Jef Ongena’s personal page

@article{1979,

title = {Analysis of metallic impurities during the application of three-ion ICRH scenario at JET-ILW},

author = {A Chomiczewska and N Krawczyk and Y. O. Kazakov and V Bobkov and Kowalska-Strz E e and E. Lerche and M J Mantsinen and J. Ongena and G Pucella and T P ü and D. Van Eester and JET Contributors},

year  = {2020},

date = {2020-09-01},

journal = {AIP Conference proceedings},

volume = {2254},

number = {1},

pages = {050005},

abstract = {The effect of the novel `three-ion' D-(3He)-H minority ICRH heating scheme on the behavior of the metallic impurities at JET-ILW is discussed. The reported experiment was performed in L-mode plasmas at a magnetic field BT = 3.2 T, plasma current Ip = 2 MA and central plasma densities ne(0) ≈ 4×1019 m-3. ICRH power was delivered with dipole or +π/2 antenna phasing at f ≈ 32.2-33MHz, placing the 3He cyclotron resonance at the plasma core. The edge isotopic ratio H/(H+D) was varied between 73 and 92%, and 3He concentration in the range of 0.1-1.5% to assess the sensitivity of the scheme to the detailed plasma composition. The results of our analysis show a linear increase of the plasma effective charge Zeff, radiated power Prad,bulk and content of metallic impurities with ICRF power. The observed scattering of the points reflects the difference in the plasma composition and ICRF antenna phasing. For discharges heated with similar ICRH power level ~4MW, our analysis indicates that for a large range of H/(H+D) the novel scenario effectively heats the plasma with reduced content of metallic impurities. The impurities are shown to be concentrated mainly around the mid- radius region of the plasma. We conclude this paper with a discussion of the effect of the long-period sawteeth on the observed dynamics of metallic impurities in the plasma core.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1973,

title = {Synergistic ICRH and NBI heating for fast ion generation and maximising fusion rate in mixed plasmas at JET},

author = {K K Kirov and Y. O. Kazakov and M Nocente and J. Ongena and Y Baranov and F Casson and J Eriksson and L Giacomelli and C Hellesen and V Kiptily and R Bilato and K. Crombé and R Dumont and P Jacquet and T Johnson and E Lerch and M Mantsinen and D. Van Eester and J Varje and H Weisen and JET Contributors},

year  = {2020},

date = {2020-09-01},

journal = {AIP Conference proceedings},

volume = {2254},

number = {1},

pages = {030011},

abstract = {The studies of recent JET experiments in H/D≈0.85/0.15 plasma (2.9T/2MA) in which neutron rate was enhanced by applying 2.5MW of ICRH using D-(DNBI)-H three-ion scheme are reported. An extensive analysis of this novel heating scenario has been carried out by means of integrated TRANSP/TORIC modelling, and a comprehensive validation of the computed Fast Ion Distribution Function (FI DF) with a range of fast ion diagnostics available at JET is presented. The predicted acceleration of D Neutral Beam Injection (NBI) ions beyond their injection energies and the associated changes in FI DF by RF waves are found to be in good agreement with measured neutron yield and TOFOR neutron spectrometer measurements, as well as with multi-channel neutron camera observations and neutral particle analyser diagnostic. An outlook of the possible applications of the developed technique for future DTE2 studies on JET has been highlighted. Controlled acceleration of TNBI ions in D-rich and DNBI ions in T-rich plasmas to optimal energies can be applied to maximise BT fusion rates and contribute to the success of future DT experiments at JET and ITER as illustrated in this study.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1971,

title = {ICRH options for JET-ILW DTE2 operation},

author = {E. Lerche and D. Van Eester and P Jacquet and F Casson and Y Baranov and P. Dumortier and D Gallart and J Graves and P Huynh and T Johnson and Y. O. Kazakov and V Kiptily and K Kirov and M Machielsen and M Mantsinen and I Monakhov and J. Ongena and JET Contributors},

year  = {2020},

date = {2020-09-01},

journal = {AIP Conference proceedings},

volume = {2254},

number = {1},

pages = {030007},

abstract = {Ion cyclotron resonance heating (ICRH) plays an important role in high performance JET-ILW plasma discharges, both for keeping the heavy impurities away from the plasma centre as for increasing the core ion temperature to boost fusion performance. While the former is needed in all high-performance discharges for steady state operation, the latter will be particularly important in the next-coming JET Deuterium-Tritium campaign (DTE2). Currently, the workhorse for impurity control in high power D plasmas is fundamental H minority ICRH (with simultaneous ω=2ωc harmonic D heating), which leads to localized core electron heating that induces turbulence (flatter density profiles) as well as peaked electron temperatures. For fusion power enhancement, dominant bulk ion heating and RF acceleration of the NBI ions to appropriate energies would be preferable and theoretical predictions suggest that ion heating is also effective for core impurity screening. In this paper, we discuss the basic modeling results of different ICRF scenarios available for the DTE2 campaign in JET-ILW, highlighting their main properties in terms of the RF absorption of the various species, their slowing-down properties and their impact on high-Z impurity transport. Correctly modeling the wave absorption, slowing-down and collisional energy redistribution of the simultaneously RF-heated species in a DT plasma mix with important neutral-beam injection (NBI) is numerically challenging and is outside the scope of this paper. The simplified calculations presented here are rather intended to give the reader an overview of the ICRH options for JET-DTE2 with references to the state-of-the-art ICRH modeling given throughout the paper.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1985,

title = {Conceptual study of an ICRH traveling wave antenna (TWA) for T-15MD at 60 MHz},

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

year  = {2020},

date = {2020-09-01},

journal = {AIP Conference proceedings},

volume = {2254},

number = {1},

pages = {070007},

abstract = {This paper proposes a Traveling Wave Antenna for ICRH heating of T-15MD located below the equatorial plane of the tokamak for operation at 60MHz. Resonant ring feeding allows the recirculation of the RF power that is not radiated to the plasma and the termination of the TWA section in 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-15MD also represents a test bed for DEMO.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1982,

title = {Effect of poloidal magnetic field and cross-coupling on a set of traveling wave antenna sections for the ICRH of fusion reactor plasmas},

author = {A. Messiaen and R. Ragona and R. Koch and V. Maquet and J. Ongena},

year  = {2020},

date = {2020-09-01},

journal = {AIP Conference proceedings},

volume = {2254},

number = {1},

pages = {060005},

abstract = {A set of Traveling Wave antenna (TWA) sections has been proposed for the ICRF heating of the reactor in view to decrease the antenna power density. The reduction of the antenna voltage and associate electric field and current is compensated by the number of radiating straps. An upgraded version of the fast semi-analytical code ANTITER-II is used to model a set of TWA sections of any arbitrary number of radiating straps facing a low coupling plasma profile with their feeding system. Now it incorporates the effect of the non-alignment of the antenna to the total steady magnetic field (toroidal + poloidal) in front of it. The model incorporates the feeding of each section by a resonant ring circuit that recirculates its output power. The cases of straps grounded at one of their ends (L grounding) or in their center (T grounding) are also compared. The model is applied to the proposed TWA section layout for the ICRF heating of DEMO. It is shown that the antenna tilting affects mostly the poloidal radiating spectrum seen by the plasma. This effect increases with the absolute value of the k// selected by the antenna system. The coupling reduction and the effect on the strap current and voltage distribution due to the tilting is compared with the ones resulting from the mutual coupling between the sections. The effects of the tilting for the expected qedge value of the reactor and of mutual coupling between toroidally spaced sections remain weak. The effect of coupling between poloidally superposed sections can become large.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1984,

title = {The ICRH system for the stellarator Wendelstein 7-X},

author = {J. Ongena and A. Messiaen and Y. O. Kazakov and B Schweer and I. Stepanov and M. Vervier and K. Crombé and M. Van Schoor and V Borsuk and Casta D n and A Kraemer-Flecken and K P Hollfeld and G Offermanns and D A Hartmann and J P Kallmeyer and R C Wolf},

year  = {2020},

date = {2020-09-01},

journal = {AIP Conference proceedings},

volume = {2254},

number = {1},

pages = {070003},

abstract = {An important test for W7-X is to demonstrate confinement of fast trapped ions at volume averaged beta values up to 5%, corresponding to plasma densities above 1020 m-3. Energetic ions in W7-X with energies 50 < E < 100 keV mimic alphas in a reactor. To generate such a population is a challenging task in high-density plasmas but this can be efficiently realized with the H- (3He)-D three-ion heating ICRH scenario, foreseen for f ~ 25 MHz in W7-X. An ICRH system is prepared for W7-X, expected to deposit RF powers up to ~1.5 MW (depending on the coupling) at frequencies between 25-38 MHz in pulses up to 10s. A two-strap ICRH antenna for W7-X is under construction. Each strap of the antenna is on one side connected to a tuning capacitor and grounded to the antenna box at the other end. A prematching has been implemented by connecting the RF transmission lines at an intermediate position on each strap. The main dimensions of straps and antenna box have been optimized to maximise the power delivered to the plasma, using the reference plasma density profile in front of the antenna, provided by the W7-X team. A dedicated test stand is under construction to check the main functional tests of the full ICRH antenna system.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1988,

title = {Progress on the design of a DEMO high power ICRH travelling wave antenna mock-up to be tested on WEST},

author = {R. Ragona and T Batal and J Hillairet and A. Messiaen and M Firdaouss and J -M Bernard and J. Ongena},

year  = {2020},

date = {2020-09-01},

journal = {AIP Conference proceedings},

volume = {2254},

number = {1},

pages = {070014},

abstract = {WEST represents the ideal device to test a reactor relevant TWA due to its long pulse capability and full metal wall configuration. Moreover, the already installed ICRF high power launchers will allow a direct comparison between a classical in-port antenna and the TWA. This paper reports the progress in the design of an actively cooled high power mock-up of the WEST TWA antenna that will be tested in the TITAN facility. The main objective of the test is to assess the voltage stand-off of the antenna at a power level relevant for future operation. In order to be installed and operated in WEST, the antenna design has to comply with the specific machine requirements, in particular active cooling, magnetic configuration and interface with existing auxiliary heating systems. Here several aspects are taken into account: toroidal magnetic field ripple, field line inter-connection and thermal loads on the antenna. An initial assessment of mechanical compatibility in case of VDE is performed. In conclusion, the next steps and implications of the project are outlined.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1975,

title = {Measurements of the scattering matrix of the W7-X prototype ICRH antenna and capacitor units},

author = {I. Stepanov and V Borsuk and K. Crombé and Casta D n and G Offermanns and J. Ongena and B Schweer and M. Vervier},

year  = {2020},

date = {2020-09-01},

journal = {AIP Conference proceedings},

volume = {2254},

number = {1},

pages = {040003},

abstract = {Low-power measurements of the W7-X prototype ICRH antenna and variable capacitor units have been performed at FZJ Jülich. The antenna scattering matrices, with and without the carbon limiter tiles, have been de-embedded from network analyzer measurements using custom-built RF adapters. The results have been compared to the matrices calculated with CST Microwave Studio 2017 using a model based on the original CAD files. A very good agreement is seen, since a) the difference in magnitude is less than 0.02 in the whole frequency range, and ~ 0.015 or less in the range of interest (between 20 and 40 MHz) and b) the difference in phase is less than 5◦ in the whole frequency range, and ~ 2◦ or less between 20 and 40 MHz. 

The S-parameters of the tuning capacitors have also been measured, to determine the relationship between the internal DC capacitance CDC of each unit, and the actual ''equivalent'' capacitance Ceq seen by the antenna at the ports. It is seen that the latter, 36-475 pF, is substantially different from the nominal DC range, which is 15-200 pF. Nonetheless this is not expected to pose a problem for antenna operation. 

The S-parameters of other key components of the ICRF system, such as the matching unit and line sections containing directional couplers, were also measured and, where applicable, compared to models or used to extract calibration data.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1957,

title = {Wall conditioning in fusion devices with superconducting coils},

author = {T. Wauters and D Borodin and R Brakel and S Brezinsek and K J Brunner and J Buermans and S Coda and A Dinklage and D Douai and O Ford and G Fuchert and A. Goriaev and H Grote and A Hakola and E Joffrin and J Knauer and T Loarer and H Laqua and A. I. Lyssoivan and V Moiseenko and D Moseev and J. Ongena and K Rahbarnia and D Ricci and V Rohde and S Romanelli and S Sereda and T Stange and Tabar F L é and Lilla Van ó and O Volzke and E Wang and and and and},

url = {https://doi.org/10.1088%2F1361-6587%2Fab5ad0},

doi = {10.1088/1361-6587/ab5ad0},

year  = {2020},

date = {2020-03-01},

journal = {Plasma Physics and Controlled Fusion},

volume = {62},

number = {3},

pages = {034002},

publisher = {IOP Publishing},

abstract = {Wall conditioning is essential in tokamak and stellarator research to achieve plasma performance and reproducibility. This paper presents an overview of recent conditioning results, both from experiments in present devices and modelling, in view of devices with superconducting coils, with focus on W7-X, JT-60SA and ITER. In these devices, the coils stay energised throughout an experimental day or week which demands for new conditioning techniques that work in presence of the nominal field, in addition to the proven conditioning methods such as baking, glow discharge conditioning (GDC) and low-Z wall coating through GDC-plasma, which do not work under such condition. The discussed techniques are RF conditioning without plasma current, both in the ion cyclotron and electron cyclotron range of frequencies, and diverted conditioning plasmas with nested magnetic flux surfaces. Similarities and differences between tokamaks and stellarators are highlighted. Finally a conditional tritium recovery strategy for ITER is proposed based on Ion Cyclotron Wall Conditioning and L-mode plasma results from JET, equipped with an ITER-like wall (beryllium main chamber wall and tungsten divertor).},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{1953,

title = {A travelling wave array system as solution for the ion cyclotron resonance frequencies heating of DEMO},

author = {R. Ragona and A. Messiaen and J. Ongena and D. Van Eester and M. Van Schoor and J -M Bernard and J Hillairet and J. -M. Noterdaeme},

url = {https://doi.org/10.1088%2F1741-4326%2Fab504a},

doi = {10.1088/1741-4326/ab504a},

year  = {2020},

date = {2020-01-01},

journal = {Nuclear Fusion},

volume = {60},

number = {1},

pages = {016027},

publisher = {IOP Publishing},

abstract = {Travelling wave array (TWA) antennas distributed along the periphery of the tokamak are presently considered as an ion cyclotron resonance frequencies (ICRF) heating solution for the DEMO reactor. Compared to the conventional ICRF antenna systems currently in use or designed for future machines like ITER, the TWA consists of antenna sections integrated in the breeding blanket scattered around the machine, each one fed through a variable coupler in a resonant ring configuration. Previous modelling of an antenna system for DEMO with 16 quadruple TWA sections of eight straps shows that a power capability exceeding 50 MW can be obtained in the frequency band of interest using the reference low coupling plasma profile of ITER. The described system optimizes the coupling to the plasma by providing a large number of radiating elements, which results in enhanced antenna directivity, hereby decreasing the antenna power density. This results in a maximum strap voltage amplitude of only 15 kV and maximum inter-strap voltage amplitude of 18 kV. The generators remain matched for all loading conditions: the system is totally load resilient. Following the recommendation of the work package heating and current drive Review Panel, a TWA ion cyclotron resonant heating (ICRH) system consisting of fewer sections concentrated in front of the equatorial ports is analysed in this paper and compared to the previous design. Reducing the number of sections increases the power density and its associated voltages. To couple 50 MW on the ITER density profile, voltages up to 30 kV are now required. Some aspects like the coupling between sections and its repercussion on the feeding network are briefly discussed. To assess the feasibility of the TWA fed by a resonant ring as an ICRH system for a DEMO reactor, a test on an existing medium size tokamak is under study.},

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. Durodié and U Fischer and T Franke and E Smigelskis and J. Ongena and M Q Tran and D. Van Eester and M. Van 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{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 Y. O. Kazakov and D. Van 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{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. Durodié and J Hillairet and J. Ongena and D. Van Eester and M. Van 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{1876,

title = {Fusion: A True Challenge For An Enormous Reward},

author = {J. Ongena},

year  = {2018},

date = {2018-10-01},

booktitle = {EPJ Web of Conferences},

volume = {189},

pages = {00015},

abstract = {Nuclear physics shows that energy can be released from both fission of heavy nuclei and fusion of light nuclei. Steady progress shows that fusion — an important additional option for energy production in the future — promises to be a clean and safe solution for mankind's long-term energy needs with minimal environmental impact. A source of energy which would be inexhaustible, inherently safe and environmentally friendly, is this not a marvellous prospect? Nuclear fusion, a possible candidate for this role, has been the energy source of our Sun and the stars in the universe for billions of years. This process requires temperatures of tens of millions of degrees, so extremely high and foreign to our daily experience that it seems out of reach. Nevertheless, these extremely high temperatures are routinely realised in several laboratories all over the world, and since the early 1990s, tens of MW fusion power have been released from fusion reactions. We are witnessing the birth of a new technology destined to meet the gigantic future energy needs of mankind with minimal impact on the environment.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}