LHCD Steady-State Technology for KSTAR

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LHCD Steady-State Technology for KSTAR J. Hosea,
S. Bernabei, R. Ellis and J.R. Wilson Presente
d at the KSTAR Workshop General Atomics, San
Diego, CA May 19 - 20, 2004
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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

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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

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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

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Design of coupler assures that wavefronts are in
phase at the mouth of the coupler
2 Pout 2 4 Pout 4
Pin 1 Pload 3

• The capacitive button, and fixed phase shifter
  provide for good power splitting
• vertically with very little power going to
  the load guide
• P2/P1 - 3.04 dB
• P4/P1 - 3.07 dB
• P3/P1 - 43.07 dB

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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

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C-MOD LH Launcher System - Elevation View
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Power Flux in the Waveguides for KSTAR and C-MOD
Waveguide dimensions KSTAR - 5.5x0.55 cm2 C-MOD
- 6.0x0.55 cm2
kW/cm2
1..5 MW net power (4 Klystrons - 11.7 kW/guide)
f2b (GHz2 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

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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

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Frascati PAM LH Coupler

• Cooling of passive guides
• between all active guides

Active guide
Passive guide
F. Mirizzi et al., Fus. Eng. Des. 66-68 (2003)
621.
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EU ITER LH PAM Design for Water Cooling
Glidcop or CuCrZr used for active guide wall
plates
SS cooling pipes HIP imbedded into
berilium passive guide spacer plates
P. Bibet and F. Mirizzi, CEAEFDA/00-553
ENEAEFDA/00-554 (2001)
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Top/Bottom Cooling of Stainless Steel Fully
Active Grill is not Acceptable
Top of grill water cooled to within 1 cm of front
SS
100 W/cm2 from plasma
1181 C

• Temperature at center of septum reaches 1181 C
  in steady state

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Inserting Dummy (Passive) Guides Between Active
SS Guides Gives Better/But Not Sufficient Cooling
Cooled top
Cooled top
Midplane
Midplane
1170C
660C
320C
410C
Glidcop septum
SS septum

• 1170 C still too high for steady-state
• Making septa out of Glidcop does give a
  reasonable temperature of 410C
• However, a solution without passive guides is
  preferred for spectral flexibility

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Top/Bottom Cooling of Fully Active Grill With
Glidcop Septa Gives Sufficient Cooling for
Steady-State
Top of grill water cooled to within 5 mm of front
SS insert
314 C
549 C
Glidcop septum
255 C

• This is the preferred design for KSTAR to
  assure optimum spectral selection
• and directivity

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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

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Placement of Windows Out of View of Plasma is
Desirable for Steady-State
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 lt fce on
  the vacuum side
• This placement will need to be an integral part
  of the launcher design

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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

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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.

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Proposed Schedule and Cost for the KSTAR LHCD
Steady-State Launcher
KSTAR 1.5 MW LHCD Launcher Schedule 2005 2006 2007 2008 2009 2010
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 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 RD prior to design of the
  launcher is needed to assure the
• viability of the launcher and its potential
  relevance to ITER