One of the focal points of the present tokamak experiments is to gain better understanding and control of the interaction between fast particles and magnetohydrodynamical (MHD) waves and instabilities.

A new model has been developed that takes toroidal rotation into account in a consistent manner. This model has been implemented in a new code suite, FINESSE–PHOENIX–HAGIS, to study the effect of flow on the interaction numerically. The model and the code suite have been applied to an n = 2 toroidal Alfvén eigenmode (TAE) occurring in a tokamak with a circular cross-section and to an n = 1 TAE mode supported by a JET-like equilibrium. These two applications show that the non-zero growth rate of the TAE mode has a complex dependence on plasma rotation which can be either stabilizing or destabilizing. Furthermore, the results show that the pitch angle distribution of the fast particles' velocity direction also plays an important role in determining the growth rate...

Recently in the National Spherical Torus Experiment (NSTX), increasing lithium wall coatings suppressed edge localized modes (ELMs), gradually but not quite monotonically. This work details profile and stability analysis as ELMs disappeared throughout the lithium scan. While the quantity of lithium deposited between discharges did not uniquely determine the presence of ELMs, profile analysis demonstrated that lithium was correlated with wider density and pressure pedestals with peak gradients farther from the separatrix. Moreover, the ELMy and ELM-free discharges were cleanly separated by their density and pedestal widths and peak gradient locations. Ultimately, ELMs were only suppressed when lithium caused the density pedestal to widen and shift inward. These changes in the density gradient were directly reflected in the pressure gradient and calculated bootstrap current. This supports the theory that ELMs in NSTX are caused by peeling and/or ballooning modes, as kink/pee...

Non-axisymmetric external magnetic fields are the primary control available for fusion-grade tokamaks. The use of two beneficial magnetic perturbations is discussed: (1) an external non-axisymmetric field to enhance the stability of the tokamak to neoclassical tearing modes, which when unstable can lead to a disruption. (2) A current induced in the first wall during a plasma disruption to have a fail-safe prevention of high-energy runaway electrons, which can heavily damage a fusion-scale tokamak.

We use the two-dimensional analysis code KUAD2 to simulate trajectories in an Inertial Electrostatic Confinement (IEC) device driven by a ring-shaped magnetron ion source (RS-MIS). This aims to maximize the path length λ _CX for ion-gas charge exchange by operating at just units of mPa D ₂ gas pressures; however, under these conditions simulations reveal a surprisingly small path length for ion loss to the (Mo) cathode grid λ _grid ~ 30 cm λ _CX. By developing an ad hoc model relating the time variation of cathode temperature and absorbed D ₂ surface density, we use the simulated flux Γ _grid of ions striking the cathode grid to obtain the neutron production rate (NPR) arisin...

The main challenge for the Thomson scattering (TS) diagnostic on the TEXTOR tokamak is the detailed study of fast plasma events at a high spatial resolution and a high repetition rate of the measurements. The diagnostic uses intra-cavity probing of the plasma with a repetitively pulsed ruby laser and a fast CMOS camera as detectors. Since 2004, the TS system on TEXTOR has been gradually and systematically enhanced for the measurements of fast plasma events. For that it has recently been upgraded to obtain a multi-pass configuration. Two spherical mirrors have been installed that force the laser beam to probe the plasma a specified number of times before it is directed back into the laser medium. The diagnostics with the upgraded probing system have achieved the measurement accuracy of 3% for the electron temperature and 1.5% for the electron density at <1 cm spatial resolution and 3 × 10 ¹⁹ m ⁻³ plasma density and can measure at 5 kHz during an interval up ...

Trace tritium experiments (TTE) on JET were analysed using Monte Carlo modelling of the neutron emission resulting from the neutral beam injection (NBI) of short (~300 ms) tritium (T) beam blips into reversed shear, hybrid ELMy H-mode and L-mode deuterium plasmas for a wide range of plasma parameters. The calculated neutron fluxes from deuterium–tritium (DT) reactions could only be made consistent with all plasmas by applying an artificial reduction of the T beam power in the modelling of between 20% and 40%. A similar discrepancy has previously been observed in both JET (Gorini et al 2004 Proc. 31st EPS Conf. on Plasma Physics (London, UK) vol 28G (ECA)) and TFTR (Ruskov et al 1999 Phys. Rev. Lett. 82 924), although no mechanism has yet been found that could explain such a difference in the measured T beam power. Applying this correction in the T beam power, good agreement between calculated and measured DT neutron emission profiles was obtaine...

In a forced laser-wakefield accelerator experiment (Malka et al 2002 Science 298 1596) where the length of the pump laser pulse is a few plasma periods long, the leading edge of the laser pulse undergoes frequency downshifting and head erosion as the laser energy is transferred to the wake. Therefore, after some propagation distance, the group velocity of the leading edge of the pump pulse—and thus of the driven electron plasma wave—will slow down. This can have implications for the dephasing length of the accelerated electrons and therefore needs to be understood experimentally. We have carried out an experimental investigation where we have measured the velocity v _f of the 'wave-front' of the plasma wave driven by a nominally 50 fs (full width half maximum), intense ( a ₀ 1), 0.815 µm laser puls...

We present a new concept for a plasma wakefield accelerator driven by magnetowaves (MPWA). This concept was originally proposed as a viable mechanism for the 'cosmic accelerator' that would accelerate cosmic particles to ultra-high energies in the astrophysical setting. Unlike the more familiar plasma wakefield accelerator (PWFA) and the laser wakefield accelerator (LWFA) where the drivers, the charged-particle beam and the laser, are independently existing entities, MPWA invokes the high-frequency and high-speed whistler mode as the driver, which is a medium wave that cannot exist outside of the plasma. Aside from the difference in drivers, the underlying mechanism that excites the plasma wakefield via the ponderomotive potential is common. Our computer simulations show that under appropriate conditions, the plasma wakefield maintains very high coherence and can sustain high-gradient acceleration over many plasma wavelengths. We suggest that in addition to its celestial applicat...