High Field Side Lower Hybrid Current Drive Launcher Design for DIII-D

Transcription

1 High Field Side Lower Hybrid Current Drive Launcher Design for DIII-D by G.M. Wallace (MIT PSFC) Presented at the American Physical Society Division of Plasma Physics Annual Meeting October 23, 2017 On behalf of: R. Leccacorvi, J. Doody, R. Vieira, S. Shiraiwa, S.J. Wukitch (MIT PSFC), C. Holcomb (LLNL), R.I. Pinsker (GA) 0 G.M. Wallace/APS-DPP/October 23, 2017

2 Efficient, reliable, off-axis current drive is desired on future reactors; HFS LHCD has potential to fill this requirement Many steady-state reactor studies require off-axis noninductive current drive to supplement bootstrap current Efficiency is critical for off-axis current drive in a reactor No currently available actuators meet all requirements Off-axis High efficiency Survivability/lifetime HFS LHCD has the potential to fulfil this role See poster NP Adapted from ARIES-ACT1 Kessel et al., FST 67, Najmabadi et al., FED 80,

3 Optimum launch location just below HFS mid-plane DIII-D shot B t = T I p = 0.9 MA n e = 4.4x10 19 m -3 n = 2.8 ± 0.2 Launch location just below mid-plane on HFS wall Strong single-pass damping at r/a ~ High current drive efficiency 210 ka/mw n*i*r/p = 0.14x10 20 A/W*m 2 2

4 Real estate is limited on HFS wall; antenna must be compact in radial dimension GEOMETRY OF THE DIII-D NEUTRAL BEAM INJECTION SYSTEM (coordinates shown in inches) 330R (-111.5, 304.0) R L 330L (-78.9, 310.1) 30R (207.5, 248.6) R 330 beamline 30 beamline L 30L (229.1, 223.4) 0 beam crossover point: (-55.3, 92.1) 270 beam crossover point: (-55.3, -92.1) beam crossover point: (52.1, 94.0) Origin: (0.0, 0.0) inches Launcher here beam crossover point: (55.3, -92.1) beamline 210L (-111.5, ) 4.33 L R R (-78.9, ) 150L (78.9, ) L R 150 beamline 150R (111.5, ) Feed waveguide 3

5 CPI VKC-7849A klystrons provide 2 MW source power f0 = 4.6 GHz PRF = 0.25 MW/klystron Gain = 55 db Vb = 46.5 kv Ib = 13 A Efficiency = 41% 8 klystrons to be located adjacent to DIII-D cell Thales/Ampegon HVPS to be installed in high voltage yard outside DIII-D building Klystron (CPI) Circulator (AFT) RF Out 4

6 Antenna design based on toroidal multijunction + poloidal slotted waveguide antenna Multijunction concept proven on many tokamaks (Tore Supra, JET, FTU, EAST) Self-matching characteristics reduce reflected power towards transmitter Phase Conventionally oriented radially in LFS port Shifter Slotted waveguide antenna Similar to successful LH2 antenna on C-Mod Tested on COMPASS Combine two concepts in series Low reflection coef. Compact radial build Toroidal & poloidal split Conventional Multijunction (top view) Slotted Waveguide (poloidal view) P L A S M A Reproduced from Helou, et al, FED,

7 Maximum achievable power density of 42 MW/m 2 consistent with operating limits on previous experiments 2 MW source power è 1.5 MW to antenna Radiating slots 5 mm (+1 mm septum) X 35 mm Passive waveguide between modules 5 rows X 4 columns X 8 modules = 160 slots m 2 total radiating area 42 MW/m 2 overall power density Power Flux (MW/m 2 ) ASDEX PLT Versator PBX-M FT C-Mod (LH2) C-Mod (LH1) Alcator A TS JET TRIAM (2.45 GHz) TRIAM (8.2 GHz) Alcator C f 2 b (GHz 2 cm) f = wave frequency b = narrow waveguide dimension 6

8 Slotted waveguide dimensions optimized for even power splitting between rows of antenna for nominal plasma load Radiating aperture 3.5 cm tall, cm C-to-C, 3.1 cm stub at top of slotted waveguide. 2D geometry for rapid optimization Plasma E z [V/m] Waveguide E z [V/m] n 0 = 1x10 18 m -3 dn/dx = 1x10 20 m cm cm (WR187) 7

9 Slotted waveguide dimensions optimized for even power splitting between rows of antenna for nominal plasma load Radiating aperture 3.5 cm tall, cm C-to-C, 3.1 cm stub at top of slotted waveguide. 2D geometry for rapid optimization Plasma E [V/m] Waveguide E [V/m] n 0 = 1x10 18 m -3 dn/dx = 1x10 20 m cm cm (WR187) 8

10 3D simulation confirms agrees well with 2D simulation Toroidal waveguide dimension = 5 mm Septum thickness = 1 mm n = 2.7 for 90 phasing Computed field pattern agrees with 2D simulations E for 1 W [V/m] 9 n 0 = 1x10 18 m -3 dn/dx = 1x10 20 m -4

11 Four-way 90 multijunction divides power toroidally Multijunction provides toroidal power splitting and 90 phase shift between columns Two-stage ideal multijunction reduces power reflection coefficient from Γ 2 on unmatched side to ~Γ 8 on matched side Γ 2 = P refl /P fwd at radiating aperture Outputs of multijunction feed into slotted waveguide array E for 1 W [V/m] 10 n 0 = 1x10 18 m -3 dn/dx = 1x10 20 m -4

12 Self-matching properties of multijunction result in very low reflection coefficients across range of densities n 0 = density at antenna mouth dn/dx = 1x10 20 m -4 S 11 at input of slotted waveguide ~-5 db S 11 at 1 st stage of multijunction ~-10 db S 11 at 2 nd stage of multijunction ~-20 db Input Power Reflection Coefficient 11 n 0 [m-3]

13 ALOHA code also predicts low reflection coefficients for multi-module antenna 2.5 Scenario Seven plasma scenarios used Four modules (16 columns) fed with 0 phasing (peak n = 2.7) 0.4 Phasing = 0 Γ 2 MJ mean Γ 2 MJ max Γ 2 active mean P(n ) [a.u.] Phasing = 0, Directivity = Row 1 Row 2 Row 3 Row 4 Row 5 Γ 2 active max Γ n 0.15 Scenario n 0 (x10 18 m -3 ) Scenario dn/dx (x10 20 m -4 )

14 Simulation of full 3D launcher structure possible using MFEM open-source finite element solver Software developed by S. Shiraiwa using MFEM package VI (4pm Thurs): From core to coax: extending core RF modelling to include SOL, Antenna, and PFC 21M degrees of freedom Solution in 17 min of wall clock 60 Cori Haswell supercomputer nodes at NERSC 120 MPI jobs, 960 threads 13

15 Transmission lines routed under divertor baffle plate and cryopump to HFS wall Broad wall of waveguide against vessel floor Broad wall of waveguide normal to vessel wall 14

16 Radial build of antenna set by waveguide twist Radial dimension of twist slightly larger than broad dimension of waveguide (i.e. hypotenuse) Increase R of HFS wall by ~1 Minimum axial length of twist ~9.5 cm 15

17 Carbon passive waveguides separate modules and provide local limiter surface to protect active waveguides TZM Active WG = gray C Passive WG = blue 16

18 Materials for launcher construction Exploring 3D printing of copper alloy (GRCo-84) for major multijunction and slotted waveguide components Surface finish of interior waveguide walls is main concern Inconel with a high conductivity plating (e.g. copper) as backup material for main components Molybdenum (TZM) for plasma facing grills Carbon for passive waveguides, protection tiles 17

19 Antenna mockup in preparation for installation during next available manned entry Mockup to be constructed of same materials as actual antenna Carbon mini limiters between modules TZM dummy waveguides Carbon spacers between rows flush with existing wall tiles No change in inner wall tiles needed for installation of mockup 18

20 Summary and next steps Preliminary RF design of high field side LHCD antenna for DIII-D complete Multi-junction (toroidal split and matching) in series with slotted waveguide (poloidal split) Antenna mockup to be installed in DIII-D during upcoming upto-air Klystrons, high voltage power supply, and controls/interlocks to be installed at DIII-D Installation of antenna during upcoming Long Torus Opening 19