List of publications

@article{1941,

title = {Ion cyclotron resonance heating scenarios for DEMO},

author = {Van D Eester and E Lerche and R Ragona and A Messiaen and T Wauters},

url = {https://doi.org/10.1088%2F1741-4326%2Fab318b},

doi = {10.1088/1741-4326/ab318b},

year  = {2019},

date = {2019-10-01},

journal = {Nuclear Fusion},

volume = {59},

number = {10},

pages = {106051},

publisher = {IOP Publishing},

abstract = {The present paper offers an overview of the potential of ion cyclotron resonance heating (ICRH) or radio frequency heating for the DEMO machine. It is found that various suitable heating schemes are available. Similar to ITER and in view of the limited bandwidth of about 10 MHz that can be achieved to ensure optimal functioning of the launcher, it is proposed to make core second harmonic tritium heating the key ion heating scheme, assisted by fundamental cyclotron heating 3He in the early phase of the discharge; for the present design of DEMO---with a static magnetic field strength of B 

 o   =  5.855 T---that places the T and 3He layers in the core for f   =  60 MHz and suggests centering the bandwidth around that main operating frequency. In line with earlier studies for hot, dense plasmas in large-size magnetic confinement machines, it is shown that good single pass absorption is achieved but that the size as well as the operating density and temperature of the machine cause the electrons to absorb a non-negligible fraction of the power away from the core when core ion heating is aimed at. Current drive and alternative heating options are briefly discussed and a dedicated computation is done for the traveling wave antenna, proposed for DEMO in view of its compatibility with substantial antenna--plasma distances. The various tasks that ICRH can fulfill are briefly listed. Finally, the impact of transport and the sensitivity of the obtained results to changes in the machine parameters is commented on.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1940,

title = {Control of the hydrogen:deuterium isotope mixture using pellets in JET},

author = {M Valovic and Y Baranov and A Boboc and J Buchanan and J Citrin and E Delabie and L Frassinetti and J M Fontdecaba and L Garzotti and C Giroud and R McKean and E Lerche and V Kiptily and F K \"{o} and M Marin and M Maslov and S Menmuir and G Tvalashvili and Weisen H and},

url = {https://doi.org/10.1088%2F1741-4326%2Fab3812},

doi = {10.1088/1741-4326/ab3812},

year  = {2019},

date = {2019-10-01},

journal = {Nuclear Fusion},

volume = {59},

number = {10},

pages = {106047},

publisher = {IOP Publishing},

abstract = {Deuterium pellets are injected into an initially pure hydrogen H-mode plasma in order to control the hydrogen:deuterium (H:D) isotope mixture. The pellets are deposited in the outer 20% of the minor radius, similar to that expected in ITER, creating transiently hollow electron density profiles. A H:D isotope mixture of approximately 45%:55% is obtained in the core with a pellet fuelling throughput of similar to previous pellet fuelling experiments in pure deuterium. Evolution of the H:D mix in the core is reproduced using a simple model, although deuterium transport could be higher at the beginning of the pellet train compared with the flat-top phase.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1935,

title = {Conceptual study of an ICRH system for T-15MD using traveling wave antenna (TWA) sections},

author = {J Ongena and A Messiaen and A V Melnikov and R Ragona and Ye. O Kazakov and Van D Eester and Yu. N Dnestrovskii and P P Khvostenko and I N Roy and A N Romannikov},

url = {http://www.sciencedirect.com/science/article/pii/S0920379619300882},

doi = {https://doi.org/10.1016/j.fusengdes.2019.01.080},

issn = {0920-3796},

year  = {2019},

date = {2019-09-01},

journal = {Fusion Engineering and Design},

volume = {146},

pages = {787-791},

abstract = {This paper describes a conceptual ICRH system for the tokamak T-15MД, in construction at the Nuclear Fusion Institute of the Kurchatov Research Centre for Atomic Energy in Moscow. The proposed system consists of a number of Travelling Wave Antenna sections, located below the equatorial plane of the tokamak. This antenna system, loaded by a simulated density profile provided by the T-15MД team, is modelled including its resonant ring feeding system. Resonant ring feeding allows the recirculation of the RF power that is not radiated to the plasma and the termination of the TWA section on its iterative impedance. The paper describes the antenna design, the feeding ring tuning algorithm and expected performances of this antenna concept. The chosen geometry of the TWA sections is compatible with that of a future reactor and therefore this ICRH antenna system for T-15MД represents also a test bed for DEMO.},

note = {SI:SOFT-30},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1933,

title = {First divertor physics studies in Wendelstein 7-X},

author = {Sunn T Pedersen and R K \"{o} and M Jakubowski and M Krychowiak and D Gradic and C Killer and H Niemann and T Szepesi and U Wenzel and A Ali and G Anda and J Baldzuhn and T Barbui and C Biedermann and B D Blackwell and H -S Bosch and S Bozhenkov and R Brakel and S Brezinsek and J Cai and B Cannas and J W Coenen and J Cosfeld and A Dinklage and T Dittmar and P Drewelow and P Drews and D Dunai and F Effenberg and M Endler and Y Feng and J Fellinger and O Ford and H Frerichs and G Fuchert and Y Gao and J Geiger and A Goriaev and K Hammond and J Harris and D Hathiramani and M Henkel and Ye. O Kazakov and A Kirschner and A Knieps and M Kobayashi and G Kocsis and P Kornejew and T Kremeyer and S Lazerzon and A LeViness and C Li and Y Li and Y Liang and S Liu and J Lore and S Masuzaki and V Moncada and O Neubauer and T T Ngo and J Oelmann and M Otte and V Perseo and F Pisano and Puig A Sitjes and M Rack and M Rasinski and J Romazanov and L Rudischhauser and G Schlisio and J C Schmitt and O Schmitz and B Schweer and S Sereda and M Sleczka and Y Suzuki and M Vecsei and E Wang and T Wauters and S Wiesen and V Winters and G A Wurden and D Zhang and Zoletnik S and},

url = {https://doi.org/10.1088%2F1741-4326%2Fab280f},

doi = {10.1088/1741-4326/ab280f},

year  = {2019},

date = {2019-09-01},

journal = {Nuclear Fusion},

volume = {59},

number = {9},

pages = {096014},

publisher = {IOP Publishing},

abstract = {The Wendelstein 7-X (W7-X) optimized stellarator fusion experiment, which went into operation in 2015, has been operating since 2017 with an un-cooled modular graphite divertor. This allowed first divertor physics studies to be performed at pulse energies up to 80 MJ, as opposed to 4 MJ in the first operation phase, where five inboard limiters were installed instead of a divertor. This, and a number of other upgrades to the device capabilities, allowed extension into regimes of higher plasma density, heating power, and performance overall, e.g. setting a new stellarator world record triple product. The paper focuses on the first physics studies of how the island divertor works. The plasma heat loads arrive to a very high degree on the divertor plates, with only minor heat loads seen on other components, in particular baffle structures built in to aid neutral compression. The strike line shapes and locations change significantly from one magnetic configuration to another, in very much the same way that codes had predicted they would. Strike-line widths are as large as 10 cm, and the wetted areas also large, up to about 1.5 m2, which bodes well for future operation phases. Peak local heat loads onto the divertor were in general benign and project below the 10 MW m−2 limit of the future water-cooled divertor when operated with 10 MW of heating power, with the exception of low-density attached operation in the high-iota configuration. The most notable result was the complete (in all 10 divertor units) heat-flux detachment obtained at high-density operation in hydrogen.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1937,

title = {Progress on an ion cyclotron range of frequency system for DEMO},

author = {J -M Noterdaeme and A Messiaen and R Ragona and W Zhang and A Bader and F Durodi\'{e} and U Fischer and T Franke and E Smigelskis and J Ongena and M Q Tran and Van D Eester and Van M Schoor},

url = {http://www.sciencedirect.com/science/article/pii/S0920379619302443},

doi = {https://doi.org/10.1016/j.fusengdes.2019.02.067},

issn = {0920-3796},

year  = {2019},

date = {2019-09-01},

journal = {Fusion Engineering and Design},

volume = {146},

pages = {1321-1324},

abstract = {An Ion Cyclotron Range of Frequency (ICRF) system can provide power for a number of tasks, experimentally verified on present machines: heating and current drive, first wall conditioning, plasma startup, removing central impurities, controlling sawteeth and current ramp down assist. The system has a high plug-to-power efficiency and most of the components external to the machine are sturdy, with industrial steady state capability. Traditional ICRF antenna systems are often characterized by a high operating voltage and high power density. Low power density and low voltage however provides a bonus in terms of reliability. Therefore, travelling wave type antennas have been proposed (Ragona and Messiaen, 2016). They can be integrated in the blanket and use only a limited number of feeders. The effect on the tritium breeding ratio of such an antenna incorporated in the blanket, including the feeders, is small. The k// spectrum is peaked and the dominant k// value can be optimized for coupling and bulk absorption, while avoiding the generation of coaxial modes in the edge. The coupling can be further enhanced with gas puffing near the antenna. Assuming the ITER-2010-low density profile, 50 MW can be coupled with a voltage on the antenna components of about 15 kV.},

note = {SI:SOFT-30},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1936,

title = {Traveling wave array for DEMO with proof of principle on WEST},

author = {R Ragona and A Messiaen and J M Bernard and E Delchambre and R Dumont and F Durodi\'{e} and J Hillairet and J Ongena and Van D Eester and Van M Schoor},

url = {http://www.sciencedirect.com/science/article/pii/S0920379619301085},

doi = {https://doi.org/10.1016/j.fusengdes.2019.01.097},

issn = {0920-3796},

year  = {2019},

date = {2019-09-01},

journal = {Fusion Engineering and Design},

volume = {146},

pages = {854-857},

abstract = {To decrease the power density and associated high voltages, a distributed antenna system is proposed as ICRH system for the DEMO reactor. Among the different solutions, a layout made from a set of travelling wave array (TWA) sections is considered as the most promising. It optimizes coupling to the plasma, is load resilient and avoids large values for the VSWR in the feeding lines. The total radiated power scales as the number of independently fed sections such that high reliability can be expected. The TWA concept for ICRH is innovative and very different from the traditional IC antennas. A test on WEST would provide a proof of principle of the validity of the TWA approach together with a comparison with the existing WEST IC antennas. The chosen geometry of the TWA section is compatible with one unit of the complete set designed for a future reactor. The paper describes the progress made in the preparation of a test on WEST along with the extrapolation for a future reactor like DEMO. A comparative modeling with the present antennas is also discussed and a preliminary RAMI analysis is introduced showing the promising positive impact of the TWA design on the RAMI scores.},

note = {SI:SOFT-30},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1934,

title = {Endoscopes for observation of plasma-wall interactions in the divertor of Wendelstein 7-X},

author = {Olaf Neubauer and Anton Charl and Guntram Czymek and Yu Gao and Martin Knaup and Ralf K \"{o} and Maciej Krychowiak and Horst-Toni Lambertz and M Lennartz and Christian Linsmeier and G Satheeswaran and B Schweer and Mathias Sch \"{u} and Stepan Sereda},

url = {http://www.sciencedirect.com/science/article/pii/S0920379618307087},

doi = {https://doi.org/10.1016/j.fusengdes.2018.11.009},

issn = {0920-3796},

year  = {2019},

date = {2019-09-01},

journal = {Fusion Engineering and Design},

volume = {146},

pages = {19-22},

abstract = {The stellarator Wendelstein 7-X is being prepared for long pulse operation. This includes diagnostics for investigation of plasma wall interaction processes. A versatile optical observation system has been developed for local characterization of the divertor plasma and the divertor target surface. The optical systems consist of two endoscopes each with perpendicular fields of view and the opportunity of tomographic reconstruction. Mirror based optics has been chosen in order to assure good optical properties independent of the wavelength. A narrow field of view allows for high spatial resolution while rotation of the first mirror covers the full poloidal divertor sections. An integrated shutter mechanism and a vacuum window far back minimize coating of optical components. For assessment of change of light transmission, a relative calibration function is implemented. The output light is split into wavelength ranges. Both, cameras equipped with narrow band filters as well as spectrometers are connected. The first endoscope was mounted at W7-X after successfully passing mechanical, optical and functional tests.},

note = {SI:SOFT-30},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1939,

title = {Experimental analysis of the particle transport in the magnetized plasma column with an application to the helicon discharge},

author = {I Shesterikov and K Cromb\'{e} and J -M Noterdaeme},

year  = {2019},

date = {2019-09-01},

journal = {Physics of Plasmas},

volume = {26},

number = {09},

pages = {093508},

abstract = {Different transport mechanisms in a magnetized radio frequency plasma discharge in the IShTAR device are compared. The total cross field particle transport systematically shows the best agreement with the turbulent diffusion. Also, the ion mobility dominated transport could substantially contribute to radial losses. The relative role of parallel and perpendicular losses in the overall particle confinement is also compared. The total perpendicular particle losses are comparable or even larger than the parallel ones, imposing a practical limitation on achieving high density plasma simply combining several helicon antennae sequentially arranged along the glass tube. For the same reason, reducing the diameter of a source tube, in an attempt to achieve a higher plasma density, could be not very efficient when perpendicular particle loss is dominant.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1929,

title = {Pellet fueling experiments in Wendelstein 7-X},

author = {J Baldzuhn and H Damm and C D Beidler and K McCarthy and N Panadero and C Biedermann and S A Bozhenkov and K J Brunner and G Fuchert and Ye. O Kazakov and M Beurskens and M Dibon and J Geiger and O Grulke and U H \"{o} and T Klinger and F K \"{o} and J Knauer and G Kocsis and P Kornejew and P T Lang and A Langenberg and H Laqua and N A Pablant and E Pasch and T S Pedersen and B Ploeckl and K Rahbarnia and G Schlisio and E R Scott and T Stange and A von Stechow and T Szepesi and Y Turkin and F Wagner and V Winters and G Wurden and Zhang D and},

url = {https://doi.org/10.1088%2F1361-6587%2Fab3567},

doi = {10.1088/1361-6587/ab3567},

year  = {2019},

date = {2019-08-01},

journal = {Plasma Physics and Controlled Fusion},

volume = {61},

number = {9},

pages = {095012},

publisher = {IOP Publishing},

abstract = {During the two most recent experimental campaigns in the advanced stellarator Wendelstein 7-X (W7-X) (Klinger et al 2017 Plasma Phys. Control. Fusion 59 014018; Bosch et al 2017 Nucl. Fusion 57 116015; Wolf et al 2017 Nucl. Fusion 57 102020; Pedersen et al 2017 Phys. Plasmas 24 0555030) hydrogen ice pellet injection was performed for the first time. In order to investigate the potential of pellet fueling in W7-X and to study the particle deposition in a large stellarator, a blower-gun system was installed with 40 pellets capability. The experience gained with this system will be used for the specification of a future steady-state pellet injector system. One important motivation for a pellet injector (Dibon 2014 Master-Thesis Technical University Munich, Max-Planck Institut IPP) on W7-X is the mitigation of hollow density profiles expected in case of predominant neoclassical transport. For long-pulse operation of up to 30 min, only electron cyclotron resonance heating is available on W7-X. Hence, pellet injection will be the only source for deep particle fueling. Deep particle fueling by pellets in tokamaks is supported by a grad-B drift, if the pellets are injected from the magnetic high-field-side. This approach was tested in W7-X, as well. The injection of series of pellets was also tested. Here, deep fueling is supported for later pellets in the series by the plasma cooling following the initial pellets in the same series. As in earlier experiments in the heliotron LHD (Takeiri et al 2017 Nucl. Fusion 57 102023), deep and rapid fueling could be achieved successfully in W7-X.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1928,

title = {Performance of Wendelstein 7-X stellarator plasmas during the first divertor operation phase},

author = {R C Wolf and A Alonso and S Akaslompolo and J Baldzhun and M Beurskens and C D Beidler and C Biedermann and H -S Bosch and S Bozhenkov and R Brakel and H Braune and S Brezinsek and K -J Brunner and H Damm and A Dinklage and P Drewelow and F Effenberg and Y Feng and O Ford and G Fuchert and Y Gao and J Geiger and O Grulke and N Harder and D Hartmann and P Helander and B Heinemann and M Hirsch and U H \"{o} and C Hopf and K Ida and M Isobe and M W Jakubowski and Ye. O Kazakov and C Killer and T Klinger and J Knauer and R K \"{o} and M Krychowiak and A Langenberg and H P Laqua and S Lazerson and P McNeely and S Marsen and N Marushchenko and R Nocentini and K Ogawa and G Orozco and M Osakabe and M Otte and D Pablant and E Pasch and A Pavone and M Porkolab and Puig A Sitjes and K Rahbarnia and R Riedl and N Rust and E Scott and H Schilling and R Schroeder and T Stange and Von A Stechow and E Strumberger and Sunn T Pedersen and J Svensson and H Thomson and Y Turkin and L Vano and T Wauters and G Wurden and M Yoshinuma and M Zanini and D Zhang and Wendelstein 7-X the Team},

year  = {2019},

date = {2019-08-01},

journal = {Physics of Plasmas},

volume = {26},

pages = {082504},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1927,

title = {Analysis of metallic impurity content by means of VUV and SXR diagnostics in hybrid discharges with hot-spots on the JET-ITER-like wall poloidal limiter},

author = {A Czarnecka and N Krawczyk and P Jacquet and E Lerche and V Bobkov and C Challis and D Frigione and J Graves and K D Lawson and M J Mantsinen and L Meneses and E Pawelec and T P \"{u} and M Sertoli and M Valisa and Van D Eester},

url = {https://doi.org/10.1088%2F1361-6587%2Fab2100},

doi = {10.1088/1361-6587/ab2100},

year  = {2019},

date = {2019-08-01},

journal = {Plasma Physics and Controlled Fusion},

volume = {61},

number = {8},

pages = {085004},

publisher = {IOP Publishing},

abstract = {In preparation for the upcoming JET D--T campaign, great effort has been devoted during the 2015--2016 JET campaigns with the ITER-like wall (ILW) to the extension of the high performance H-mode phase in baseline and hybrid scenarios. Hybrid discharges were the only ones that have been stopped by the real-time vessel protection system due hot-spot formation on the outboard poloidal limiter. Generation of hot-spots was linked to the application of high neutral beams injection and ion cyclotron resonance heating (ICRH) power. In tokamaks with high-Z plasma components, the use of ICRH heating is also accompanied by an increased metallic impurity content. Simultaneous control of hot-spot temperature and the core impurity content was crucial due to the fact that the same plasma-wall interaction mechanism is responsible for both phenomena. Impurity data collected by SXR, EUV and VUV diagnostics were able to provide for the first time comprehensive information concerning tungsten and mid-Z impurities such as nickel, iron, and cooper. To determine absolute mid-Z impurity concentrations a new relative calibration technique, compatible with JET-ILW, has been developed based on cross-calibration with a calibrated spectrometer via the quasicontinuum of W in the 200--400 r{A} wavelength range. In hybrid discharges, it was found that local D2 gas injection, plasma current, separatrix density, and fast ion losses appeared to impact hot-spot temperature and core impurity levels. Analysis showed a reduced maximum hot-spot temperature and impurity concentration at higher gas rate. Changes in the plasma current had a strong impact on the plasma-wall interaction, both via modifications in the edge density and in the fast ion losses. At constant gas injection rate, both the hot-spot temperature and the core impurity content decreased with the separatrix density. The main mechanism responsible for the formation of the hot-spots was found to be linked to the fast ion losses, but RF sheath effects may also be playing a role in the high limiter temperatures observed in these experiments.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1930,

title = {IShTAR: A test facility to study the interaction between RF wave and edge plasmas},

author = {I Shesterikov and K Cromb\'{e} and A Kostic and D A Sitnikov and M Usoltceva and R Ochoukov and S Heuraux and J Moritz and E Faudot and F Fischer and H Faugel and H F \"{u} and G Siegl and J -M Noterdaeme},

year  = {2019},

date = {2019-08-01},

journal = {Review of Scientific Instruments},

volume = {90},

number = {8},

pages = {083506},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1912,

title = {COREDIV numerical simulation of high neutron rate JET-ILW DD pulses in view of extension to JET-ILW DT experiments},

author = {G Telesca and I Ivanova-Stanik and R Zagorski and S Brezinsek and P J Carvalho and A Czarnecka and C Giroud and A Huber and E Lerche and S Wiesen},

url = {https://doi.org/10.1088%2F1741-4326%2Fab0c47},

doi = {10.1088/1741-4326/ab0c47},

year  = {2019},

date = {2019-05-01},

journal = {Nuclear Fusion},

volume = {59},

number = {5},

pages = {056026},

publisher = {IOP Publishing},

abstract = {Two high performance JET-ILW pulses, pertaining to the 2016 experimental campaign, have been numerically simulated with the self-consistent code COREDIV with the aim of predicting the ELM-averaged power load to the target when extrapolated to DT plasmas. The input power of about 33 MW as well as the total radiated power and the average density are similar in the two pulses, but for one of them the density is provided by combined low gas puff and pellet injection, characterized by low SOL density, for the other one by gas fuelling only, at higher SOL density. Considering the magnetic configuration of theses pulses and the presence of a significant amount of Ni (not included in the version of the code used for these simulations), a number of assumptions are made in order to reproduce numerically the main core and SOL experimental data. The extrapolation to DT plasmas at the original input power of 33 MW, and taking into account only the thermal component of the alpha-power, does not show any significant difference regarding the power to the target with respect to the DD case. In contrast, the simulations at auxiliary power 40 MW, both at the original I p  =  3 MA and at I p  =  4 MA, show that the power to the target for both pulses is possibly too high to be sustained for about 5 s by strike-point sweeping alone without any control by Ne seeding. Even though the target power load may decrease to about 13--15 MW with substantial Ne seeding for both pulses, as from numerical predictions, there are indications suggesting that the control of the power load may be more critical for the pulse with pellet injection, due to the reduced SOL radiation.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1911,

title = {Fast ion synergistic effects in JET high performance pulses},

author = {K K Kirov and Yu. Baranov and I S Carvalho and C D Challis and J Eriksson and D Frigione and L Garzotti and J Graves and P Jacquet and D L Keeling and E Lerche and P J Lomas and C Lowry and M Mantsinen and Rimini F and},

url = {https://doi.org/10.1088%2F1741-4326%2Fab02ae},

doi = {10.1088/1741-4326/ab02ae},

year  = {2019},

date = {2019-05-01},

journal = {Nuclear Fusion},

volume = {59},

number = {5},

pages = {056005},

publisher = {IOP Publishing},

abstract = {Fast ion synergistic effects were studied by predictive modelling of JET best performing pulses for various levels of neutral beam injection (NBI) and radio frequency (RF) power. Calculated DD neutron yields were analysed with the intention of separating the impact of RF synergistic effects due to changes in fast ion (FI) distribution function (DF) from secondary effects accompanying the application of RF power, namely changes in T 

e and T 

i. A novel approach in analysing the efficiency of fast ions in fusion reactions based on evaluation of the cumulative reaction rates is outlined and used in the study. Conclusions on the impact of fast ion synergistic effects on fusion performance are based on comparisons of beam-target (BT) and thermal (Th) DD reaction rates. It was found that changes in auxiliary heating power, NBI and RF, by 4 MW will affect DD fusion performance and neutron rates significantly. Simulations of the best performing JET pulses show that for H minority RF heating scheme with available RF power the impact of RF synergistic effects is somewhat lesser than the secondary effects related to changes in T 

e and T 

i. In conditions of much higher RF power the modification in fast ion distribution function (FI DF) and the impact of the fast ions on BT DD fusion becomes significant. The impact of the RF and NBI power on the BT reactivities was found to be of similar order; however, the NBI power has greater impact on reaction rates due to its larger effect on fast ion density.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1909,

title = {RF sheath modeling of experimentally observed plasma surface interactions with the JET ITER-Like Antenna},

author = {A K v r and V Bobkov and L Colas and P Dumortier and F Durodi\'{e} and P Jacquet and C C Klepper and D Milanesio and G Urbanczyk},

url = {http://www.sciencedirect.com/science/article/pii/S2352179118301741},

doi = {https://doi.org/10.1016/j.nme.2019.03.009},

issn = {2352-1791},

year  = {2019},

date = {2019-05-01},

journal = {Nuclear Materials and Energy},

volume = {19},

pages = {324 - 329},

abstract = {Waves in the Ion Cyclotron Range of Frequencies (ICRF) enhance local Plasma-Surface Interactions (PSI) near the wave launchers and magnetically-connected objects via Radio-Frequency (RF) sheath rectification. ITER will use 20MW of ICRF power over long pulses, questioning the long-term impact of RF-enhanced localized erosion on the lifetime of its Beryllium (Be) wall. Recent dedicated ICRF-heated L-mode discharges documented this process on JET for different types of ICRF antennas. Using visible spectroscopy in JET ICRF-heated L-mode discharges, poloidally-localized regions of enhanced (by ∼2--4x) Be I and Be II light emission were observed on two outboard limiters magnetically connected to the bottom of the active ITER-Like Antenna (ILA). The observed RF-PSI induced by the ILA was qualitatively comparable to that induced by the JET standard, type-A2 antennas, for similar strap toroidal phasing and connection geometries. The Be II line emission was found more intense when powering the bottom half of the ILA rather than its top half. Conversely, more pronounced SOL density modifications were observed with only top array operation, on field lines connected to the top half of the ILA. So far the near-field modeling of the ILA with antenna code TOPICA (Torino Polytechnic Ion Cyclotron Antenna), using curved antenna model, was partially able to reproduce qualitatively the observed phenomena. A quantitative discrepancy persisted between the observed Be source amplification and the calculated, corresponding increases in E// field at the magnetically connected locations to the ILA when changing from only top to only bottom half antenna operation. This paper revisits these current drive phased and half-ILA powered cases using for the new simulations flat model of the ILA and more realistic antenna feeding to calculate the E// field maps with TOPICA code. Further, the Self-consistent Sheaths and Waves for Ion Cyclotron Heating Slow Wave (SSWICH-SW) code, which couples slow wave evanescence with DC Scrape-Off Layer (SOL) biasing, is used to estimate the poloidal distribution of rectified RF-sheath Direct Current (DC) potential VDC in the private SOL between the ILA poloidal limiters. The approach so far was limited to correlating the observed, enhanced emission regions at the remote limiters to the antenna near-electric fields, as calculated by TOPICA. The present approach includes also a model for the rectification of these near-fields in the private SOL of the ILA. With the improved approach, when comparing only top and only bottom half antenna feeding, we obtained good qualitative correlation between all experimental measurements and the calculated local variations in the E// field and VDC potential.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1910,

title = {Scrape-off layer density tailoring with local gas puffing to maximize ICRF power coupling in ITER},

author = {W Zhang and R Bilato and T Lunt and A Messiaen and R A Pitts and S Lisgo and X Bonnin and V Bobkov and D Coster and Y Feng and P Jacquet and JM. Noterdaeme},

url = {http://www.sciencedirect.com/science/article/pii/S2352179118301236},

doi = {https://doi.org/10.1016/j.nme.2018.12.025},

issn = {2352-1791},

year  = {2019},

date = {2019-05-01},

journal = {Nuclear Materials and Energy},

volume = {19},

pages = {364 - 371},

abstract = {The coupling of ion cyclotron range of frequencies (ICRF) power to the plasma depends critically on the scrape-off layer (SOL) density since the fast wave is evanescent below the cut-off density. The ICRF power coupling can be improved by increasing the SOL density locally in front of the antenna by means of local gas puffing/fueling. To understand the influence of local gas puffing on the SOL and ICRF coupling and to find the optimized gas valve positions to maximize ICRF coupling in ITER, the 3D SOL code EMC3-EIRENE is used to calculate the SOL density, and the ICRF antenna codes ANTITER and FELICE are then used to calculate the coupling resistances. Purely deuterium plasma is simulated and the total gas puff rate for all studied cases is 4.5e22 el/s. The divertor gas puffing case is considered as the reference case. The density and temperature profiles in the reference case are well fitted to the standard ITER profiles (both for the low and medium density) with proper transport parameter profiles. The gas source is then switched to other local positions of the main chamber while all other simulation parameters are kept the same. The simulation results indicate that midplane gas puffing increases the antenna coupling resistance most significantly (by 150%-200%) for both ICRF antennas. This increase is at the same level as long as the gas valve is located toroidally close to the antenna, no matter if the gas valve is right to or left to the antenna. Outer top gas puffing increases the coupling resistance less significantly (by 100%--150%) for the antenna with good magnetic field line connections to the gas valve, but the increase is at a much smaller level (by ∼30%--60%) for the other antenna with only partial field line connections to the valve. The simulations thus confirm for ITER a behavior similar as seen experimentally in current devices and strongly suggest that ITER should modify the existing main chamber injection configuration to bring one of the four planned injection points closer to the antennas.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1908,

title = {First mirror test in JET for ITER: Complete overview after three ILW campaigns},

author = {Sunwoo Moon and P Petersson and M Rubel and E Fortuna-Zalesna and A Widdowson and S Jachmich and A Litnovsky and E Alves},

url = {http://www.sciencedirect.com/science/article/pii/S2352179118300814},

doi = {https://doi.org/10.1016/j.nme.2019.02.009},

issn = {2352-1791},

year  = {2019},

date = {2019-05-01},

journal = {Nuclear Materials and Energy},

volume = {19},

pages = {59 - 66},

abstract = {The First Mirror Test for ITER has been carried out in JET with mirrors exposed during: (i) the third ILW campaign (ILW-3, 2015--2016, 23.33 h plasma) and (ii) all three campaigns, i.e. ILW-1 to ILW-3: 2011--2016, 63,52 h in total. All mirrors from main chamber wall show no significant changes of the total reflectivity from the initial value and the diffuse reflectivity does not exceed 3% in the spectral range above 500 nm. The modified layer on surface has very small amount of impurities such as D, Be, C, N, O and Ni. All mirrors from the divertor (inner, outer, base under the bulk W tile) lost reflectivity by 20--80% due to the beryllium-rich deposition also containing D, C, N, O, Ni and W. In the inner divertor N reaches 5 × 1017 cm−2, W is up to 4.3 × 1017 cm−2, while the content of Ni is the greatest in the outer divertor: 3.8 × 1017 cm−2. Oxygen-18 used as the tracer in experiments at the end of ILW-3 has been detected at the level of 1.1 × 1016 cm−2. The thickness of deposited layer is in the range of 90 nm to 900 nm. The layer growth rate in the base (2.7 pm s − 1) and inner divertor is proportional to the exposure time when a single campaign and all three are compared. In a few cases, on mirrors located at the cassette mouth, flaking of deposits and erosion occurred.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1907,

title = {Modeling in front of a plasma profile of a set of traveling wave antenna sections in view of the ion cyclotron range of frequencies heating of the fusion reactor},

author = {A Messiaen and R Ragona},

url = {https://doi.org/10.1088%2F1361-6587%2Faaf8bd},

doi = {10.1088/1361-6587/aaf8bd},

year  = {2019},

date = {2019-04-01},

journal = {Plasma Physics and Controlled Fusion},

volume = {61},

number = {4},

pages = {044004},

publisher = {IOP Publishing},

abstract = {An upgraded version of the fast semi-analytical code ANTITER-II is used to model the traveling wave antenna (TWA) sections of any arbitrary number of radiating straps facing a low coupling plasma profile with their feeding system. The code computes the Y, Z and S matrices of the antenna array from which the performances of the TWA sections and of their feeding system are deduced as a function of the geometrical parameters of the TWA. The model incorporates the feeding of each section by a resonant ring circuit that re-circulates its output power. The cases of straps grounded at one of their ends (L grounding) or in their center (T grounding) are also compared. This model is extended to a number n 

B of TWA sections of n 

str straps with arbitrary positions in the y, z plane (i.e. machine wall). The full matrices of the resulting array of n 

str 

n 

B straps are derived and connected to the resonant ring circuits feeding each TWA sections to incorporate the feeding in the model. Examples of toroidal and/or poloidal set of sections with T or L grounding and symmetric or asymmetric k 

// spectra are analyzed. First conclusions for the design of a set of TWA sections for the reactor are already drawn.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1901,

title = {First results from divertor operation in Wendelstein 7-X},

author = {T S Pedersen and R K \"{o} and M Krychowiak and M Jakubowski and J Baldzuhn and S Bozhenkov and G Fuchert and A Langenberg and H.Niemann and D Zhang and K Rahbarnia and H -S Bosch and Ye. O Kazakov and S Brezinsek and Y Gao and N Pablant and W7-X the Team},

url = {http://stacks.iop.org/0741-3335/61/i=1/a=014035},

year  = {2019},

date = {2019-01-01},

journal = {Plasma Physics and Controlled Fusion},

volume = {61},

number = {1},

pages = {014035},

abstract = {Wendelstein 7-X is a highly optimized stellarator that went into operation in 2015. With a 30 cubic meter volume, a superconducting coil system operating at 2.5 T, and steady-state heating capability of eventually up to 10 MW, it was built to demonstrate the benefits of optimized stellarators at parameters approaching those of a fusion power plant. We report here on the first results with the test divertor installed, during the second operation phase, which was performed in the second half of 2017. Operation with a divertor, and the addition of several new fueling systems, allowed higher density operation in hydrogen as well as helium. The effects that higher density operation had on both divertor operation and global confinement will be described. In particular, at high densities detachment was observed, and the highest fusion triple product for a stellarator was achieved.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1902,

title = {Electron-cyclotron-resonance heating in Wendelstein 7-X: A versatile heating and current-drive method and a tool for in-depth physics studies},

author = {R C Wolf and S Bozhenkov and A Dinklage and G Fuchert and Ye. O Kazakov and H P Laqua and S Marsen and N B Marushchenko and T Stange and M Zanini and I Abramovic and A Alonso and J Baldzuhn and M Beurskens and C D Beidler and H Braune and K J Brunner and N Chaudhary and H Damm and P Drewelow and G Gantenbein and Yu Gao and J Geiger and M Hirsch and U H \"{o} and M Jakubowski and J Jelonnek and T Jensen and W Kasparek and J Knauer and S B Korsholm and A Langenberg and C Lechte and F Leipold and Trimino H Mora and U Neuner and S K Nielsen and D Moseev and H Oosterbeek and N Pablant and E Pasch and B Plaum and Sunn T Pedersen and Puig A Sitjes and K Rahbarnia and J Rasmussen and M Salewski and J Schilling and E Scott and M Stejner and H Thomsen and M Thumm and Y Turkin and F Wilde and Wendelstein 7-X the Team},

url = {http://stacks.iop.org/0741-3335/61/i=1/a=014037},

year  = {2019},

date = {2019-01-01},

journal = {Plasma Physics and Controlled Fusion},

volume = {61},

number = {1},

pages = {014037},

abstract = {For stellarators, which need no or only small amounts of current drive, electron-cyclotron-resonance heating (ECRH) is a promising heating method even for the envisaged application in a fusion power plant. Wendelstein 7-X (W7-X) is equipped with a steady-state capable ECRH system, operating at 140 GHz, which corresponds to the 2nd cyclotron harmonic of the electrons at a magnetic field of 2.5 T. Ten gyrotrons are operational and already delivered 7 MW to W7-X plasmas. Combined with pellet injection, the highest triple product (0.68 × 10 20 keV m −3 s), observed up to now in stellarators, was achieved (Sunn Pedersen et al 2018 Plasma Phys. Control. Fusion 61 014035). For the first time, W7-X plasmas were sustained by 2nd harmonic O-mode heating, approaching the collisionality regime for which W7-X was optimized. Power deposition scans did not show any indication of electron temperature profile resilience. In low-density, low-power plasmas a compensation of the bootstrap current with electron-cyclotron current drive (ECCD) was demonstrated. Sufficiently strong ECCD close to the plasma centre produced periodic internal plasma-crash events, which coincide with the appearance of low order rationals of the rotational transform.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1904,

title = {Impact of ICRF on the scrape-off layer and on plasma wall interactions: From present experiments to fusion reactor},

author = {V Bobkov and D Aguiam and R Bilato and S Brezinsek and L Colas and A Czarnecka and P Dumortier and R Dux and H Faugel and H F \"{u} and Ph. Jacquet and A Kallenbach and A Krivska and C C Klepper and E Lerche and Y Lin and D Milanesio and R Maggiora and I Monakhov and R Neu and J -M Noterdaeme and R Ochoukov and Th. P \"{u} and M Reinke and W Tierens and A Tuccilo and O Tudisco and Van D Eester and J Wright and S Wukitch and W Zhang},

url = {http://www.sciencedirect.com/science/article/pii/S2352179118301091},

doi = {https://doi.org/10.1016/j.nme.2018.11.017},

issn = {2352-1791},

year  = {2019},

date = {2019-01-01},

journal = {Nuclear Materials and Energy},

volume = {18},

pages = {131 - 140},

abstract = {Recent achievements in studies of the effects of ICRF (Ion Cyclotron Range of Frequencies) power on the SOL (Scrape-Off Layer) and PWI (Plasma Wall Interactions) in ASDEX Upgrade (AUG), Alcator C-Mod, and JET-ILW are reviewed. Capabilities to diagnose and model the effect of DC biasing and associated impurity production at active antennas and on magnetic field connections to antennas are described. The experiments show that ICRF near-fields can lead not only to E × B convection, but also to modifications of the SOL density, which for Alcator C-Mod are limited to a narrow region near antenna. On the other hand, the SOL density distribution along with impurity sources can be tailored using local gas injection in AUG and JET-ILW with a positive effect on reduction of impurity sources. The technique of RF image current cancellation at antenna limiters was successfully applied in AUG using the 3-strap AUG antenna and extended to the 4-strap Alcator C-Mod field-aligned antenna. Multiple observations confirmed the reduction of the impact of ICRF on the SOL and on total impurity production when the ratio of the power of the central straps to the total antenna power is in the range 0.6 < Pcen/Ptotal< 0.8. Near-field calculations indicate that this fairly robust technique can be applied to the ITER ICRF antenna, enabling the mode of operation with reduced PWI. On the contrary, for the A2 antenna in JET-ILW the technique is hindered by RF sheaths excited at the antenna septum. Thus, in order to reduce the effect of ICRF power on PWI in a future fusion reactor, the antenna design has to be optimized along with design of plasma-facing components.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1905,

title = {Development of glow discharge and electron cyclotron resonance heating conditioning on W7-X},

author = {A Goriaev and T Wauters and R Brakel and H Grote and M Gruca and O Volzke and S Brezinsek and A Dinklage and M Kubkowska and U Neuner},

url = {http://www.sciencedirect.com/science/article/pii/S2352179118302059},

doi = {https://doi.org/10.1016/j.nme.2018.12.010},

issn = {2352-1791},

year  = {2019},

date = {2019-01-01},

journal = {Nuclear Materials and Energy},

volume = {18},

pages = {227 - 232},

abstract = {For successful operation of Wendelstein 7-X (W7-X) control of plasma impurity content and fuel recycling is required. This can be achieved by using wall conditioning methods. During the first divertor operation campaign (OP1.2a) of W7-X glow discharge conditioning (GDC), weekly in hydrogen and daily in helium for impurity and hydrogen removal respectively, was used in the absence of the magnetic field. He electron cyclotron resonance heating (ECRH) discharges were applied for density control in hydrogen plasmas during experimental days. The optimization of GDC and He ECRH wall conditioning on W7-X are presented. Solutions for glow discharge ignition problems are examined. The suitable He -- GDC parameters, i.e. anode current and neutral gas pressure, are defined to keep the balance between maximum possible hydrogen removal rate and minimum plasma -- facing component (PFC) erosion. Sequences of short He -- ECRH pulses, so-called pulse trains, has been successfully implemented. The effect of pulse train main parameter variation such as gas prefill, input power, pulse length, duty cycle is described. The efficiency of single He recovery discharges and pulse trains are compared. The results of this work show significant improvement of wall cleaning efficiency.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1903,

title = {Determination of tungsten sources in the JET-ILW divertor by spectroscopic imaging in the presence of a strong plasma continuum},

author = {A Huber and S Brezinsek and A Kirschner and Str P \"{o} and G Sergienko and V Huber and I Borodkina and D Douai and S Jachmich and C h Linsmeier and B Lomanowski and G F Matthews and P h Mertens},

url = {http://www.sciencedirect.com/science/article/pii/S2352179118301406},

doi = {https://doi.org/10.1016/j.nme.2018.12.009},

issn = {2352-1791},

year  = {2019},

date = {2019-01-01},

journal = {Nuclear Materials and Energy},

volume = {18},

pages = {118 - 124},

abstract = {The identification of the sources of atomic tungsten and the measurement of their radiation distribution in front of all plasma-facing components has been performed in JET with the help of two digital cameras with the same two-dimensional view, equipped with interference filters of different bandwidths centred on the W I (400.88 nm) emission line. A new algorithm for the subtraction of the continuum radiation was successfully developed and is now used to evaluate the W erosion even in the inner divertor region where the strong recombination emission is dominating over the tungsten emission. Analysis of W sputtering and W redistribution in the divertor by video imaging spectroscopy with high spatial resolution for three different magnetic configurations was performed. A strong variation of the emission of the neutral tungsten in toroidal direction and corresponding W erosion has been observed. It correlates strongly with the wetted area with a maximal W erosion at the edge of the divertor tile.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1897,

title = {EMC3-EIRENE modeling of edge plasma to improve the ICRF coupling with local gas puffing in DEMO},

author = {W Zhang and T Franke and J -M Noterdaeme and Van D Eester},

url = {http://stacks.iop.org/0029-5515/58/i=12/a=126005},

year  = {2018},

date = {2018-12-01},

journal = {Nuclear Fusion},

volume = {58},

number = {12},

pages = {126005},

abstract = {We report the first 3D EMC3-EIRENE simulations of scrape-off layer (SOL) plasma in DEMO. EMC3-EIRENE is a 3D edge plasma fluid and neutral particle transport code. Effects of local gas puffing on the SOL density and ion cyclotron range of frequencies (ICRF) power coupling have been studied. A pure deuterium plasma is simulated and the puffing/fueling gas is deuterium gas. The gas puffing cases investigated include divertor, top, midplane and antenna gas puffing. The ICRF antenna is distributed through 360$,^circ$ toroidally, and poloidally located in the outer top of the vessel. The results show that toroidally distributed but poloidally localized antenna gas puffing increases the density in front of the antenna most significantly, while top or midplane gas puffing increases this antenna density to a moderate level. Influences of gas puff rate and particle transport parameters on the SOL density are investigated. The parameter scans indicate that the shift of the fast wave cut-off density position to the antenna depends almost linearly on the total gas puff rate. To achieve a significant antenna density increase, the antenna gas puff rate should be at the level of 1.8  ×  10 23 el s −1 (i.e. 1.0  ×  10 22 el s −1 per tokamak segment). As the total gas puff rate increases to 4.0  ×  10 23 el s −1 , the evanescent layer of the fast wave (with ##IMG## [http://ej.iop.org/images/0029-5515/58/12/126005/nfaaddaeieqn001.gif]   =  2 m −1 ) almost vanishes. Moreover, it is found that antenna gas puffing reduces the local power flux to the main chamber wall near the gas valve due to a local decrease of the SOL temperature.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1899,

title = {Wall conditioning throughout the first carbon divertor campaign on Wendelstein 7-X},

author = {T Wauters and A Goriaev and A Alonso and J Baldzuhn and R Brakel and S Brezinsek and A Dinklage and H Grote and J Fellinger and O P Ford and R K \"{o} and H Laqua and D Matveev and T Stange and Van L \'{o}},

url = {http://www.sciencedirect.com/science/article/pii/S2352179118300966},

doi = {https://doi.org/10.1016/j.nme.2018.11.004},

issn = {2352-1791},

year  = {2018},

date = {2018-12-01},

journal = {Nuclear Materials and Energy},

volume = {17},

pages = {235 - 241},

abstract = {Controlling the recycling of hydrogen and the release of impurities from the plasma facing components proved to be essential and challenging throughout the first divertor campaign on W7-X. This paper discusses the conditioning requirements throughout the first divertor campaign on Wendelstein 7-X. Baking at 150 $,^circ$C and glow discharge conditioning (GDC) in H2 is performed after the initial pump down of the vacuum vessel. Experimental programs in hydrogen are interlaced with He discharges to desaturate the wall from hydrogen, recover good recycling conditions and hence establish plasma density control. Optimized He ECRH wall conditioning procedures consisted of sequences of short discharges with fixed duty cycle. He-GDC remained however needed before each experimental day to fully offset the hydrogen inventory build-up. A significant increase in the divertor temperature is observed throughout an operational day, enhancing outgassing of CO and H2O. Preliminary recombination-diffusion modelling of hydrogen outgassing suggests enhanced diffusion to deeper surface layers with increasing wall temperature, which results in better wall pumping. This indicates that the experienced plasma performance degradation throughout an operational day results from increased impurity outgassing at higher wall temperature rather than hydrogen saturation of the wall.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1898,

title = {Characterization of wall conditions in Uragan-2M stellarator using stainless steel thermal desorption probe},

author = {G P Glazunov and D I Baron and V E Moiseenko and M N Bondarenko and A L Konotopskiy and A V Lozin and A I Lyssoivan and T Wauters and I E Garkusha},

url = {http://www.sciencedirect.com/science/article/pii/S0920379618306355},

doi = {https://doi.org/10.1016/j.fusengdes.2018.09.010},

issn = {0920-3796},

year  = {2018},

date = {2018-12-01},

journal = {Fusion Engineering and Design},

volume = {137},

pages = {196 - 201},

keywords = {},

pubstate = {published},

tppubtype = {article}

}