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RF Power Generation and PETS Design I. Syratchev

The Syratchev Layout #2 is the best compromise in terms of power production, beam stability, and cost. This design has fixed input parameters for the CLIC and 12 GHz PETS design, with a power production of 76 MW and a WDS length of 0.246 m.

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RF Power Generation and PETS Design I. Syratchev

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  1. RF Power Generation and PETS Design I. Syratchev

  2. Layout #2 is the best compromise in terms of power production, beam stability and cost • Fixed input parameters for the CLIC • 12 GHz PETS design: • - Power production: • Power/WDS = 76 MW • WDS length (physical)=0.246 m • Power limit/PETS ~ WDS ? • Drive beam frequency = 12 GHz • (first harmonic) • Module layout: • Quad + BPM length = 0.35 m • PETS specific: • Extractor length = 0.075 m • Drive beam energy < 2.5 GeV • Beam stability: Quad spacing  1 m PETS slotted configuration bring ~ 30% Wu enchantment. About 10% can be played back with optimizing the iris profile Module layouts #1 #2 #3 Unit length, m 1.0 Drive beam, GeV 2.25 Drive beam , A 93 Aperture, mm 15.7 23 30.8 Length, m 0.10 23 56.4 Power/PETS,MW 79 160 317 Wu/WDS (slotted) 0.46 1.0 1.37 Wt (norm./23mm) 3.1 1.0 0.42 Qt (norm./23 mm) 1.65 1.0 0.8 Module layouts #1 #2 #3

  3. 23 mm 12 GHz PETS base line RF design • PETS parameters: • Aperture = 23 mm • Period = 6.253 mm (900/cell) • Iris thickness = 2 mm • R/Q = 2258 Ω • V group= 0.453 • Q = 7200 • E surf. (160 MW)= 61 MV/m • H surf. (160 MW) = 0.1 MA/m (ΔT max (140 ns, Cu) = 2.0 C0)

  4. ΔF, MHz Eff., % E0, GeV I,A 0 85.9 2.259 97.43 125 84 2.361 95.32 Power production efficiency • In a structure with a high group velocity, the tail of the single bunch get the stronger deceleration. This effect can be compensated with a slight detuning of the structure synchronous mode frequency (Daniel). • In general: • the longer the structure and shorter the bunch, the less detuning • detuning reduces beam stability Note: this method was developed for the ancient 30 GHz CLIC PETS with ~ 80% Vg and provided efficiency recuperation about 7%

  5. GDFIDL/HFSS/Wake model/PLACET: PETS Transverse wake Wake expression for the structure with high group velocity. Structure length – Ls. PLACET Loads Beta=0.702 C F=14.707 GHz Q=285 Kt=0.89 HFSS data Moderate damping Wt, V/pC/m/mm (log) Reflected wave |Ez| |E| Wake (single mode model) Wake (GDFIDL) Distance, m (log) Wt vs. aperture Heavy damping No damping EH Transverse wakes spectra, GDFIDL Moderate damping 23 mm 16 mm In a presence of the damping slots, the two competing transverse modes appear. The optimal balance between them should be found to provide stable beam transportation. Re (Zt) V/A/m/mm (log) 30 mm HE 12 Frequency, GHz Frequency, GHz

  6. First and second harmonic, detuning and beam stability. For the given aperture and chosen method of damping, the wake amplitude and Q-factor can be estimated quite accurately. The draft PLCET simulations (W,Q f(Freq)) for the transverse frequency scan, Wake amplitude and Q scaling where done using layout #2. Drive beam frequency 12 GHz Drive beam frequency 6 GHz 84.% 80.1% 85.9% 86.1% For the CLIC PETS operating at a first harmonic the situation with the beam stability is rather critical (no safe margins) because of the natural frequency of the dominant transverse mode ~ 15 GHz. The detuning make the situation even worse and should be seriously discussed. The same time, operating at the second harmonic, the bunches sit close to the wake zero crossing providing a good stability

  7. The control of the transverse modes frequencies and damping #1. Phase advance Radial #3. Damping slot configuration Inclined Iris 2.0 mm 900 1200 Impedance Impedance Frequency, GHz Flat #2. Iris thickness 3.5 mm 2.0 mm Phase/cell 1200 Impedance Frequency, GHz Wake integral at the punches center position Wt Frequency, GHz • The lower phase advances and thinner irises favor the beam stability • The damping slot configuration can be used for the fine tuning of the dangerous modes balance Distance, m Bunch number

  8. Initial beam offset ~ Wt Q F GDFIDL & 9 modes model PETS with radial slots Beam envelope along decelerator simulated with PLACET (9 modes). Erik Adli Without detuning Q nominal Q nominal x 1.5 Frequency, GHz Q nominal x 1.5 With detuning Distance, m Q nominal

  9. Further study towards 12 GHz CLIC PETS • Power production: • Optimization of the iris profile to reduce the surface peak power plow. • Beam stability: • Low frequencies HOM. Optimization of the damping slots and loads configuration. • High frequencies HOM. Frequency detuning if necessary (phase advance). • ON/OF capability: • Integration of the detuning wedges. Minimization of their impact on the beam stability. Conclusion: Unit layout with 2 WDS/PETS and 2 PETS/ Quad is recommended as a baseline for configuration 12 GHz CLIC. Unit length 1.0 m, girder length 2.0 m. The PETS with 23 mm aperture, 900 phase advance per cell and iris thickness 2 mm is considered.

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