Tailoring the ESS Reliability and Availability needs to satisfy the users Enric Bargalló WAO October 27, 2014

Outline Introduction Experiments at ESS and their needs – Kinetic experiments – Integrated-flux experiments Possible requirements Conclusions 2

Introduction 3

ESS overview 4 Linear proton accelerator (600 m) Neutron science systems Target station 5 MW proton accelerator providing long pulse (2.86 ms at 14 Hz) Target: Rotating wheel, He gas cooling 22 instruments

Objectives of this work The main goal is to clarify and document the needs of ESS users: – Describe the different kinds of experiments expected at ESS – Define their needs in terms of neutron beam availability, reliability and quality Compare current definitions and requirements with user needs. Examples: – Failure considered only when beam trips for more than 1 minute? – Is the same to have 10 trips of 10 minutes than 1 trip of 100 minutes? – For how long can we operate at reduced power? Extract plausible availability and reliability requirements 5

Work done and future steps People involved – Instruments scientists – Reliability and availability experts – With the collaboration of the ESS XFWG on Reliability Outcomes – Document “Experiments expected at ESS and their neutron beam needs” (not yet official) – Reliability and availability requirements (first proposal) – Allocation between subsystems (accelerator, target, conventional…) 6

Experiments at ESS and their needs 7

Definitions Experiment: – Beamtime allocated to users. Typically one or more days. – An experiment consists of a series of measurements. Measurement: – The length is typically minutes or hours, but will occasionally be as short as a single ESS time frame (71ms) or as long as several days. 8

Experiments at ESS Kinetic experiments – About 10% of the total number of experiments – Very important, because they constitute an essential part of the science case of the ESS – Short beam trips might be problematic Integrated-flux experiments – About 90% of the total number of experiments – Short interruptions to beam delivery has no significant impact on the experimental outcome 9

Kinetic experiments Contain one or more time-sequences of data sets measured during an irreversible process. If enough data sets fail during each time-sequence, then the measurement fails and has to be repeated. If enough measurements fail, then the user experiment fails and the beamtime needs to be rescheduled. 10

Kinetic experiments Losses with a duration of less than 1/10 th of the length of the measurement will be acceptable. For example: – Trips longer than 6s may not occur in the 1-minute measurements. – Trips longer than 1min may not occur in the 10-minutes measurements. – … Typical duration of the measurements: from seconds to hours – Many measurements at the 1-10 minute scale – Considerable fraction of 5-10 seconds measurements – Some measurements might last several hours 11

Kinetic experiments Time-scales in a kinetic measurement 12

Kinetic experiments The key metric is beam reliability: minimize the probability of having a beam trip during a measurement. A beam trip is defined as a period during which the power falls to <50% of the scheduled power. Kinetic experiments needs: a reliability of at least 90% should be provided for the duration of the measurement. The measurement will be considered failed when the beam power is reduced to less than 50% of the scheduled power for more than 1/10 th of the measurement length. 13

Integrated-flux experiments Main parameter for success: integrated neutron flux over the duration of the experiment. Two metrics to quantify the beam quality: – Beam availability – Average beam power Short beam trips are acceptable. Some examples: – 1 pulse lost: no one cares – 5 seconds trip: no one cares – 5 minutes trip: a few people care – 2 hours of downtime: inconvenient, some measurements fail – 1 day of downtime: 1-2 day experiments fail Beam trips of less than 1 minute in duration should be excluded from the availability analysis, while all others are included. 14

Integrated-flux experiments Experiments duration: No less than one day and no longer than one week (typically is 3 days). Beam availability definition: is the fraction of time over an experiment during which the beam was available at more than 50% nominal power, excluding beam trips of less than 1 minute. Integrated neutron flux experiments needs: at least 90% of the experiments should have at least 90% of beam availability and more than 80% of the scheduled beam power for the duration of the experiments. The beam will be considered unavailable when its power is less than 50% of its scheduled power for more than one minute. 15

Possible requirements 16

Possible requirements for Kinetic experiments Measurement durationMax trip length acceptedMax number of trips per day 10 seconds1 second minute6 seconds minutes1 minute hour6 minutes hours1 hour hours3 hour Where: -R is the reliability desired (90%) -t is the duration of the measurement (h) -λ is the failure rate (h -1 )

Possible requirements for Kinetic experiments Simplification of the requirements: – Easy way to track and evaluate them – Possible to compare with other facilities Beam trip bins by duration of the trip and its requirement 18 Beam trip binsMaximum number of trips per dayApproximate MTBF 1 second - 6 seconds minutes 6 seconds - 1 minute minutes 1 minute - 6 minutes hours 6 minutes - 20 minutes hours 20 minutes - 1 hour0.512 days 1 hour - 3 hours0.176 days

Comparison with values achieved at SNS 19 Many measurements Only some measurements Data from SNS provided by Charles C. Peters

Focus on each bin from SNS data 20

Possible requirements for Integrated-flux experiments Duration of the experiments: – From 1 day to 7 days – Typically 3 days Assumptions to extract requirements – Less than 90% probabilities of having an event with a duration of more than one 10 th of the length of the experiment – More than 90% beam availability over the duration of the experiment 21

Possible requirements for Integrated-flux experiments 22 Data from SNS provided by George Dodson

Integrated-flux experiments availability Rough calculation on downtime considering – No ramp-up time due to target – Beam trips of more than one minute Most demanding case is for the 7 days experiments: Beam availability for 7-days experiments is 94.3% 23 Downtime in 7 days Short beam trips (1 minute to 1 hour)5.02 hours Long beam trips (1 hour to 16.8 hours) 5.10 hours TOTAL10.12 hours

Estimation of the total downtime Rough calculation done with some assumptions Beam availability for ESS would be 92.8% 24 Downtime per year (200 days) Short beam trips (1 minute to 1 hour) 145 hours Long beam trips (1 hour or more)200 hours TOTAL345 hours

Conclusions 25

Conclusions Good communication between the instrument scientists and the machine designers and future operators – Match the expectations and needs from the users and instrument scientists to the reliability and availability values achievable by the machine More detail in the ESS reliability and availability requirements – It defines specific requirements – Possible to compare to other facilities – Easy to track, evaluate and analyze Basic information to start ESS RAMI analyses 26

Thank you! 27

Extra slides 28

Comparison with other facilities 29

RAMI definitions Reliability: probability of continuous and correct operation of a system or component during a time interval. Availability: probability of having a system or component in correct operation in a specific moment. (uptime)/(uptime + downtime) – Inherent availability: scheduled operation time – Operational availability: including scheduled maintenance periods Maintainability: capability of performing maintenance to a system or component. Inspectability: capability of inspect, test and monitor a system and its possible failures. 30