List of publications

@article{1796,

title = {Overview of progress in European medium sized tokamaks towards an integrated plasma-edge/wall solution},

author = {H Meyer and G. Verdoolaege and T. Wauters},

url = {http://stacks.iop.org/0029-5515/57/i=10/a=102014},

year  = {2017},

date = {2017-10-01},

journal = {Nuclear Fusion},

volume = {57},

number = {10},

pages = {102014},

abstract = {Integrating the plasma core performance with an edge and scrape-off layer (SOL) that leads to tolerable heat and particle loads on the wall is a major challenge. The new European medium size tokamak task force (EU-MST) coordinates research on ASDEX Upgrade (AUG), MAST and TCV. This multi-machine approach within EU-MST, covering a wide parameter range, is instrumental to progress in the field, as ITER and DEMO core/pedestal and SOL parameters are not achievable simultaneously in present day devices. A two prong approach is adopted. On the one hand, scenarios with tolerable transient heat and particle loads, including active edge localised mode (ELM) control are developed. On the other hand, divertor solutions including advanced magnetic configurations are studied. Considerable progress has been made on both approaches, in particular in the fields of: ELM control with resonant magnetic perturbations (RMP), small ELM regimes, detachment onset and control, as well as filamentary scrape-off-layer transport. For example full ELM suppression has now been achieved on AUG at low collisionality with n = 2 RMP maintaining good confinement ##IMG## [http://ej.iop.org/images/0029-5515/57/10/102014/nfaa6084ieqn001.gif] $Ħ_textĦłeft(98,texty2right)approx 0.95$ . Advances have been made with respect to detachment onset and control. Studies in advanced divertor configurations (Snowflake, Super-X and X-point target divertor) shed new light on SOL physics. Cross field filamentary transport has been characterised in a wide parameter regime on AUG, MAST and TCV progressing the theoretical and experimental understanding crucial for predicting first wall loads in ITER and DEMO. Conditions in the SOL also play a crucial role for ELM stability and access to small ELM regimes.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1797,

title = {Major results from the first plasma campaign of the Wendelstein 7-X stellarator},

author = {R C Wolf and T. Wauters and F. Durodié and A. Goriaev and J. Ongena and M. Vergote},

url = {http://stacks.iop.org/0029-5515/57/i=10/a=102020},

year  = {2017},

date = {2017-10-01},

journal = {Nuclear Fusion},

volume = {57},

number = {10},

pages = {102020},

abstract = {After completing the main construction phase of Wendelstein 7-X (W7-X) and successfully commissioning the device, first plasma operation started at the end of 2015. Integral commissioning of plasma start-up and operation using electron cyclotron resonance heating (ECRH) and an extensive set of plasma diagnostics have been completed, allowing initial physics studies during the first operational campaign. Both in helium and hydrogen, plasma breakdown was easily achieved. Gaining experience with plasma vessel conditioning, discharge lengths could be extended gradually. Eventually, discharges lasted up to 6 s, reaching an injected energy of 4 MJ, which is twice the limit originally agreed for the limiter configuration employed during the first operational campaign. At power levels of 4 MW central electron densities reached 3 × 10 19 m −3 , central electron temperatures reached values of 7 keV and ion temperatures reached just above 2 keV. Important physics studies during this first operational phase include a first assessment of power balance and energy confinement, ECRH power deposition experiments, 2nd harmonic O-mode ECRH using multi-pass absorption, and current drive experiments using electron cyclotron current drive. As in many plasma discharges the electron temperature exceeds the ion temperature significantly, these plasmas are governed by core electron root confinement showing a strong positive electric field in the plasma centre.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1841,

title = {Progress in reducing ICRF-specific impurity release in ASDEX upgrade and JET},

author = {V Bobkov and D Aguiam and M Baruzzo and D Borodin and I Borodkina and S Brezinsek and I Coffey and L Colas and A Czarnecka and E Delabie and P. Dumortier and F. Durodié and R Dux and H Faugel and H F ü and C Giroud and M Goniche and J Hobirk and A Herrmann and J Jacquot and Ph. Jacquet and A Kallenbach and A. Krivska and C C Klepper and E. Lerche and S Menmuir and D Milanesio and R Maggiora and I Monakhov and F Nave and R Neu and J. -M. Noterdaeme and R Ochoukov and Th. P ü and M Reinke and A Tuccilo and O Tudisco and D. Van Eester and Y Wang and Q Yang and W Zhang},

url = {http://www.sciencedirect.com/science/article/pii/S2352179116300746},

doi = {https://doi.org/10.1016/j.nme.2016.10.026},

issn = {2352-1791},

year  = {2017},

date = {2017-08-01},

journal = {Nuclear Materials and Energy},

volume = {12},

pages = {1194 - 1198},

abstract = {Use of new 3-strap ICRF antennas with all-tungsten (W) limiters in ASDEX Upgrade results in a reduction of the W sources at the antenna limiters and of the W content in the confined plasma by at least a factor of 2 compared to the W-limiter 2-strap antennas used in the past. The reduction is observed with a broad range of plasma shapes. In multiple locations of antenna frame, the limiter W source has a minimum when RF image currents are decreased by cancellation of the RF current contributions of the central and the outer straps. In JET with ITER-like wall, ITER-like antenna produces about 20% less of main chamber radiation and of W content compared to the old A2 antennas. However the effect of the A2 antennas on W content is scattered depending on which antennas are powered. Experiments in JET with trace nitrogen (N2) injection show that a presence of active ICRF antenna close to the midplane injection valve has little effect on the core N content, both in dipole and in -90$,^circ$ phasing. This indicates that the effect of ICRF on impurity transport across the scape-off-layer is small in JET compared to the dominant effect on impurity sources leading to increased impurity levels during ICRF operation.},

note = {Proceedings of the 22nd International Conference on Plasma Surface Interactions 2016, 22nd PSI},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1792,

title = {Analytical study of the wave polarisation in the `three-ion' radio frequency heating scheme},

author = {D. Van Eester and Y. O. Kazakov and E. Lerche},

url = {http://stacks.iop.org/0741-3335/59/i=8/a=085012},

year  = {2017},

date = {2017-08-01},

journal = {Plasma Physics and Controlled Fusion},

volume = {59},

number = {8},

pages = {085012},

abstract = {The `three-ion' scheme (Kazakov et al 2015 Nucl. Fusion 55 032001) is a new, high-potential ion cyclotron resonance heating scheme that has recently been proposed and experimentally tested. In this paper a simple cold plasma analytical model is introduced, which shows the beneficial effect of the changes of wave polarisation brought about by a tiny third minority when added to 2 majority ion species. This causes a second ion–ion hybrid layer to appear and allows to maximise the absorption of wave power on the minority ions. We also show by analytical modelling the effect of the wave interference on double-pass wave absorption in plasmas with two ion–ion hybrid layers.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1791,

title = {Modelling of advanced three-ion ICRF heating and fast ion generation scheme for tokamaks and stellarators},

author = {J Faustin and Y. O. Kazakov and D. Van Eester},

url = {http://stacks.iop.org/0741-3335/59/i=8/a=084001},

year  = {2017},

date = {2017-08-01},

journal = {Plasma Physics and Controlled Fusion},

volume = {59},

number = {8},

pages = {084001},

abstract = {Absorption of ion-cyclotron range of frequencies waves at the fundamental resonance is an efficient source of plasma heating and fast ion generation in tokamaks and stellarators. This heating method is planned to be exploited as a fast ion source in the Wendelstein 7-X stellarator. The work presented here assesses the possibility of using the newly developed three-ion species scheme (Kazakov et al (2015) Nucl. Fusion 55 032001) in tokamak and stellarator plasmas, which could offer the capability of generating more energetic ions than the traditional minority heating scheme with moderate input power. Using the SCENIC code, it is found that fast ions in the MeV range of energy can be produced in JET-like plasmas. The RF-induced particle pinch is seen to strongly impact the fast ion pressure profile in particular. Our results show that in typical high-density W7-X plasmas, the three-ion species scheme generates more energetic ions than the more traditional minority heating scheme, which makes three-ion scenario promising for fast-ion confinement studies in W7-X.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1839,

title = {Investigation of probe surfaces after ion cyclotron wall conditioning in ASDEX upgrade},

author = {A Garcia-Carrasco and P Petersson and T Schwarz-Selinger and T. Wauters and D Douai and V Bobkov and R Cavazzana and K Krieger and A. I. Lyssoivan and S M ö and M Spolaore and V Rohde and M Rubel},

url = {http://www.sciencedirect.com/science/article/pii/S2352179116302058},

doi = {https://doi.org/10.1016/j.nme.2016.12.018},

issn = {2352-1791},

year  = {2017},

date = {2017-08-01},

journal = {Nuclear Materials and Energy},

volume = {12},

pages = {733 - 735},

abstract = {For the first time, material analysis techniques have been applied to study the effect of ion cyclotron wall conditioning (ICWC) on probe surfaces in a metal-wall machine. ICWC is a technique envisaged to contribute to the removal of fuel and impurities from the first wall of ITER. The objective of this work was to assess impurity migration under ICWC operation. Tungsten probes were exposed in ASDEX Upgrade to discharges in helium. After wall conditioning, the probes were covered with a co-deposited layer containing D, B, C, N, O and relatively high amount of He. The concentration ratio He/C+B was 0.7. The formation of the co-deposited layer indicates that a fraction of the impurities desorbed from the wall under ICWC operation are transported by plasma and deposited away from their original location.},

note = {Proceedings of the 22nd International Conference on Plasma Surface Interactions 2016, 22nd PSI},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1838,

title = {Plasma impact on diagnostic mirrors in JET},

author = {A Garcia-Carrasco and P Petersson and M Rubel and A Widdowson and E Fortuna-Zalesna and S. Jachmich and M Brix and L Marot},

url = {http://www.sciencedirect.com/science/article/pii/S2352179116300503},

doi = {https://doi.org/10.1016/j.nme.2016.12.032},

issn = {2352-1791},

year  = {2017},

date = {2017-08-01},

journal = {Nuclear Materials and Energy},

volume = {12},

pages = {506 - 512},

abstract = {Metallic mirrors will be essential components of all optical systems for plasma diagnosis in ITER. This contribution provides a comprehensive account on plasma impact on diagnostic mirrors in JET with the ITER-Like Wall. Specimens from the First Mirror Test and the lithium-beam diagnostic have been studied by spectrophotometry, ion beam analysis and electron microscopy. Test mirrors made of molybdenum were retrieved from the main chamber and the divertor after exposure to the 2013–2014 experimental campaign. In the main chamber, only mirrors located at the entrance of the carrier lost reflectivity (Be deposition), while those located deeper in the carrier were only slightly affected. The performance of mirrors in the JET divertor was strongly degraded by deposition of beryllium, tungsten and other species. Mirrors from the lithium-beam diagnostic have been studied for the first time. Gold coatings were severely damaged by intense arcing. As a consequence, material mixing of the gold layer with the stainless steel substrate occurred. Total reflectivity dropped from over 90% to less than 60%, i.e. to the level typical for stainless steel.},

note = {Proceedings of the 22nd International Conference on Plasma Surface Interactions 2016, 22nd PSI},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1793,

title = {The effect of the isotope on the H-mode density limit},

author = {A Huber and S. Jachmich and contributors},

url = {http://stacks.iop.org/0029-5515/57/i=8/a=086007},

year  = {2017},

date = {2017-08-01},

journal = {Nuclear Fusion},

volume = {57},

number = {8},

pages = {086007},

abstract = {In order to understand the mechanisms for the H-mode density limit in machines with fully metallic walls, systematic investigations of H-mode density limit plasmas in experiments with deuterium and hydrogen external gas fuelling have been performed on JET-ILW. The observed H-mode density limit on JET in D- as well as in H-plasmas demonstrates similar operation phases: the stable H-mode phase, degrading H-mode, breakdown of the H-mode with energy confinement deterioration accompanied by a dithering cycling phase, followed by the L-mode phase. The density limit is not related to an inward collapse of the hot core plasma due to an overcooling of the plasma periphery by radiation. Indeed, independently of the isotopic effect, the total radiated power stay almost constant during the H-mode phase until the H-L back transition. It was observed in D- and H-plasmas that neither detachment, nor the X-point MARFE itself do trigger the H-L transition and that they thus do not present a limit on the plasma density. It is the plasma confinement, most likely determined by edge parameters, which is ultimately responsible for the H-mode DL. By comparing similar discharges but fuelled with either deuterium or hydrogen, we have found that the H-mode density limit exhibits a dependence on the isotope mass: the density limit is up to 35% lower in hydrogen compared to similar deuterium plasma conditions (the obtained density limit is in agreement with the Greenwald limit for D-plasma). In addition, the density limit is nearly independent of the applied power both in deuterium or hydrogen fuelling conditions. The measured Greenwald fractions are consistent with the predictions from a theoretical model based on an MHD instability theory in the near-SOL. The JET operational domains are significantly broadened when increasing the plasma effective mass (e.g. tritium or deuterium–tritium operation), i.e. the L to H power threshold is reduced whereas the density limit for the L-mode back transition is increased.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1836,

title = {Comparative H-mode density limit studies in JET and AUG},

author = {A Huber and M Bernert and S Brezinsek and A V Chankin and G Sergienko and V Huber and S Wiesen and P Abreu and M N A Beurskens and A Boboc and M Brix and Calabr G `o and D Carralero and E Delabie and T Eich and H G Esser and M Groth and C Guillemaut and S. Jachmich and A J ä and E Joffrin and A Kallenbach and U Kruezi and P Lang and Ch. Linsmeier and C G Lowry and C F Maggi and G F Matthews and A G Meigs and Ph. Mertens and F Reimold and J Schweinzer and G Sips and M Stamp and E Viezzer and M Wischmeier and H Zohm},

url = {http://www.sciencedirect.com/science/article/pii/S2352179116300588},

doi = {https://doi.org/10.1016/j.nme.2017.01.005},

issn = {2352-1791},

year  = {2017},

date = {2017-08-01},

journal = {Nuclear Materials and Energy},

volume = {12},

pages = {100 - 110},

abstract = {Identification of the mechanisms for the H-mode density limit in machines with fully metallic walls, and their scaling to future devices is essential to find for these machines the optimal operational boundaries with the highest attainable density and confinement. Systematic investigations of H-mode density limit plasmas in experiments with deuterium external gas fuelling have been performed on machines with fully metallic walls, JET and AUG and results have been compared with one another. Basically, the operation phases are identical for both tokamaks: the stable H-mode phase, degrading H-mode phase, breakdown of the H-mode with energy confinement deterioration usually accompanied by a dithering cycling phase, followed by the l-mode phase. The observed H-mode density limit on both machines is found close to the Greenwald limit (n/nGW=0.8–1.1 in the observed magnetic configurations). The similar behavior of the radiation on both tokamaks demonstrates that the density limit (DL) is neither related to additional energy losses from the confined region by radiation, nor to an inward collapse of the hot discharge core induced by overcooling of the plasma periphery by radiation. It was observed on both machines that detachment, as well as the X-point MARFE itself, does not trigger a transition in the confinement regime and thus does not present a limit on the plasma density. It is the plasma confinement, most likely determined by edge parameters, which is ultimately responsible for the transition from H- to l-mode. The measured Greenwald fractions are found to be consistent with the predictions from different theoretical models [16,30] based on MHD instability theory in the near-SOL.},

note = {Proceedings of the 22nd International Conference on Plasma Surface Interactions 2016, 22nd PSI},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1837,

title = {Energy balance in JET},

author = {G F Matthews and P Bunting and S Devaux and P Drewelow and C Guillemaut and D B King and E. Lerche and S Silburn and G Szepesi and V Riccardo and V Thompson},

url = {http://www.sciencedirect.com/science/article/pii/S2352179116301661},

doi = {https://doi.org/10.1016/j.nme.2016.12.012},

issn = {2352-1791},

year  = {2017},

date = {2017-08-01},

journal = {Nuclear Materials and Energy},

volume = {12},

pages = {227 - 233},

abstract = {In this paper we discuss results from the study of the energy balance in JET based on calculated heating energies, radiated energy from bolometry and tile calorimetry. Recent data enables us to be more confident in the numbers used and to exclude certain possibilities but the overall energy imbalance which typically amounts to 25% of total input remains unexplained. This shows that caution is required in interpreting fractional radiated powers which are commonly used to measure the effectiveness of impurity seeded scenarios at reducing divertor heat load.},

note = {Proceedings of the 22nd International Conference on Plasma Surface Interactions 2016, 22nd PSI},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1840,

title = {The isotope effect on divertor conditions and neutral pumping in horizontal divertor configurations in JET-ILW Ohmic plasmas},

author = {J Uljanovs and M Groth and A E Jaervinen and D Moulton and M Brix and G Corrigan and P Drewelow and C Guillemaut and D Harting and J Simpson and A Huber and S. Jachmich and U Kruezi and K D Lawson and A G Meigs and A C C Sips and M F Stamp and S Wiesen},

url = {http://www.sciencedirect.com/science/article/pii/S2352179116301892},

doi = {https://doi.org/10.1016/j.nme.2017.03.028},

issn = {2352-1791},

year  = {2017},

date = {2017-08-01},

journal = {Nuclear Materials and Energy},

volume = {12},

pages = {791 - 797},

abstract = {Understanding the impact of isotope mass and divertor configuration on the divertor conditions and neutral pressures is critical for predicting the performance of the ITER divertor in DT operation. To address this need, ohmically heated hydrogen and deuterium plasma experiments were conducted in JET with the ITER-like wall in varying divertor configurations. In this study, these plasmas are simulated with EDGE2D-EIRENE outfitted with a sub-divertor model, to predict the neutral pressures in the plenum with similar fashion to the experiments. EDGE2D-EIRENE predictions show that the increased isotope mass results in up to a 25% increase in peak electron densities and 15% increase in peak ion saturation current at the outer target in deuterium when compared to hydrogen for all horizontal divertor configurations. Indicating that a change from hydrogen to deuterium as main fuel decreases the neutral mean free path, leading to higher neutral density in the divertor. Consequently, this mechanism also leads to higher neutral pressures in the sub-divertor. The experimental data provided by the hydrogen and deuterium ohmic discharges shows that closer proximity of the outer strike point to the pumping plenum results in a higher neutral pressure in the sub-divertor. The diaphragm capacitance gauge pressure measurements show that a two to three-fold increase in sub-divertor pressure was achieved in the corner and nearby horizontal configurations compared to the far-horizontal configurations, likely due to ballistic transport (with respect to the plasma facing components) of the neutrals into the sub-divertor. The corner divertor configuration also indicates that a neutral expansion occurs during detachment, resulting in a sub-divertor neutral density plateau as a function of upstream density at the outer-mid plane.},

note = {Proceedings of the 22nd International Conference on Plasma Surface Interactions 2016, 22nd PSI},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1790,

title = {ICRF Traveling Wave launcher for fusion devices},

author = {R. Ragona},

url = {http://stacks.iop.org/1742-6596/841/i=1/a=012022},

year  = {2017},

date = {2017-06-01},

journal = {Journal of Physics: Conference Series},

volume = {841},

number = {1},

pages = {012022},

abstract = {Ion Cyclotron Resonance Heating and Current Drive is a method that has the ability to heat directly the ions in the Deuterium-Tritrium fuel to the high temperature needed for the fusion reaction to works. The capability of efficiently couple the Radio Frequency power to the plasma plays a big role in the overall performance of a fusion device. A Traveling Wave Antenna in a resonant ring configuration is a good candidate for an Ion Cyclotron Resonance Heating and Current Drive system. It has the capability to increase the coupled power with respect to present designs and to have a highly selective power spectrum that can be peaked around the maximally absorbed wave. It is also insensitive to the loading variations due to fluctuation of the plasma edge increasing the reliability and the efficiency of the system. It works as a low power density launcher due to the possible large number of current carrying elements.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1764,

title = {Uncertainty estimation and a stopping rule in nonlinear gyrokinetic simulations},

author = {Michael Oberparleiter and Hans Nordman and G. Verdoolaege and Frank Jenko},

url = {http://stacks.iop.org/1742-6596/775/i=1/a=012009},

year  = {2016},

date = {2016-12-01},

journal = {Journal of Physics: Conference Series},

volume = {775},

number = {1},

pages = {012009},

abstract = {We present a method to estimate the mean and uncertainty of fluctuating quantities, such as spatially averaged density and temperature fluctuations or radial fluxes, from initial value simulations of the Eulerian gyrokinetic code GENE[1, 2]. Since the time series are autocorrelated in time, the data is grouped into batches based on the autocorrelation time and their means form the sample for further statistical treatment, such as calculating the standard error of the mean.Based on this uncertainty estimate we develop a stopping rule for a nonlinear simulation: First, regression tests ensure that it has reached a stationary (quasisteady) state and data before this point is discarded. Then the previously described estimate is calculated. If the estimated relative error is below a prescribed threshold, the simulation is stopped. This scheme is applied to several previously performed GENE simulations ranging from simple benchmarks to modelling of JET and ASDEX discharges. It can be demonstrated that a number of simulations could be around 30% shorter if a maximal statistical relative uncertainty of 5% is desired for all monitored quantities.},

note = {Presented at the Joint Varenna-Lausanne International Workshop on the Theory of Fusion Plasmas 2016, 29 August to 2 September 2016, Varenna, Italy},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1762,

title = {Contribution of LPP/ERM-KMS to the modern developments of ICRH antenna systems},

author = {A. Messiaen and J. Ongena and P. Dumortier and F. Durodié and F. Louche and R. Ragona and M. Vervier},

url = {http://dx.doi.org/10.1016/j.fusengdes.2016.06.035},

doi = {10.1016/j.fusengdes.2016.06.035},

issn = {09203796},

year  = {2016},

date = {2016-11-01},

journal = {Fusion Engineering and Design},

volume = {112},

pages = {21-35},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1761,

title = {Fusion product studies via fast ion D-D and D-3 He fusion on JET},

author = {S E Sharapov and T Hellsten and V G Kiptily and T Craciunescu and J Eriksson and M Fitzgerald and J -B Girardo and V Goloborodko and C Hellesen and A Hjalmarsson and T Johnson and Y. O. Kazakov and T Koskela and M Mantsinen and I Monakhov and F Nabais and M Nocente and Perez C Thun and F Rimini and M Santala and M Schneider and M Tardocchi and M Tsalas and V Yavorskij and V Zoita and JET Contributors},

url = {http://stacks.iop.org/0029-5515/56/i=11/a=112021},

year  = {2016},

date = {2016-11-01},

journal = {Nuclear Fusion},

volume = {56},

number = {11},

pages = {112021},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1756,

title = {ITER-like antenna capacitors voltage probes: Circuit/electromagnetic calculations and calibrations},

author = {W Helou and F. Durodié and P. Dumortier},

url = {http://aip.scitation.org/doi/full/10.1063/1.4964137},

year  = {2016},

date = {2016-10-01},

journal = {Review of Scientific Instruments},

volume = {87},

number = {10},

pages = {104705},

keywords = {},

pubstate = {published},

tppubtype = {article}

}