Proposed High Voltage Power Supply for the ITER relevant Lower Hybrid Current Drive system P.K. Sharmaa, F. Kazarianb, P. Garibaldi, T. Gassmanb, J. F. Artaud, Y.S. Baec, J. Belod, G. Berger-By, J.M. Bernard, Ph. Cara, A. Cardinalie, C. Castaldoe, S. Ceccuzzie, R. Cesarioe, J. Decker, L. Delpech, A. Ekedahl, J.Garcia, M. Goniche, D. Guilhem, C.Hamlyn-Harrisb, J. Hillairet, G.T. Hoang, H. Jiaf, Q.Y. Huangf, F. Imbeaux, S.H. Kim, Y. Lausenaz, R. Maggiorag, R. Magne, L. Marfisi, S. Meschinoh, D. Milanesiog, F. Mirizzie, W. Namkungi, L. Pajewskih, L. Panaccionee, Y. Peysson, A. Saille, G. Schettinih, M. Schneider, O. Tudiscoe, G. Vecchig, S. R. Villarie, K. Vulliez, Y. Wuf, Q. Zengf CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France. aPermanent address: Institute for Plasma Research, Bhat, Gandhinagar, Gujarat, India. bITER Organization,, CS 90 046, 13067 Saint-Paul-Les-Durance,France. cNational Fusion Research Institute, Daejeon, Korea. dAssociaçao Euratom-IST, Centro de Fusao Nuclear, Lisboa, Portugal. eAssociazione Euratom-ENEA sulla Fusione, CR Frascati, Roma, Italy. fInstitute of Plasma Physics, CAS, Hefei, Anhui, China. gPolitecnico di Torino, Dipartimento di Elettronica, Torino, Italy. hRoma Tre University, Rome, Italy. iPohang Accelerator Laboratory, Pohang Univ. of Science and Technology, Pohang, Korea. Poster ID SOFT 2010 P1-16, Mon. 27th Sept., 2010. Introduction. In the framework of the EFDA task HCD-08-03-01, the ITER Lower Hybrid Current Drive (LHCD) system design has been reviewed [1,2]. The system aims to generate 24 MW of RF power at 5GHz., of which 20 MW would be coupled to the plasmas [1,2]. The present state of the art does not allow envisaging a unitary output of the klystrons exceeding 500 kW, so the project is based on 48 klystron units, leaving some margin when the transmission lines losses are taken into account. A High Voltage Power Supply (HVPS), required to operate the klystrons, is proposed. A single HVPS would be used to feed and operate four klystrons in parallel configuration. Based on the above considerations, it is proposed to design and develop twelve HVPS, based on pulse step modulator (PSM) technology, each rated for 90kV/90A. In this concept several independent power supplies (modular type) are stacked together and are connected in series through fast electronic switches, like insulated gate bipolar transistors (IGBT’s) [3,4]. This poster displays the typical electrical requirements and the conceptual design of the proposed HVPS for the ITER LHCD system. Main application Electrical requirements of HVPS Typical specification of the LHCD HVPS unit (a) for operating klystrons at rated power and * The 5 GHz. source (for LH H&CD system in Parameter Values (b) to condition the klystrons. ITER) yet to be fully developed. Voltage range Upto -90 kV * The HVPS rating estimated on existing klystrons Accuracy 1% of maxi. value. Functional requirements of HVPS efficiency (~38% min. for the highest reflection Ripple 1% of maxi. value. Max. current 90 A coefficient). Max. CW power 8.1 MW * fast recovery time, switch-off time, high efficiency * A 600 kW RF power (with some margins for the Fault energy < 10 J * minimal indoor/outdoor space requirements operation of the klystron) at 38% efficiency leads Response time of load * unconventional crow bar unit at the load end to avoid to 1.6 MW of beam energy that can be managed protection system < 10 sec complexities and minimize failure risk. with 80kV/20A HVPS. Re-switching time < 200 msec. * High availability target * To accommodate more margin, the rating for an Total no. of units 12 * Modular approach (1 HVPS for 4 klystrons) Capacity of one unit 8.1 MW HVPS is proposed at 90kV/90A to feed and Total capacity 97.2 MW * flexibility to operate operate four klystrons by using a single high (a) over wide range of voltages (25kV – 90kV), (b) over wide range of pulse length (~few msecs. to 3000 secs.) & voltage power supply system. Table-1: Typical specification of HVPS for ITER- (c) with train of pulses (modulation) with varying voltages/frequency LH system. Following ITER’s power distribution layout, the high voltage electrical network includes 400 kV AC transformers, each one having two secondaries: one secondary delivers 66 kV while the other delivers 22 kV. All RF H&CD systems, including LHCD will be connected to the 22 kV lines. The typical grid capacity is ~97.2 MVA (90kV/90A for four klystrons x 12 units). First Block: The feeder lines are Third Block: It refers to the stack of Conceptual design of HVPS ninety power modules connected in series, connected to the 22kV busbar. The feeders are protected by the vacuum to convert the ac supply voltage from circuit breaker (VCB) with over transformer system to regulated DC current relays, an earth fault relay, voltages. All the modular power supplies, an under voltage relay and an over each rated at 1.2kV/90A, are stacked voltage relay. Each VCB is rated for together and are connected in series 24kV/300A, with a breaking through fast electronic switches, like capability of ~3.8 kA (12.5 times the insulated gate bipolar transistors (IGBT). average current). Each of these power modules has its own dc rectification unit, protection unit, crowbar unit, control and protection unit. Second Block: It refers to the multi- secondary transformer. A cast resin Fourth Block: It accounts for control transformer is proposed with very low electronics, which provides regulation, harmonic content in the input current protection, control and interface among and in star-delta configuration. The all the power modules. The modulation and 22 kV input is fed to the primary of various settings of the HVPS are this transformer and ninety controlled through this stage. It connects secondary, each of 1 kV, provides ac all the modular power supplies through Klystrons operation in power to downstream parts with fibre optic cables ensuring fast control First Block Second Block Third Block Fourth Block Parallel configuration appropriate electrical insulation. and noise immunity. * Each modular power supply when activated by closing of the series IGBT switch, adds a voltage step to the total output voltage and the total output voltage, thus available, is governed by the number of power modules activated by closing of the series switches. * This scheme also guarantees the flexibility of using the HVPS even when a few power modules become faulty. The faulty power modules can be easily replaced later by stand-by modules kept in reserve because of its modular plug-in capability and the faulty power module may be repaired and kept ready, as stand by, for future replacement. * It is proposed to accommodate all the twelve HVPS in the Assembly Hall. High voltage cables would be used to connect the klystrons, placed in the LHCD source area in the same building. * The solid state devices available for both higher voltages and higher switching frequencies have several advantages to replace traditional system like extended life, higher efficiency, easy and reliable operation, etc. * Further series connection of ninety elementary power modules does not require direct series connection of semiconductor devices. Thus each module is designed for ~1.2 kVDC (~90A) and has its own DC PS. * Module components are low voltage devices, low cost and each step of the voltage is lower than the allowable peak-to-peak ripple and provides an additional degree of freedom in the dimensioning of output filter. * It also provides complete flexibility since the number of switched-on modules in quantized steps of voltage controls the output voltage. * The design also aims to enhance reliability, decrease costs, plug-in modularity, provide redundancy, components de-rating, components standardization and easy availability. However the above advantages come at the cost of relatively high complexity of multi-secondary transformer and cabling of multiple power modules. References: Conclusions:  G. T. Hoang, et. al., A Lower Hybrid Current Drive System for ITER, Nuclear Fusion, 49 * In the framework of an EFDA task, the design of HVPS for 24 MW ITER LHCD system is proposed. (075001), 2009. * Each HVPS would cater to four klystrons, operated in parallel configuration.  A. Bécoulet, et. al., Steady State Long Pulse Tokamak Operation Using LHCD, SOFT- * The HVPS employs PSM technology to operate several modular IGBT’s based power supplies. 2010, 27th Sept. – 1st Oct, 2010, Porto, Portugal, 2010. * In particular, the technology foreseen for the HVPS is similar to other H&CD systems in IO (in  G. Taddia, M. Pretelli, L. Rinaldi, V. Rossi, et. al., Main high voltage solid state gyrotron particular DNB HVPS, rated 100kV/75A) and most of the components are industrially available, power supply 60kV/80A, Proceedings of FEL, 2006, Pg-633-636, Bessy, Berlin, Germany. therefore detailed R&D may not be required.  I. S. Roth, J. A. Casey, M. P. J. Gaudreau, M. A. Kempkes, et. al., A solid state * As a consequence, the proto-type development time phase is ignored and delivery time estimated is opening switch and mod anode supply for the advanced light source klystrons, Proceedings of ~7yrs. EPAC, 2002, Pg-2484-2486, Paris, France. Acknowledements: This work, supported by the European Communities under the contract of Association between EURATOM and CEA, was carried out within the framework of the EFDA task HCD-08-03-01. The views and opinions expressed herein do not necessarily reflect those of the European Commission.