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.

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

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)

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

Mode Launcher (A set Of 4 hybrids) ~7.4 cm Circular Waveguide Single-moded DLDS Klystron ~53 m ~12.7 cm Circular Waveguide Propagating The TE 01 mode Tantawi 8/97 Load

Single Moded DLDS This system contains ~260 km of vacuum 4.75”-diameter waveguides Propagation of TE 01 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

Experience gained from NLCTA –Propagation of the TE 01 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

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.

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

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. a b

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

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

3.81 cm cm cm Type 1: TE 01 Circular to Square Taper Coupling of the TE 01 in the circular guide to spurious modes in the square guide. At the design length for Type 2 taper. Field pattern of Type 2 taper when coupling from TE 12 in the circular guide to TE 03 in the square guide Type 2: TE 01 and TE 12 Circular to Square Taper cm

3.81 cm A straight section. The cross section shape is given by 2.54 cm cm 2.54 cm cm cm Field Pattern as TE 01 in the circular guide get converted to TE 20 in the rectangular guide Type 3: TE 01 Circular to TE 20 Rectangular Taper.

Accelerator Structure Distribution System

8 Klystrons grouped in pairs Single-moded DLDS Mode Launcher (A set Of 4 hybrids) ~7.4 cm Circular Waveguide Accelerator Structure (~1.8 m) ~ 6 m ~53 m ~12.7 cm Circular Waveguide TE 12 Mode Extractor TE 01 TE 12 (Vertical) TE 12 (Horizontal) TE 01 TE 12 (Vertical) TE 01 TE 12 Mode Extractor Mode Launcher (Fed by four rectangular waveguides) ~7.4 cm Circular Waveguide Accelerator Structure (~1.8 m) 8 Klystrons grouped in pairs ~ 6 m TE 01 Mode TE 01 Tap-off Multi-moded DLDS

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

TE 21 TE 01 Mode Extractor TE 01 TE 12 (Vertically Polarized) TE 01 TE 12 (Vertically Polarized) TE 12 (Horizontally Polarized) Accelerator Structure (~1.8 m) ~7.4 cm Circular Waveguide TE 01 Mode Launcher (Fed by Four Rectangular Waveguides) Klystrons ~ 6 m TE 12 to TE 01 Mode Converter ~53 m ~12.7 cm Circular Waveguide TE 01 Tap-Off TE 01 Mode Converter (Fed by Four Rectangular Waveguides) TE 21 -TE 01 Mode Converter TE 01 Mode Extractor (Power is Extracted Evenly Between Four Waveguides)

~7.4 cm Circular Waveguide TE 01 Mode Extractor (Power is Extracted Evenly Between Four Waveguides) TE 01 TE 12 (Vertically Polarized) TE 12 (Horizontally Polarized) TE 01 TE 12 (Vertically Polarized) TE 01 TE 01 Mode Extractor Mode Launcher (Fed by Four Rectangular Waveguides) TE 21 TE 21 -TE 01 Mode Converter Klystrons ~ 6 m TE 01 Mode Converter (Fed by Four Rectangular Waveguides) TE 12 to TE 01 Mode Converter ~12.7 cm Circular Waveguide TE 01 Tap-Off SLAC KEK

Multi-Moded Structure test Setup Mode Launcher (TE 11 and TE 01 ) Mode Pre-launcher, for testing launchers. The output phase of the four-waveguide output is controlled by the choice between the two inputs

TE 11 (Vertical) TE 12 (Horizontal) TE 01 TE 11 (Vertical) TE 11 (Horizontal) TE 11 (Vertical) TE 01 TE 01 Extractor To Accelerator Structures TE 01 Launcher Extractor Schematic Diagram

TE 12 -TE 11 Mode Converter TE 11 -TE 01 Mode Converter TE 01 Mode Extractor 5”

Compression Ratio=

Cost Model

Single Moded DLDS

Single-Moded DLDS

Multi-Moded DLDS

Active DLDS

Single-Moded BPC

Multi-Moded BPC

~7.4 cm Circular Waveguide TE 01 Mode Extractor (Power is Extracted Evenly Between Four Waveguides) TE 01 TE 12 (Vertically Polarized) TE 12 (Horizontally Polarized) TE 01 TE 12 (Vertically Polarized) TE 01 TE 01 Mode Extractor Mode Launcher (Fed by Four Rectangular Waveguides) TE 21 TE 21 -TE 01 Mode Converter Klystrons ~ 6 m TE 01 Mode Converter (Fed by Four Rectangular Waveguides) TE 12 to TE 01 Mode Converter ~12.7 cm Circular Waveguide TE 01 Tap-Off SLAC KEK

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

Mode Launcher (A set Of 4 hybrids) ~7.4 cm Circular Waveguide Single-moded DLDS Klystron ~53 m ~12.7 cm Circular Waveguide Propagating The TE 01 mode Tantawi 8/97 Load

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

A short circuit Y 0 =1 Port 1 Port 2 Port 3 Port 4 If a signal is injected in port 1, it will all appear in port 3.

TE 12 -TE 01 Mode Converter TE 01 Mode Extractor Compact Mode Extractor

Compact Launcher

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

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

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, L 1 is the distance between the launcher and first extractor, L 2 is the distance between first and second extractor, L 3 is the length of the delay line after the second extractor, v TE01 and v TE12 are the group velocities of the TE 01 and TE 12 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, L 1 through L 3, and through that satisfy the above set of equations. An attractive choice is to set L 1 through L 3 equal to L, == and (2) This would lead to a fairly symmetric system.

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.

Advanced Concepts Distributed Elements Circulators Switches

Summary We have a design for all components required to implement the Single Moded DLDS, and the Multi-Moded DLDS. Going from single-moded to multi-moded systems will be decided after the KEK-SLAC experiment which will study the propagation properties of the TE 12 mode (Details of the experiment described by Y. H. Chin). High power experimental setups are being prepared to demonstrate these systems.