Progress Towards RF Steady State Systems For Fusion Devices

Progress Towards RF Steady State Systems For Fusion Devices A.Argouarch, B.Beaumont, G.Berger-By, P.Bibet, F.Bouquey, S.Brémond, C.Darbos, L.Delpech, , G.T.Hoang, F.Kazarian, M.Lennholm, R.Magne, L.Millon, P.Mollard, M.Prou, K.Vulliez and Tore Supra Team Association Euratom-CEA, Centre de Cadarache, 13108 SAINT PAUL LEZ DURANCE, France Presented by B.Beaumont

Introduction • RF systems are widely used on magnetically confined fusion experiments. • Developments during many years have produced RF systems which have supported the progress of plasma performance and opened up new areas of investigation. • For the next step devices, long pulse operation is essential and it is a new challenge for the integration of the RF systems. They have to be highly reliable, with built-in strategies to recover from trips and breakdowns.

A selection of recent Tore Supra experimental results System integration RF techniques developments and R&D LHCD power upgrade, ITER-like ICRH antenna Antenna studies Example of RF design for ITER : in-port matching ICRH antenna Conclusion Outline

The progress in term of RF assisted discharges can be expressed in the domain Energy/Duration. Recent experimental work is focused on : Combined operation of RF systems : The high power & performance quest Interaction studies : try to live together Identify and study specific issues : Heat : Private heat flux, local RF losses, heat flux from other antennas, limiter connections, Protons impacts… + for ITER : shadowing of blanket modules, a's contributions…, NB shine through… Coupling : Plasma/antenna distance, location of fuelling, pellet injector, relative antenna radial positions,… Local enhanced RF fields .. Even far from antennas 2 MW After the 20th IAEA 8 MW 2001- the 20th IAEA Tore Supra Exp. Results

ICRH+LHCD Multi-MW MW Ptot PICRH • Simultaneous use of multi-frequencies RF heating/CD systems(ICRH, LHCD, ECH) • Power level in excess of 10 MW, mainly ICRH,during pulses lasting up to several tens of resistive times • 9MW of ICRH coupled to plasma sustained by LHCD is safe condition required for continuous operation • 4MW/one minute ICRH pulse in LHCD (3MW) plasmas Line density (1019m-2) PLH Ip (MA) Stored energy (MJ) keV Te(0) Ti, @r/a=0.2 shot 33612, Combination of ICRH (57 MHz - 8.5 MW) and LHCD (3.7 GHz -1.4 MW). (R=2.4m, a=0.72m, Ip= 0.9MA, BT=3.7T)

Safety Control loops IR image of IC antenna, at t = 63.7s, in a combined ICRH (4MW)/LHCD (3MW) discharge • Various hot spots on the ICRH antennae are identified • 1: sensitive to the total power • 2: mixed total IC power and private IC power • 3: sensitive to LH power only • 4: predominantly private IC power •  input for RT Controls & Algorithms • Reality is far from the classical ln & lq theory. Large peaking of heat fluxes: • governing the temperature and the coupled power • inducing shear stress in the components -> CFC !

System integration Successful operation of RF systems depends on integration in Tokamak system : Arc protection / RF diagnostics / matching reliability discrimination (cross-talk) Response time Power controls Current balance control Array phase control Power Ramp-up balance RT control loops (internal and external to RF syst.) Recovery after trip : strategy (reduced power, counters, …) on/off solid state switch Degraded mode of operation part of antenna missing => Stresses=> power limit maintenance schemes Long process : Trial and errors Water leaks… Breakdowns… Improvements Time…

RF developments • Tore Supra is exploring long duration plasmas • Plasma size (a~0.7m) : need for non inductive CD • Large operational domain = large power • Large power = appropriate PFC and controls • Highest efficiency for volume CD is LHCD • On going upgrade of LHCD system to 8MW: • New LHCD launcher • New high power CW klystron • ITER support : • New TS LHCD launcher is ITER-like Design • ITER-like ICRH antenna

CIMES LHCD upgrade 500 kW CW Mock up • High power CW klystron development with TED: • Target = 700 kWCW on VSWR=1.4 any phase (and 750 kW on matched load) • 5 years effort nearing completion: • Large collector (~1600kW beam power) • 2 windows output circuit +recomb. circuit • Diode type klystron • Prototype has delivered 700kW on load during several hours • problem on geometry assembly faulty brazing suspected (under investigation) • Lessons from this R&D program: • Close collaboration with supplier essential • Intermediate tests to validate sub components and steps mandatory. Specific field => Dedicated test beds

LHCD upgrade • Passive/Active Multijunction Launcher: • Large cooling efficiency • Target n//= 1.72 +/- 0.28 @ +/- 90° • CW power ~3MW at 25 MW/m² • 200 waveguides in total, 16 RF inputs (windows) • 3 years fabrication inc. Specific R&D • Lessons from this R&D program • Example of plug antenna (like all TS antennas) • Integration of many different components & contracts • Firms are very skilled…until they have to do the real thing • stop points on brazing, material procurement,… • Specific R&D performed on explosion bonding • Tests and samples essential (as usual) Stainless steel 1.82 mm Copper

X I c1 1 X c3 I I 3 a I R b s V a k R t s V b X s X s k p k p R s R s k X t s I X 2 s X I c2 4 X c4 jXc1 Rin+jXin I1 R0 I2 Ifeed Rin+jXin jXc2 ITER like ICRH Antenna Conventional Conjugate-T concept = ITER Relevance : ELM Resilient Antenna • First experiments in 2003 • Faraday shield modified to reduce coupling • Experiments in end 2006/2007 with improved current control loops

RF loads 3 dB coupler TE10-TE30 Mode Converter PAM Antenna Studies Studies of RF components : PAM launcher for JET PAM launcher for ITER East ICRF Antenna ITER ICRF antenna … JET PAM Launcher features 300 waveguides showing the mechanical structure which holds the wave guide array from the back flange • ITER LHCD launcher issues : • Efficient water cooling and neutron shielding • Antenna tip: erosion; low Z materials: brazing? • Technology options for antenna realisation: • technology based on uni-axial iso-static pressure • machining and electron beam welding • Materials: Glidcop or CuCrZr, Be facing plasma The ITER array is based on the PAM concept for its cooling capabilities. More than 1000 waveguides facing the plasma.

ITER- ICRH antenna proposal Rear part Front part Interface (vacuum tight) between front and rear parts Modular construction Shielding in front part Remote RF windows Every component is water cooled • ICRH antenna is constituted of 2 parts • Front part which is under the machine vacuum and is supported by the front part of the antenna port plug • Rear part which is under a private vacuum isolated from the machine vacuum and is supported by the rear part of the antenna port plug

ITER- ICRH antenna proposal ICRH antenna constituted of 6 modules all identical except the front face (Faraday screen + current straps) that has to shape the blanket modules and plasma This design has been made with the constraint to be able to assemble/disassemble each of the components that constitute the antenna: Commissioning Tests Repair are possible on sub assemblies Example of mechanical study : disruption

Internal components : Front part : static structure, vacuum tight Rear part : adjustable impedance, private vacuum Compact in port design, integrated matching ITER- ICRH antenna proposal RF windows RF input Outer conductor Central conductor Driving mechanisms, cooling Central conductor detailed

Conclusion • Significant progress of injected RF power has been obtained • in steady state operation in Tore Supra • On going studies on RF systems, incl. ITER, take into account integration aspects, key element for success: • Magnetic field lines connections (shadows, fuelling system, connection length…) • Interaction with other antennas, beams,… • Protections, RT control loops  Safe operation (Machine&RF) • Degraded modes of operation • Recovery from trips • Commissioning and conditioning • Readiness tests • BUT it could be a long process • Uncertainties on design parameters call for margins

It is not guaranteed that one has a fully operational system even though all bits and pieces described in the WBS are available: Epilogue Figueras, Spain, near Dali Museum

Progress Towards RF Steady State Systems For Fusion Devices