MPI fur plasma physik

Garching bei München, Germany

MPI fur plasma physik

Garching bei München, Germany
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Lawson K.D.,Culham Center for Fusion Energy | Groth M.,Aalto University | Harting D.,Culham Center for Fusion Energy | Menmuir S.,Culham Center for Fusion Energy | And 9 more authors.
Nuclear Materials and Energy | Year: 2016

A discrepancy in the divertor radiated powers between EDGE2D-EIRENE simulations and JET-ILW experiments employing a set of NBI-heated L-mode discharges with step-wise density variation is investigated. The analysis shows the importance of the contributions from the deuterium fuel to the divertor radiated power, making these discharges ideal for this study. Molecular radiation losses from D2 molecules have been included for the first time and the present simulations allow the atomic and molecular electron power loss terms in EIRENE to be independently scaled in order to understand their importance in determining the simulated electron temperatures and distribution of radiated power. © 2017.

Lang P.T.,MPI fur plasma physik | Maingi R.,Princeton Plasma Physics Laboratory | Mansfield D.K.,Princeton Plasma Physics Laboratory | McDermott R.M.,MPI fur plasma physik | And 24 more authors.
Nuclear Fusion | Year: 2017

The impact of lithium (Li) on plasma performance was investigated at the ASDEX Upgrade tokamak, which features a full tungsten wall. Li pellets containing 1.6 × 1020 Li atoms were launched with a speed of 600 m s-1 to achieve deep penetration into the plasma and minimize the impact on the first wall. Homogeneous transient Li concentrations in the plasma of up to 15% were established. The Li sustainment time in the plasma decreased with an increasing heating power from 150 to 40 ms. Due to the pellet rate being restricted to 2 Hz, no Li pile-up could take place. No significant positive impact on plasma properties, as reported from other tokamak devices, could be found; the Li pellets rather caused a small reduction in plasma energy, mainly due to enhanced radiation. Due to pellet injection, a short-lived Li layer was formed on the plasma-facing components, which lasted a few discharges and led to moderately beneficial effects during plasma start-up. Most pellets were found to trigger type-I ELMs, either by their direct local perturbation or indirectly by the altered edge conditions; however, reliability was less than 100%. © 2016 EURATOM.

Huber V.,Jülich Research Center | Huber A.,Jülich Research Center | Kinna D.,Culham Center for Fusion Energy | Balboa I.,Culham Center for Fusion Energy | And 12 more authors.
Review of Scientific Instruments | Year: 2016

The in situ absolute calibration of the JET real-time protection imaging system has been performed for the first time by means of radiometric light source placed inside the JET vessel and operated by remote handling. High accuracy of the calibration is confirmed by cross-validation of the near infrared (NIR) cameras against each other, with thermal IR cameras, and with the beryllium evaporator, which lead to successful protection of the JET first wall during the last campaign. The operation temperature ranges of NIR protection cameras for the materials used on JET are Be 650-1600 °C, W coating 600-1320 °C, and W 650-1500 °C. © 2016 EURATOM.

Lovell J.,Durham University | Lovell J.,Culham Center for Fusion Energy | Naylor G.,Culham Center for Fusion Energy | Field A.,Culham Center for Fusion Energy | And 2 more authors.
Review of Scientific Instruments | Year: 2016

A new resistive bolometer system has been developed for MAST-Upgrade. It will measure radiated power in the new Super-X divertor, with millisecond time resolution, along 16 vertical and 16 horizontal lines of sight. The system uses a Xilinx Zynq-7000 series Field-Programmable Gate Array (FPGA) in the D-TACQ ACQ2106 carrier to perform real time data acquisition and signal processing. The FPGA enables AC-synchronous detection using high performance digital filtering to achieve a high signal-to-noise ratio and will be able to output processed data in real time with millisecond latency. The system has been installed on 8 previously unused channels of the JET vertical bolometer system. Initial results suggest good agreement with data from existing vertical channels but with higher bandwidth and signal-to-noise ratio. © 2016 EURATOM.

Hender T.C.,Culham Center for Fusion Energy | Alper B.,Culham Center for Fusion Energy | Angioni C.,MPI fur plasma physik | Baranov Y.,Culham Center for Fusion Energy | And 8 more authors.
41st EPS Conference on Plasma Physics, EPS 2014 | Year: 2014

With the C-wall sustained high performance (with H98y > 1.2 for > 5s) has been achieved in the hybrid regime and is compatible with core n = 1 activity. With the ILW sustained high performance is not achieved and confinement degradation is coincident with core n = 1 MHD (but causality between the MHD and confinement degradation has yet to be established). Due to their effects in causing tungsten impurity accumulation n = 2 and 3 NTMs have a much more significant effect with the ILW than with the C-Wall. This work was carried out within the framework of the EFDA. This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement number 633053 and from the RCUK Energy Programme [grant number EP/I501045]. The views and opinions expressed herein do not necessarily reflect those of the European Commission.

Lang P.T.,MPI fur plasma physik | Meyer H.,Culham Center for Fusion Energy | Birkenmeier G.,MPI fur plasma physik | Burckhart A.,MPI fur plasma physik | And 14 more authors.
Plasma Physics and Controlled Fusion | Year: 2015

In ITER, pellets are used for ELM pacing and fueling. More importantly, ELM control and in particular control of the first ELM needs to be demonstrated in the non-nuclear phase of ITER during operation in H or He. Whilst D pellets have been established as an ELM control technique in the stationary phase with D target plasmas in devices with C as plasma-facing component, the behavior of other isotopes in non-stationary phases are not so well known. Here, we report on new pellet triggering experiments in ASDEX Upgrade and JET that mimic specific ITER operating scenarios. Both machines are equipped with an all-metal wall; recent investigations have shown that pellet triggering and pacing become more intricate when an all-metal wall surface is employed. In both machines, ELM triggering has been shown to occur after injection of D pellets into D plasmas during extended ELM-free phases, often following the L → H transition. In both devices the pellets are found to induce ELMs under conditions far from the stability boundary for type-I ELMs. Near the L → H transition, induced ELMs in some cases are more likely to have type-III rather than type-I characteristics. Furthermore, in ASDEX Upgrade this study was conducted during L → H transitions in the current ramp-up phase as envisaged for ITER. In addition, the pellet's ELM trigger potential has been proven in ASDEX Upgrade with a correct isotopic compilation for the non-nuclear phase in ITER, viz. H pellets into either He or H plasmas. Results from this study are encouraging since they have demonstrated the pellets' potential to provoke ELMs even under conditions that are quite far from the stability boundaries attributed to the occurrence of spontaneous ELMs. However, with the recent change from carbon to an all-metal plasma-facing component, examples have been found in both machines where pellets failed to establish ELM control under conditions where this would be expected and needed. Consequently, a major task of future investigations in this field will be to shed more light on the underlying physics of the pellet ELM triggering process to allow sound predictions for ITER. © 2015 IOP Publishing Ltd.

Geraud A.,French Atomic Energy Commission | Lennholm M.,Culham Center for Fusion Energy | Alarcon T.,French Atomic Energy Commission | Bennett P.,Culham Center for Fusion Energy | And 6 more authors.
Fusion Engineering and Design | Year: 2013

A new high frequency pellet injector, part of the JET programme in support of ITER, has been installed on JET at the end of 2007. Its main objective is the mitigation of the Edge Localized Modes (ELMs), responsible for unacceptable thermal loads on the wall when their amplitude is too high. The injector was also required to have the capability to inject pellets for plasma fuelling. To reach this double goal, the injector has to be capable to produce and accelerate either small pellets to trigger ELMs (pace making), allowing to control their frequency and thus their amplitude, or large pellets to fuel the plasma. Operational since the beginning of the 2009 JET experimental campaign, the injector, based on the screw extruder technology, suffered from a general degradation of its performance linked to extrusion instability. After modifications of the nozzle assembly, re-commissioning on plasma has been undertaken during the first half of 2012 and successful pellet ELM pacing was achieved, rising the intrinsic ELM frequency up to 4.5 times. © 2013 EURATOM.

Urso L.,MPI fur plasma physik | Fischer R.,MPI fur plasma physik | Isayama A.,Japan Atomic Energy Agency
Plasma Physics and Controlled Fusion | Year: 2010

The determination of the free parameters present in the modified Rutherford equation (MRE), which is routinely used for studying the physics of neoclassical tearing mode (NTM) stabilization, is addressed by making use of the Bayesian probability theory. The evaluation of the free coefficients is particularly sensitive to the assumptions used in the modelled equation, to the correlation of various physical parameters and to the uncertainties of the experimental measurements. A probabilistic method was applied for the consistent evaluation of the coefficients and their uncertainties using a large database of discharges and by considering the correlations and the uncertainties of the multiple physical quantities present in the MRE. The estimated values and uncertainties of the coefficients are related to the precise determination of the minimum amount of electron cyclotron current drive power necessary to stabilize NTMs in the International Thermonuclear Experimental Reactor. © 2010 IOP Publishing Ltd.

Li E.,CAS Hefei Institutes of Physical Science | Igochine V.,MPI fur plasma physik | Dumbrajs O.,Institute of Solid State Physics | Xu L.,CAS Hefei Institutes of Physical Science | And 3 more authors.
Plasma Physics and Controlled Fusion | Year: 2014

Evolution of the safety factor (q) profile during L-H transitions in the Experimental Advanced Superconducting Tokamak (EAST) was accompanied by strong core crashes prior to regular sawtooth behavior. These crashes appeared in the absence of q = 1 (q is the safety factor) rational surface inside the plasma. Analysis indicates that the m/n = 2/1 tearing mode is destabilized and phase-locked with the m/n = 1/1 non-resonant kink mode (the q = 1 rational surface is absent) due to the self-consistent evolution of plasma profiles as the L-H transition occurs (m and n are the poloidal and toroidal mode numbers, respectively). The growing m/n = 1/1 mode destabilizes the m/n = 2/2 kink mode which eventually triggers the strong crash due to an anomalous heat conductivity, as predicted by the transport model of stochastic magnetic fields using experimental parameters. It is also shown that the magnetic topology changes with the amplitude of m/n = 2/2 mode and the value of center safety factor in a reasonable range. © 2014 IOP Publishing Ltd.

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