RF for Linacs. Erk Jensen CERN AB/RF

Transkript

1 RF for Linacs Erk Jensen CERN AB/RF Outline RF Power Sources (solid state, tetrodes, klystrons,...) RF Pulse Compression (principle, flat pulses, BOC) Accelerating Structures (Brillouin diagram, HOMs, beam loading, SC accelerating structures, HDS) E. Jensen, RF for Linacs 1

2 RF Power sources Typical ranges (commercially available) CW/Average power [kw] Transistors SSPAs (x32) Grid tubes IOT Klystrons CCTWT f [MHz] E. Jensen, RF for Linacs 2

3 RF power transistors MOSFET VDMOS Vertical Doubly Diffused LDMOS Lateral Doubly Diffused E. Jensen, RF for Linacs 3

4 LEIR SSPA, 1 kw, MHz MRF151G E. Jensen, RF for Linacs 4

5 Soleil Booster SSPA, 40 kw, 352 MHz 147 modules DU1029UK E. Jensen, RF for Linacs 5

6 Tetrode control grid screen grid Ra cathode anode (plate) +Ua potential Ia=0 Ua Ia max Ug2 4CX250B (Eimac/CPI), < 500 MHz, 600 W (Anode removed) Ug1 RS 1084 CJ (ex Siemens, now Thales), < 30 MHz, 75 kw YL1520 (ex Philips, now Richardson), < 260 MHz, 25 kw E. Jensen, RF for Linacs 6

7 Tetrode operation (AB1) operating line This example: Thales TH 681 Classes of operation: A: large DC bias current, η < 50 % AB: small DC bias current, η % B: 0 bias current, halfwave, η < 78 % C: current only with large modulation, η 90 % Ia(t) E. Jensen, RF for Linacs 7

8 High power tetrode amplifier CERN Linac3: 100 MHz, 350 kw 50 kw Driver: TH345, Final: RS 2054 SK CERN PS: MHz, 30 kw Driver: solid state 400 W, Final: RS 1084 CJSC E. Jensen, RF for Linacs 8

9 Klystron principle velocity modulation drift density modulation t RF in RF out z -V 0 Cathode Collector E. Jensen, RF for Linacs 9

10 Klystrons CERN CTF3 (LIL): 3 GHz, 45 MW, 4.5 μs, 50 Hz, η 45 % CERN LHC: 400 MHz, 300 kw, CW, η 62 % E. Jensen, RF for Linacs 10

11 RF Pulse Compression 6 Input pulse 360 Input phase 6 SLED output pulse SLED: SLAC Energy Doubler LIPS: LEP Injector Power Saver E. Jensen, RF for Linacs 11

12 Flat output pulses Standard SLED Pulse RF phase modulation Flat pulse khz Old New Flat pulse RF phase modulation Distorted pulse E. Jensen, RF for Linacs 12

13 Pulse compressor BOC Barrel Open Cavity E. Jensen, RF for Linacs 13

14 BOC GHz, S11: db Electric field, logarithmic scale Magnetic field E. Jensen, RF for Linacs 14

15 Travelling Wave Structure st 31 disc SiC wedges Coupler cell (2 waveguide ports) total length: 1.10 m dimple tuning holes E. Jensen, RF for Linacs 15

16 Travelling wave structure Input coupler shown: Re {Poynting vector} (power density) Output coupler 4-cell travelling wave structure ¼ of geometry shown E. Jensen, RF for Linacs 16

17 Iris loaded waveguide 11.4 GHz structure (NLC) 1 cm 30 GHz structure (CLIC) E. Jensen, RF for Linacs 17

18 Brillouin diagram ω Higher order modes (HOM) speed of light line, ω = k /c Stop band or band gap Pass band synchronous interaction π 2 π k d = phase advance per cell E. Jensen, RF for Linacs 18

19 Brillouin Diagram ω d/c π 2π speed of light line, ω = β /c 2π/3 π π/2 synchronous π/2 0 π/2 k d π 0 E. Jensen, RF for Linacs 19

20 Brillouin diagram Brillouin diagram TM 0n modes iris variation (parameter a ): blue solid: 1st cell (17 mm) red dashed: 32nd cell (13.3 mm) Brillouin diagram dipole modes iris variation (parameter a ): blue solid: 1st cell (17 mm) red dashed: 32nd cell (13.3 mm) speed of light line E. Jensen, RF for Linacs 20

21 Higher order modes r E r H Fundamental accelerating mode (TM0n) v E 1st dipole mode Higher order longitudinal mode (TM0n) E. Jensen, RF for Linacs 21

22 Choke mode cavity E. Jensen, RF for Linacs 22

23 TDS: Tapered Damped Structure accelerating mode: cut-off in waveguide shown E, color coding logarithmic SiC load Dipole mode: Poynting vector towards SiC load E. Jensen, RF for Linacs 23

24 Slotted iris structure E. Jensen, RF for Linacs 24

25 HOM damping at work FRAME: 1 01/06/00-17:06:38 VERSION[V4.024] SICA32.DRD transverse wake for 3 cells. offset 10 mm, 2.5 mm σ SI: A+3,10,4, B-5,CELL-6,15 A: 1.700E+01 MM, B: 3.703E+01 MM. FOR REF., E.J., JUNE 2000 X COMPONENT OF WAKE POTENTIAL IN V [INDIRECT CALC.] OP-:4024 #1DGRAPH 3 GHz SICA structure: Transverse wake suppression W [V/pC] t 4.00 ORDINATE: WAKET COMPONENT: X FIXED COORDINATES: DIM...MESHLINE X 11 Y ABSCISSA: GEOMWAKE [BASE OF WAKET] 0.000E+00 REFERENCE COORDINATE: S VARY...MESHLINE FROM 0 TO E s [m] E. Jensen, RF for Linacs 25

26 SICA 3 GHz structures lined up waiting for installation mounted on the girder in CTF3 E. Jensen, RF for Linacs 26

27 Beam Loading E. Jensen, RF for Linacs 27

28 Beam loading compensation Methods of beam loading compensation: Ramped RF pulse Staggered timing I.V. Syrachev, T.Higo: Numerical investigation of transient beam loading compensation in JLC X-band main linac, KEK Report 96-8 E. Jensen, RF for Linacs 28

29 Superconducting RF 10.2 MV/ per cavity E. Jensen, RF for Linacs 29

30 SC cavities for small β 115 MHz split-ring cavity, MHz β = 0.19 lollipop cavity 57.5 MHz cavities: β= 0.06 QWR (quarter wave resonator) β = 0.03 fork cavity 345 MHz β = 0.4 spoke cavity β = fork cavity E. Jensen, RF for Linacs 30

31 TESLA/ILC SC cavities MV/m E. Jensen, RF for Linacs 31

32 Surface field breakdown limits Surface field [MV/m] Kilpatrick, 1957 Wang&Loew '88, SLAC-pub-4647 Wang&Loew '97, SLAC-pub-7684 CLIC design f E e E = c c f in GHz, E c in MV/m Frequency [GHz] 100 Normal conducting, on Cu E. Jensen, RF for Linacs 32

33 Pulse length dependence 6 1 τ E. Jensen, RF for Linacs 33

34 CLIC HDS structure 30 GHz, phase advance per cell: 70, Cell length: 1.94 mm, Smallest iris diameter: 3 mm, accelerating gradient 150 MV/m, Max surface field 380 MV/m, max. ΔT 56 K, Optimized for Mo iris, CuZr cavities E. Jensen, RF for Linacs 34

35 HDS: Optimizing the cavity contour E r H r Field distribution in the optimized HDS cell geometry. The contour optimization is done to prevent hot spots. E. Jensen, RF for Linacs 35

36 HDS: Cu prototype 1 cm E. Jensen, RF for Linacs 36