Investigation of energy and mass balance “Trimyx-3M” Galatea multipole magnetic trap

In the work using Rogowski loop, measurements of the diamagnetic current, generating in the plasma volume of the “Trimyx-3M” Galatea multipole magnetic trap under its filling by plasmoids have been carried out. These measurements are confirmed by signals from diamagnetic probes. The mean value of the energy in plasma volume in the process of the trap filling by plasma and during plasma decay have been determined by the magnitude of diamagnetic current. These measurements are carried out simultaneously with the measurement of the time dependence of mean plasma density by microwave interferometer.За допомогою поясу Роговського здійснено виміри діамагнітного струму, що виникає в плазмовому об’ємі мультипольної магнітної пастки-Галатеї "Трімікс-3М" при наповненні її плазмовими згустками. Ці виміри підтверджені сигналами з діамагнітних зондів. За величиною діамагнітного струму визначалася величина енергії в плазмовому об’ємі і її зміна в процесі заповнення пастки плазмою і її розпаду. Виміри проведено одночасно з вимірами за допомогою СВЧ-інтерферометра часової залежності середньої концентрації плазми.С помощью пояса Роговского произведены измерения диамагнитного тока, возникающего в плазменном объеме мультипольной магнитной ловушки-Галатеи «Тримикс-3М» при наполнении ее плазменными сгустками. Эти измерения подтверждены сигналами с диамагнитных зондов. По величине диамагнитного тока определялась величина энергии в плазменном объеме и ее изменение в процессе заполнения ловушки плазмой и её распада. Измерения проведены одновременно с измерением с помощью СВЧ-интерферометра временной зависимости средней концентрации плазмы

Velocity-space sensitivity of the time-of-flight neutron spectrometer at JET

The velocity-space sensitivities of fast-ion diagnostics are often described by so-called weight functions. Recently, we formulated weight functions showing the velocity-space sensitivity of the often dominant beam-target part of neutron energy spectra. These weight functions for neutron emission spectrometry (NES) are independent of the particular NES diagnostic. Here we apply these NES weight functions to the time-of-flight spectrometer TOFOR at JET. By taking the instrumental response function of TOFOR into account, we calculate time-of-flight NES weight functions that enable us to directly determine the velocity-space sensitivity of a given part of a measured time-of-flight spectrum from TOFOR

Relationship of edge localized mode burst times with divertor flux loop signal phase in JET

A phase relationship is identified between sequential edge localized modes (ELMs) occurrence times in a set of H-mode tokamak plasmas to the voltage measured in full flux azimuthal loops in the divertor region. We focus on plasmas in the Joint European Torus where a steady H-mode is sustained over several seconds, during which ELMs are observed in the Be II emission at the divertor. The ELMs analysed arise from intrinsic ELMing, in that there is no deliberate intent to control the ELMing process by external means. We use ELM timings derived from the Be II signal to perform direct time domain analysis of the full flux loop VLD2 and VLD3 signals, which provide a high cadence global measurement proportional to the voltage induced by changes in poloidal magnetic flux. Specifically, we examine how the time interval between pairs of successive ELMs is linked to the time-evolving phase of the full flux loop signals. Each ELM produces a clear early pulse in the full flux loop signals, whose peak time is used to condition our analysis. The arrival time of the following ELM, relative to this pulse, is found to fall into one of two categories: (i) prompt ELMs, which are directly paced by the initial response seen in the flux loop signals; and (ii) all other ELMs, which occur after the initial response of the full flux loop signals has decayed in amplitude. The times at which ELMs in category (ii) occur, relative to the first ELM of the pair, are clustered at times when the instantaneous phase of the full flux loop signal is close to its value at the time of the first ELM

Impact of nitrogen seeding on confinement and power load control of a high-triangularity JET ELMy H-mode plasma with a metal wall

This paper reports the impact on confinement and power load of the high-shape 2.5MA ELMy H-mode scenario at JET of a change from an all carbon plasma facing components to an all metal wall. In preparation to this change, systematic studies of power load reduction and impact on confinement as a result of fuelling in combination with nitrogen seeding were carried out in JET-C and are compared to their counterpart in JET with a metallic wall. An unexpected and significant change is reported on the decrease of the pedestal confinement but is partially recovered with the injection of nitrogen.Comment: 30 pages, 16 figure

An arc control and protection system for the JET lower hybrid antenna based on an imaging system

Arcs are the potentially most dangerous events related to Lower Hybrid (LH) antenna operation. If left uncontrolled they can produce damage and cause plasma disruption by impurity influx. To address this issue an arc real time control and protection imaging system for the Joint European Torus (JET) LH antenna has been implemented. The LH system is one of the additional heating systems at JET. It comprises 24 microwave generators (klystrons, operating at 3.7 GHz) providing up to 5 MW of heating and current drive to the JET plasma. This is done through an antenna composed of an array of waveguides facing the plasma. The protection system presented here is based primarily on an imaging arc detection and real time control system. It has adapted the ITER like wall hotspot protection system using an identical CCD camera and real time image processing unit. A filter has been installed to avoid saturation and spurious system triggers caused by ionization light. The antenna is divided in 24 Regions Of Interest (ROIs) each one corresponding to one klystron. If an arc precursor is detected in a ROI, power is reduced locally with subsequent potential damage and plasma disruption avoided. The power is subsequently reinstated if, during a defined interval of time, arcing is confirmed not to be present by image analysis. This system was successfully commissioned during the restart phase and beginning of the 2013 scientific campaign. Since its installation and commissioning, arcs and related phenomena have been prevented. In this contribution we briefly describe the camera, image processing, and real time control systems. Most importantly, we demonstrate that an LH antenna arc protection system based on CCD camera imaging systems works. Examples of both controlled and uncontrolled LH arc events and their consequences are shown