ILC High Power Distribution Chris Adolphsen, Chris Nantista and Faya Wang SLAC

ILC: Distributed Klystron Scheme (DKS) Similar to two tunnel RDR design but in one ‘Kamaboko’ shaped tunnel with a cement partition (shielding)

Klystron Cluster Scheme RF power sources clustered in surface buildings. Power combined, transported through overmoded waveguide, and tapped off locally at each ML Unit. Two KCS systems per building/shaft feed upstream and downstream, ~1 km each. Shaft Layout and ML Units Powered  KCS + cryo shaft  KCS shaft 26 e- beam 26 25 26 26 26 26 26 I.P. undulator main linac totals: 12 shafts 22 KCS systems 567 rf units (285+282) 1,701 cryomodules 14,742 cavities 26 26 e+ beam 26 26 25 25 25 25 26 I.P.

Combining and Tapping Off Power Combine power from 19 klystrons – effectively a 190 MW klystron 1 2 3 l … -3 dB -4.8 dB -7 dB -6 dB … Tap-Off 10 MW every 38 m (three cryomodules) 1 2 3 l -3 dB -4.8 dB … WC1890 CTO

Klystron to CTO Considered remote-controlled mechanical rf switches to isolate region upstream of CTO if circulators fail – removed to save cost KLY 5 MW Circulator CTO Switch and Load

RF Control Overview Have rf feedback loop to control net combined power from 19 klystrons Only need precise power summation when running at full beam energy Run klystrons in saturation and use alternating +phi/-phi phasing to control amplitude: phi nominally 22 deg to give 5% useable rf overhead Can shutoff rf at breakdown site within 7.4 us (propagation delay) RF Amplitude Minimum Nominal Phase (deg)

Coupling into the Circular Waveguide To couple power to the pipe, developed a “coaxial (wrap-around) tap-off”, or CTO Couplings range from -3 dB to ~-14 dB are needed, controlled by gap width CTO (Coaxial Tap-Off) 2 |E| on cut planes |H| on surfaces determines coupling 3 dB design Coupling due to beating with TE02 3 customized to coupling gap 1 Prototype CTO’s built for R&D program.

KCS Power Transmission Main Waveguide: For low-loss and high power handling, the TE01 mode is used in pressurized (3 bar N2), copper-plated, overmoded, 0.48m-diameter circular waveguide (WC1890). Loss at this diameter = 8.44 %/km Bends: 90 bends are needed to bring the KCS main waveguide to the linac tunnel. TE01 TE20 Electric field pattern Mode converting sections allow the actual bending to be done in the rectangular TE20 mode. WC1375 ports connect to WC1890 through step-tapers.

KCS Tolerances Q0, theor. = 187,230 Q0, meas. = 181,310 The 0.48m-diameter KCS Main Waveguide supports 20 parasitic modes. To avoid significant mode conversion losses, we set the radius tolerance at ~±0.5 mm. This was achieved within a factor of ~2. Because TM11 is degenerate with TE01, tilt (local and cumulative), should be kept within ~ 1 (17 mrad). target: 240.03 mm mean: 239.7 mm max-min: 1.08 mm std.: 0.234 mm For the CTO and bend, fabrication tolerances were set at ~±127mm for critical dimensions and ~±178mm for concentricities. Our transmission tests with 2 CTO’s shorted for launching (not fine tuned) demonstrated ~9899% transmission and a CTO match of ~-2128 dB. For ILC, may tune CTO coupling after fabrication The Q0 for the 40 m resonant waveguide with CTO at one end and a bend at the other measured within 3.2% of the theoretical value! This is a good indication that mode conversion wasn’t a problem. Q0, theor. = 187,230 Q0, meas. = 181,310

Ten Meter Test Setup CTO cold tests input assembly transmission tests resonant line tests Location: Roof of NLCTA bunker Power source: SNS modulator and Thales “5 MW” klystron

Forty Meter Test Setup Operated 100+ hours breakdown free at field levels that would be seen in the ILC KCS with the beam current upgrade CTO coupling RF power from P1 Marx-driven Toshiba MBK into TE01 mode in resonant line using KEK circulator. 40 m of pressurized (30 psig) , 0.48m diameter circular waveguide. Shorted bend with input mode converter at end of run. Recording run data.

Surface Electric Field in 90 Degree Bend |Es|pk = 3.34 MV/m for 37.5 MW input (= 75 MW full geometry  300 MW TW equiv. at SW anti-nodes) Equivalent to 72 MW TW in WR650 !

Cold Test of 40 m Setup 1.3005025 GHz fr = 1.300502 GHz (cold, unpress.) QL = 78,839 b = 1.2997 Q0 = 181,310

First Run: 1 MW input (255 MW field equivalent – ILC needs only 190 MW initially), no breakdown in 120 hours with 1.6 ms pulses at 3 Hz

Second Run: 1.25 MW input (313 MW field equivalent – ILC needs only 190 MW initially), one breakdown in 140 hours with 1.6 ms pulses at 3 Hz Coupling coefficient β = 1.17 Power needed for equivalent field of 300 MW is 1.18 MW.

Breakdown Rate at Various N2 Pressures ILC Max with 9 mA upgrade Peak Surface Field (MV/m) in the Bend

Resonant Line Resonant Ring In FY12: Installed 40 m of pipe system and bend prototype (have an additional unused 40 m of pipe) 1.0 MW Resonant Line back-shorted tap-in 40 m of WC1890 Equivalent Field for 300 MW Transmission In FYxx: Use resonant ring to test ‘final design’ bends and tap-in/off Resonant Ring phase shifter directional coupler tap-off tap-in 80 m of WC1890 300 MW

Quantifying the CTO-to-CTO Reliability Want to verify that each 1.0 km CTO-to-CTO region either breaks down rarely (< 0.1/year) if the repair time is long (24 hours), or break downs modestly (< 1/day) if the recovery is quick (1 minute). For ILC Power in tunnel (P) = Po*(L – z)/L, where z is distance from first feed and L = distance from first to last feed RF shut off time (t) = (zo + z)*2.25/c where zo is the distance from the cluster to first feed Max of P*t/Po = 3.2 us for zo = 100 m, L = 1.0 km Max t = 7.4 us for zo = 100 m, L = 1.0 km For an 80 m resonant ring, t equals the rf roundtrip time = 0.33 us, so P*t would be at least ~ 1/10 of the max at ILC. Would need ~ 1 km of pipe and thee 10 MW klystrons to ensure the maximum energy absorption (P*t) of ILC But it would be delivered at ~ twice the power in ~ half the time

Local RF Distribution at DESY TESLA/TTF/FLASH and ILC RDR – use fixed power dividers along a main waveguide feed EXFEL: Streamlined, no back termination, customizable dividers Cost Driver: 400 kW isolator

Achieving a Flat Gradient Profile with a 20% Gradient Spread With 39 to 676 cavities having a common source timing, achieving a constant cavity gradient during the pulse is possible by adjusting Pk and Qe for each cavity depending its relative gradient (V/Vo), although some power is reflected into the isolator loads. For a flat distribution over 0.8  V/V0  1.2, 5.4 % extra power is needed on average QL/QL0 P/P0

ILC Local Power Distribution System Unused power can be dumped to the loads Power to ½ CM’s fully adjustable without affecting phases. pressurizable, 0-100%, phase stable non-press., limited range pressure window 5 MW load from CTO 9 cavities 4 cavities quad 4 cavities Each cavity feed line has a phase shifter, isolator, bi-directional coupler, and flex guide

SLAC Variable Power Divider Tested to 2 MW No significant field enhancement or mismatch Rate of phase change with mechanical position independent of position Mean loss: ~0.51% (-.0221 dB) Max reflection: ~0.025% (-36 dB)

KEK Variable Power Divider Uses an H-shaped hybrid (2 mode) power splitter design with pontoon-shaped conductors to control split – has limited range of power division and changes phase as well.

Phase Shifters DESY/SPA Ferrite KEK/Toshiba

SLAC Air-to-Air Window High power tested up to 3 MW, 1 ms. Ceramic Plug Pressure Window

Local RF Distribution for FNAL CM’s Same components used in distribution systems built for FNAL: all commercially made except U-bend phase shifters and pressure window One of eight, 2-cavity feed systems assembled by SLAC for FNAL – all parts tested successfully at full power

26 ML Unit KCS Average Power Flow Diagram “Wall plug” Heat Loads Flow (MW) 2.764 2.543 2.416 1.5703 1.492 1.477 1.373 1.349 1.285 1.208 1.133 0.465 Power supplies (.92) 221 kW 127 kW 846 kW 78.5 kW 14.9 kW 103 kW 24.7 kW 63.4 kW 77.1 kW 74.9 kW 668.5 kW Modulator (.95) 19 klystrons (.65) Klystron waveguide + circ. (.95) 50.8% Combining circuit (.99) Kly circulator loads (for 7% O.H.) Surface Shaft & bends (.982) Tunnel KCS tunnel waveguide (Cu) (.953) Local PDS waveguide + circ. (.94) 32.4% Distribution end loads (.938) Cavity circulator loads (.410-.417) 16.8% Efficient 57% AC  RF 30% RF  Beam Beam