INFN School on Electron Accelerators. RF Power Sources and Distribution

Transcription

1 INFN School on Electron Accelerators September 2007, INFN Sezione di Pisa Lecture 7b RF Power Sources and Distribution Carlo Pagani University of Milano INFN Milano-LASA & GDE

2 The ILC Double Tunnel scheme The Second Tunnel is mainly occupied by the RF Power Plants Three RF/cable penetrations every rf unit Safety crossovers every 500 m 34 kv power distribution Carlo Pagani 2

3 Linear Colliders are pulsed LCs are pulsed machines to improve efficiency. As a result: duty factors are small pulse peak powers can be very large <1 µs-1ms < ms RF Pulse 100 m km nsec... Bunch Train accelerating field pulse: gradient with further input without input Beam Loading filling loading Carlo Pagani 3

4 High Power RF System Tasks Task: Conversion of AC Line Power to Pulsed RF Power and distribution of the Pulsed RF Power to the cavities of the Linear Collider Structure: Several RF Station consisting of certain components make up the RF System of a linear collider The number of station depends on the maximum power which can be handledreliablybyonestation( and of courseon availablityof components, costs etc) ILC Numbers: Pulse Power per Station: 10MW RF Pulse Width: 1.5 ms Repetition Rate: 5 Hz Average power per Station: ~100kW Carlo Pagani 4

5 RF Station Components (1) phase AC DC HV Pulsed HV Pulsed HV HVPS Pulse Generating Unit Pulse Transformer (opt.) Klystron Auxiliary PS Interlock Control Modulator LLRF Preamplifier Pulsed RF RF Waveguide Distribution SC Cavities Carlo Pagani 5

6 RF Station Components (2) Modulator: HVPS: Conversion of AC line voltage (~400V AC) to DC HV (~1-10kV (100kV)) Pulse Generating Unit: Conversion of DC HV (~1-10kV (100kV)) to Pulsed HV (~1-10kV (100kV)) Pulse Transformer: Transformation of Pulsed HV (typ. ~10kV) to higher Pulsed HV (~100kV) Klystron: Conversion of Pulsed HV (~100kV) to pulsed RF (~10MW) RF Waveguide Distribution: Distribution of RF power (~10MW) to the cavities (~100kW) Other Auxiliary PS: Certain voltages for the klystron ion pumps or the klystron solenoid Interlock and Controls: Protection and Control LLRF: Control of phase, shape and amplitude (other lecture this school) Preamplifier: Amplification of ~1mW RF to ~100W RF Carlo Pagani 6

7 ILC Main Linac RF Unit (1 of 560) Gradient = 31.5 MV/m Rep Rate = 5 Hz # of Bunches = 2670 Bunch Spacing = 363 ns Beam Current = 9.0 ma Input Power = 284 kw Fill Time = 596 μs Train Length = 969 μs (9-8-9 Cavities per Cryomodule) Carlo Pagani 7

8 TESLA 500 RF Requirements TDR 2001 (ILC Baseline is similar) Number of sc cavities: total Frequency: 1.3 GHz (L-Band) Power per cavity: 231 kw Gradient at 500GeV: 23.4 MV/m Power per 36 cavities (3 cryo modules): 8.3 MW Power per RF station: 9.7MW (including 6% losses and a 10% reserve) Number of RF stations: 572 Macro beam pulse duration: 950 μs RF pulse duration: 1.37 ms Repetition rate: 5Hz Average RF power per station: 66.5 kw For TESLA 800 the number of stations must be doubled. The gradient is 35MV/m. Carlo Pagani 8

9 RF System Components developed for Tesla and installed at TTF RF Waveguide Distribution Klystron Modulator Pulse Transformer Carlo Pagani 9

10 Modulator Carlo Pagani 10

11 BCD and ACD Modulators for ILC (116 kv, 133 A, 1.6 ms, 5 Hz) Baseline: Pulse Transformer Style Modulator Alternative: Marx Generator Modulator Carlo Pagani 11

12 ILC Baseline Modulator IGCT s Carlo Pagani 12

13 Pulse Transformer Modulator Status 10 units have been built, 3 by FNAL and 7 by industry (PPT with components from ABB, FUG, Poynting) thru DESY funding. 8 modulators are in operation. 10 years operation experience. Working towards a more cost efficient and compact design. FNAL building two more, one each for ILC and HINS programs SLAC has built switching circuits with more up-to-date technology. Transforme r (red) and Lead Box (black) Containing Klystron 3 m HVPS and Pulse Forming Unit Carlo Pagani 13

14 Pulse Transformer Modulator Layout Capacitor Banks IGBT Redundant Switch Bouncer Choke Carlo Pagani 14

15 Klystron Carlo Pagani 15

16 Klystron Principle Example: 150MW, 3GHz S-Band Klystron The cathode is heated by the heater to ~1000 C. The cathode is then charged (pulsed or DC) > 100kV. Electrons are accelerated form the cathode towards the anode at ground, which is isolated from the cathode by the high voltage ceramics. The electron beam passes the anode hole and drifts in the drift tube to the collector. The beam is focussed by a bucking coil and a solenoid. By applying RF power to the RF input cavity the beam is velocity modulated. On its way to the output cavity the velocity modulation converts to a density modulation. This effect is reinforced by additional buncher and gain cavities. The density modulation in the output cavity excites a strong RF oscillation in the output cavity. RF power is coupled out via the output waveguides and the windows. Vacuum pumps sustain the high vacuum the klystron in. The beam is finally dumped in the collector, Carlo Pagani 16

17 Klystron Perveance Perveance, p is a quality parameter of the klystron gun, determined by the gun geometry I = klystron current U = Klystron voltage p = IU 3/ 2 Example: THALES TH2104C: 5 MW, 1.3 GHz Klystron U=128kV I = 89 A p = [A/V 3/2 ] (μperveance = 1.94) Carlo Pagani 17

18 Klystron Output Power P P P RF Beam Beam η =η PRF = ηp = = UI U Beam pu >5/ 2 5/ 2 > 0 ( U ) U Output Power / MW Output Power versus Cathode Voltage Cathode Voltage / kv Example: RF output power of a 3GHz (S-band) klystron as function of the voltage Carlo Pagani 18

19 Klystron Efficiency Efficiency of a klystron depends on bunching and therefore on space charge forces Lower space forces allow for easier bunching and more efficiency Decreasing the charge density (current) and increasing the stiffness (voltage) of the beam increase the efficiency Higher voltage and lower current, thus lower perveance would lead to higher efficiency efficiency / % Efficiency 0 0,5 1 1,5 2 2,5 3 microperveance Rule of thumb formula from fit to experimental data η = p Carlo Pagani 19

20 Multibeam Klystron Idea Klystron with low perveance: high efficiency but high voltage Klystron with low perveance and low high voltage: low high voltage but low power Solution Klystron with many low perveance beams: low perveance per beam thus high efficiency low voltage compared to klystron with single beam with low perveance Carlo Pagani 20

21 Multi Beam Klystron TH1801 by Thales Measured performance Operation Frequency: 1.3GHz Cathode Voltage: 117kV Beam Current: 131A μperveance: 3.27 Number of Beams: 7 Cathode loading: 5.5A/cm 2 Max. RF Peak Power: 10MW RF Pulse Duration: 1.5ms Repetition Rate: 10Hz RF Average Power: 150kW Efficiency: 65% Gain: 48.2dB Solenoid Power: 6kW Length: 2.5m Lifetime (goal): ~40000h Carlo Pagani 21

22 Multi Beam Klystron VKL-8301 by CPI Specified Operating Parameters Peak Power Output 10 MW (min) Ave. Power Output 150 kw (min) Beam Voltage 114 kv (nom) Beam Current 131 A (nom) μperveance 3.40 Frequency 1300 MHz Gain 47 db (min) Efficiency 67 % (nom) Cathode Loading 2.0 A/cm 2 Dimensions H,Ø: 2.3 by 1.0 meters Weight 2000 lbs Electromagnet Solenoid Power 4 kw (max) Coil Voltage 200 V (max) Weight 2800 lbs Klystron during construction Carlo Pagani 22

23 Multi Beam Klystron E3736 MBK by Toshiba Measured performance Voltage: 115 kv Current: 135 A mperveance: 3.46 Output Power: 10.4 MW Efficiency: 67 % Pulse duration: 1.5 ms Rep. Rate: 10 Hz Design Layout As biult Carlo Pagani 23

24 Sheet-Beam Klystron from SLAC Carlo Pagani 24

25 Beam Transport and RF The elliptical beam is focused in a periodic permanent magnet stack that is interspersed with rf cavities Lead shielding Magnetically shielded from outside world Have done: Electron beam RF cavity Permanent Magnet Cell 3D Gun simulations of a 130 A, 40:1 aspect ratio elliptical beam traversing 30 period structures. 3D PIC Code simulations of rf interaction with the beam. Carlo Pagani 25

26 RF Waveguide Distribution Carlo Pagani 26

27 RF Distribution Development Carlo Pagani 27

28 ILC RF Distribution (for 33 MV/m Max Operation) 10 MW Klystron 33 MV/m * 9.0 ma * m = 308 kw (Cavity Input Power) 26 Cavities 1/.93 (Distribution Losses) 1/.86 (LLRF Tuning Overhead) 10.0 MW Carlo Pagani 28

29 XFEL RF Distribution System Switched from a TTF- Like (3D) System To a Tree-Like (2D) System Carlo Pagani 29

30 RF Waveguide Components 3 Stub Tuner (IHEP, Bejing, China) E and H Bends (Spinner) Circulator (Ferrite) Changing phase, degree 60 Impedance matching range 1/3Z w 3Z w Max power, MW 2 * Z w waveguide impedance Hybrid Coupler (RFT, Spinner) Type WFHI 3-4 Peak input power, MW 0.4 Average power, kw 8 Min isolation at 1.3 GHz, db >30 Max insertion loss at 1.3 GHz, db 0.08 Input SWR at 1.3 GHz 1.1 (for full reflection) RF Load (Ferrite) RF Load (Ferrite) Directivity, db Return loss, db Coupling factor, db (due to tolerance overlapping only 13 different coupling factors instead 18 are nessesary) Accuracy of coupling factor, db ; 12.0; 11.4; 10.7; 10.1; 9.6; 9.1; 8.5; 7.8; 7.0; 6.0; 4.8; Type WFHLL 3-1 Peak input power, MW 1.0 Average power, kw 0.2 Min return loss at 1.3GHz, db Max VSWR at 1.3 GHz 1.05 Max surface temperature, T C 50 (for full average power) Physical length, mm 230 Type WFHL 3-1 WFHL 3-5 Peak input power, MW Average power, kw Min return loss at 1.3 GHz, db Max VSWR at 1.3 GHz <1.05 <1.05 Max surface temperature, ΔT C (for full average power) Physical length, mm Carlo Pagani 30