UKAEA Papers

Showing 491 - 500 of 1892 UKAEA Paper Results
2019
UKAEA-CCFE-PR(19)69

The equipment used in some welding techniques (e.g. tungsten inert gas alternating current welding or capacitor discharge stud welding) can induce high electromagnetic fields inside the operator due to the large time-varying electric currents involved in the process. The European Union (EU) Directive 2013/35/EU provides guidelines and recommendatio…

Preprint
2019
UKAEA-CCFE-PR(19)68

We report a theoretical study of microstructure, magnetic properties, and their relationship in relatively concentrated Fe-Cr alloys in both Fe- and Cr-rich regions. Annealing of initially random systems at 500° C for times of the order of 106 s substantially changes their microstructure. In both systems, solute atoms form clusters with…

Preprint Published
2019
UKAEA-CCFE-PR(19)67

Analysis of the L-H and H-L transition power thresholds (Pth) and pedestal parameters are presented for the Mega Ampere Spherical Tokamak (MAST). The dependencies of Pth on the average, core plasma electron density, X-point height and plasma current are described. Increasing X-point distance from the divertor floor over 10-12 cm, is found to inc…

Preprint Published
2019
UKAEA-CCFE-PR(19)66

We use deep neural networks to classify time series generated by discrete and continuous dynamical systems based on their chaotic behavior. Our approach to circumvent the lack of precise models for some of the most challenging real-life applications is to train different neural networks on a data set from a dynamical system with a basic or low-dime…

Preprint Published
2019
UKAEA-CCFE-PR(19)65

Alfven frequency sweeping modes in stellarator plasmas with normal and reversed shear rotational transform are modelled using a reduced MHD model. We focus on a TJ-II dynamic discharge in which a sequence of frequency sweeping modes with a frequency sweeping range from 20 kHz to 140 kHz (Melnikov A.V. et al 2014 Nucl. Fusion 54 123002) have been ob…

Preprint Published
2019
UKAEA-CCFE-PR(19)64

Observations have recently been made of ion cyclotron emission (ICE) that originates from the core plasma in the DIII-D [1, 2] and ASDEX-Upgrade [3, 4] tokamaks. The ICE spectral peaks correspond to the local cyclotron harmonic frequencies of fusion-born ions close to the magnetic axis, in contrast to the hitherto usual spatial localisation of …

Preprint Published
2019
UKAEA-CCFE-PR(19)63

The laser flash method is highly regarded due to its applicability to a wide temperature range, from cryogenic temperatures to the melting point of refractory metals, and to extreme environments involving radioactive or hazardous materials. Although instruments implementing this method are mostly produced on a commercial basis by major manufactu…

Preprint Published
2019
UKAEA-CCFE-PR(19)62

The pedestal structure, ELM losses and linear MHD stability are analysed in a series of JET-ILW H and D type I ELMy H-mode plasmas. The pedestal pressure (pPED) is typically higher in D than in H at the same input power, with the difference mainly due to lower density in H than in D. At the same input power, the pedestal electron pres…

Preprint Published
2019
UKAEA-CCFE-PR(19)61

A novel multicomponent alloy, V2.5Cr1.2WMoCo0.04, produced from elements expected to favour a BCC crystal structure, and to be suitable for high temperature environments, was fabricated by arc melting and found to exhibit a multiphase dendritic microstructure with W-rich dendrites and V-Cr segregated to the inter-de…

Preprint Published
2019
UKAEA-CCFE-PR(19)60

Toroidal Alfven Eigenmode (TAE) excitation can be caused by fusion-born or Ion Cyclotron Resonance and neutral beam heating fast particles through wave-particle resonance. TAEs may affect fast particle confinement, reduce heating and current drive efficiency, cause damage to the first wall, and decrease overall plasma performance. Excitation of TA…

Preprint Published