LHCD Steady-State Technology for KSTAR J. Hosea, S. Bernabei, R. Ellis and J.R. Wilson Presented at the KSTAR Workshop General Atomics, San Diego, CA May , 2004

May 2004 LHCD Steady-State Technology for KSTAR The present LHCD design for KSTAR has been developed based on TPX considerations and with PPPL supporting the KSTAR team effort It has many of the design features for the C-MOD LHCD system –C-MOD operation will serve to test these features for relatively short pulses (5 sec) However, the near steady-state of KSTAR operation (300 sec) presents some new challenges which will require new coupler 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 We propose to enhance our collaboration with KSTAR to help address these challenges and provide a suitable steady-state launcher design for KSTAR

May 2004 Very Good Spectral Control is Provided by Phasing of Each of 32 Columns of KSTAR Design Maintaining this spectral control will be a primary objective for the steady-state KSTAR design 32 columns x 4 rows = 128 active guides 4 x 0.5 MW klystrons power 8 columns each Each column is individually phase controlled with high power phase shifters Microwave windows need to be placed outside of stacked coupler region to avoid sight of plasma

May 2004 The power splitter/grill guides and water loads fit into a very compact design It is important to maintain this compact design to preserve spectral control and to minimize waveguide losses Cooling of the components - grill, guides, and loads - is more difficult for a compact design Input H-plane taper Fixed phase shifter 4.75 cm 5.5 cm Capacitive button Plasma boundary Matched load

May 2004 Design of coupler assures that wavefronts are in phase at the mouth of the coupler The capacitive button, and fixed phase shifter provide for good power splitting vertically with very little power going to the load guide – P 2 /P 1 = dB – P 4 /P 1 = dB – P 3 /P 1 = dB P in 1 P load 3 2 P out 2 4 P out 4

May 2004 C-MOD LHCD Antenna has a Similar Design to KSTAR 24 columns x 4 rows = 96 active guides 12 x 0.25 MW klystrons power 2 columns each Each column is individually phase controlled with high power phase shifters Microwave windows are placed in nose of coupler

May 2004 C-MOD LH Launcher System - Elevation View front coupler vacuum windowH-taper 3 dB splitter E-taper short or dump loads diagnostic probes diagnostic probes C-MOD port flange

May 2004 C-MOD KSTAR f 2 b (GHz 2 cm) C-MOD LH operations will serve to test short pulse (5 sec) features of the KSTAR design Critical steady state (300 sec) design features required for KSTAR LH design 1..5 MW net power (4 Klystrons kW/guide) Waveguide dimensions: KSTAR - 5.5x0.55 cm 2 C-MOD - 6.0x0.55 cm 2 Power Flux in the Waveguides for KSTAR and C-MOD kW/cm 2

May 2004 Heat Removal From the Coupler Nose is the Major Critical Issue for Steady-State Two possible solutions for KSTAR LH coupler cooling: – Incorporate Frascati ITER PAM (passive-active- multi-junction) grill cooling design  good cooling but reduces active guides by half and reduces directivity of spectrum – Design cooling into the present stacked plate KSTAR coupler design  Heat conductivity of 2 mm SS septum is two low  Material must be changed to Glidcop or CuCrZr or cooling tubes imbedded into septum We propose to keep optimum spectral control - design cooling into the stacked plate design – LHCD operation on KSTAR can then serve to set the optimum phase properties for the ITER PAM design and possibly lead to a better launcher option

May 2004 Frascati PAM LH Coupler Cooling of passive guides between all active guides Active guide Passive guide F. Mirizzi et al., Fus. Eng. Des (2003) 621.

May 2004 EU ITER LH PAM Design for Water Cooling SS cooling pipes HIP imbedded into berilium passive guide spacer plates Glidcop or CuCrZr used for active guide wall plates P. Bibet and F. Mirizzi, CEA:EFDA/00-553; ENEA;EFDA/ (2001)

May 2004 Top/Bottom Cooling of Stainless Steel Fully Active Grill is not Acceptable Top of grill water cooled to within 1 cm of front 100 W/cm 2 from plasma 1181° C Temperature at center of septum reaches 1181° C in steady state SS

May 2004 Inserting Dummy (Passive) Guides Between Active SS Guides Gives Better/But Not Sufficient Cooling 1170° C still too high for steady-state Making septa out of Glidcop does give a reasonable temperature of 410°C However, a solution without passive guides is preferred for spectral flexibility Cooled top Glidcop septum Cooled top Midplane 1170°C660°C Midplane SS septum 320°C410°C

May 2004 Top/Bottom Cooling of Fully Active Grill With Glidcop Septa Gives Sufficient Cooling for Steady-State This is the preferred design for KSTAR to assure optimum spectral selection and directivity Top of grill water cooled to within 5 mm of front Glidcop septum 255° C SS insert 314° C 549° C

May 2004 First Pass Power Spectrum for Fully Active vs Passive/Active Grill Fully active grill gives much better directivity and a wider range for n || If lower n || proves to be optimum on KSTAR then the PAM design may prove to be acceptable for ITER

May 2004 Placement of Windows Out of View of Plasma is Desirable for Steady-State Stacked guide/power splitter Source 1 feed Phase Shifter Dummy load 3 dB hybrids Cooled SS vacuum flange Ceramic window location Titanium guide C-MOD window location Feed guide/power splitter system for C-MOD 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 < f ce on the vacuum side This placement will need to be an integral part of the launcher design

May 2004 Further Development of Compact Reflected Power Loads for Arm 4 of Splitter is Proposed 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

May 2004 Summary and Proposal Alternatives for US Support of LHCD on KSTAR 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.

May 2004 Proposed Schedule and Cost for the KSTAR LHCD Steady-State Launcher KSTAR 1.5 MW LHCD Launcher Schedule Design/develop concept for steady- state 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 1.0 M2.0 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