Aiello, G.

Avramidis, K.A.

Bruschi, A.

Franke, T.

Gantenbein, G.

Garavaglia, S.

Granucci, G.

Grossetti, G.

Jelonnek, J.

Litvak, A.G.

Moro, A.

Poli, E.

Rispoli, N.

Strauss, D.

Thumm, M.

Tigelis, I.

Tran, M.Q.

Tsironis, C.

Avramidis, K. A.

Tran, M. Q.

Litvak, A. G.

KITopen

  The EC-system of EU DEMO: concepts for a reactor heating system G. Granucci1, G. Aiello2b, K.A. Avramidis2a, A. Bruschi1, G. Gantenbein2a,  S. Garavaglia1, G. Grossetti2b, J. Jelonnek2a, A. Moro1, E. Poli5, N. Rispoli1, D. Strauss2b, M. Thumm2a, I. Tigelis4, C. Tsironis4, T. Franke5,6 and M.Q. Tran3 1 Institute of Plasma Physics “P.Caldirola”, National Research Council of Italy, Milan, Italy 2a IHM, 2b IAM-AWP, Karlsruhe Institute of Technology (KIT), D-76131 Karlsruhe, Germany 3 Swiss Plasma Center, EPFL, CH-1015 Lausanne, Switzerland 4 NCSRD/National and Kapodistrian University of Athens, Faculty of Physics, & National Technical University of Athens,  School of Electrical and Computer Engineering, Athens, (Greece) 5 Max-Planck-Institut für Plasmaphysik, Boltzmannstr. 2, D-85748 Garching, Germany 6 EUROfusion Consortium, Boltzmannstr. 2, D-85748 Garching, Germany In the frame of the project for a European DEMOn-stration Fusion Power Plant (FPP), the design of the aux-iliary heating systems is one of the keys to heat and con-trol the burning plasma (i.e. a plasma in reactor producing electricity to the grid from fusion reactions). The heating mix considered in EU DEMO bases on Electron Cyclo-tron Resonance Heating and Current Drive (ECRH&CD), Neutral Beam Injection (NBI) and Ion Cyclotron Reson-ance Heating (ICRH). In this first phase of the design process (called Pre-Conceptual phase) each system is un-der study with 50 MW as a reference power to the plasma [1]. The main tasks assigned to the EC system are reported in the Table 1, assuming the full use of the 50 MW: Table 1. Main Physical Requirements for EC system EC Task Power [MW] Localiza-tion [] Mode Assisted Break-down 6–10 < 0.3 Heating Ramp up and L-H transition 50 < 0.3 Heating/CD Main heating 50 < 0.3 Heating/CD Sawtooth control 2–10 < 0.3 CD NTM control (q = 2; q = 3/2) 10–15 0.85; 0.75 CD Ramp down 40 0.3–0.5 Heating  These heating tasks require different radial localiza-tion and combination of heating and non-inductive cur-rent drive (CD). A possible solution is a gyrotron capable to operate at two (or more) different frequencies, in order to cover all the physical requirements in the easiest way. Moreover in designing an EC system for DEMO, it is necessary to consider the peculiarities of a fusion power plant reactor, which are significantly different from those of any existing tokamak experiments. The power relia-bility and availability are major targets for the system, because in case of fault of EC system the pulse must be terminated, with a consequent unacceptable economic impact. Therefore, reliability of any each sub-system is taken into consideration when choosing the architecture of the EC system. A second objective is to minimize the recirculating power to guarantee the higher possible ener-gy gain of the reactor with the use of a highly efficient gyrotrons [2] (above 60 %) and low losses (10%) trans-mission lines. The present design considers 2 MW gyrotron units, capable to operate at 170 GHz for heating and 204 GHz for current drive. This last corresponds to a moderate upshift of 1.2 for the CD function while the two frequen-cies (170/204 GHz) have been selected to satisfy the  /2-resonances of the diamond-disc window. These fre-quencies have been selected for the pulsed EU DEMO1 2015 baseline [3] and used as reference to calculate CD efficiency and localization. At the end of the EU DEMO Conceptual Design phase, the appropriate frequencies will be selected. Within EUROfusion research is ongoing to consider gyrotron operating frequencies of up to 240 GHz. The transmission line (TL) is based on a quasi-optical approach, inspired to the Multi-beam (MB)TL of W7-X stellarator experiment [4], enclosing the mirrors in an evacuated pipe to make it compatible with the nuclear environment. The concept is based on a mirror confocal layout with single units composed by two mirrors form-ing a dog-leg and replicated few times for transmitting along straight paths (150 m as reference length).  Table 2. Transmission losses estimation of DEMO EQO  for a length of 150 m Distance between mirrors = 8 m 170 GHz 204 GHz Ohmic Losses (H-plane - 45°) 3.2% 3.5% Truncation (40 mirrors) 1.5% 1.4% Mode conversion 1.5% 1.4% Total Losses 6.2% 6.3%  One pumping system is located in each mirror unit. As reference it is considered to transmit 8 beams with one MBTL, with an overall losses estimated to be <10%  (see Table 2). This choice would allow a simpler and compact solution capable to reduce the complexity of the system and to save space.  The design of the launching system is strongly li-mited by severe constrains imposed by the environment of a nuclear reactor as the vicinity of a hot burning plas-ma and under a heavy neutron bombardment. In particu-lar, no movable parts are allowed in proximity of a burn-ing plasma, and shielding and suitable structural compo-nent need to be included in the design [5]. A remote steering antenna, with a dogleg in the vessel port, is under study as one of the options for a launcher concept. The proper choice of steering plane and the inclination of the corrugated square waveguide are the free parameters for the required EC power localization and CD efficiency, to be combined with the engineering requirements. In Fig. 1 the result of a beam tracing performed with TORBEAM [6] is shown. Using both the frequencies the possibility to cover the assigned tasks of Table 1 is demonstrated,      DOI: 10.1051/, 03003 (2017) 714901EPJ Web of Conferences epjconf/2014910th International  Workshop  2017  "Strong  Microwaves  and  Terahertz  Waves:  Sources  and  Applications"3003© The Authors,  published  by EDP Sciences.  This  is  an  open  access  article  distributed  under  the  terms  of  the Creative Commons Attribution License 4.0 (http://creativecommons.org/licenses/by/4.0/). while the 204 GHz exhibits a higher central CD efficien-cy (for ST control), the 170 GHz can be efficiently used for NTM control and for central or off-axis heating.Fig. 1. With full lines (dashed lines) calculated CD profiles for 170 GHz (204 GHz) launched from equatorial plane with an-tenna toroidally inclined of of 17° (22°). For the different depo-sitions a steering of ±12°is consideredA comparison of remote steering antennas and al-ternative simpler solutions, truncated waveguides used as launchers with step tunable gyrotron, is ongoing, on the basis of the physical requirements of Table 1. This study can be complemented considering the use of step tunable gyrotrons used in the truncated waveguide launcher con-cept, in order to have enough localization control for NTM stabilization. The other tasks can be satisfied in-creasing the number of launching points with the aid of fast microwave switches. The reliability of the auxiliary power to be deli-vered, and, more in general, the RAMI of the whole EC system, is another characterizing point of the conceptual design. The maximization of reliability is obtained with appropriate system architecture, characterized by a mod-ular design. An ideal overall reliability of 100 % to deliv-er 50 MW to the DEMO plasma using an EC system is possible to reach by considering a proper redundancy in the different sub units. Therefore, the system concept is based on a strong modularity which considers a cluster of 8 sources (gyrotrons) fed by one high voltage cathode power supply and individual anode power supply. The  8 beams are transmitted to the launchers with a single MBTL. The launcher of each cluster is individual and in the same port plug in structure. The best combination [7] is composed by 5 clusters of 8 units, with 7 gyrotrons operating in each cluster (and one in standby) and one full cluster in standby. Therefore only 28 lines will be on simultaneously with 12 lines off ready to substitute the unit (gyrotron or line / launcher) eventually in fault.  Acknowledgement Parts of this work are carried out within the frame-work of the EUROfusion Consortium and have received funding from the Euratom research and training pro-gramme 2014-2018 under grant agreement No. 633053. The views and opinions expressed herein do not necessar-ily reflect those of the European Commission. References 1. M. Q. Tran et al. D. EU DEMO Heating and Current Drive: Physics and Technology // 26th FEC – Kyoto (2016) FIP/7-7. 2. J.Jelonek et al European Research Activities Towards a Future DEMO Gyrotron // SMP, 2017, Nhizhny Novgorod. 3. R. Wenninger et al. The physics and technology basis entering European system code studies for DEMO // Nucl. Fu-sion 57, 016011 (2017).4. V. Erckmann et al. Electron cyclotron heating for W7-X:physics and technology // Fusion Sci. Technol. 52, 291-312 (2006).5. G. Grossetti et al. DEMO Port Plug design and integra-tion studies // 26th FEC – Kyoto (2016) FIP/7-4.6. E. Poli et al. TORBEAM, a beam tracing code for elec-tron-cyclotron waves in tokamak plasmas // Comput. Phys. Comm. 136, 90 (2001).7. S. Garavaglia et al., Preliminary conceptual design of DEMO EC system // AIP Conference Proceedings 1689,090009 (2015).      DOI: 10.1051/, 03003 (2017) 714901EPJ Web of Conferences epjconf/2014910th International  Workshop  2017  "Strong  Microwaves  and  Terahertz  Waves:  Sources  and  Applications"30032

The EC-system of EU DEMO: concepts for a reactor heating system

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The EC-system of EU DEMO: concepts for a reactor heating system

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