ECE4312_Lecture 01_2024_Summer course.pdf
- 1. Lecture01:IntroductiontoRF ECE 4312:RF Circuit Design 6/7/2024 DR. ENG. MOHAMED ISMAIL 1
- 2. DR. ENG. MOHAMED ISMAIL 2 Course Grading method Score % Quizzes 5 Lab performance 7 Midterm exam 18 Final exam 70 Total 100
- 3. 3 What is RF? RF = Radio frequency Used as shorthand for Alternating voltages at radio frequencies Alternating currents at radio frequencies Electromagnetic waves at radio frequencies Power carried in electromagnetic waves Apparatus generating RF power ...
- 4. 4 What are radio frequencies? Long waves ~200 kHz Medium waves ~1 MHz Short waves ~3– 30 MHz VHF radio ~100 MHz TV ~500 MHz Mobile phones ~1000– 2000 MHz Satellite TV ~10000 MHz Accelerators ~1 MHz – 10000 MHz http://www.ofcom.org.uk/static/archive/ra/publication/ra_info/ra365.htm#table
- 5. 5 Wavelengths and frequencies? c = l f Velocity = wavelength × frequency
- 6. 6 Wavelengths and frequencies? c = l f Velocity = wavelength × frequency Velocity of light = 3×108 metres/second = 186,000 miles/second = 670,000,000 miles/hour = 300 m/µs
- 7. 7
- 8. 8 Frequencies Wavelengths Long waves ~200 kHz ~1500 m Medium waves ~1 MHz ~300 m Short waves ~3– 30 MHz ~10–100 m VHF radio ~100 MHz ~3 m TV ~500 MHz ~2 feet Mobile phones ~1000– 2000 MHz ~6– 12 inches Satellite TV ~10000 MHz ~1 inch Accelerators ~1 MHz – 10000 MHz 240 VAC mains 50 Hz ~4000 miles
- 10. BBC Droitwich transmitter — Long wave Radio 4
- 11. Marconi’s transmitter, 1902 — Nova Scotia
- 12. Marconi’s spark transmitter, 1910
- 13. Steam engine and alternator
- 14. Two of four 5 kV DC generators
- 15. 12 kV stand-by battery (6000 cells! 2 GJ stored energy!) (cf. RAL SC3: 5 J)
- 16. Marconi’s 1920 valve transmitter
- 17. 17 Alternating voltages, currents, electric fields, magnetic fields, ... Need to describe by three quantities Frequency, amplitude and phase E.g. three-phase AC mains: All phases “240 V” But different phases are very different! Phase varies along a wire carrying alternating current How much phase changes depends on wavelength and hence on frequency
- 18. 18 y = sin (2 f t + ) -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 0 90 180 270 360 450 540 630 720 810 900 990 1080 Degrees Amplitude Alternating voltage V(t) = A sin (2p f t + f) f = 240° 120° 0° E.g. three-phase AC mains Phase
- 19. 19 Why is RF used at all in accelerators? Cathode ray tube in TV set doesn’t need RF
- 20. 20 Particles accelerated using electric field For 100 keV can use 100 kV DC power supply unit. Even 665 kV for old Cockcroft-Walton But 800,000,000 V DC power supply unit for accelerating protons in ISIS not possible Instead, for high energies, use RF fields, and pass particles repeatedly through these fields RF fields produce bunched beams DC RF ns – µs spacing
- 21. 21 Air Sound waves set up inside milk bottle RF Electromagnetic waves set up inside hollow metal cylinder
- 22. 22 RF
- 23. 23 + – + – + – + – + – RF
- 24. 24
- 25. 25 – + – + – + – + – +
- 26. 26
- 27. 27 Two commercial 0.5 MW short wave radio transmitters
- 28. 28 RF powers Big radio and TV transmitters 0.5 MW Mobile phone transmitters 30 W Mobile phones 1 W Sensitivity of mobile phones 10–10 W
- 29. 29 Where does RF power come from? Big amplifiers Usually purpose built The basics: Accelerator RF amplifier Frequency source
- 30. ~1 W RF ~1 MW RF
- 31. 31 Devices that amplify RF Transistors ~100 watts maximum per transistor Couple lots together for kilowatts Valves / vacuum tubes Triodes, tetrodes Largest can deliver several megawatts (peak) Klystrons High powers, high gains Limited to frequencies >300 MHz IOTs (inductive output tubes) Often used in TV transmitters (esp. digital TV) Output limited to ~50 kW
- 32. 32 Transistors usually junction transistors (NPN, PNP) Essentially minority carrier device But RF transistors usually field effect transistors Majority carrier device
- 35. Solid state RF amplifier: few watts in, 3 kW max out
- 36. 3 kW max. solid state amplifier mounted in rack
- 37. 1 kW solid state driver RF amplifier for synchrotron
- 38. Valves / vacuum tube made in 1915
- 40. Valve-based audio hi-fi amplifiers
- 41. Debuncher amplifier: commercial TV transmitter
- 42. Linac triode 5 MW peak 75 kW mean Synchrotron tetrode 1000 kW peak 350 kW mean
- 43. 43 Typical valve parameters at ISIS TH116 4648 Type Triode Tetrode Heater 20 V, 500 A 4 V, 1600 A Anode volts 35 kV 16 kV Anode current 175 A 8 A Peak power o/p 2 MW 75 kW Mean power o/p 40 kW 40 kW Cooling water 100 l/min 200 l/min
- 44. 44 Resonant circuits Parallel LC-circuit Impedance Z “infinite” at f = f0 (2pf0)² = 1 / LC L C length l Shorted line Impedance Z “infinite” at l = l/4, 3l/4, 5l/4, ... Only ratio of diameters matters
- 45. 45 Output Input HT (+ve) Anode Screen grid Control grid Cathode Heater Tetrode Essence of a tuned RF amplifier — 1
- 46. 46 Output Input HT (+ve) Anode Screen grid Control grid Cathode Heater Tetrode Essence of a tuned RF amplifier — 2
- 47. ISIS RFQ 200 kW tetrode driver Input (grid) tuned circuit Output (anode) tuned circuit Tetrode
- 48. 48 Klystron gain ~50 dB (× 105 power gain) E.g. 10 W in, 1 MW out IOT gain ~25 dB (× 300 power gain) E.g. 200 W in, 60 kW out
- 49. Toshiba E3740A 3 MW 324 MHz klystron 5 metres, 3 tons
- 50. 50 Skin depth RF currents flow in surface of conductor only Skin depth d 1 (frequency) (exponential) In copper, d = 7 / (frequency) (cm) 50 Hz 1 cm 1 MHz 70 µm 200 MHz 5 µm In sea water 50 Hz ~100 feet ELF / submarines 10 kHz ~10 feet VLF / submarines
- 51. ISIS RFQ — vessel copper-plated stainless steel
- 52. Different currents on different surfaces of same piece of metal Linac high power RF amplifier
- 53. 53 – + – + – + – + Electric field Dielectric material No external electric field Atoms
- 54. 54 Dielectric material Dielectric constant Ceramic 6 Nylon 3 Perspex 3½ Polystyrene 2½ Water 80 Loss tangent — leads to dielectric heating Ceramic 0.001 Nylon 0.02 Perspex 0.01 Polystyrene 0.0001 Water 0.1 — microwave ovens
- 56. RF feed to linac tank
- 58. Good and failed RF windows
- 59. Linac RF block diagram Low level RF Cavity n RF amp. chain Tuner V ref. accel. field Phase comp. Volt. comp. Phase comp. Motor drive beam Servo systems on amplitude, phase and cavity tuning
- 60. Three amplifiers in previous slide
- 61. Synchrotron high power RF systems
- 62. Synchrotron low-level RF systems block diagram Beam compensation loop Phase loop Voltage loop Frequency sweeper Cavity tuning
- 63. Driver amplifier
- 64. Cavity and high power RF driver
- 65. High power RF drive