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CLIC drive beam accelerating (DBA) structure Rolf Wegner

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14-Oct-2009CLIC DBA Rolf Wegner2 Outline CLIC drive beam complex, 3 GHz DBA structure design of 1 GHz DBA structure optimisations for efficiency and filling time damping and detuning summary

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14-Oct-2009CLIC DBA Rolf Wegner3 CLIC RF power source f acc = GHz I pulse = 4.2 A V acc = 2.37 GV P peak,RF ≈ 12 GW P avg,RF ≈ 90 MW

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14-Oct-2009CLIC DBA Rolf Wegner4 3 GHz DBA structure f acc = 3 GHz P in = 33 MW n cell = 33 Length= 1.22 m Ø outside = 17.4 cm weight ≈ 200 kg 17.4 cm

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14-Oct-2009CLIC DBA Rolf Wegner5 3 GHz DBA structure SICA = Slotted Iris – Constant Aperture

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14-Oct-2009CLIC DBA Rolf Wegner6 1 GHz DBA structure SICA principle but no direct scaling possible 3 GHz: Ø= 17.5 cm, L= 1.2 m, weight= 200 kg 1 GHz: Ø= 52.5 cm, L= 1.2 m, weight= 1800 kg klystron P RF ~ 10 to 15 MW (optimising klystron cost per MW and per operating hour and modulator cost) noise, phase error reduction if t fill = 240…250 ns (combination scheme => multiplication of phase noise, t DL ≈ 245 ns, t CR I ≈ 2*245 ns, t CR II ≈ 6*245 ns)

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14-Oct-2009CLIC DBA Rolf Wegner7 basic cell geometry RbRb gap b LbLb gap a LaLa R BP RaRa R 6 R basic cells typical dimensions

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14-Oct-2009CLIC DBA Rolf Wegner8 simulations of basic cells variations: R BP gap vgr/c tuning R a => f 0 = GHz vgr/c range: min ~ 0.4% to 0.5%

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14-Oct-2009CLIC DBA Rolf Wegner9 design of TWS gap n R BP E 0 T V acc Ncells P out P in PbPb PbPb constant aperture η= ΔP b /P in t fill mode spectrum

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14-Oct-2009CLIC DBA Rolf Wegner10 design of TWS example: P in = 10 MW I b = 4.21 A N cells = 10 R BP = 39 mm vgr/c (gap) const η= 97.7% t filling = ns vgr/c lin. distribution η= 98.0% t filling = ns

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14-Oct-2009CLIC DBA Rolf Wegner11 design of TWS example: P in = 10 MW I b = 4.21 A N cells = 10 R BP = 39 mm vgr/c const η= 97.7% t filling = ns vgr/c lin. distribution η= 98.0% t filling = ns

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14-Oct-2009CLIC DBA Rolf Wegner12 design of TWS example: P in = 10 MW I b = 4.21 A N cells = 10 R BP = 39 mm vgr/c const η= 97.7% t filling = ns vgr/c lin. distribution η= 98.0% t filling = ns

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14-Oct-2009CLIC DBA Rolf Wegner13 optimisations P in = 10 MW I b = 4.21 A R BP = 39 mm Ncells= 10 vgr/c lin. distribution vgr/c= [2.2% to 0.86%] vgr/c= [1.7% to 0.86%] vgr/c= [1.7% to 1.28%]

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14-Oct-2009CLIC DBA Rolf Wegner14 optimisations - efficiency P in = 10 MW I b = 4.21 A R BP = 39 mm Ncells= vgr/c lin. distribution optimised for efficiency efficiency

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14-Oct-2009CLIC DBA Rolf Wegner15 noise damping => D, t fill combined optimisations DBA structure tasks: acceleration => η RF Drive Beam Accelerator Delay Loop 2 gap creation, pulse compression & frequency multiplication 1 st Combiner Ring 3 2 nd Combiner Ring 4 pulse compression & frequency multiplication t DL ~ 245 ns appropriate t fill => noise suppression at f = 1/t DL

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14-Oct-2009CLIC DBA Rolf Wegner16 t fill [ns] damping factor D 245 ns D ≈ 1/ ns D ≈ 1/4 124 ns D ≈ 1/4 combined optimisations 245 ± 8.5 ns D ≈ 1/17 t 0 = 245 ns Δt= 8.5 ns α= 2% combination for optimisation C(η RF,t fill )= f 1 (η RF ) + f 2 (t fill ) DBA structure tasks: acceleration => η RF noise damping => D, t fill f 1 (η RF )= 1- η RF f 2 (t fill )= α ((t fill -t 0 )/Δt) 2 appropriate t fill => noise suppression at f = 1/t DL

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14-Oct-2009CLIC DBA Rolf Wegner17 optimisations

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14-Oct-2009CLIC DBA Rolf Wegner18 optimisations

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14-Oct-2009CLIC DBA Rolf Wegner19 optimisations

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14-Oct-2009CLIC DBA Rolf Wegner20 optimisations η RF ≥ 97.5 % |t fill – 245 ns| ≤ 5 ns

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14-Oct-2009CLIC DBA Rolf Wegner21 damping and detuning reduction of transverse wakefields by damping and detuning Alexej Grudiev’s suggestion: dampers in web (~18 mm tick) acc. mode Q 0 = 2.2 ∙10 4, Q ext = 3.7∙10 7 distorted, 0.1° 0.1 nose Q ext = 1.5 ∙10 6 P ext,peak = 110 W, P ext,avg = 0.83 W (P cell,peak = 30 kW, d.c. 0.75%) Ø≈ 25 cm

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14-Oct-2009CLIC DBA Rolf Wegner22 damping and detuning reduction of transverse wakefields by damping and detuning beam may excite multiples of 0.5 GHz (only every other bucket filled) 11 cell structure R BP = 41 mm

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14-Oct-2009CLIC DBA Rolf Wegner23 damping and detuning reduction of transverse wakefields by damping and detuning Q_11= 28 Q_07= 34 Q_01= 33 Q_11= 31

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14-Oct-2009CLIC DBA Rolf Wegner24 next steps wakefield calculation optimisation of damping RF design beam dynamics mechanical design => iterations

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14-Oct-2009CLIC DBA Rolf Wegner25 summary travelling wave structure for CLIC DBA efficiency ≥ 97% filling time 245 ns ± 5 ns input RF power 5 to 40 MW degree of freedom: no of cells BP radius transverse wakefield reduction by detuning and damping compact and effective damping

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14-Oct-2009CLIC DBA Rolf Wegner26 additional slides

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14-Oct-2009CLIC DBA Rolf Wegner27 additional slides

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14-Oct-2009CLIC DBA Rolf Wegner28 additional slides

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14-Oct-2009CLIC DBA Rolf Wegner29 additional slides

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14-Oct-2009CLIC DBA Rolf Wegner30 additional slides

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