sensors were equally useful, it is not clear if they can truly be used to predict the purity, validate the CFD, etc. Even with the data, once the cryostat is full there is little that can be done to change the conditions of the system. One can change the circulation flow rate, change (a bit) the pressure of the LAr returned to the cryostat (hence the Temperature), and change (maybe) the GAr withdrawn from the chimneys. That’s pretty much it. In ProtoDUNE–SP the temperature sensors all performed within the relative specification.The dynamic profiler has the advantage of being calibrated in situ. The data of the temperature profilers may be adequate, but the comparison between the measurement and the simulation needs still to be deepened.The liquid argon dynamics (distribution of temperature -drift speed- and purity -charge attenuation-) affects the data treatment and the systematic error in the reconstructed events.Purity monitors and temperature sensors are the instruments considered by the CISC to compare the measurements to the simulations and to make corrections to reduce systematic errors on quantities such as the electron lifetime.The requirements on the number, position and sensitivity of the instruments must be more related to the physics measurement that needs to be performed.Additional instruments may be needed. For instance, the speed and the direction of the liquid argon would give valuable information for the simulation comparison.One committee member wonders if people have considered this when proposing a certain array of T sensors or Purity Monitors, etc. The number of parameters that can vary is very little. The proponents of all the monitors should be aware that they may have information, but are not able to use this to change the performance of the system in any major way.It was not clear to the committee if all three different types of temperature monitors employed in the ProtoDUNE-SP cryostat will be necessary for the DUNE far detector. It was noted that the temperature monitor strings currently being implemented in the ProtoDUNE-DP cryostat are potentially a simpler and less expensive option to the three types of devices implemented in the ProtoDUNE-SP cryostat. The mechanics is simpler and cheaper, nonetheless, without radically changing the mechanism of installation, the sensors can be installed only in the vicinity of the corners. Data from these sensors will not be representative of the rest of the cryostat. The PD-DP sensors are not adequate to perform precision measurement at the level of few mK, but they could be replaced with more precise and calibrated sensor like the one used in PD-SP.The design of the temperature sensors deployment must be properly engineered and integrated with existing and planned interfaces.?During the cool down the cameras were extremely useful to verify what was going on. The current plan calls for 12 cold cameras in each Far Detector module which will provide excellent coverage of the full LBNF cryostat/DUNE detector.The focus of the cameras needs to be remotely adjustable. As further developments: remote optical zoom and the possibility of remotely rotate the camera should be explored.The committee heard that the proposed instrumentation is fairly inexpensive, but notes that there are a lot of sensors and monitors proposed and the cost may start to add up. We encourage the consortia to look at the overall picture and whether it fits within their available resources. In other words, look carefully at what is a requirement and what is a “wish list”. RecommendationsCome up with a motivated suggestion on the duty cycle of purity monitor operation during LAr filling, commissioning and physics data taking.?Carry out a cost/benefit analysis for the possibility of additional purity monitors (beyond the baseline presented), both inside the cryostat and inline.?Investigate the improvement on the purity monitor systematic uncertainty potentially offered by longer purity monitor detectors and additional calibrations. Suggest possible measurements to provide an experimental relation between the attachment coefficient and electric field in order to reliably extrapolate purity monitor results to the purity inside the TPC (the E-field used in PrM and TPC differ significantly).?Carry out a thorough investigation of the purity stratification issue in ProtoDUNE. In particular effort should be invested in more sophisticated cosmic ray data analysis in the attempt to correlate it with purity monitor measurements for data sets with recirculation pumps on and off.?Investigate and conclusively identify possible ageing effects of purity monitor photocathodes and reasons behind them. Investigate possible use of alternative (i.e. not gold) photocathodes, i.e. sliver photocathodes as it has a lower work function compared to gold. Investigate alternative ways of generating electrons at the purity monitor cathodes (LED, radioactive sources). The latter can also address the question of systematic error and make the installation simpler and more reliable by removing rigid and fragile optical fibers.?Provide justification for the number and type of temperature sensors in the DUNE cryostat. Quantify the precision with which CFD can be validated as a function of the number, type and position of temperature sensors.?Work with the other consortia to develop a deployment plan for the temperature sensors that is compatible with all mechanical and grounding requirements of the other systems.Work with the calibration consortia to present a workable plan for the deployment of both cryogenic instrumentation and calibration hardware proposed for deployment in the ProtoDUNE-IIs. Investigate the issue of cold camera lifetime and develop a mitigation strategy if necessary.The CISC Consortia should identify the resources, both capital investment and labor needed to carry out the proposed scope of work for ProtoDUNE-II and ultimately for two DUNE far detector modules. ................
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