Jet Operating Research Articles

Overview of disruptions with JET-ILW

The paper presents an analysis of disruptions occurring during JET-ILW plasma operations covering the period from the start of ILW (ITER-like wall) operation up to completion of JET operation in 2016. The total number of disruptions was 1951 including 466 with deliberately induced disruptions. The average rate of unintended disruptions was 16.1 %, which is significantly above the ITER target at 15 MA. The pre-disruptive plasma parameters are: plasma current Ip = (0.82–3.38) MA, toroidal field BT = (0.98–3.4) T, safety factor q95 = (1.52–9.05), plasma internal inductance li = (0.58–1.86), Greenwald density limit fraction FGWL = (0.04–1.61), with 720 X-point plasma pulses from a subset of 1420 unintended disruption shots. Massive gas injection (MGI) has been routinely used in protection mode both to terminate pulses when the plasma is at risk of disruption and to mitigate against disruption effects. The MGI was mainly triggered by the n = 1 locked mode (LM) amplitude exceeding a threshold or by the disruption itself, namely, either dIp/dt (specifically, a fast drop in Ip) or the toroidal loop voltage exceeding threshold values. For mitigation purposes, only the LM was used as a physics precursor and threshold on the LM signal was used to trigger the MGI prior to disruption. Long lasting LM (≥ 100 ms) do exist prior to disruption in 75% of cases. However, 10% of non-disruptive pulses have a LM which eventually vanished without disruption. The plasma current quench (CQ) may result in 3D configurations, termed as asymmetrical disruptions, which are accompanied by sideways forces. Unmitigated vertical displacement events (VDEs) generally have significant plasma current toroidal asymmetries. Unmitigated non-VDE disruptions also have large plasma current asymmetries presumably because there is no plasma vertical position control during the CQ and so they too are subject to large vertical displacements. MGI is a reliable tool to mitigate 3D effects and correspondingly sideways forces during the CQ. The vessel structure loads depend on the force impulse and force time behaviour, including their rotation. The toroidal rotation of 3D configuration may cause resonance with the natural frequencies of the vessel components in large tokamaks such as ITER. The JET-ILW amplitude-frequency interdependence of toroidal rotation of 3D configurations is presented.

Cryogenic Liquid Jets for High Repetition Rate Discovery Science

This protocol presents a detailed procedure for the operation of continuous, micron-sized cryogenic cylindrical and planar liquid jets. When operated as described here, the jet exhibits high laminarity and stability for centimeters. Successful operation of a cryogenic liquid jet in the Rayleigh regime requires a basic understanding of fluid dynamics and thermodynamics at cryogenic temperatures. Theoretical calculations and typical empirical values are provided as a guide to design a comparable system. This report identifies the importance of both cleanliness during cryogenic source assembly and stability of the cryogenic source temperature once liquefied. The system can be used for high repetition rate laser-driven proton acceleration, with an envisioned application in proton therapy. Other applications include laboratory astrophysics, materials science, and next-generation particle accelerators.

Investigating the thermal stability of highly radiative discharges on JET with a new tomographic method

The next generation of Tokamak devices is expected to work at very high radiated fractions, well above 90%, to preserve the integrity of the plasma facing components in general and the divertor in particular. In addition to maintaining high confinement, these configurations will also have to guarantee a low disruptivity. An accurate determination of the emitted radiation will therefore become increasingly important, not only for the global power balances but also for specific regions of the plasma cross section (for example to properly control detachment). In this perspective, a new tomographic inversion method, based on the maximum likelihood (ML) approach, capable of providing routinely confidence intervals in the estimates of the radiated power, has been applied to the investigation of high radiative discharges on JET with the ITER like wall (ILW). The emission has been increased with injection of extrinsic impurities. Taking into account all the major sources of uncertainties, a systematic analysis of the configurations has shown that it has not been possible to develop stable configurations with radiated fraction higher than 70% of the input power. At higher radiated fractions the discharges always disrupt. Therefore significant work remains to be done to extend JET operation in a reactor relevant regime of sufficient radiation in preparation for ITER and DEMO.

Wall-Pressure Fluctuations Induced by a Compressible Jet in Installed Configuration

Wall-pressure fluctuations induced by a subsonic jet over a wing/flap scaled model have been experimentally investigated in a large-scale wind-tunnel facility. The pressure field on the wing was measured by flush-mounted pressure transducers installed on the pressure side, whereas synchronized near- and far-field pressures were measured using microphone arrays. Experiments were carried out with the coaxial jet operating in single-stream-like jet conditions (that is, with the primary and secondary jets at the same flow conditions) for two different jet Mach numbers of and . Flight effects were explored as well for the jet flow condition of and the flight-stream Mach number set equal to 0.18. Data were analyzed in the time and frequency domains in order to characterize the wall-pressure statistics as well as the cross statistics between the wall-pressure fluctuations and the near-/far-field pressure. Particular attention was devoted to determining universal scalings of the spectral quantities using both static and flight parameters. Semiempirical models commonly used in canonical turbulent boundary layers to reproduce the wall-pressure coherence were tested and verified for both the static and flight conditions.

On diagnostics of annular-shape radio-frequency plasma jet operating in argon in atmospheric conditions

One of the driving forces behind the development of cold plasma sources at atmospheric pressure is their application in the biomedical field. In this respect, radio-frequency (RF) plasma jets are of particular importance due to their possible safe operation on humans and the generation of the high amount of reactive species. For this reason, we designed an RF plasma jet in co-axial geometry with the possibility of aerosol introduction, where its characteristics were evaluated by electrical diagnostics, optical emission and laser scattering spectroscopy. The RF plasma jet operation and stability of diffuse mode were analysed based on energy balance. It was observed that α-mode diffuse discharge characterised by an effluent length up to 5 mm was sustained at a power density below 30 W cm−3. The gas and rotational temperature were determined by means of spectroscopy methods and compared with the results of direct laser scattering. It was established that the gas temperature obtained from N2 emission of transition C3Пu → B3Пg (0, 2) is highly overestimated whereas the gas temperature estimated from OH transition A2Σ+ → X2Пi (0, 0) gave a reasonable agreement with both Rayleigh and Raman spectroscopy. Based on the Rayleigh scattering method, uniform gas temperature distribution in the discharge effluent was found at a power below 15 W with the average temperature below 340 ± 15 K. The low gas temperature of argon plasma jets would allow use of this source in temperature-sensitive material applications including skin treatments.

Flow-Field and Performance Study of Coaxial Supersonic Nozzles Operating in Hypersonic Environment

The integration of multiple propulsion systems in a coaxial configuration is one of the challenges to realize hypersonic passenger transportation. This study is an attempt to understand the performance of two co-axial jets exiting from the base of slender body, operating in single and dual operation mode in freestream hypersonic flow environment. In addition, the effects on performance by adding a different length common channel to both co-axial jets are studied. In the first part of this study, the experiments have been performed for small slender body kept in hypersonic Mach 7 flow, which consists of two inner high-pressure chambers and two co-axial nozzles at the base: central nozzle (Mach 4) and surrounding nozzle (Mach 2.8) along with extended common region, termed as common channel. Schlieren images have been captured for single and dual operation modes. Axisymmetric numerical simulations have been performed for further understanding of the flow interactions and have been qualitatively validated with experimental images. In the second part, the parametric study has been performed using numerical simulations for resized model with various exit Mach numbers for central and surrounding jets along with effect of no common channel and with common channel for various operation modes. One of the findings of the study is that dual jets should operate and exit at same plane (no common channel) with the same exit area (each nozzle with half of total available exit area) in order to have higher total thrust from both jets than the sum of individual jets operating in single operation mode. For higher central jet Mach numbers, the corresponding surrounding jet Mach number will be lower, and in dual operation mode (without common channel), the total thrust will be the same or lower than the sum of the individual jet operations. Regarding the effect of common channel, it has been found out that the introduction of the extended short or long common channel in dual mode operation does not have significant effect on thrust, while the jet flow field is strongly affected by the common channel presence. In single operation mode, for Mach 2 central-jet, the thrust performance decreases 12.2-14.6 % in presence of short and long (29.5 mm and 59 mm) common channel, while for Mach 2 surrounding jet, the thrust performance increases by 15-17.4 % in presence of common channel.

Energy and particle confinement in JET H-mode plasma

This work describes the behaviour of the global energy and particle confinement on JET observed in a massive database of H-mode plasmas covering almost the whole lifetime of JET operations, both with the carbon and metal wall. The analysis is focused on type I ELMy H-modes in stationary phases. It is shown that plasma density in that regime is determined mainly by the plasma current, edge safety factor, triangularity of the last closed flux surface and the hydrogenic isotope mass. Behaviour is consistent for the whole database regardless of divertor configuration or the plasma facing materials. On average, thermal energy confinement time in JET with the carbon wall (JET-C) is accurately predicted by the IPB98(y,2) scaling. For JET with the ITER-like wall (JET-ILW), the energy confinement is found to be lower than expected from the scaling. The difference is found to be much stronger in a divertor configuration with the outer strike point at a vertical target and the pumping throat at the private flux. Observed lower confinement in JET-ILW can partially be attributed to the additional operational constraints of the metal wall machine, i.e. the avoidance of heavy impurity accumulation via additional gas dosing, but not fully. The isotope effect on the energy confinement in the Meff = 1–2 range is found to be the same in JET-C and JET-ILW, thus is independent of the wall material, if correlation with plasma density is accounted for. The effect of the toroidal magnetic field on the confinement is between zero and slightly negative. Triangularity has a generally favourable effect on the energy confinement, but the magnitude changes across the database. The effect of triangularity on plasma density is always much stronger than on energy confinement however, therefore plasmas with high triangularity are in general more dense and colder than at lower triangularities. The work described in this paper is completed under the EUROfusion global confinement database project, and the data shown here will be available to EUROfusion collaborators shortly. The data are also either already included in the international H-mode confinement database, or will be in the future updated version.

Operation of Rectangular Jet using a Rectangular Notch at the Midspan

The mean and turbulent flowfields of turbulent jet issuing from a rectangular nozzle (AR: Aspect Ratio = 12.5) with a rectangular notch at the midspan, have been investigated, experimentally. The object of this experiment is to investigate a possibility of the operation of both the mean and the turbulent velocity fields in the rectangular jet field by the attachment of a rectangular notch perpendicular to the rectangular jet. Four notch aspect ratios (NAR: Notch Aspect Ratio) of the rectangular notch used were 2.5, 7.5, 12.5 and 165, respectively.

Violation of the Kluberg-Stern-Zuber theorem in SCET

A classic result, originally due to Kluberg-Stern and Zuber, states that operators that vanish by the classical equation of motion (eom) do not mix into “physical” operators. Here we show that and explain why this result does not hold in soft-collinear effective theory (SCET) for the renormalization of power-suppressed operators. We calculate the non-vanishing mixing of eom operators for the simplest case of N -jet operators with a single collinear field in every direction. The result implies that — for the computation of the anomalous dimension but not for on-shell matrix elements — there exists a preferred set of fields that must be used to reproduce the infrared singularities of QCD scattering amplitudes. We identify these fields and explain their relation to the gauge-invariant SCET Lagrangian. Further checks reveal another generic property of SCET beyond leading power, which will be relevant to resummation at the next-to-leading logarithmic level, the divergence of convolution integrals with the hard matching coefficients. We propose an operator solution that allows to consistently renormalize such divergences.

Erosion, screening, and migration of tungsten in the JET divertor

The erosion of tungsten (W), induced by the bombardment of plasma and impurity particles, determines the lifetime of plasma-facing components as well as impacting on plasma performance by the influx of W into the confined region. The screening of W by the divertor and the transport of W in the plasma determines largely the W content in the plasma core, but the W source strength itself has a vital impact on this process. The JET tokamak experiment provides access to a large set of W erosion-determining parameters and permits a detailed description of the W source in the divertor closest to the ITER one: (i) effective sputtering yields and fluxes as function of impact energy of intrinsic (Be, C) and extrinsic (Ne, N) impurities as well as hydrogenic isotopes (H, D) are determined and predictions for the tritium (T) isotope are made. This includes the quantification of intra- and inter-edge localised mode (ELM) contributions to the total W source in H-mode plasmas which vary owing to the complex flux compositions and energy distributions in the corresponding phases. The sputtering threshold behaviour and the spectroscopic composition analysis provides an insight in the dominating species and plasma phases causing W erosion. (ii) The interplay between the net and gross W erosion source is discussed considering (prompt) re-deposition, thus, the immediate return of W ions back to the surface due to their large Larmor radius, and surface roughness, thus, the difference between smooth bulk-W and rough W-coating components used in the JET divertor. Both effects impact on the balance equation of local W erosion and deposition. (iii) Post-mortem analysis reveals the net erosion/deposition pattern and the W migration paths over long periods of plasma operation identifying the net W transport to remote areas. This W transport is related to the divertor plasma regime, e.g. attached operation with high impact energies of impinging particles or detached operation, as well as to the applied magnetic configuration in the divertor, e.g. close divertor with good geometrical screening of W or open divertor configuration with poor screening.JET equipped with the ITER-like wall (ILW) provided unique access to the net W erosion rate within a series of 151 subsequent H-mode discharges (magnetic field: T, plasma current: MA, auxiliary power MW) in one magnetic configuration accumulating 900 s of plasma with particle fluences in the range of 5– in the semi-detached inner and attached outer divertor leg. The comparison of W spectroscopy in the intra-ELM and inter-ELM phases with post-mortem analysis of W marker tiles provides a set of gross and net W erosion values at the outer target plate. ERO code simulations are applied to both divertor leg conditions and reproduce the erosion/deposition pattern as well as confirm the high experimentally observed prompt W re-deposition factors of more than 95% in the intra- and inter-ELM phase of the unseeded deuterium H-mode plasma. Conclusions to the expected divertor conditions in ITER as well as to the JET operation in the DT plasma mixture are drawn on basis of this unique benchmark experiment.

Influences of the inner diameter of the solid shielding tube on the characteristics of the radio-frequency cold atmospheric plasma jet

Active control of the local environment of the cold atmospheric plasma (CAP) jet is of great importance in actual applications since the CAP operates in an open atmosphere with the inevitable entrainment of the surrounding cold air. In this paper, the solid shielding effects of the cylindrical quartz tubes with different inner diameters on the characteristics of the CAP jets driven by a radio-frequency (RF) power supply are studied experimentally. The experimental results show that the total length of the shielded plasma jet can be increased significantly by an appropriate combination of the quartz tube inner diameter and that of the plasma generator nozzle exit with other parameters being unchanged. This phenomenon may be qualitatively attributed to the loss of diffusion of the charged particles in the radial direction under different inner diameters of the quartz tubes. Compared with the plasma free jet, the plasma shielding jet is produced with optimized parameters including longer plasma jet length, higher concentrations of chemically reactive species, higher rotational, vibrational, and electron excitation temperatures when the inner diameters of the solid shielding tube and the generator nozzle exit are the same. A maximum plasma jet length of 52.0 cm is obtained in contrast to that of 5.0 cm of the plasma free jet in this study. The experimental results indicate that the solid shielding effect provides a new method for the active control of the local environment of the RF-CAP jet operating in an open atmosphere.

Study on abrasive water jet drilling for graphite filled glass/epoxy laminates

The effect of Abrasive Water Jet (AWJ) machining parameters on quality of the drilled holes in Glass Fiber Reinforced Polymer (GFRP) composite is reported. In this work a hybrid composite laminates of glass fabric reinforced epoxy with 2%, 4% and 6% graphite were studied. Experiments were designed using Taguchi L9 orthogonal array and conducted using five-axis CNC AWJ machine. The influence of process parameters such as jet operating pressure, feed rate and stand-off distance (SOD) on quality of drilled holes were investigated and results are reported. Further, the process parameter were optimized using statistical method. The study show that jet operating pressure is the most influential operating parameter affecting the response. SEM investigation reveals that use of graphite in GFRP composite helps in improving machinability of the laminates.

The software and hardware architecture of the real-time protection of in-vessel components in JET-ILW

For the first time, the JET operation in deuterium–tritium (D–T) plasma, which is scheduled to take place on JET in 2020, will be performed in the ITER mix of plasma-facing component materials. In view of the preparation of the DT campaign (DTE2), several aspects of the plasma operation require significant improvements, such as a real-time protection of the first wall. The risk of damaging the metallic PFCs caused by beryllium melting or cracking of tungsten owing to thermal fatigue required a new reliable D–T compatible active protection system. Therefore, the future development of the JET real time first wall protection is focused on the D–T campaign and the ITER relevant conditions which may cause failure of camera electronics within the Torus hall. In addition to the technological aspect, the intensive preparation of the diverse software tools and real time algorithms for hot spot detection as well as alarm handling strategy required for the wall protection is in progress.This contribution describes the improved design, implementation, and operation of the near infrared (NIR) imaging diagnostic system of the JET-ILW plasma experiment and its integration into the existing JET protection architecture. To provide the reliable wall protection during the DTE2, two more sensitive logarithmic NIR camera systems equipped with new optical relays to take images and cameras outside of the biological shield have been installed on JET-ILW and calibrated with an in-vessel calibration light source (ICLS). Additionally, post-pulse data visualization and advanced analysis of all types of imaging data is provided by the new software framework JUVIL (JET users video imaging library). The formation of hot spots is recognized as a significant threat due to rapid surface temperature rise. Because it could trigger the protection system to stop a pulse, it is important to identify the mechanisms and conditions responsible for the formation of such hot spots. To address this issue the new software tool ‘Hotspot Editor’ has been developed.

Measurement of density with an auxiliary measuring electrode in atmospheric pressure plasma jet

In this study, the density of metastable in an atmospheric-pressure plasma jet operating in helium with 0.001% nitrogen has been measured using an auxiliary measuring electrode technique. In the glow discharge mode, waveforms from two grounding electrodes, including one main discharge electrode and one auxiliary electrode, are captured. The isolated current peak formed by Penning ionization in waveforms from the auxiliary measuring electrode is identified to calculate the density of metastable In our discharge environment, the helium metastable densities along the jet axis direction are between and which is in good agreement with the results measured by other techniques. This measurement technique can be conveniently applied to the diagnosis of metastable in an atmospheric-pressure plasma jet array.

Maximizing JET divertor mechanical performance for the upcoming deuterium-tritium experiments

The next D-T campaign will push the JET ITER-like wall to high divertor power and energy levels. During the 2016 campaign, Strike Point (SP) sweeping permitted relevant H-mode scenarios without exceeding the temperature limits imposed by JET Operation Instructions (JOIs). In the subsequent shutdowns, six outer divertor tungsten-coated 2D carbon fibre composite tiles were found to have inter-laminar cracks.Here we describe the results of a 3D thermo-mechanical analysis aimed at understanding the origin of the cracks. A sensitivity assessment has been carried out on the temperature time-evolution of a realistic tile 3D model during high power pulses, both with fixed and sweeping SPs. Time and space-varying heat flux density loads on the divertor have been calculated using different techniques for reconstructing the power footprint. The results have been benchmarked against the temperature measurements by high resolution infrared diagnostic systems.The study confirmed the source of the cracks and their localization in the upper part of the tile, giving inter-laminar tension higher than the Ultimate Tensile Stress. Plasma input power, radial location of the SP and sweeping amplitude play an important role on the stress field whose maximum value strongly depends on the SP location. Their influence on the maximum stress value has been investigated and optimized to maximize the performance of divertor tiles without exceeding the limits on input energy and maximum surface temperature imposed by the JOIs.

Cold Atmospheric Pressure Nitrogen Plasma Jet for Enhancement Germination of Wheat Seeds

The possibility to improve the germination characterization of the wheat seeds by cold atmospheric nitrogen plasma jet treatment was report. Spectroscopic measurements were performed to identify the constituent particles of a nitrogen atmospheric plasma jet. Spectroscopic measurements revealed that the particles with relatively high energy excited states exist inside the jet nozzle. During this study the cold atmospheric plasma parameters were set for attain the highest rate of the germination seeds. The nitrogen used in this system as carrier gas. The nitrogen cold atmospheric plasma operated at 14 l/min as a fixed flow rate. The operation of plasma jet at 14 l/min was represented the suitable plasma dose to enhancement the germination parameters. The N2 first positive system (N2 1+), N2 second positive system (N2 2+) and N2 ion first negative system (N2+ 1−) were represented the emission spectra observed inside the jet nozzle. The germination characteristics of wheat seeds have been significantly enhanced after cold atmospheric plasma treatment. The mean weight of fresh sprout was 823.82 mg for untreated seeds and increased to 1231.80, 1369.50 and 1342.46 mg for 2 min, 4 min, and 6 min treatments respectively. The effects of nitrogen cold atmospheric plasma jet on the growth parameter depended on exposure time.

Robust configuration of the JET Real-Time Protection Sequencer

The JET Real-Time Protection Sequencer (RTPS) co-ordinates responses for magnetic and kinetic actuators to protect the ITER-Like Wall from possible melting events and other undesirable scenarios. It allows programmable stop responses per pulse, based on alarms raised by other systems.The architecture combines a modular run-time application developed using MARTe (Multithreaded Application Real-Time executor) with the top-level JET supervisory and configuration software, Level-1. Operational experience since 2011 drove a requirement to refactor the system in 2017, moving the maximum degree of functionality from compiled code to configuration data, providing more flexibility, maintainability and verifiability of action(s) to be taken during a pulse.This paper discusses the features of the architecture that made this clean separation of rule-based logic and real-time signal processing possible and practical, including how functions and interfaces between MARTe and Level-1 are organised. It also explains management of configuration data to address development, testing, commissioning and operations, each with individual ownership, responsibility and lifecycles. The core technology enabling this is the Level-1 domain specific language, able to manipulate, validate and load into plant configuration parameter sets. The language also enables implementation of advanced user interfaces, providing operators with the tools to focus on essentials tasks for their area of responsibility. It exemplifies this with recent verification and validation of the refactored protection system: unit/low-level integration tests defined by core developers and integration/behavioural tests defined by JET’s Plasma Operations Group, respectively, ensuring robust and consistent behaviour. We show how the wide scope and power of this language has enabled evolution of JET operations efficiently and correctly over decades of operational experience.

JET FIR Interferometer laser operation and interlock system upgrade to an open automation system

We report on the selection, implementation and successful demonstration of a new automated laser control system for JET’s Far Infrared Interferometer, a diagnostic essential for machine protection. The new control system allows all laser subsystems and sensors to be interlocked and operated remotely in a precise and preprogramed manner, functionalities that are essential for reliable operation with the additional access restrictions foreseen in the upcoming D-T operation of JET. Our selection process gave priority to known technologies that conform to industry standards and have been proven within the JET operational environment. Weighting was also given to the accessibility of the software interface and the scalability of the technology.The new laser control system was installed and tested at the end of 2017. It comprises an Industrial PC(IPC), running Windows Embedded Standard 7 and a real-time Programmable Logic Controller (PLC) using the proprietary protocol TwinCAT developed by Beckhoff. This technology is extremely compact (DIN rail mountable), scalable, modular and does not require additional wiring between modules. A particularly noteworthy feature is the ability to run applications written in high level languages which interact with the PLC. In this example, the main code for control and monitoring of the system was developed in Python using Finite State Machine algorithms.This technology has applications beyond laser control in a wide variety of application areas where reliable and robust remote operation and easy maintenance/service is a priority. Indeed, similar systems have been reliably used in the JET Plant Essential Monitoring System since 2015.

Development of Organosilicon-Based Superhydrophobic Coatings through Atmospheric Pressure Plasma Polymerization of HMDSO in Nitrogen Plasma.

Water-repellent surfaces, often referred to as superhydrophobic surfaces, have found numerous potential applications in several industries. However, the synthesis of stable superhydrophobic surfaces through economical and practical processes remains a challenge. In the present work, we report on the development of an organosilicon-based superhydrophobic coating using an atmospheric-pressure plasma jet with an emphasis on precursor fragmentation dynamics as a function of power and precursor flow rate. The plasma jet is initially modified with a quartz tube to limit the diffusion of oxygen from the ambient air into the discharge zone. Then, superhydrophobic coatings are developed on a pre-treated microporous aluminum-6061 substrate through plasma polymerization of HMDSO in the confined atmospheric pressure plasma jet operating in nitrogen plasma. All surfaces presented here are superhydrophobic with a static contact angle higher than 150° and contact angle hysteresis lower than 6°. It is shown that increasing the plasma power leads to a higher oxide content in the coating, which can be correlated to higher precursor fragmentation, thus reducing the hydrophobic behavior of the surface. Furthermore, increasing the precursor flow rate led to higher deposition and lower precursor fragmentation, leading to a more organic coating compared to other cases.

Overview of the JET operation reliability

The JET tokamak has been in operation since 1983. Information on every shutdown, commissioning phase and experimental campaign has been logged electronically since the year 2000, a model for RAMI analyses in fusion experiments. The JET operation reliability statistics record the time taken to install major upgrades, commission systems with plasma, the downtime for maintenance and the achieved experimental campaign days. On average, JET achieves 82% of the planned experimental days during a calendar year. For unplanned interventions the systems that failed are identified together with the impact on machine availability. A total of 14 unplanned interventions are recorded over 19 years with durations of up to 8 weeks. During experimental campaigns, delays from essential subsystems are recorded; computer systems, power supplies, neutral beam systems and delays attributed to human operators. On average 21% of the time is lost due to delays during operations. From the operation reliability data, refurbishments and maintenance are planned at JET to prepare for the upcoming campaigns using deuterium-tritium mixtures.