A HIGH EFFICIENCY 17GHz TW CHOPPERTRON

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Howard McDaniel
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1 1 SLAC 07 A HIGH EFFICIENCY 17GHz TW CHOPPERTRON J. Haimson and B. Mecklenburg Work performed under the auspices of the U.S. Department of Energy SBIR Grant No.DE-FG02-06ER84468

2 2 SLAC 07 Figure 1. Centerline Layout of the Chopper Driven Traveling Wave RF Generator.

3 3 SLAC 07 Figure 3. Fourier Analysis Coefficients of GHz Chopped Beam versus Normalized Deflection.

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6 6 SLAC 07 Ω = 0 Ω = mm Ω = mm

7 7 SLAC 07 RELATIVE CHARGE f = MHz V O = 511 kv I = 84 A E M = 29 MV/m kv 456 kv BUNCH (degrees) Bunch Charge and Energy Distribution after the Centroid has Drifted 6.8 cm from the Prebuncher Exit Plane (ωt = 1730 ).

8 8 SLAC 07 A 17GHz TW CHOPPERTRON CHOPPING COLLIMATOR TW OUTPUT STRUCTURE CHOPPER CAVITY PREBUNCHER CAVITY STEERING DIPOLE BOOSTER CAVITY ISOLATED COLLECTOR

9 9 SLAC 07

10 10 SLAC 07 6x10 4 4x10 4 Integral H x (t) dz = A H x f = MHz H x (A/m) 2x10 4 H x at r = 0 0 Field seen by particle H x (t) at r = 0-2x x10 6 4x10 6 Integral E y (t) dz = kev E y f = MHz E y (V/m) 0-4x10 6 Field seen by particle E y (t) at r = 0 E y at r = 0-8x z (m)

11 11 SLAC 07

12 12 SLAC 07 λ B / DEFLECTOR CAVITY CHOPPING SEPTUM (b) (a) Early Late SEPTUM PLANE Chopped Bunch Length (10 /div)

13 13 SLAC 07 RELATIVE TRANSMITTED CHARGE f = MHz 2ρ = 6.2 mm S = 2.5 mm ωt = 90 FULLY GATED MHz BUNCH INJECTED INTO THE TW OUTPUT STRUCTURE FWHM (70% bunch charge) CHOP DRIFT DISTANCE FROM DEFLECTOR CAVITY (cm)

14 14 SLAC RELATIVE CURRENT ω/(2π) = MHz a 0 /2 + a 1 cos (ωt) + a 2 cos(2ωt) + a 3 cos(3ωt) + a 4 cos(4ωt) + a 5 cos(5ωt) + a 6 cos(6ωt) = cos(ωt) cos(2ωt) cos(3ωt) cos(4ωt) cos(5ωt) cos(6ωt) a 0 /2 I ωt (degrees)

15 15 SLAC 07 DESIGN PARAMETERS OF THE 17 GHz CHOPPERTRON MAGNETIC/ELECTRIC DIPOLE DEFLECTOR CAVITY SYSTEM Deflector Cavity Operating Mode TM 110 Input Beam Tunnel Diameter mm Operating Dipole Mode Frequency GHz Degenerate Dipole Mode Frequency GHz Beam Energy Operating Range kv Nominal Beam Energy kv Transverse Momentum Imparted to the Beam [58.5%(H x ), 41.5%(E y )] kev/c RF Deflection Angle mradian Deflector Drift Distance to Chopping Collimator.. 72 mm Beam Deflection at Chopping Collimator mm

16 16 SLAC 07 Deflector Cavity Unloaded Q Deflector Cavity External Q Dissipation in Cavity Walls kw Beam Loading Losses for I DC = 90 A kw Cavity Peak Magnetic Field with Beam Loading (H φ ) ka/m (B φ ) gauss Cavity Peak Electric Field with Beam Loading MV/m Matching Coefficient (β)( :1 Cavity Peak Electric Field without Beam MV/m Beam Loaded Quality Factor (Q L ) e - 1 Response Time [Q L (πf) - 1 ] ns

17 17 SLAC 07 A 17GHz TW CHOPPERTRON CHOPPING COLLIMATOR TW OUTPUT STRUCTURE CHOPPER CAVITY PREBUNCHER CAVITY STEERING DIPOLE BOOSTER CAVITY ISOLATED COLLECTOR

18 18 SLAC 07 E z (z)

19 19 SLAC 07

20 20 SLAC Particle Energy Late Arrival 2.0 PARTICLE ENERGY, γ Early Arrival ωt = DISTANCE ALONG TW STRUCTURE, Z/L

21 21 SLAC Run 15 P(MW) 25 PEAK PULSE POWER CIRCUIT LOSS (MW/m) f = MHz V = 511 kv I 0 = 84 A Circuit E-Field (E 0 ) Peak RF Power (P) Circuit Loss E 0 (MV/m) DISTANCE ALONG TW STRUCTURE (Z/L) 0

22 22 MICROWAVE DESIGN PARAMETERS OF THE SLAC GHz CHOPPERTRON TW OUTPUT STRUCTURE Operating Frequency MHz Traveling Wave Longitudinal Mode π/3 Number of Cavities Length of Output Structure mm Structure Attenuation Parameter Np Harmonic Mean Group Velocity c RF Filling Time ns Output Phase/Frequency Sensitivity deg/mhz Output Phase/Temperature Sensitivity C Input Beam Mean Energy (Nominal) kev Input Beam Current A I RF (fundamental frequency) A Peak RF Output Power MW RF Conversion Efficiency % Output Cavity E-Field (E o ) MV/m Output Cavity E smax /E o

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29 29 SLAC 07 A 17GHz TW CHOPPERTRON CHOPPING COLLIMATOR TW OUTPUT STRUCTURE CHOPPER CAVITY PREBUNCHER CAVITY STEERING DIPOLE BOOSTER CAVITY ISOLATED COLLECTOR

30 Conclusions SLAC 07 Charge Enhancement can be Combined with a Helical Trajectory Deflected Beam to Substantially Increase the RF Conversion Efficiency of a Short Wavelength Choppertron. Making Use of Existing HV Electron Gun Components and WR62 Waveguide Drive Components will Allow the 17GHz High Power Choppertron to be Built and Tested within the Budget Constraints of a Phase II SBIR.

31 31 SLAC 07 A HIGH EFFICIENCY 17GHz TW CHOPPERTRON J. Haimson and B. Mecklenburg Work performed under the auspices of the U.S. Department of Energy SBIR Grant No.DE-FG02-06ER84468

RF Design of Normal Conducting Deflecting Cavity

RF Design of Normal Conducting Deflecting Cavity Valery Dolgashev (SLAC), Geoff Waldschmidt, Ali Nassiri (Argonne National Laboratory, Advanced Photon Source) 48th ICFA Advanced Beam Dynamics Workshop