KCS Operational Issues Chris Adolphsen, Chris Nantista and Faya Wang GDE PAC Review at KEK 12/12/12

 KCS + cryo shaft  KCS shaft e - beam e + beam undulator I.P main linac totals: 12 shafts 22 KCS systems 567 rf units ( ) 1,701 cryomodules 14,742 cavities 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. Klystron Cluster Scheme Shaft Layout and ML Units Powered

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

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

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 with 7.4 us (propagation delay) RF Amplitude Phase (deg) Minimum Nominal

Prototype CTO’s built for R&D program. |E| on cut planes |H| on surfaces CTO (Coaxial Tap-Off) Coupling into the Circular Waveguide determines coupling 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 3 dB design customized to coupling gap Coupling due to beating with TE 02

TE 01 TE 20 Electric field pattern TE 01 Main Waveguide: For low-loss and high power handling, the TE 01 mode is used in pressurized (3 bar N 2 ), copper-plated, overmoded, 0.48m-diameter circular waveguide (WC1890). Loss at this diameter = 8.44 %/km KCS Power Transmission Bends: 90  bends are needed to bring the KCS main waveguide to the linac tunnel. Mode converting sections allow the actual bending to be done in the rectangular TE 20 mode. WC1375 ports connect to WC1890 through step-tapers.

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 TM 11 is degenerate with TE 01, tilt (local and cumulative), should be kept within ~ 1  (17 mrad). The Q 0 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. target: mm mean: mm max-min: 1.08 mm std.: mm For the CTO and bend, fabrication tolerances were set at ~±127  m for critical dimensions and ~±178  m 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. KCS Tolerances Q 0, theor. = 187,230 Q 0, meas. = 181,310 For ILC, may tune CTO coupling after fabrication

into beam 16.8% not into beam 83.2% inefficiencies & losses 52.6% AC  RF 43.2% transmission losses 9.4% kly to ML unit: 6.8% LPDS: 2.6% into loads 30.6% operational 28.7% fill time: 21.4% beam phase: 0.31% LLRF overhead: 3.9% due to gradient spread 1.9% statistics: 0.61% unoptimized match: 1.3% KCS system (19 kly)Full Machine (413 kly) AC power2.764 MW60.08 MW lost above ground1.404 MW30.52 MW lost below ground0.895 MW19.45 MW into beam0.465 MW10.11 MW MW (83.2%) 16.8% KCS Losses

CTO cold tests Ten Meter Test Setup m m 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 CTO coupling RF power from P1 Marx-driven Toshiba MBK into TE 01 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.

|E s | 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 ! Surface Electric Field in 90 Degree Bend

GHz f r = GHz (cold, unpress.) Q L = 78,839  = Q 0 = 181,310 Cold Test of 40 m Setup

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

1.Coupling coefficient β = Power needed for equivalent field of 300 MW, Pin = 1.18 MW. 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

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

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 is at minimum equal to 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

Other Questions Modulator What is the plan to prove reliability of the Marx modulator design? We have not tested the P2 MARX enough to know where improvements need to be made. For the P1 Marx, the concern is still with the capacitor lifetime, but since we are focusing on the P2 and have little funds anyway, there is no further plans to develop the P1 or continue long-term testing it. How to find weak components in the design? We plan to do long term testing of the P2 starting next Feb. A large number of modulators operated at 5Hz would have an impact on the electrical grid. How is constant power consumption from the mains achieved ? The charging supply will present a constant load to the grid, so this should not be a problem What is the strategy for industrialization? We have been trying to find companies that will license the P2 design - Thompson showed some interest but have not followed up. Also, KEK has a DTI Marx modulator that they will evaluate - if it works well, maybe Toshiba or other companies will buy them

Other Questions (cont) Klystron: How is klystron lifetime defined? The expected klystron lifetime is based on the cathode loading - we have ran our MBK at 10 MW with ms pulses for 5000 hours at 5 Hz without major incident (except for the cavity detuning from a one-phase loss of AC power to the solenoid when the klystron beam was off), so at least we know the MBK lifetime is not very low - for either the KCS or DKS layout, there is no need to have a long lifetime other than cost since the klystrons are readily accessible if they fail. What is the plan to handle non-conforming klystrons during conditioning and testing, which takes place not at the manufacturers site? I would hope that the klystron contract would be such that the manufacturer would replace any non-conforming tubes as I believe the failure rate will be low

Other Questions (cont) Waveguide: What is the plan to prove reliability of the waveguide distribution system? We have already tested the rf distribution systems sent to FNAL at full power, but only for an hour or so. Hopefully, FNAL will be able to run them longer. There are some components which have sliding contacts, which seem to have poor reliability at high power. I believe only the U-bead phase shifters have the sliding contacts - they seem to work fine in the full power for the testing done so far (no breakdowns and no arcing damage observed) - note also that these shifters should not have to be adjusted often. Operation at overpressure might need approval by the national authorities ( TÜV or similar). This might lead to higher prices during the production process. Has that been considered? The waveguide has been designed for high pressure operation (and certified in most cases by the vendor) and costed accordingly. Unlike He systems, designing and qualifying for 3 atm absolute operation is not that difficult (e.g. to qualify our 40 m big pipe + bend + CTO, we pressurized system at 25% above design for a few hours).