Array of Stripline Kickers S. De Santis and H. Qian Lawrence Berkeley National Laboratory

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Array of Stripline KickersS. De Santis and H. Qian

Lawrence Berkeley National Laboratory

LIU-SPS HIGH BANDWIDTH DAMPER REVIEW – CERN JULY 30TH, 2013

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Choice of stripline kickerNumber of modulesStripline lengthStripline width

Kicker OptimizationTaperingField uniformity

Beam Coupling ImpedanceConclusions

Summary2

S. DE SANTIS – JULY 30TH, 2013

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Compromise between cost vs. maximum total lengthMax. total length = impedance, system complexityCost = Max. amplifier power

Number of Kicker Modules

With the SPS stay-clear in mind:

€

Nmod ≈18.4

Δp⊥e

c

L[cm]eff Pamp

Max. Nmod also depends on amplifier cost vs. additional stripline module cost. When they are about the same…

500 W amplifiers with 10 cm long striplines can achieve the spec with Nmod = 8

€

Leff =Lsin(ωL/ c)ωL/ c

Frequency dependentHigher frequency needs higher power/more modules

15 kV ?

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Compromise between response at low vs. high frequency

Stripline Kicker Length

€

Rs(ω ) =2Zcg⊥

(h/ 2) ⎛ ⎝ ⎜

⎞ ⎠ ⎟2

Lsin(ωL/ c)ωL/ c

⎛ ⎝ ⎜

⎞ ⎠ ⎟2

A stripline length is optimal at

€

f[GHz] =7.5/ L[cm]

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Compromise between field uniformity and impedance matching

Stripline Kicker Width

Stripline width determines vacuum pipe size, since we want to keep the distance between electrodes as small as the vertical stay-clear allows, with a 50 Ω characteristic impedance.

New tapered design, with 56 mm wide electrodes

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Old vs. New Design6


150 mm

No taper Taper

130 mmTE01 cutoff: 1.08 GHz TE01 cutoff: 1.3 GHz

100 mm 100 mm

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Field uniformity vs. frequency response

STAY-CLEARUNIFORM FIELD

50 Ω

MORE UNIFORM FIELD

50 Ω

LONGER FEEDTHROUGH-STRIPLINE TRANSITION

WIDER STRIPLINES

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The Final Product: Integrated Deflecting VoltagePERFORMANCE OF 1 METER WORTH OF KICKER

Comparison of 4 stripline modules (10 cm) with 1 m long slotted line kickerTARGET

4 striplines occupy around 1 m of beampipe length: 20 cm separation reduces crosstalk between adjacent strips to -23 dB @ 1 GHz (worst case).

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…or 6 modules with 250 W amp!

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We can do “virtual” coaxial wire measurementsActual impedanceBeam coupling impedance/Loss factor

How Does a Real Stripline Kicker Perform ?

2-wire measurement suggests a loss between 20% and 30% in the actual shunt impedance. It can be improved and we also plan to check this result by wakefield simulations (code just acquired).

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Beam Coupling Impedance

Shaded area coincides with most of the SPS beam power spectrum (98% reduction @ 800 MHz), with σz=12 cm.Even assuming uniform spectrum and uniform 40 Ω impedance over 800 MHz, the loss factor is around 0.03 V/pC. To be multiplied by Nmod.

- Loss per bunch: <18 μJ -> ΔE/E < 750 eV/26 GeV ≈ 0- Power absorbed by load: 750 W (@ 40 MHz rep rate, ~1kW @ 20 MHz)

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Deflecting Field Uniformity - Simulation2% isolines

33 mm

The new tapered design also improves on the field uniformity. Previous 2% aperture was 25 mm.

Is 2% uniformity enough ? Are 30 mm required ? (bunch horizontal size, dispersion, drift during ramp,…)Smaller values make it easier to obtain a better response at higher frequencies

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Conclusions12

Stripline kicker advantagesBest response at lower frequenciesIdeally suited for subdividing power over many modules Relatively simple mechanical design (stripline BPM+HV feedthrough)Low beam coupling impedance

Key aspect TBDHow much kick, at which frequenciesField uniformity requirements

Depending on exact specs a stripline array can go from being a slam dunk choice (relaxed high frequency performance) to an impractical one. Worth investigating combined stripline + slotted line kicker use since one is more effective at lower frequencies and the other is more effective at higher frequencies


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Array of Stripline Kickers S. De Santis and H. Qian Lawrence Berkeley National Laboratory