The Culham Centre for Fusion Energy (CCFE) is the UK's national laboratory for fusion research. It is located at the Culham Science Centre, near Culham, Oxfordshire, and is the site of the Joint European Torus (JET), Mega Ampere Spherical Tokamak (MAST) and the now closed Small Tight Aspect Ratio Tokamak (START).Formerly known as UKAEA Culham, the laboratory was renamed in October 2009 as part of organisational changes at its parent body, the United Kingdom Atomic Energy Authority (UKAEA).Since 2016, the director has been Professor Ian Chapman, and the centre has been engaged in work towards the final detailed design of ITER as well as preparatory work in support of DEMO.In 2014 it was announced the centre would house the new RACE (Remote Applications in Challenging Environments).
An effective fusion reactor maintenance scheme enables safe operations and short downtimes. This in turn leads to high availability, which is critical to the commercial viability of a power-producing plant. In tokamak-based fusion power plants, the chosen maintenance approach has a significant impact on the spatial design of the tokamak, as well as the surrounding infrastructure, and therefore needs to be considered from the outset. Tokamak Energy has developed a pre-concept design of a fusion power plant, ST-E1. This work describes the major drivers and constraints that have been considered, presents the tokamak architecture and chosen maintenance regime, and discusses how this enables the plant’s two-phased approach to demonstrating commercial operations. It also shows the implications for the design of other systems areas, in particular the machine structural arrangement and bioshield and hot cell layout. The reactor core segmentation and removal scheme replaces entire toroidal segments radially through a large vacuum port, along a single axis only. The result is a change-tolerant machine and plant layout that can accommodate the evolving designs of the tokamak.
Radiation damage profoundly alters the physicochemical properties of materials subjected to extreme environments. A key question within this context is whether radiation damage accumulation reaches saturation, particularly at elevated temperatures relevant to advanced nuclear energy systems. Employing well-designed irradiation protocols and a suite of advanced characterization techniques, we have experimentally demonstrated damage saturation in the stage III recovery regime in heavy-ion irradiated tungsten-a candidate plasmafacing material expected to operate reliably at/above this baseline temperature in fusion reactors. We validated that damage saturation reflects an asymptotic steady-state, established via the dynamic equilibrium between defect generation and annihilation. This phenomenon represents a limit to damage accommodation capacity in tungsten, independent of irradiation sources, although the onset of damage saturation exhibits a temperaturedependent shift. While observed in BCC tungsten, this phenomenon of damage saturation is not exclusive to this system and is expected to apply broadly across FCC and HCP materials. Therefore, defining these saturation conditions will offer a critical benchmark for assessing the mid- to long-term performance of materials and guiding the design of more radiation-tolerant systems.
This work presents a systematic study of the impact of neon seeding on pedestal performance and stability in JET-ITER baseline scenario discharges in deuterium at high input power, extending previous JET impurity seeding experiments. A neon-seeding scan of the JET-ITER baseline at I p = 2.5 MA, B T = 2.7 T, q 95 = 3.2 with high triangularity is studied with a neon pedestal concentration up to 1.7% at the pedestal top. As is typical in these discharges, the global confinement is increased approaching unity and the β N parameter reaches up to 2.3 with the increased radiation fraction. A detailed pedestal profile analysis showed that neon seeding reduces the pedestal density while substantially increasing both the electron and ion pedestal temperatures, resulting in an overall ∼50% increase in pedestal pressure compared to unseeded plasmas. Simultaneously, the total pressure pedestal width broadens, mostly due to the increased T e width ( n e broadening has a negligible impact on the total pressure width). The total pressure gradient develops in a way that stabilizes the pedestal against ideal peeling–ballooning (PB) modes. Ideal magnetohydrodynamics (MHD) stability calculations confirm that unseeded pedestals lie close to the PB boundary, while neon-seeded cases move deep into the PB stable domain, consistent with the observed transition to small or no edge-localized mode (ELM) operation. Comparison with the Europed predictions exhibits good qualitative agreement in pedestal height trends, though systematic offsets and the underestimation of pedestal widths highlight the limitations of the current model.
This work advances the quantitative validation of SOLPS-ITER against Tokamak & agrave; Configuration Variable (TCV) ohmic L-mode discharges. It shows that the treatment of the ion parallel heat flux limiter and the assumptions adopted for chemical sputtering result in a consistent explanation for the divertor over-cooling and excessive divertor density predicted by earlier simulations. A systematic heat flux limiter scan highlights that a strong restriction of ion heat conduction significantly reduces both electron Te,t and ion target temperatures Ti,t and drives a compensating increase in plasma density ne,t, resulting in an overly cold and dense divertor solution. The availability of new Te and Ti measurements along the outer divertor leg of TCV additionally constrains the model and supports the use of a weakly limited ion heat flux to best reproduce experimental observations. Restricting chemical sputtering to only tiles in the immediate vicinity of the strike points suppressed a spurious low-field-side carbon source associated with thermal molecules and significantly improves agreement with two-dimensional C iii emissivity reconstructions. The resulting SOLPS-ITER setup achieves improved agreement across multiple diagnostics simultaneously for upstream, divertor-leg, and target electron density and temperature profiles, as well as for target heat fluxes and radiation measurements.
We propose a novel method for generating high-harmonic ion Bernstein waves in the lower hybrid (LH) range of frequencies-here referred to as LH waves-in the confined region of magnetized plasmas. The method relies on stimulating a cascaded parametric down-conversion of electron Bernstein waves (EBWs). In addition to a primary microwave source (such as a gyrotron), cascaded parametric amplification (CPA) of LH waves requires either a low-power EBW or a low-power LH wave for seeding. The CPA mechanism is demonstrated with a 1D Wentzel-Kramers-Brillouin (WKB) model, which is benchmarked against a fully kinetic particle-in-cell simulation, showing quantitative agreement. Our calculations predict attainable conversion efficiencies to LH waves around 10% in steady state, exceeding the Manley-Rowe limit more than tenfold. The CPA mechanism could provide a path for LH wave generation in magnetic confinement fusion reactors that rely on microwaves in the electron cyclotron range of frequencies for plasma heating.
