Development Status of KSTAR LHCD System

Development Status of KSTAR LHCD System September 24, 2004 Y. S. Bae,, M. H. Cho, W. Namkung Plasma Sheath Lab. Department of Physics, Pohang University of Science and Technology

LHCD system overview Objectives Required for the the steady-state operation of KSTAR. Non-inductive current drive Off-axis current-profile control, so that q profile control, Efficient bulk current drive at low plasma temperatures, Electron heating. RF source: Four TOSHIBA Klystrons (5-GHz, 500 kw CW) Transmission line system: Oversized circular waveguides between klystron and divider/phase shifter networks for low RF loss 3-dB dividers (standard WR187 waveguide size) Phase shifters DC breaks Etc Power dividing and phase shifting network Development Status of KSTAR ECH and LHCD System (September, 2004) 2

Conceptual schematic of the transmission system E-plane taper 3-dB splitter Phase shifter 3-dB divider Launcher Dummy-load Klystron Development Status of KSTAR ECH and LHCD System (September, 2004) 3

Power dividing and phase shifting network Directional coupler DC Break 3-db splitter Launcher Column 1 32 waveguides Low power phase shifter Dummy Load 1 3-dB Divider Column 2 4 waveguides Oscillator & driver Network 1 Klystron Waveguide antenna (Grill) Network 2 Network 3 Network 4 High power phase shifter Medium power phase shifter E-Taper Column 8 One klystron feeds RF power to 8 columns of the grill t = 0.15 cm h = 5.5 cm b = 0.55 cm Waveguide dimensions at grill Development Status of KSTAR ECH and LHCD System (September, 2004) 4

Power coupling at grill of the LHCD launcher Number of Waveguide : 32, Scale length, Ln = 1 cm φ = 60 o φ = 90 o φ = 120 o φ = 150 o Number of Waveguide = 32 Edge Density = 1.0 x 10 12 cm -3, Ln = 1 cm Reflection (%) 50 40 30 20 10 Edge density scan With density gradient of 1 x 10 20 m -3 1000 A.U. 500 φ = 60 o φ = 90 o φ = 120 o φ = 150 o 100 80 60 40 20 0-20 Average power coupling (%) 0 0-40 Reflection (%) 100 90 80 70 60 50 40 30 20 10 0 1E12 Edge density scan (cm -3 ) Edge density = 1.0 x 10 18 m -3, Density gradient = 1.0 x 10 20 m -3 xp is the vacuum gap distance between grill and plasma xp = 5 mm xp = 2 mm xp = 1 mm xp = 0 mm 1E13 60 80 100 120 140 160 Phase difference (deg) -8-6 -4-2 0 2 4 6 8 N (N z ) PIC simulation For LH-wave propagation in high density plasma Loaded with density gradient Edge density: 4 x 10 19 m -3 Density gradient: 8 x 10 21 m -3 Development Status of KSTAR ECH and LHCD System (September, 2004) 5

Design progress of 5.0-GHz LHCD launcher Conceptual physics design of the single waveguide channel has been done (using HFSS and ANSYS) E-plane taper 3-dB power splitter Fixed phase shifter Water-load Co-work with PPPL for the KSTAR launcher design It has many of the design feature of C-MOD launcher (5 sec operation) However, the near steady-state of KSTAR operation (300 sec) presents some new challenges which will require new launcher design features Better heat removal from the coupler grill Shielding of the microwave windows from direct line of sight to the plasma Compact water loads for capturing power reflected from the grill/plasma interface The collaboration with PPPL is expected to provide a suitable steady-state launcher design for KSTAR. A reasonable cooling structure is presented by Dr. J. Hosea in US-KO collaboration meeting, May 19. Development Status of KSTAR ECH and LHCD System (September, 2004) 6

C-MOD Launcher vacuum window H-taper diagnostic probes E-taper loads diagnostic probes front coupler short or dump C-MOD port flange 3 db splitter Development Status of KSTAR ECH and LHCD System (September, 2004) 7

Launcher Design Phased-array waveguide antenna Waveguide channels - Waveguide pattern milled on the metal plate (3-dB power splitter, phase shifter, H-plane taper, water-load) - 32 metal plates in upper and lower part each Grill Motional structure (wheel, rails, bellows, etc) E-plane taper 3-dB power splitter Phase shifting region Grill Cooling channels Bellows H-plane taper The cross-section view of the launcher Development Status of KSTAR ECH and LHCD System (September, 2004) 8

Cold model test results of 3-dB power splitter Power dividing: -3.43 db at both outputs Phase shift: 90.3 0 Return loss: -27.4 db Coupling to port 3: -27.7 db E-plane taper E-plane taper Development Status of KSTAR ECH and LHCD System (September, 2004) 9

Design of Fixed Phase Shifter Previous Design Designed for maintaining two vertical outputs in the same phase. p = 8.1 mm 4.75 cm H-plane taper 5.5 cm φ 90 0 delay λ G λ λ 1 2 λ G 0.3 cm x y 2π λ 1 2π λ 2π λ π 2 ( 2y) + ( 2x) = (2y + x) ( φ) 2π φ = p ' λ G 2 G Fixed phase shifter φ is the additional phase delay from p = 8.1 mm. face to Plasma boundary surface Input Phase difference between two vertical outputs : 0 degree

New Design Offset the start position of the tapering between two arms. x a t y a KSTAR Plasma Boundary Primary arm 47.5 mm 55 mm p 90 o delay Secondary arm 47.5 mm 55 mm x b t y b 2π x λ x g1 a + a y a + 2π y λ = g 2 x b + a y 2π = x λ b g1 + p b + 2π y λ g 2 b π + 2 x λ x a g1 a x λg1(4 p λg 2) = 4( λ λ ) g1 = 77.4 mm, λ x b b g 2 g 2 = 86.74 mm ( x = 71.6 mm, p = 11.4 mm b = x a + 86.74 mm) Development Status of KSTAR ECH and LHCD System (September, 2004) 11

HFSS Simulation 3-dB power splitter, H-plane taper, and fixed phase shifter Input port Water-load In phase output Out-of phase reflection Development Status of KSTAR ECH and LHCD System (September, 2004) 12

Steady-state LHCD Launcher Grill Design In collaboration with PPPL Top of grill water cooled to within 5 mm of front 314 C 549 C Glidcop septum SS insert 255 C Glidcop/SS Sandwich KSTAR LHCD Launcher Development Status of KSTAR ECH and LHCD System (September, 2004) 13

Placement of Windows The windows for the C-MOD LH coupler are placed in the grill nose The placement of the windows for KSTAR launcher need to be placed after splitter if possible - but where f (5 GHz) < f ce on the vacuum side This placement will need to be an integral part of the launcher design Cooled SS vacuum flange Ceramic window location Ceramic window location Low vacuum due to bad pumping conduction Titanium guide Alcator C-MOD window location 7 m Ceramic window location KSTAR window location f ce = 28 B T R 0 /R = 28 x 3.5 x 1.8/7 = 25.2 GHz f < f ce (OK) Development Status of KSTAR ECH and LHCD System (September, 2004) 14

Compact Reflected Water-loads of Arm 4 of Splitter Minimization of the recirculation of reflected power is essential for controlling the spectra Shorting plates are acceptable for equal reflections from the guide ends poloidally Compact loads are needed for non-uniform reflections (e.g., for vertical plasma shifts and arcs) Water tube insertion designs have been studied Heat transfer is not totally satisfactory and insulating tubes may prove too fragile Improved design needs to be developed Placement of Water-loads 3-dB power splitter Development Status of KSTAR ECH and LHCD System (September, 2004) 15

Improved Design of Water-load L = 2 λ G, α = 0.5, s = 19.6 mm, d = 19.8 mm HFSS simulation VSWR = 1.00038 at 5.0 GHz (Reflection = -37 db) (VSWR < 1.001 and maximum temperature < 70 o C) ANSYS analysis for temperature distribution Maximum temperature : 61 o C Constraints for water cooling film coefficient = 4 W/cm 2o K bulk temperature of 300 o K Development Status of KSTAR ECH and LHCD System (September, 2004) 16

Summary and proposal alternatives for US support We propose to help address the important steady-state LH launcher issues Design, analyze and prototype (at high power) fully active grills that can sustain steady-state operation on KSTAR - a Glidcop/SS sandwich design is probably best for heat/disruption loads Design proper placement of windows out-of-sight of plasma Develop new compact water load for arm 4 of splitter - design and prototype (low and high power) This task is estimated to take two years at ~ $400 k per year We could also undertake to design and fabricate the entire LH launcher for KSTAR This would involve integrating the designs above into a splitter/guide arrangement that would fit into the KSTAR port envelope Most likely a three-way splitter poloidally would be designed so that the number of windows could be reduced to 32 and could all be placed inside the port space This task is roughly estimated to take ~ 3 years after the development above and to cost ~ $5 M in as spent dollars with 30% contingency. Development Status of KSTAR ECH and LHCD System (September, 2004) 17

Proposed schedule and cost by PPPL KSTAR 1.5 MW LHCD Launcher Schedule 2005 2006 2007 2008 2009 2010 Design/develop concept for steadystate grill, power splitter, launcher, window placement, water load Prototype steady-state grill, power splitter, water load Design KSTAR launcher based on prototype results Fabricate and assemble launcher Projected Costs with Inflation and 30% Contingency 400 k 400k 1.0 M 2.0 M 2.0 M We project that a robust steady-state launcher can be provided for KSTAR at a cost of ~ $ 5 M and can be ready to support operations in 2010 Two years of R&D prior to design of the launcher is needed to assure the viability of the launcher and its potential relevance to ITER Development Status of KSTAR ECH and LHCD System (September, 2004) 18

5 GHz RF test System PFN Pulse Modulator (Max 45 kv, 96 A, 4 µs) 5 GHz, 1.5 MW, 1 µs, magnetron Pulse TR Cathode Voltage Cathode Current RF Pulse RF test system of a single waveguide of LHCD launcher Development Status of KSTAR ECH and LHCD System (September, 2004) 19

5 GHz,1.5 MW CW LHCD System KSTAR ECCD SYSTEM WILL BE DEVELOPED IN COLLABORATION WITH US AND EU. TOSHIBA Klystron Waveguide Network Korea Korea Launcher PPPL, USA EU Dummy Load Power Supplies 5 GHz, 500 kw CW Klystrons KSTAR Development Status of KSTAR ECH and LHCD System (September, 2004) 20