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The information obtained from the chemical analysis of specific human excretion products (biomarkers) in urban wastewater can be used to estimate the exposure or consumption of the population under investigation to a defined substance. A proper biomarker can provide relevant information about lifestyle habits, health and wellbeing, but its selection is not an easy task as it should fulfil several specific requirements in order to be successfully employed. This paper aims to summarize the current knowledge related to the most relevant biomarkers used so far. In addition, some potential wastewater biomarkers that could be used for future applications were evaluated. For this purpose, representative chemical classes have been chosen and grouped in four main categories: (i) those that provide estimates of lifestyle factors and substance use, (ii) those used to estimate the exposure to toxicants present in the environment and food, (iii) those that have the potential to provide information about public health and illness and (iv) those used to estimate the population size. To facilitate the evaluation of the eligibility of a compound as a biomarker, information, when available, on stability in urine and wastewater and pharmacokinetic data (i.e. metabolism and urinary excretion profile) has been reviewed. Finally, several needs and recommendations for future research are proposed. © 2016 Elsevier Ltd

Integrated modelling of important plasma physics issues related to the design of a steady-state spherical tokamak (ST) fusion power plant is described. The key is a steady-state current drive, and 92% of this is provided by a combination of bootstrap and diamagnetic currents, both of which have a substantial toroidal component in a ST. The remaining current is to be provided by either neutral beam injection or radio-frequency waves, and various schemes for providing this are discussed and quantified. The desire to achieve a high bootstrap current drives the design to high plasma pressure, ? (normalized to the magnetic field pressure), and high elongation. Both these requirements have implications for ideal magneto-hydrodynamic instability which are discussed. Confinement is addressed both through comparison with the recent scaling laws developed from the conventional tokamak database and self-consistent one-dimensional modelling of the transport processes. This modelling shows that the power required for the current drive (~50?MW) is sufficient to heat the plasma to a regime where more than 3?GW of fusion power is produced, taking into account the dilution due to He ash and prompt ?-particle losses, which are small. A preliminary study of the micro-instabilities, which may be responsible for the turbulent transport is provided. Given assumptions about the particle confinement, we make estimates of the fuelling requirements to maintain the steady state. Finally, the power loading due to the exhaust is derived using theory-based scalings for the scrape-off layer width.

An advanced mathematical model is developed for a self-consistent description of the evolution of free boundary toroidal plasmas. New numerical algorithms for the solution of the appropriate non-linear system of integro-differential equations are presented. An unusual feature of the system is that time derivatives enter only one of the equations. The model and algorithms are implemented in the SCoPE code. Examples of numerical modelling for tokamak plasmas are given.

The Mega Ampère Spherical Tokamak (MAST) programme is strongly focused on addressing key physics issues in preparation for operation of ITER as well as providing solutions for DEMO design choices. In this regard, MAST has provided key results in understanding and optimizing H-mode confinement, operating with smaller edge localized modes (ELMs), predicting and handling plasma exhaust and tailoring auxiliary current drive. In all cases, the high-resolution diagnostic capability on MAST is complemented by sophisticated numerical modelling to facilitate a deeper understanding. Mitigation of ELMs with resonant magnetic perturbations (RMPs) with toroidal mode number n RMP = 2, 3, 4, 6 has been demonstrated: at high and low collisionality; for the first ELM following the transition to high confinement operation; during the current ramp-up; and with rotating n RMP = 3 RMPs. n RMP = 4, 6 fields cause less rotation braking whilst the power to access H-mode is less with n RMP = 4 than n RMP = 3, 6. Refuelling with gas or pellets gives plasmas with mitigated ELMs and reduced peak heat flux at the same time as achieving good confinement. A synergy exists between pellet fuelling and RMPs, since mitigated ELMs remove fewer particles. Inter-ELM instabilities observed with Doppler backscattering are consistent with gyrokinetic simulations of micro-tearing modes in the pedestal. Meanwhile, ELM precursors have been strikingly observed with beam emission spectroscopy (BES) measurements. A scan in beta at the L–H transition shows that pedestal height scales strongly with core pressure. Gyro-Bohm normalized turbulent ion heat flux (as estimated from the BES data) is observed to decrease with increasing tilt of the turbulent eddies. Fast ion redistribution by energetic particle modes depends on density, and access to a quiescent domain with ‘classical’ fast ion transport is found above a critical density. Highly efficient electron Bernstein wave current drive (1 A W−1) has been achieved in solenoid-free start-up. A new proton detector has characterized escaping fusion products. Langmuir probes and a high-speed camera suggest filaments play a role in particle transport in the private flux region whilst coherence imaging has measured scrape-off layer (SOL) flows. BOUT++ simulations show that fluxes due to filaments are strongly dependent on resistivity and magnetic geometry of the SOL, with higher radial fluxes at higher resistivity. Finally, MAST Upgrade is due to begin operation in 2016 to support ITER preparation and importantly to operate with a Super-X divertor to test extended leg concepts for particle and power exhaust.

The effect of nuclear elastic scattering (NES) of deuterium and tritium in close collisions with hot alpha-particles is considered. Calculations of the perturbed deuterium and tritium distribution functions are based on numerical solution of the three-dimensional trajectory averaged kinetic equation. The equation includes the full drift trajectory averaged Coulomb collision operator and the NES particle source. Modelling is carried out for parameters relevant to JET DT experiments and results of calculations are compared with typical measurements of NES deuterons. In addition, we evaluate the maximum achievable NES perturbation to the DT plasma. Finally, a potential opportunity for estimation of alpha-particle pitch-angle anisotropy, using measurements of NES perturbed deuterium or tritium distributions is discussed. We show that it is important to account for NES effects in order to accurately diagnose the alpha-particle distribution.

For a fusion power plant to be economically and technologically attractive, it should be as compact as possible and capable of `steady state' operation. One approach is based upon the spherical tokamak (ST) concept. This configuration features many of the qualities of the conventional aspect ratio tokamak, such as good confinement and MHD stability, together with a number of highly promising features for the realization of a cost effective, steady state fusion power core. In particular, it allows high β capability due to the high I/B achievable at low A and strong, natural shaping of the configuration, together with the possibility of approaching 100% pressure driven currents through high natural elongation and access to second stability to ideal ballooning modes. The physics insights gained from experiments on START are discussed and the theoretical modelling work summarized, describing how the beneficial properties of STs can be combined in steady state ST power plant designs such as the Culham STPP concept. Where appropriate, we shall refer to the two new mega-amp machines MAST and NSTX, both designed for a plasma duration approaching the plasma current relaxation time and also other new, smaller, STs, designed to expand the knowledge gained so far.

This paper is devoted to an advanced mathematical model for a self-consistent description of the evolution of free boundary toroidal plasmas, with a description of numerical algorithms for the solution of the appropriate nonlinear system of integro-differential equations, and discussion of some results from the model.

This paper is devoted to the development of finite difference methods for the solution of problems involving the three-dimensional kinetic equation with a Coulomb collision operator. New conservative difference schemes are presented and analysed. The schemes include a new approximation for mixed derivatives and accurate treatment of internal separatrix layers. The main advantages of the new schemes are improved stability and accuracy which, for example, allows calculation of the ion distribution function in thermonuclear experiments for a wider range of parameters.

Neoclassical magnetic islands are observed to limit the achievable beta in COMPASS-D low collisionality single null divertor tokamak plasmas with ITER-like geometry (R0=0.56 m, B0=1.2 T, Ip=120-180 kA, k=1.6, epsilon =0.3). The limiting beta is typically well below that expected from ideal instabilities with maximum beta N in the range of 1.6 to 2.1. The plasma is heated with up to 1.8 MW of 60 GHz electron cyclotron resonance heating (ECRH) at the second harmonic with X mode polarization. The time history of the measured island width is compared with the predictions of neoclassical tearing mode theory, with good agreement between theory and experiment. The measured islands have a threshold width below which the mode will not grow. The density scaling of the point of onset of the measured instabilities is compared with two theories that predict a threshold island width for the onset of neoclassical tearing modes. Applied resonant helical error fields are used to induce islands in collisionality regimes wherein the neoclassical islands do not occur naturally, allowing the study of the behaviour of neoclassical tearing modes in this regime. The critical beta for the onset of neoclassical tearing modes is seen to be ~3 times higher in the naturally stable region. This observation is compared with the predictions of both threshold theories. A simple expression for the q scaling of the maximum achievable beta N in the presence of neoclassical tearing modes is derived on the basis of the assumption of a maximum allowable island width. The predicted q scaling of this beta limit is compared with data from a q scan, and the results are in good agreement

Electron cyclotron (EC) power has technological and physics advantages for heating and current drive (CD) in a tokamak reactor, and advances in source development make it credible for applications in the International Thermonuclear Experimental Reactor (ITER). Strong single pass absorption makes heating to ignition in ITER particularly simple. At densities to 3.6*1020 m-3, with ohmic temperatures and wave frequency 170 GHz, heating in the plasma core is readily obtained. For outside launch of an ordinary mode (O mode) near the fundamental EC frequency, the optimized EC current drive (ECCD) efficiency ((n)IR/P) shows a linear temperature scaling at temperatures up to ~15 keV. For temperatures above 30 keV, the efficiency saturates at approximately 0.3*1020 A/W.m2 for a frequency of 220 GHz in an ITER target plasma with a toroidal field of 6 T, due primarily to harmonic overlap and to a lesser extent due to limitations arising from relativistic effects. The same efficiency can also be obtained at 170 GHz for the same plasma equilibrium and q profile except that the magnetic field is reduced to (170/220)*6 T=4.6 T. The ECCD efficiencies are obtained with the comprehensive 3-D, bounce averaged Fokker-Planck codes CQL3D and BANDIT3D

Modulated ECRH has been used to study electron thermal transport in DITE. In most cases the spatial structure of the thermal waves produced is consistent with a simple diffusive transport model in which the heat flux is proportional to the electron temperature gradient, q = -ne?e ?Te. At low density (ne ? 1019 m-3) the values of electron thermal diffusivity deduced from modulation experiments (?emod) are ? 2.5 m2.s-1, similar to the values deduced from power balance analysis (?ePB and sawtooth heat pulse propagation (?est). At higher density (ne ? 3 × 1019 m-3) the interpretation of the modulation data is sensitive to details of the ECRH power deposition profile. The high density data are fitted best by assuming that approximately 30% of the ECRH power is deposited with a broad profile with the remainder more localized, in qualitative accordance with ray tracing code predictions. The values of ?emod deduced are then ? 1.3 m2.s-1, again similar to the values of ?ePB and ?est

A two-stage operator splitting algorithm has been used to time advance the three-dimensional Fokker-Planck equation for the electron distribution function in a tokamak. In the first stage, derivatives in the two velocity-space dimensions are advanced together implicitly. Derivatives in the remaining (spatial) dimension are advanced in the second stage. The treatment is restricted to problems which are diagonal in the spatial dimension. The algorithm gives accurate solutions in modest CPU times unlike alternative schemes considered. We described the technique which includes features that accomodate the internal boundary conditions arising from trapped electron effects.

The influence of radial transport of electrons on radiofrequency and Ohmic current drive in tokamaks is discussed. It is found that such processes can reduce the efficiency of current drive in tokamaks in which the energy confinement time is comparable with or less than the collision time of the heated electrons and that, even if this is not the case, they significantly broaden the driven current profile.

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New diagnostic, modelling and plant capability on the Mega Ampère Spherical Tokamak (MAST) have delivered important results in key areas for ITER/DEMO and the upcoming MAST Upgrade, a step towards future ST devices on the path to fusion currently under procurement. Micro-stability analysis of the pedestal highlights the potential roles of micro-tearing modes and kinetic ballooning modes for the pedestal formation. Mitigation of edge localized modes (ELM) using resonant magnetic perturbation has been demonstrated for toroidal mode numbers n = 3, 4, 6 with an ELM frequency increase by up to a factor of 9, compatible with pellet fuelling. The peak heat flux of mitigated and natural ELMs follows the same linear trend with ELM energy loss and the first ELM-resolved Ti measurements in the divertor region are shown. Measurements of flow shear and turbulence dynamics during L-H transitions show filaments erupting from the plasma edge whilst the full flow shear is still present. Off-axis neutral beam injection helps to strongly reduce the redistribution of fast-ions due to fishbone modes when compared to on-axis injection. Low-k ion-scale turbulence has been measured in L-mode and compared to global gyro-kinetic simulations. A statistical analysis of principal turbulence time scales shows them to be of comparable magnitude and reasonably correlated with turbulence decorrelation time. Te inside the island of a neoclassical tearing mode allow the analysis of the island evolution without assuming specific models for the heat flux. Other results include the discrepancy of the current profile evolution during the current ramp-up with solutions of the poloidal field diffusion equation, studies of the anomalous Doppler resonance compressional Alfvén eigenmodes, disruption mitigation studies and modelling of the new divertor design for MAST Upgrade. The novel 3D electron Bernstein synthetic imaging shows promising first data sensitive to the edge current profile and flows. © 2013 IAEA, Vienna.

Electron Bernstein wave (EBW) assisted plasma current start-up has been demonstrated for the first time in a tokamak. It was shown that plasma currents up to 17 kA can be generated non-inductively by 100 kW of RF power injected. With optimized vertical field ramps, plasma currents up to 33 kA have been achieved without the use of solenoid flux. It is shown that the plasma formation and current generation are governed predominantly by EBW current drive. Experimental results are consistent with ray-tracing and quasilinear Fokker–Planck modelling.

Several improvements to the MAST plant and diagnostics have facilitated new studies advancing the physics basis for ITER and DEMO, as well as for future spherical tokamaks (STs). Using the increased heating capabilities P NBI ⩽ 3.8 MW H-mode at I p = 1.2 MA was accessed showing that the energy confinement on MAST scales more weakly with I p and more strongly with B t than in the ITER IPB98(y, 2) scaling. Measurements of the fuel retention of shallow pellets extrapolate to an ITER particle throughput of 70% of its original designed total throughput capacity. The anomalous momentum diffusion, χϕ, is linked to the ion diffusion, χi, with a Prandtl number close to P ϕ ≈ χϕ/χi ≈ 1, although χi approaches neoclassical values. New high spatial resolution measurements of the edge radial electric field, E r , show that the position of steepest gradients in electron pressure and E r (i.e. shearing rate) are coincident, but their magnitudes are not linked. The T e pedestal width on MAST scales with rather than ρpol. The edge localized mode (ELM) frequency for type-IV ELMs, new in MAST, was almost doubled using n = 2 resonant magnetic perturbations from a set of four external coils (n = 1, 2). A new internal 12 coil set (n ⩽ 3) has been commissioned. The filaments in the inter-ELM and L-mode phase are different from ELM filaments, and the characteristics in L-mode agree well with turbulence calculations. A variety of fast particle driven instabilities were studied from 10 kHz saturated fishbone like activity up to 3.8 MHz compressional Alfvén eigenmodes. Fast particle instabilities also affect the off-axis NBI current drive, leading to fast ion diffusion of the order of 0.5 m2 s−1 and a reduction in the driven current fraction from 40% to 30%. EBW current drive start-up is demonstrated for the first time in a ST generating plasma currents up to 55 kA. Many of these studies contributed to the physics basis of a planned upgrade to MAST.

A simple analytical model of the non-Maxwellian electron velocity distribution, whose parameters are constrained by the observed plasma current and soft X-ray emission spectrum, is used in conjunction with a fully three-dimensional ray tracing code to calculate the absorption of radiation in the electron cyclotron range of frequencies by WT-2 discharges. This gives a quantitative, theoretical description of the way in which a drifting population of energetic electrons appears to dominate WT-2 current drive experiments. Calculation of the proportion of source power absorbed by the plasma helps to determine the efficiency factor of the current drive mechanism in this context. The strong dependence of current drive on the extraordinary mode launch direction is given theoretical support.

A bounce-averaged Fokker-Planck code has been developed for studying electron cyclotron heating in tokamak experiments. The equation solved and the numerical scheme used are discussed, and the advantages of the implicit time advancement emphasised. The numerical problems encountered while developing the code are described. The distribution functions predicted by the code are shown to be in good agreement with those produced in experiments.

Two independent approaches, based on the inclusion of model loss terms in analytical Fisch-Boozer and numerical Fokker-Planck models, give good quantitative agreement on the reduction of electron cyclotron current drive (ECCD) efficiency by non-Coulomb energy loss. By fitting recent tokamak measurements of ECCD efficiency to these results, the characteristic time-scale for non-Coulomb energy loss by current carrying electrons is calculated.

A Fokker–Planck formalism has been developed to interpret experimental data from high power electron cyclotron heating of tokamak plasmas in which the electron distribution function can be substantially distorted. The Fokker–Planck equation is solved using a 2-D code which incorporates electron trapping, a steady Ohmic electric field and a bounce averaged electron cyclotron heating term. The quasilinear RF diffusion coefficient is calculated using a single particle model which includes the mildly relativistic resonance condition and takes into account localized RF power injection and tokamak rotational transform effects. Comparisons are presented of the calculated and observed soft X-ray spectra from 60 GHz second harmonic electron cyclotron heating experiments on the CLEO tokamak. Good agreement between theory and experiment is found. In addition, predicted RF current drive efficiencies for the COMPASS tokamak are presented.

For typical reactor conditions lower hybrid (LH) waves are a strong candidate for bulk heating and for profile control via current drive in the outer regions of the plasma. However, limited accessibility, strong electron damping and the need to avoid damping on fusion‐produced alpha particles probably exclude the use of such a scheme in the plasma core. Therefore, it is likely that lower hybrid heating/current drive in the outer regions of the plasma will be combined with either ECRF, ICRF or NBI in the core. Electron cyclotron (EC) waves are particularly attractive since they offer the possibility of localised absorption and in addition may be used to facilitate low voltage start‐up of the tokamak. Recent experimental and theoretical research on current drive at Culham has concentrated on some of the outstanding critical issues concerning the reactor applications of LH and EC waves. These include studies of the interaction of lower hybrid waves with energetic ions including alpha particles, the effect of...

Non-inductive current drive using second harmonic ECRH at both 28 GHz and 60 GHz has been studied in the CLEO tokamak. At 60 GHz, RF driven currents of up to 5 kA have been observed at e = 4 × 1018m−3 for 185 kW of injected power, indicating an efficiency of η ≡ eIRFR0/PRF = 0.001 (1020 m−3, A, m, W−1). The RF driven current scaled linearly with total plasma current in the range of 5-15 kA and was maximized when the cyclotron resonance was located near to the centre of the plasma. Sawtooth activity was normally strongly affected and transient sawtooth stabilization was often observed. With detailed theoretical studies it is possible to reproduce both the high absorption efficiencies and the scaling of RF driven current with resonance position seen in the 60 GHz experiments. However, the magnitude of the observed current is a factor of about three below that theoretically predicted. At 28 GHz, no evidence of RF driven current could be detected. Possible reasons for this are discussed.