Xband travelling wave structure design for TERA A

X-band travelling wave structure design for TERA A. Grudiev 10/12/2008

Beta=0. 5, 120 degree backward wave TWS In a TWS with a small beam aperture and with magnetic coupling through 4 holes in the iris, backward wave accelerates the beam propagating in opposite direction

Beta=0. 5, 120 degree backward wave TWS rc = 1. 5 mm cell, radius of coupling hole a=1. 3 mm h=8. 332/2 mm d=1 mm dn=2 mm b=9. 012 mm rc=1. 5 mm f 0=11. 994 GHz QCu=3624 Vg=0. 57% R/Q=21057 Ohm/m Es/Ea=3. 05 Hs/Ea=4. 3 m. A/V Sc/Ea 2=0. 35 m. A/V

Beta=0. 5, 120 degree backward wave TWS rc = 2 mm cell, radius of coupling hole a=1. 3 mm h=8. 332/2 mm d=1 mm dn=2 mm b=8. 74 mm rc=2 mm f 0=11. 994 GHz QCu=3455 Vg=1. 52% R/Q=22288 Ohm/m Es/Ea=3. 1 Hs/Ea=5. 3 m. A/V Sc/Ea 2=0. 58 m. A/V

Beta=0. 5, 120 degree backward wave TWS rc = 2. 5 mm cell, radius of coupling hole a=1. 3 mm h=8. 332/2 mm d=1 mm dn=2 mm b=8. 412 mm rc=2. 5 mm f 0=11. 994 GHz QCu=3261 Vg=2. 77% R/Q=25334 Ohm/m Es/Ea=3. 1 Hs/Ea=5. 6 m. A/V Sc/Ea 2=0. 82 m. A/V

Beta=0. 5, 120 degree backward wave TWS rc = 2. 9 mm cell, radius of coupling hole a=1. 3 mm h=8. 332/2 mm d=1 mm dn=2 mm b=7. 85 mm rc=2. 9 mm f 0=11. 994 GHz QCu=2860 Vg=4. 72% R/Q=32403 Ohm/m Es/Ea=3. 5 Hs/Ea=6. 4 m. A/V Sc/Ea 2=1. 4 m. A/V

Beta=0. 5, 120 degree backward wave TWS Parameters profile along the structure Rc: 2. 78 mm linear decrease to 1. 48 mm Vg [%]: 4. 0082 1. 7720 0. 5228 Ls = 412. 5 mm – structure length <Ea> = 30 MV/m, Pin = 5. 3 MW <R’> = 70 Mohm/m; V = 12. 4 MV tf=100 ns; tb = 100 ns; tb = 300 ns; frep=400 Hz; <P> = 424 W; <P> = 848 W Vtot = 400 Me. V; Ptot ~ 14 k. W; Ltot ~ 16 m structure beam Focusing magnet RF 0. 5 m

VKX-7993 Klystron 2. 7 MW Pulsed Typical Operating Parameters Frequency Peak Power (goal) Saturated Gain Bandwidth (-1 d. B ) Efficiency Beam Voltage Beam Current 9. 3 2. 7 5. 5 52 65 43 120 52 GHz MW MW d. B MHz % k. V A Compact device, recently in production

Conclusions • X-band TWS has been designed. It shows that – Compactness. (YES) X-band structure is more compact – Shunt impedance. (not obvious). The sqrt(f)-scaling from S- to X-band does not work because of the difference in geometry – Efficiency. (YES) X-band is more efficient. But it comes more from a shorter filling time rather than from a higher shunt impedance • Based on the above, it is probably better to go to 9 -10 GHz range where commercial sources are available.