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 19 - 20, 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 isProvided by Phasing of Each of32 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

Input

H-plane taper

Fixed phase shifter

4.75 cm 5.5 cm

Capacitivebutton

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

– P2/P1 = - 3.04 dB – P4/P1 = - 3.07 dB– P3/P1 = - 43.07 dB

Pin 1

Pload 3

2 Pout 2

4 Pout 4

May 2004

C-MOD LHCD Antenna has a Similar Design to KSTARKLYSTRONlow power

phase shifter24193 dB splitter10#5high power

phase shifter

• 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

frontcoupler

vacuum window H-taper

3 dB splitter

E-taper

shortor dump

loadsdiagnostic

probes

diagnosticprobes

C-MOD port flange

May 2004

02468100510152025 power flux in the waveguidesf2b (GHz2 cm)kW/cm2breakdownweak conditioning

waveguide dimensions 6.0x0.55 cm2*Æ2.3 MW net power (12 Klystrons - 24 kW/guide)1.5 MW net power (8 Klystrons - 15.5 kW/guide)*ÆJET 2 secJET, TS long pulse PBX-M 0.5 sec££ûû

C-MOD

KSTAR

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

1..5 MW net power (4 Klystrons - 11.7 kW/guide)

Waveguide dimensions:KSTAR - 5.5x0.55 cm2

C-MOD - 6.0x0.55 cm2

Power Flux in the Waveguides for KSTAR and C-MOD

kW/cm2

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. 66-68 (2003) 621.

May 2004

EU ITER LH PAM Design for Water Cooling

SS cooling pipes HIP imbedded into beriliumpassive guide spacer plates

Glidcop or CuCrZr used foractive guide wall plates

P. Bibet and F. Mirizzi, CEA:EFDA/00-553; ENEA;EFDA/00-554 (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/cm2

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°C 660°C

Midplane

SS septum

320°C 410°C

May 2004

Top/Bottom Cooling of Fully Active Grill With Glidcop SeptaGives 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 insert314° C

549° C

May 2004

First Pass Power Spectrum for Fully Active vs Passive/Active Grill

0 1 2 3 4 5

0

1 0 0 0

2 0 0 0

3 0 0 0

4 0 0 0

5 0 0 0

6 0 0 0

n parallel

Pow

er

a.

u.

all waveguides active

every other waveguide is passive and 90 phasedo

same total power

directivity

60 o

90 o

120 o

60o

90 o

120 o

with 90o passive

with 90o passive

with 90o passive

95%

90%

80%

79%

58%

50%

Passive/Active

Fully Active

60°

90°

120°

120°

90°

60°

• 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

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are needed to see this picture.

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 < fce 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

water inwater out

• 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

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 R&D prior to design of the launcher is needed to assure the viability of the launcher and its potential relevance to ITER