Multipaction Breakdown Prediction of Passive Microwave Devices with CST Particle-Studio José R. Montejo Garai (1), Carlos A. Leal (1), Jorge A. Ruiz Cruz (2) Jesús M. Rebollar Machaín (1) (1) Dpto. de Electromagnetismo y Teoría de Circuitos Universidad Politécnica de Madrid jr@etc.upm.es (2) Escuela Politécnica Superior Universidad Autónoma de Madrid
Outline 1. Introduction a) Particle accelerators, vacuum electronics, stellarators,, etc. b) Satellite communication devices. 2. Multipactor prediction a) Classical method: Hatch and Williams susceptibility curves. - ESA/ESTEC Multipactor Calculator. b) PIC technique: simulation of electrons motion inside the device. 3. Results - CST Particle Studio. a) Stop-band filter for plasma diagnosis. b) OMT for antenna feeder on board communication satellite. e. 4. Conclusions
1. Introduction. Multipactor is an electron resonance effect that occurs when RF fields accelerate electrons in a vacuum and cause them to impact with a surface, which depending on its energy, release one or more electrons into the vacuum. When a sustained multiplication of the number of electrons occurs, the phenomenon will grow exponentially and may lead to operational problems. RF CYCLE + RF CYCLE RF CYCLE _ (1) (2) (3) RF CYCLE RF CYCLE + RF CYCLE (4) (5) (6)
1. Introduction. a) Particle accelerators, vacuum electronics, stellarators,, etc. b) Satellite communication devices.
2. Multipactor prediction. a) Classical method: Hatch and Williams susceptibility curves. - ESA/ESTEC Multipactor Calculator. x=d x=0
2. Multipactor prediction. b) PIC technique: simulation of electrons motion inside the device. - CST Particle Studio
3. Results: stop-band filter for plasma diagnosis. Magnetically confined fusion plasmas Stellarator TJ-II in CIEMAT with its main components http://www-fusion.ciemat.es
3. Results: stop-band filter for plasma diagnosis. Block diagram of the heterodyne receiver for CTS (Collective Thomson Scattering)
3. Results: stop-band filter for plasma diagnosis. 0-10 -20 s 11 Simulation s 21 Simulation s 11 Measurement s 21 Measurement s 11 (db) -30 Center frequency 28 GHz -40-50 -60 s 21 Bandwith 560 MHz (2%) Stopband attenuation 40 db Return Loss 18 db Spurious free frequency bands 26.5-27.72 GHz 28.28-40 GHz 28 30 32 34 36 38 40 Frequency (GHz)
3. Results: stop-band filter for plasma diagnosis. Graphical representation of electrical field to foresee the maximum strength. Electric field configuration at 32 GHz (frequency in the bandpass) Electric field configuration at 27.705 GHz (first transmission zero)
3. Results: stop-band filter for plasma diagnosis. Integration lines used to calculate the breakdown voltages Two transmission frequencies f t1 =27.0 GHz f t2 =32.0 GHz Lref L1 L2 L3 L4 L5 Five transmission zeros f tz1 =27.705 GHz f tz2 =27.812 GHz f tz3 =27.971 GHz f tz4 =28.115 GHz f tz5 =28.207 GHz
3. Results: stop-band filter for plasma diagnosis. Voltages (rms( values) along the six integration lines (mm) for the seven frequencies (GHz). Lref = 3.556 L1=0.569 L2=1.4342 L3=1.3755 L4=1.7484 L5=0.7764 ft 1 =27.0 27.3 1.8 6.9 5.7 9.3 5.4 f tz1 =27.705 48.9 47.9 3.9 0.040 0.005 0.003 f tz2 =27.812 46.2 45.7 17.3 0.031 0.101 0.030 f tz3 =27.971 21.9 46.2 55.8 22.9 1.02 0.037 f tz4 =28.115 46.3 18.5 91.9 91.6 21.6 1.3 f tz5 =28.207 44.3 11.6 42.9 78.4 35.2 2.7 f t2 =32.0 23.9 4.5 3.4 5.1 6.8 3.7
3. Results: stop-band filter for plasma diagnosis. Classical method: Hatch and Williams susceptibility curves. Gap=0.569 mm Silver V p = 983.7 P = 210.87 ( w) Analysis margin 8 db P = 33.4( w)
3. Results: stop-band filter for plasma diagnosis. Characteristics: The emission type follows the Furman model The maximum number of secondary electrons emitted per incident electron is 10 The maximum number of generations which a primary source can produce is 1000 Silver coated surfaces with Emax =165 ev, δmax = 2.22 The initial energy of the electrons 10eV
3. Results: stop-band filter for plasma diagnosis. CST Particle Studio: PIC technique. Number of Particles 5000 4500 4000 3500 3000 2500 2000 1500 300 W 310 W 320 W 330 W 340 W 350 W 360 W 370 W 380 W 390 W 400 W Threshold: 400 W exponential increase 1000 500 0 0 5 10 15 20 25 t(ns)
3. Results: stop-band filter for plasma diagnosis. Multipaction breakdown 5000 4500 4000 3500 Number of Particles 3000 2500 2000 1500 1000 Threshold: 400 W 500 0 0 5 10 15 20 25 t(ns)
3. Results. P=400 w Multipaction
3. Results: stop-band filter for plasma diagnosis. Breakdown power for the critical element of the band stop filter. Element Slot of the first cavity at f tz1 =27.705 GHz ECCS model 210 W Particle Studio (PIC) 400 W 5000 4500 4000 P=400 w 1600 3500 1400 Number of Particles 3000 2500 2000 1500 Number of Particles 1200 1000 800 600 400 200 P=210 w 1000 500 0 0 5 10 15 20 25 t(ns) 0 0 5 10 15 20 25 t(ns)
4. Results: OMT on board satellite 0-10 S 11 TE 10 S 11 TE 01-20 (db) -30-40 TE 01-50 TE V 11-60 TE 10 TE H 11 Frequency 10.65-12.55 GHz -70 10.5 11 11.5 12 12.5 Frequency (GHz)
4. Results: OMT on board satellite Vertical Polarization Voltages (rms( values) along the six integration lines (mm) at 10.65 (GHz) Lref = 15.5 L1=5.86 L2=7.31 L3=5.86 L4=7.31 L5=10.16 f=10.65 42.7 20.4 24.4 20.3 24.1 20.6 Classical method: Hatch and Williams susceptibility curves. Gap=5.86 mm Silver P = 18150 ( w) Lref L1 L2 L3 L4 L5 Electric field configuration at 10.65 GHz
4. Results: OMT on board satellite Horizontal Polarization Voltages (rms values) along the four integration lines (mm) at 10.65 (GHz) Lref = 15.5 L1=5.51 L2=8.94 L3=10.16 f=10.65 41.0 31.6 26.7 20.6 L3 Classical method: Hatch and Williams susceptibility curves. Gap=5.51 mm Silver P = 6709 ( w) L2 L1 Lref Electric field configuration at 10.65 GHz
4. Results: OMT on board satellite Breakdown power for the critical element of the OMT Element Iris (horizontal polarization) at f=10.65 GHz ECCS model 6709 W Particle Studio (PIC) > 50000 W 10000 9000 8000 70 lines per λ 7000 Number of Particles 6000 5000 4000 3000 2000 1000 10 kw 20 kw 30 kw 40 kw 50 kw 0 0 5 10 15 t(ns) No exponential increase L3 L2 L1 Lref
4. Conclusions. A multipactor breakdown threshold analysis of a microwaves passive devices, (stop-band filter and OMT), has been presented. Firstly, the standard approach has been used. However, the standard multipactor susceptibility curves underestimate the thresholds. In order to avoid this limitation, a rigorous analysis which takes into account the actual electromagnetic field distribution and the geometry dimensions has been performed using the CST Particle Studio. This allows a more realistic evaluation of the breakdown threshold, and therefore, a safer design of microwave filters at much higher breakdown levels. This is extremely important in different areas like nuclear fusion research and satellite industry.