Breakdown Test of SW Accelerator Cavity with Shaped Iris

In a study by J.M. Neilson, V. Dolgashev, and S. Tantawi at SLAC National Accelerator Laboratory, planned breakdown tests were conducted on a single-cell SW accelerator cavity with shaped iris geometries. The research assessed breakdown dependence, different iris parameters, and compared elliptical and round iris structures. Detailed analysis of magnetic and electric fields, Q-values, shunt impedance, stored energy, and breakdown probabilities were presented. The results highlighted factors affecting breakdown probability and performance characteristics of thick elliptical and thin round iris structures.

• SW accelerator
• Cavity breakdown
• Shaped iris
• Electric fields
• SLAC

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1. Planned Breakdown Test of SW Accelerator Cavity with Shaped Iris J.M Neilson, V. Dolgashev and S. Tantawi SLAC National Accelerator Laboratory IWLC 2010 Geneva

2. Outline Previous breakdown results for elliptical and rounded iris Calculations for shaped iris geometry

3. Two Single-Cell-SW Structures with same magnetic but different electric fields Thick elliptical iris Thin round iris 1C-SW-A3.75-T2.0-Cu 1C-SW-A3.75-T1.66-Cu Thin round iris Thick elliptical iris

4. Parameter Values for Simple Iris (Field Normalized for 100MeV/m Gradient) T=2.6mm Elliptical Iris Parameter T=1.66 Round Iris Stored Energy [J] 0.189 0.189 Q-value 8820 8560 Shunt Impedance [MOhm/m] 85.2 82.6 Max. Mag. Field [KA/m] 314 325 Max. Electric Field [MV/m] 266 203 Losses in one cell [MW] 1.54 1.59 Hmax*Z0/Eacc 1.18 1.22 Max. Im{E x H*} W/ m2 42.8 44.4 Max. Im{E x H*}/H2 417 407

5. Breakdown Dependence a 0.105, t 2.0mm, SLAC 0.143, t 2.6mm, SLAC 1 a 0.105, t 2.0mm, SLAC 1 Breakdown Probability1 pulsemeter Breakdown Probability1 pulsemeter Breakdown Probability1 pulsemeter 100 100 Breakdown Probability1 pulsemeter a 1 a 0.143, t 2.6mm, SLAC 0.215, t 4.6mm, KEK 1 100 100 a 4 a 0.215, t 4.6mm, KEK 0.143, t 1.66mm, KEK 4 a 1 1 10 1 10 1 10 1 10 thick elliptical iris 2 10 2 10 2 10 2 10 3 10 103 103 103 4 10 4 10 4 10 4 10 105 10 5 5 10 a 0.105, t 2.0mm, SLAC 1 a 0.105, t 2.0mm, SLAC 0.143, t 2.6mm, SLAC 1 5 10 a 1 a 0.143, t 2.6mm, SLAC 0.215, t 4.6mm, KEK 1 4 thin round iris 6 6 10 10 106 106 a a 0.215, t 4.6mm, KEK 0.143, t 1.66mm, KEK 4 a 1 107 107 107 107 80 100 100 120 120 140 140 Gradient MV m 160 160 180 180 200 200 220 220 80 0 100 100 200 300 400 500 0 200 300 400 500 Gradient MV m Peak Electric Field MV m Peak Electric Field MV m a a 0.105, t 2.0mm, SLAC 0.143, t 2.6mm, SLAC 1 a 0.105, t 2.0mm, SLAC 1 Breakdown Probability1 pulsemeter 100 Breakdown Probability1 pulsemeter 1 a a 0.143, t 2.6mm, SLAC 0.215, t 4.6mm, KEK 1 4 Breakdown Probability1 pulsemeter Breakdown Probability1 pulsemeter 100 100 100 a a 0.215, t 4.6mm, KEK 0.143, t 1.66mm, KEK 4 1 1 10 1 1 10 10 101 102 10 2 2 10 10 2 thin round iris 3 3 10 10 103 103 4 4 10 10 4 10 104 5 5 10 10 5 5 10 10 thick elliptical iris a 0.105, t 2.0mm, SLAC 1 a 0.105, t 2.0mm, SLAC 0.143, t 2.6mm, SLAC 1 6 6 a 1 10 10 a 0.143, t 2.6mm, SLAC 0.215, t 4.6mm, KEK 1 106 a 4 6 10 a 0.215, t 4.6mm, KEK 0.143, t 1.66mm, KEK 1 a 4 7 7 10 10 7 10 0 0 100 100 200 200 300 300 400 400 500 500 600 600 7 10 20 30 40 50 60 70 80 90 20 30 40 Peak Pulse Heating deg. C Peak Pulse Heating deg. C 50 60 70 80 90 Peak Magnetic Field kA m Peak Magnetic Field kA m

6. 1C-SW-A3.75-T2.6-Cu 10 MW input Maximum magnetic field 390 MV/m Maximum magnetic field 672 kA/m Resonance at 11.4212 GHz = 0.988 V.A. Dolgashev, 25 September 2007

7. 1C-SW-A3.75-T2.2-Cu 10 MW input Resonance at 11.424 GHz = 1.007

8. Shaped Iris Thin round iris Thick elliptical iris - Iris profile designed to maximize shunt impedance, minimize peak surface magnetic field

9. SW Cells a/ =0.143, Phase Shift Field Normalized for 100MeV/m Acceleration T=2.6mm Elliptical Iris T=1.66 Round Iris T=2.2mm Shaped Iris Parameter Stored Energy [J] 0.189 0.189 0.186 Q-value 8820 8560 10090 Shunt Impedance [MOhm/m] 85.2 82.6 99.2 Max. Mag. Field [KA/m] 314 325 294 Max. Electric Field [MV/m] 266 203 268 Losses in one cell [MW] 1.54 1.59 1.32 Hmax*Z0/Eacc 1.18 1.22 1.11 Max. Im{E x H*} W/ m2 42.8 44.4 56.5 Max. Im{E x H*}/H2 417 407 650

10. Summary New structure designed with lower magnetic field However local Poynting vector significantly increased compared to other structure