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Future fusion reactors like ITER and DEMO will have all-tungsten (W) walls and long pulses. These features will make wall conditioning more difficult than in most of the existing devices. The W Environment Steady-state Tokamak (WEST) is one of the few long pulse (364 s) fusion devices with actively cooled W plasma-facing components in the world. WEST is a unique test bed to study impurity migration and plasma density control via reactor relevant wall conditioning techniques. The phase II of WEST operations began in 2022, after the installation of a new lower divertor, now entirely equipped with actively cooled, ITER grade, W monoblocks. After pump down, we baked WEST between 90 °C and 170 °C for ∼2 weeks. After 82.5 h at 90 °C and 33 h at 170 °C, vacuum conditions were stable with a vessel pressure of 6x10-5 Pa and mass spectra dominated by H2 molecules. While at 170 °C, we performed ∼40 h of D2 glow discharge cleaning (GDC) and ∼5 h of glow discharge boronization (GDB), using a 15 %-85 % B2D6-He mix and a total boron mass of ∼12 g. This was the very first GDB at such high temperature for WEST. The whole wall conditioning sequence led to a ∼10 times reduction of the H2O signal as well as to a ∼3 times reduction of the O2 signal, according to mass spectra. Once back to 70 °C, the vessel pressure was 5.5x10-6 Pa and plasma restart was seamless with ∼30 s cumulated over the very first 5 pulses and an Ohmic radiated power fraction Frad = 0.6, showing successful conditioning of the new ITER grade divertor. The effect of the first, ‘hot’ GDB faded with a characteristic cumulative injected energy of 2.45 GJ and saturation towards Frad ∼0.8. After 1.4 h and 7.5 GJ of cumulative plasma time and injected energy, we carried out a second GDB, this time at 70 °C. This ‘cold’ GDB initially led to a much lower Ohmic Frad = 0.3–0.4 but the effect lasted ∼7 times less, with a characteristic cumulative injected energy of 0.37 GJ. At the end of the campaign, we cumulated ∼3h and ∼30 GJ through repetitive, minute long pulses without any boronization. Throughout this 4-weeks-long experiment, Frad in the 4 MW heating phase evolved only marginally (from 0.5 to 0.55). This increase is mostly due to the build-up of re/co-deposited layers on both lower divertor targets.

This paper summarizes the observations on the Unidentified Flying Object (UFO) observed during the first high fluence campaign performed in WEST. The campaign was characterized by high erosion and deposition rates, generating dusts and deposits prone to flaking during plasma operation. A total of 686 UFOs have been detected for 384 discharges executed, in which 133 UFOs lead to a disruption. These UFOs appear mostly during the low hybrid heating ramp-up early in the discharges. The mechanisms leading to a disruption is described as well as the delay available to react after the UFO entering in the plasma. The UFOs originate mostly from the high field side corresponding to the thick deposit area. These UFOs can be debris from a preceding disruption (≈27 %) or come from progressive loss of adherence of the thick deposits (≈55 %) under plasma cycling or more likely by disruption on this area. Finally, the thermal resistance of the poorly attached deposits has been calculated in the range from 2.10−4 °C m2/W to 1.10−3 °C m2/W coherent with previous observations in the high field side of the JET divertor.

Assessing the performance of the ITER design for the tungsten (W) divertor Plasma Facing Units (PFUs) in a tokamak environment is a high priority issue to ensure efficient plasma operation. This paper reviews the most recent results derived from experiments and post-mortem analysis of the ITER-grade PFUs exposed in the WEST tokamak and the associated modelling, with a focus on understanding heat loading and damage evolution. Several shaping options, sharp or chamfered leading edge (LE), unshaped or shaped blocks with a toroidal bevel as foreseen in ITER, were investigated, under steady state heat fluxes of up to 120 MW⋅m−2 and 6 MW⋅m−2 on the sharp LE and top surface of the block, respectively. A very high spatial resolution (VHR) infrared (IR) camera (0.1 mm/pixel) was used to derive the temporal and surface distribution of the temperature and heat load on the castellated tungsten blocks for different geometric alignment and plasma conditions. Photonic modelling was required to reproduce the IR measurements in particular in the toroidal and poloidal gaps of the mono-block (MB) stacks where high apparent temperatures are observed. Specular reflection is found to be the dominant emitter in these parts of the blocks. W-cracking was observed on the leading edge of the blocks already within the first phase of plasma operation, during which the divertor was equipped with unshaped PFUs, including some intentionally misaligned blocks. Numerical analysis taking into account softening processes and mechanical stresses, revealed brittle failure due to transients as the dominant failure mechanisms. Ductile failure was observed in one particular block used for the melting experiment, therefore under extremely high steady state heat load conditions. W-melting achieved on actively cooled PFU exhibits specific features: shallow melting and slow melt displacement. Plasma exposure of pre-damaged PFUs at various damage levels (crack network and melted droplets) was carried out under high heat load conditions with several hours of cumulated plasma duration. IR data and preliminary surface analyses show no evidence of significant degradation damage progression under these conditions.

Abstract This paper is a contribution to the exploration of the parametric Kalman filter (PKF), which is an approximation of the Kalman filter, where the error covariances are approximated by a covariance model. Here we focus on the covariance model parameterized from the variance and the anisotropy of the local correlations, and whose parameters dynamics provides a proxy for the full error‐covariance dynamics. For this covariance model, we aim to provide the boundary condition to specify in the prediction of PKF for bounded domains, focusing on Dirichlet and Neumann conditions when they are prescribed for the physical dynamics. An ensemble validation is proposed for the transport equation and for the heterogeneous diffusion equation over a bounded 1D domain. This ensemble validation requires to specify the auto‐correlation time‐scale needed to populate boundary perturbation that leads to prescribed uncertainty characteristics. The numerical simulations show that the PKF is able to reproduce the uncertainty diagnosed from the ensemble of forecast appropriately perturbed on the boundaries, which show the ability of the PKF to handle boundaries in the prediction of the uncertainties. It results that Dirichlet condition on the physical dynamics implies Dirichlet condition on the variance and on the anisotropy.

The coronavirus disease (COVID-19) pandemic and the social distancing resulting thereof are having a great impact on psychological well-being. Studies investigating resilience found that it impacts mental health during crises. This study aimed to evaluate the influence of pre-crisis temperament on resilience in individuals with bipolar disorder during the COVID-19 pandemic. An online survey was conducted in Austria between April and June 2020, including 36 individuals with bipolar disorder and 39 healthy controls. Resilience was assessed with the 13-item resilience scale, and temperament was measured with the Temperament Evaluation of Memphis, Pisa, Paris and San Diego-autoquestionnaire (TEMPS-A). The bipolar disorder group showed lower resilience than the control group, and scored higher on the TEMPS-A for depressive, cyclothymic, and anxious temperaments. Resilience could be predicted by anxious temperament in individuals with bipolar disorder, and correlated negatively with depressive symptoms in both groups. The results suggest that anxious temperament influences the resilience of individuals with bipolar disorder, likely more than temporary hardships, such as the first months of the COVID-19 crisis. It is therefore important to improve the resilience of individuals with bipolar disorder not only by short-term interventions, but by strengthening resilience and reducing anxious temperament in the long term.

Within the 9th European Framework programme, since 2021 EUROfusion is operating five tokamaks under the auspices of a single Task Force called ‘Tokamak Exploitation’. The goal is to benefit from the complementary capabilities of each machine in a coordinated way and help in developing a scientific output scalable to future largre machines. The programme of this Task Force ensures that ASDEX Upgrade, MAST-U, TCV, WEST and JET (since 2022) work together to achieve the objectives of Missions 1 and 2 of the EUROfusion Roadmap: i) demonstrate plasma scenarios that increase the success margin of ITER and satisfy the requirements of DEMO and, ii) demonstrate an integrated approach that can handle the large power leaving ITER and DEMO plasmas. The Tokamak Exploitation task force has therefore organized experiments on these two missions with the goal to strengthen the physics and operational basis for the ITER baseline scenario and for exploiting the recent plasma exhaust enhancements in all four devices (PEX: Plasma EXhaust) for exploring the solution for handling heat and particle exhaust in ITER and develop the conceptual solutions for DEMO. The ITER Baseline scenario has been developed in a similar way in ASDEX Upgrade, TCV and JET. Key risks for ITER such as disruptions and run-aways have been also investigated in TCV, ASDEX Upgrade and JET. Experiments have explored successfully different divertor configurations (standard, super-X, snowflakes) in MAST-U and TCV and studied tungsten melting in WEST and ASDEX Upgrade. The input from the smaller devices to JET has also been proven successful to set-up novel control schemes on disruption avoidance and detachment.

Superconducting (SC) tokamak JT-60SA plays an essential role in fusion research and development by supporting and complementing the ITER project, providing directions to the DEMO design activity and fostering next generation scientists and engineers. Since the short circuit incident at the terminal joints of equilibrium field coil #1 during the integrated commissioning (IC) in March 2021, both EU and JA implementing agencies (IAs) have examined how to ensure safe operation of JT-60SA by mitigating the risk of possible discharge occurrence inside the cryostat. Based on the experience of the global Paschen tests, the IAs have established a strategy of risk mitigation measures, which is a combination of (i) reinforcement of insulation, (ii) avoiding unnecessary voltage application to the coil systems and (iii) immediate de-energization of the coils when deteriorated vacuum conditions are detected. Thanks to the considerable efforts of the Integrated Project Team members, the IC restarted in May 2023. After confirmation of the SC state of the coil systems (TF, EF and CS), the coil energization test and the plasma operation phase 1 (OP-1) started. The first plasma was successfully achieved on 23 October 2023 with a limited value of voltage and current applied to the coils. The plasma configuration control was also confirmed with low plasma current and low auxiliary heating power conditions. Based on the IO–F4E–QST collaboration, activities of JT-60SA have been shared with the IO and provided an important lesson for ITER assembly and commissioning, and will provide an outstanding contribution to fusion research at large. After OP-1, maintenance & enhancement phase 1 (M/E-1) starts from January 2024, in which in-vessel components are installed, and heating and diagnostic systems are extensively upgraded to allow a high power heating experiment planned in OP-2. In order to make the best use of JT-60SA, a newly organized JT-60SA experiment team will refine the research plan for the future high heating power operation phase.

The mission of WEST (tungsten-W Environment in Steady-state Tokamak) is to explore long pulse operation in a full tungsten (W) environment for preparing next-step fusion devices (ITER and DEMO) with a focus on testing the ITER actively cooled W divertor in tokamak conditions. Following the successful completion of phase 1 (2016-2021), phase 2 started in December 2022 with the lower divertor made entirely of actively cooled ITER-grade tungsten mono-blocks. A boronization prior the first plasma attempt allowed for a smooth startup with the new divertor. Despite the reduced operating window due to tungsten, rapid progress has been made in long pulse operation, resulting in discharges with a pulse length of 100 s and an injected energy of around 300 MJ per discharge. Plasma startup studies were carried out with equatorial boron nitride limiters to compare them with tungsten limiters, while Ion Cyclotron Resonance Heating assisted startup was attempted. High fluence operation in attached regime, which was the main thrust of the first campaigns, already showed the progressive build up of deposits and appearance of dust, impacting the plasma operation as the plasma fluence increased. In total, the cumulated injected energy during the first campaigns reached 43 GJ and the cumulated plasma time exceeded 5 h. Demonstration of controlled X-Point Radiator regime is also reported, opening a promising route for investigating plasma exhaust and plasma-wall interaction issues in more detached regime. This paper summarises the lessons learned from the manufacturing and the first operation of the ITER-grade divertor, describing the progress achieved in optimising operation in a full W environment with a focus on long pulse operation and plasma wall interaction.

Tungsten peaking is predicted in the core of a WEST plasma with total-f gyrokinetic simulations, including both collisional and turbulent transport. This prediction is validated with a synthetic diagnostic of the bolometry. Although nitrogen impurities are shown to reduce the neoclassical peaking of tungsten on-axis, the overall tungsten peaking increases when nitrogen impurities are present, as they reduce the turbulence screening off-axis. This finding is important for the plasma current ramp-up phase of ITER, where light impurities seeding will be desirable to achieve low temperatures at the plasma-facing components and reduce tungsten sputtering. It provides further argument for applying early ECRH heating to maintain margins on the core power balance. The neoclassical peaking factor is cross-verified between XGC and FACIT. The heat flux at separatrix and the heat load width are modeled by XGC and compared to WEST data.

Introduction Patients with bipolar disorder have a hig risk of becoming overweight and obese, associated with an increased risk of somatic diseases and premature mortality. The Austrian BIPFAT/BIPLONG study aims at investigating lipid metabolism, psychosocial functioning, and cognitive parameters in bipolar disorder (BD). Objectives The aim was to investigate to what extent overweight, obesity and metabolic syndrome (MetS) are associated with clinical symptoms (e.g. suicidality, depressive symptoms) and cognitive factors (attention, memory, executive function) in BD. Methods In addition to anamnestic interview and psychological tests, all participants were tested with a neuropsychological test battery including the Trail Making Test A/B, the Stroop Color and Word Interference Test, the d2 Test of Attention Revised, Digit Span, Digit-Symbol-Test, and the California Verbal Learning Test. Additionally, body mass index (BMI) and variables defining MetS including waist circumference, serum triglycerides, high-density lipoprotein, blood pressure, and fasting glucose levels have been collected in DSM-5 diagnosed patients with BD and healthy controls. Results In our Austrian bipolar cohort (n=290), the median BMI was 27.9 (SD=5.9), 30.5 % of the patients were overweight (BMI = 25.5-29.9) and 24.6% of the patients were obese (BMI ≥ 30.0). In the control group (n=183), the median BMI was 24.5 (SD=4.8), 15.2% were overweight and 8.0% were obese. A sub-analysis in 215 patients showed that compared to overweight patients, normal weight patients showed more suicidal ideation in psychiatric history (χ2(2)=7.97, p=.019). In addition, there was a significant association between suicidal ideation and glucose (r=.15, p=.043) and cholesterol (r=−.17, p=.028). In another sub-analysis with 148 euthymic bipolar patients, we found a high prevalence of MetS in patients with BD (30.4% versus 15.4% in healthy controls) associated with impaired executive function compared to patients without MetS or healthy controls with and without MetS (p=.020). Clinical variables (illness duration, suicidality, number of affective episodes, medication, age of onset, and history of psychosis) did not relate to MetS in BD (p > .05). A longitudinal analysis in 52 patients (35 without MetS and 17 with MetS) did not find an association of MetS on the one-year trajectory of cognitive decline in BD. In contrast, high baseline BMI predicted a decrease in the patient’s performance in working memory in the 12-months observation period. Conclusions The BIPFAT/BIPLONG study demonstrated a high prevalence of overweight, obesity and MetS in bipolar patients with adverse effects on cognitive function. Clinical variables such as suicidality were not related to the presence of obesity or MetS. Clinical impact and further (unpublished) results will be presented. Disclosure of Interest None Declared

Abstract Background The coronavirus disease (COVID-19) pandemic, a global health crisis, has resulted in widespread socioeconomic restrictions including lockdown, social distancing, and self-isolation. To date, little is known about the psychological impact of the COVID-19 pandemic and lockdown on patients with bipolar disorder as a particularly vulnerable group. Methods An online survey was conducted in Austria at two points of measurement (T1 April 2020 during the first lockdown vs. T2 May 2020 at post-lockdown). The sample comprises 20 patients with bipolar disorder (mean age = 49.4 ± 15.6 years) and 20 healthy controls (mean age = 32.7 ± 9.6 years). A 2 × 2 factorial design to compare two time points (T1 vs. T2) and two groups (patients vs. healthy controls) was used. Main outcome measures included the Brief Symptom Inventory-18 (BSI-18) and a (non-validated and non-standardized) assessment to determine COVID-19 fears and emotional distress due to social distancing. Multiple linear regression analyses were used to assess the longitudinal association of COVID-19 fears/emotional distress due to social distancing during lockdown (T1) and psychological symptoms after lockdown (T2). Results At T1, results demonstrated higher scores in BSI-18 subscales depression, anxiety and global severity index as well as emotional distress due to social distancing in bipolar patients compared to controls. There was a significant time x group interaction in the BSI-18 subscale somatization showing a decreasing trend in patients with BD compared to controls. No time effects in BSI-18 subscales or COVID-19 fears/emotional distress due to social distancing were observed. Regression analyses showed that COVID-19 fears during lockdown predicted somatization, only in patients. Conclusions There was a connection between the lockdown measures and somatization symptoms observed in patients. When the first steps of easing the social restrictions in May 2020 took place, somatization decreased only in the bipolar compared to the control group. Higher COVID-19 fears during lockdown predicted later symptoms at post-lockdown. Long-term impacts of the COVID-19 pandemic need further investigations to improve current therapeutic approaches and prevent fears and distress during lockdown in individuals with bipolar disorder in times of crisis.

Introduction Immune mediated inflammatory processes are involved in the aetiopathogenesis of bipolar disorder (BD) and weight associated comorbidities. Tryptophan breakdown via indoleamine 2,3-dioxygenase-1 (IDO-1) along the kynurenine axis concomitant with a pro-inflammatory state was found more active in BD but also associated with overweight/obesity. Objectives Aims of our study were to investigate 1.) the tryptophan metabolism in BD compared to mentally healthy controls, 2.) differences in weight classes, 3.) in a longitudinal setting, dependent on the incidence of BD episodes and euthymia. Methods At the Medical University Graz anthropometric and clinical data as well as peripheral tryptophan and kynurenine were assessed in serum samples of 226 individuals with BD and 142 controls. For 75 individuals with BD a longitudinal assessment with three samples was performed. Serum concentrations of tryptophan and kynurenine were determined by reverse-phase high-performance liquid chromatography. The kynurenine/tryptophan was used as a proxy for IDO-1 activity. Results showed a higher kynurenine/tryptophan ratio in BD compared to controls and in overweight compared to normal weight persons. Levels remained stable over time. In the longitudinal course, no differences were found between individuals who were constantly euthymic or not as well who had an illness episode or none. Conclusions Findings indicate that IDO-1 activity might constitute more a trait and not a state marker of BD. Accelerated tryptophan breakdown along the kynurenine axis may be further facilitated by overweight. This may increase the risk of accumulation of neurotoxic metabolites which impacts BD symptomatology, cognition, and somatic comorbidities. Disclosure No significant relationships.

Quantitative risk assessment is required by some regulations in specific situations, such as major risk evaluations. The bowtie method, which combines fault and event trees and includes safety barriers, is a valid quantitative method for analyzing industrial risks and a tool for decision-making and safety management. At present, accounting for uncertainties associated with reliability data is not necessarily mandatory in quantitative risk assessment. The quantitative method, as currently implemented, introduces uncertainties that are not addressed in the bowtie. Input data uncertainties linked to choosing values among different sources lead to variability in the results. The possibility method, presented in this article corrects this bias by considering all scenarios, without excluding those with a very low probability. For an industrial company, this specificity can allow to ensure the completeness and the robustness of its risk analysis. This study highlights the impact of uncertainties on the quantification of a bowtie. Besides obtaining a probability, it enables decision-makers to have access to the uncertainty related to the result. This information is essential to judge the trustworthiness of the analysis and to manage risks based on uncertainties. This study allows the development of an advanced bowtie method, by considering the uncertainties associated with the input data.

The connection between cognitive function and the “Big Five” personality traits (openness, conscientiousness, extraversion, agreeableness, and neuroticism) in the general population is well known; however, studies researching bipolar disorder (BD) are scarce. Therefore, this study aimed to investigate the Big Five as predictors of executive function, verbal memory, attention, and processing speed in euthymic individuals with BD (cross-sectional: n = 129, including time point t1; longitudinal: n = 35, including t1 and t2). Participants completed the NEO Five-Factor Inventory, the Color and Word Interference Test, the Trail Making Test, the d2 Test of Attention Revised, and the California Verbal Learning Test. The results showed a significant negative correlation between executive function and neuroticism at t1. Changes in cognitive function between t1 and t2 did not correlate with and could not be predicted by the Big Five at t1. Additionally, worse executive function at t2 was predicted by higher neuroticism and lower conscientiousness at t1, and high neuroticism was a predictor of worse verbal memory at t2. The Big Five might not strongly impact cognitive function over short periods; however, they are significant predictors of cognitive function. Future studies should include a higher number of participants and more time in between points of measurement.

The ongoing pandemic of coronavirus disease (COVID-19) is a global health crisis that has posed enormous pressure on workers in the health sector (WHS), having a massive impact on their mental health. In this study, we aimed to evaluate the sleep quality of WHS during the pandemic and compare frontline WHS to those who are not directly engaged in the care of COVID-19 patients. This cross-sectional, self-reported online survey assessed the sleep quality of WHS in Austria using the Pittsburgh Sleep Quality Index (PSQI). The same questionnaire was sent out two times. Due to the unequal sample and anonymity of the study participants, we analyzed the data of each time point separate from each other. The first study was conducted in April/May 2020, during the first lockdown in Austria (Study1), and the second study was conducted in July/August 2020, when the social restrictions were loosened (Study2). T-test was used to compare the mean values of PSQI scores between frontline vs. non-frontline WHS, while two two-way ANCOVAs were used to analyze differences in the PSQI mean scores (controlled for age) for male vs. female between frontline vs. non-frontline WHS. During the first lockdown in Austria (Study1) we identified a shorter sleep duration of frontline WHS compared to the non-frontline group, however the difference in global PSQI score between these groups was statistically not significant. In the period after loosened restrictions (Study2) the sleep quality, sleep latency, sleep duration, sleep efficiency and global PSQI score was worse in frontline WHS compared to the non-frontline WHS. Furthermore, female WHS scored higher in the PSQI indicating a worse sleep than male WHS. In addition, nurses and nursing assistants had a higher prevalence of poor sleep quality than other occupational groups. Our results indicate that the COVID-19 pandemic negatively impacts the sleep of WHS, affecting particularly frontline WHS. Preventive interventions aiming to promote good sleep quality in WHS during a healthcare crisis like this pandemic are essential to enhance resilience and mitigate the vulnerability of this specific population.

The ECRH system formerly used in Tore Supra is being upgraded to start on WEST in 2023, at a power level of 1MW and frequency of 105 GHz. Its ultimate 3MW/1000s capability is expected to enlarge the WEST operational domain by increasing margins with respect to H-mode access, and by providing additional flexibility in terms of achievable scenarios using impurity and/or MHD control. This flexibility is made possible using an antenna based on three steerable mirrors for controlled power injection. In order to determine an appropriate range of EC wave injection angles for WEST scenarios, the fast and reliable ray-tracing code REMA has been interfaced with the WEST IMAS database. This allows the EC power damping rate to be quickly assessed, as well as deposition profiles to be predicted in realistic plasma conditions. Based on a typical WEST discharge at central magnetic field B0~3.6 T, central line-averaged electron density nl~4 × 1019 m−3 and central electron temperature Te0~3keV, ray-tracing calculations have been performed. Comprehensive poloidal and toroidal angle scans, as well as variations of Bt, nl and Te0 with respect to the reference parameters have allowed an adequate range of injection angles to be determined for efficient use of ECRH and/or ECCD in typical WEST scenarios, and compared with the mechanical limits set by the antenna mechanical characteristics. In order to further characterize the effect of this new power source in WEST scenarios, EC wave deposition and current profiles from ray-tracing calculations have been included in integrated simulation codes. It has been shown that this additional power source could allow central electron heating to be achieved, potentially alleviating the issue of radiative collapse caused by impurities observed in some situations.

Combined high-fusion performance and long-pulse operation is one of the key integration challenges for fusion energy development in magnetic devices. Addressing these challenges requires an integrated vision of physics and engineering aspects with the purpose of simultaneously increasing time duration and fusion performance. Significant progress has been made in tokamaks and stellarators, including very recent achievement in duration and/or performance. This progress is reviewed by analyzing the experimental data (109 plasma pulses with a total of 3200 data points, i.e. on average 29 data per pulse) provided by ten tokamaks (in alphabetical order: Axially Symmetric Divertor Experiment Upgrade, DIII-D, Experimental Advanced Superconducting Tokamak, Joint European Torus, JT-60 Upgrade, Korea Superconducting Tokamak Advanced Research, tokamak à configuration variable, Tokamak Fusion Test Reactor, Tore Supra, W Environment in Steady-State Tokamak) and two stellarators (Large Helical Device and Wendelstein 7-X) expanding the pioneering work of Kikuchi (Kikuchi M. and Azumi M. 2015 Frontiers in Fusion Research II: Introduction to Modern Tokamak Physics (Springer)). Data have been gathered up to January 2022 and coordination has been provided by the recently created International Energy Agency-International Atomic Energy Agency international C oordination on I nternational C hallenges on L ong duration OP eration group. By exploiting the multi-machine international database, recent progress in terms of injected energies (e.g. 1730 MJ in L-mode, 425 MJ in H-mode), durations (1056 s in L-mode, 101 s in H-mode), injected powers, and sustained performance will be reviewed. Progress has been made to sustain long-pulse operation in tokamaks and stellarators with superconducting coils, actively cooled components, and/or with metallic walls. The graph of the fusion triple products as a function of duration shows a dramatic reduction of, at least two orders of magnitude when increasing the plasma duration from less than 1 s to 100 s. Indeed, long-pulse operation is usually reached in dominant electron-heating modes at reduced density (current drive optimization) but with low ion temperatures ranging from 1 to 3 keV for discharges above 100 s. Difficulties in extending the duration may arise from coupling high heating powers over long durations and the evolving plasma-wall interaction towards an unstable operational domain. Possible causes limiting the duration and critical issues to be addressed prior to ITER operation and DEMO design are reported and analyzed.