The NLC RF Pulse Compression and High Power RF Transport Systems

1. The NLC RF Pulse Compression and High Power RF Transport Systems Sami G. Tantawi, G.Bowden, K.Fant, Z.D.Farkas, W.R.Fowkes J.Irwin, N.M.Kroll, Z.H.Li, R.Loewen, R.Miller, C.Nantista, J.Rifkin, R.Ruth, A.Vlieks, P.Wilson.

2. Outline System Requirements Comparison between Different Pulse Compression Systems Single Moded Delay Line Distribution System (DLDS) Multi-Moded DLDS Summary Collaborative work with KEK (Y. H. Chin) Development of multi-moded components Mode stability experiment

3. System Requirements and Goals Efficiency from klystrons to accelerator structures should exceed 85%. Limited choice of systems Component efficiency including copper losses should be better than 99%. Output Pulse should be flat for approximately 253 nS with a linear ramp at the beginning for approximately 104 nS. (Again this limits the choice of possible systems) The system should be cost effective Reduced length of vacuum over-moded delay lines Compact, and mechanically simple components. Peak surface field should be less than 40 MV/m at the rated rf power (600 MW for most components)

4. The development of various pulse compression systems has been an ongoing program at SLAC for over 10 years. Pulse compression systems that have the potential of achieving the NLC requirements and have been studied are: Resonant Delay Lines (SLED-II) Active SLED-II Multi-moded SLED-II Binary Pulse Compression (BPC) Multi-Moded Reflective BPC Delay Line Distribution System (DLDS) Multi-Moded DLDS Active DLDS For each of these systems we calculated the following: efficiency number and cost of components length and cost of delay lines cost of klystrons cost of modulators

5. Klystron ~12.7 cm Circular Waveguide Propagating The TE01 mode Load ~7.4 cm Circular Waveguide Mode Launcher (A set Of 4 hybrids) ~53 m Single-moded DLDS Tantawi 8/97

6. Single Moded DLDSThis system contains ~260 km of vacuum 4.75”-diameter waveguides Propagation of TE01 mode in circular over-moded waveguides, NLCTA experience Pump-outs Mode Converters Hybrids Flanges Tapers 90-Degree Bends Power Dividers for the Local Distribution System

7. Experience gained from NLCTA Propagation of the TE01 mode in highly over-moded waveguides (94 modes in the WC475, and 41 modes in WC293 Effect of Mechanical Tolerances on Circular Waveguides Diameter, Offset, Tilt, and Roundness Resonant Effects, and Mode Filters Design of Flanges Assembly Procedures Pump-outs Tapers Mode Converters (Flower Petal) Hybrids (Magic Tees) Measurement Techniques

10. Most components have been designed with different concepts, for example: Mode Converters based on the wrap-around concept based on the Circular to Square Tapers Hybrids Magic Tee based on wrap around mode converters (Old concept) based on circular to rectangular tapers (New Concept, presented here) However, we present here only the most recent developments.

11. Old Marie’ Mode Converter Short Marie’ Mode Converter (GA) Flower Petal Mode Converter Wrap-Around Mode Converter. Tested up to 480 MW Several Generations of Mode Converter Development

12. a b HFSS simulation results for the wrap around mode converter. The color shades represents the magnitude of the electrical field. a. is a cut plane through the slots, b is a cut plane in the circular guide 2.5 cm away from the slots.

13. Input H-Plane Over-moded Hybrid Output Iris Delay Lines Wrap-around Mode Converter Sled-II Configuration

14. New 90-degree Bend Based on Circular to Square Waveguide Tapers

15. 3.556 cm Type 1: TE01 Circular to Square Taper 3.81 cm 1.905 cm Type 2: TE01 and TE12 Circular to Square Taper. 10.16 cm Field pattern of Type 2 taper when coupling from TE12 in the circular guide to TE03 in the square guide Coupling of the TE01 in the circular guide to spurious modes in the square guide. At the design length for Type 2 taper.

16. 3.81 cm A straight section. The cross section shape is given by 2.54 cm Type 3: TE01 Circular to TE20 Rectangular Taper. 3.286 cm 2.54 cm 3.131 cm 3.696 cm Field Pattern as TE01in the circular guide get converted to TE20in the rectangular guide

17. Accelerator Structure Distribution System

18. 8 Klystrons grouped in pairs Mode Launcher (A set Of 4 hybrids) ~12.7 cm Circular Waveguide Accelerator Structure (~1.8 m) ~7.4 cm Circular Waveguide ~ 6 m ~53 m Single-moded DLDS TE01 TE12 (Vertical) TE01 TE12 (Vertical) TE12 (Horizontal) 8 Klystrons grouped in pairs TE12 Mode Extractor TE01 ~7.4 cm Circular Waveguide TE12 Mode Extractor Accelerator Structure (~1.8 m) ~ 6 m Mode Launcher (Fed by four rectangular waveguides) TE01 Tap-off TE01 Mode Multi-moded DLDS

19. Multi-Moded Delay Line Distribution System This system contains ~130 km of vacuum 4.75”-diameter waveguides • Introduction • Experimental Tools • Components required to implement the system (Launcher and Extractor) • Components based on over-moded rectangular waveguides • Components based on the wrap-around mode converter (will be presented by Y. H. Chin as part of component development at KEK) • Flanges • Tapers • Mode Rotation Problems

21. TE01 TE12 (Vertically Polarized) TE12 (Horizontally Polarized) ~12.7 cm Circular Waveguide TE01 TE12 (Vertically Polarized) Klystrons TE01 Mode Extractor (Power is Extracted Evenly Between Four Waveguides) ~7.4 cm Circular Waveguide TE01 Mode Extractor TE01 Accelerator Structure (~1.8 m) TE21 ~ 6 m TE01 Mode Converter (Fed by Four Rectangular Waveguides) TE01 Tap-Off Mode Launcher (Fed by Four Rectangular Waveguides) TE12 to TE01 Mode Converter TE21-TE01 Mode Converter ~53 m

22. TE01 TE12 (Vertically Polarized) TE12 (Horizontally Polarized) TE01 TE12 (Vertically Polarized) Klystrons ~7.4 cm Circular Waveguide ~12.7 cm Circular Waveguide TE01 Mode Extractor TE01 Mode Extractor (Power is Extracted Evenly Between Four Waveguides) TE01 ~ 6 m TE01 Mode Converter (Fed by Four Rectangular Waveguides) TE01 Tap-Off TE12 to TE01 Mode Converter TE21-TE01 Mode Converter TE21 Mode Launcher (Fed by Four Rectangular Waveguides) SLAC KEK

23. Multi-Moded Structure test Setup Mode Pre-launcher, for testing launchers. The output phase of the four-waveguide output is controlled by the choice between the two inputs Mode Launcher (TE11 and TE01)

24. TE11 (Vertical) TE12 (Horizontal) TE01 TE11 (Vertical) TE01 TE11 (Vertical) TE11 (Horizontal) TE01 To Accelerator Structures TE01 Launcher TE01 Extractor Extractor Schematic Diagram

25. TE12-TE11 Mode Converter TE11-TE01 Mode Converter TE12-TE11 Mode Converter 5” TE01 Mode Extractor

26. TE01 Launcher TE01 Launcher TE11 Launcher Both Polarizations of TE11 TE01 2” TE01 Modular Launcher

27. Compression Ratio=

28. Cost Model

30. Single Moded DLDS

31. Single Moded DLDS

32. Single-Moded DLDS

33. Multi-Moded DLDS

34. Active DLDS

35. Single-Moded BPC

36. Multi-Moded BPC

37. TE01 TE12 (Vertically Polarized) TE12 (Horizontally Polarized) TE01 TE12 (Vertically Polarized) Klystrons ~7.4 cm Circular Waveguide ~12.7 cm Circular Waveguide TE01 Mode Extractor TE01 Mode Extractor (Power is Extracted Evenly Between Four Waveguides) TE01 ~ 6 m TE01 Mode Converter (Fed by Four Rectangular Waveguides) TE01 Tap-Off TE12 to TE01 Mode Converter TE21-TE01 Mode Converter TE21 Mode Launcher (Fed by Four Rectangular Waveguides) SLAC KEK

38. RF Power Sources RF A Cluster of 9 Multi-Moded DLDS Sections e+ or e- Eight 75-megawatt klystrons Delay Lines Accelerator Structures A Single Multi-Moded Delay Line RF Distribution System

39. Single-moded System Relative Cost Efficiency Waveguide Diameter (cm) Relative Cost Multi-Moded System Efficiency Waveguide Diameter (cm)

41. Klystron ~12.7 cm Circular Waveguide Propagating The TE01 mode Load ~7.4 cm Circular Waveguide Mode Launcher (A set Of 4 hybrids) ~53 m Single-moded DLDS Tantawi 8/97

42. Wrap-Around Mode Converter for Tap-off, and extraction, tested to 320MW

43. Instead of using a cutoff section to allow the extraction of the TE01 mode, one can use two mode converters cascaded together

44. A short circuit Y0=1 Y0=1 Y0=1 Port 3 Port 2 Y0=1 Y0=1 Port 1 Port 4 Y0=1 Y0=1 Y0=1 If a signal is injected in port 1, it will all appear in port 3.

45. TE12-TE01 Mode Converter TE01 Mode Extractor Compact Mode Extractor

46. Compact Launcher

47. Mode Pre-launcher, for testing launchers. The output phase of the four-waveguide output is controlled by the choice between the two inputs

48. ~7” 1.5” A bend based on transition from an over-moded rectangular waveguide to a circular waveguide

49. TIMING • Because the rf power is being injected at different times into different modes that have different group velocities, one must pay a special attention to timing. The set of equation that need to be satisfied so that the each accelerator structure set get an rf pulse for a duration at the appropriate time are: • (1) • where L is the distance between accelerator structure sets, L1 is the distance between the launcher and first extractor, L2 is the distance between first and second extractor, L3 is the length of the delay line after the second extractor, vTE01 and vTE12 are the group velocities of the TE01 and TE12 modes respectively, and through are the delays due to the transmission of power from the main rf delay line system to the accelerator structure sets, i.e., the delay through and after the extractors. • There are several choices for the lengths L, L1 through L3, and through that satisfy the above set of equations. An attractive choice is to set L1 through L3 equal to L, == and • (2) • This would lead to a fairly symmetric system.

50. LAUNCHER • Several ideas for the launcher have been proposed (8-9). In all of them a fundamental property of the launcher has been preserved: the launcher has only four inputs and the launcher has to launch four and only four modes. If this is preserved and the launcher is matched for all four different input conditions, because of unitarity and reciprocity the scattering matrix representing the launcher has to take the following form: • (3) • This form forces the isolation between inputs; i.e., if one of the four power supplies drops out or fails, the rest of the power supplies will not receive any reflected power.