SIMULATION OF : H.O.M DAMPED CAVITIES

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1 E.S.L.S Radio Frequency Meeting Aarhus, DENMARK Sept 2005 SIMULATION OF : H.O.M DAMPED CAVITIES Grenoble - FRANCE

2 MHz) TO ATTENUATE HIGHER ORDER MODES WITH RIDGE

2 TARGET OF SIMULATIONS AT E.S.R.F DEVELOPPING A PROTOTYPE OF NORMAL CONDUCTING CAVITY (at MHz) TO ATTENUATE HIGHER ORDER MODES WITH RIDGE WAVEGUIDE DAMPERS INCLUDING FERRITE BASED ON R&D OF EU PROJECT (NTHU)

3 SUMMARY 1- OPTIMISATION OF THE BODY (Naked Cavity) 2- OPTIMISATION OF THE FERRITE LOADED RIDGE WAVEGUIDE 3- SIMULATION OF THE GLOBAL CAVITY : BODY + 3 DAMPERS 4- COMPARISON : MAFIA / GDFIDL FOR SIMULATION OF THE BESSY II CAVITY (a design which doesn t t use Ferrite)

4 1 - FIRST STEP : OPTIMIZATION OF THE BODY* - Superfish (2D) calculates Eigenvalues and main parameters of RF symmetrical cavities - GDFIDL (3D) is used as Eigenvalue or Time domain solver for arbitrary RF structures TYPE OF CAVITY SIMULATION TOOLS f RF (MHz) Q R/Q (Ohms) R (k Ohms) Scaled BESSY II Cavity Optimised SUPERFISH GDFIDL Scaled BESSY II Cavity Not Optimised SUPERFISH LEP Model Cavity / ESRF URMEL [Dr H.Henke / Dr T.Weiland ] SUPERFISH BESSY II MAFIA [Dr F.Marhauser / Bessy ] SUPERFISH GDFIDL (* PERFECT BODY WITHOUT HOLE)

5 A- GDFIFL AS EIGENVALUE SOLVER FOR H.O.M STUDY OF THE BODY GDFIDL is a Finite Difference solver for the Maxwell and Helmholz equations. Can be used as Eigenvalues or Time domain solver for arbitraries rf structures. LIST OF THE MOST INFLUENTIALS LONGITUDINAL MODES TILL 1.3 GHz MODE TYPE FREQUENCY (MHz) Q R (kω) R/Q (Ω) 0-E M M E E M Conditions : simulation of half cavity with electric or magnetic boundary for a meshing of 2 mm. Notations : m-e-n or m-h-n, m for azimuthal dependency, n as sequential index.

6 B- GDFIDL AS FINITE DIFFERENCES IN TIME DOMAIN SOLVER (FDTD) FOR THE T BODY 40x10 3 Impedance (Ohms) MHz Remark : For modes which should have an high Q value, the calculated impedance isn t accurate It d require a longer wake length MHz x10 9 Frequency (Hz) Conditions : Simulation on only 200 meters of half the cavity with magnetic boundary for a meshing of 2 mm. (No offset on transverse plane)

2 - SECOND STEP : OPTIMIZATION OF FERRITE LOADED RIDGE WAVEGUIDE WITH 3D SIMULATION SOFT : High Frequency Structure Simulator (HFSS ) HFSS is based on a Finite Element Method with adaptive mesh

7 2 - SECOND STEP : OPTIMIZATION OF FERRITE LOADED RIDGE WAVEGUIDE WITH 3D SIMULATION SOFT : High Frequency Structure Simulator (HFSS ) HFSS is based on a Finite Element Method with adaptive mesh refinement. Eigenmodes of arbitrary RF strucutres are solved, including materials losses. BASED ON DESIGN of N.T.H.U and BESSY [P.Z Rao / F.Marhauser / E.Weihreter 05/2004] FERRITE VACUUM BASIC MODEL (Longitudinal cut) Waveguide part long enough to attenuate the f RF mode P/P o = exp [ -(4.π.Z / λ).( 1-(λ c / λ) 2 ) 1/2 ] METALLIC RIDGE Here, for : z = 0.25 m P/P o 0.07 f c = 435 MHz

8 0.8 A- BASIC FERRITE MODEL Effect induced by variation of Ferrite thickness (e) S e = mm 0.2 e = mm 0.1 e = mm 0.0 fc RWG = 435 MHz 600 f RF < fc RWG < f 0M Frequency (MHz)

9 B- TAPERED FERRITE MODEL No Ferrite Step

10 0.8 Effect induced by variation of Ferrite thickness (e) for BASIC ASIC MODELODEL (BM)) and TAPERED FERRITE ERRITE MODELODEL (TFM) TFM - e = 12 mm TFM - e = 3 mm TFM - e = 6 mm S BM - e = mm 0.2 BM - e = mm TFM Frequency (MHz) 800 BM - e = mm

11 C- TILE FERRITE MODEL TILES WITH PROGRESSIVE THICKNESS NO STEP TO OBTAIN AN HOMOGENEOUS REPARTITION OF THE ABSORBED POWER

0.80 0.75 RESULTS OF SIMULATIONS TO COMPARE 3 TYPES OF FERRITE LOADED RIDGE WAVEGUIDE MODELS S11 0.70 0.65 0.60 0.55 0.50 0.45 0.40 0.35 0.30 0.

12 RESULTS OF SIMULATIONS TO COMPARE 3 TYPES OF FERRITE LOADED RIDGE WAVEGUIDE MODELS S TAPERED MODEL - e = 12 mm BASIC MODEL - e = mm TILE MODEL - e : 1 to 20 mm Frequency (MHz)

13 (FOR 1W INCIDENT) EVOLUTION OF DENSITY POWER ABSORBED BY FERRITE FOR 3 MODELS : BASIC, TAPERED, TILE 0.99 Absorbed Power (W) TILE MODEL (7 Tiles, e = 1/1.5/3/4/6/8/20) BASIC MODEL (e = mm) 0.96 TAPERED MODEL (e = 12mm) Frequency (MHz)

14 3 - THIRD STEP : THE GLOBAL CAVITY - Body + 3 Dampers - With GDFIDL only Including Ferrite VIEW OF THE WHOLE CAVITY

15 100x10 3 FDTD SIMULATION WITH GDFIDL FOR THE GLOBAL CAVITY WITH 3 DAMPERS 80 For material properties at 500 MHz IMPEDANCE (Ohms) BODY + 3 RIDGE WAVEGUIDES : WITHOUT FERRITE BODY + 3 DAMPERS : TILE MODEL BODY + 3 DAMPERS : BASIC MODEL The TILE MODEL is a better absorber than the BASIC one HOM max for 300 ma / 18 cavities (normalised) HOM max for 500 ma / 18 cavities (normalized) HOM max for 1A / 18 cavities (normalized) x10 9 FREQUENCY (Hz) Conditions : Simulation on 600 meters and 2 mm meshing. (No offset on transverse plane)

16 ZOOM ON BANDWITH : 0.9 to 2.2 GHz 25x10 3 BODY + 3 RIDGE WAVEGUIDES : WITHOUT FERRITE BODY + 3 DAMPERS : TILE MODEL BODY + 3 DAMPERS : BASIC MODEL 20 IMPEDANCE (Ohms) HOM max for 300 ma / 18 cavities HOM max for 500 ma / 18 cavities 5 HOM max for 1A / 18 cavities x10 9 FREQUENCY (Hz)

17 GDFIDL AS EIGENVALUE SOLVER FOR THE GLOBAL CAVITY Parameters f RF (MHz) Study of the fundamental mode only - 2 mm meshing BODY BODY + 3 WAVEGUIDES : WITHOUT FERRITE * BODY + 3 DAMPERS : BASIC FERRITE MODEL Q R/Q (Ω) R (k Ω) *Remark Remark : Insertion of Ridge Waveguides had induced a huge shift on the fundamental frequency

120x10 3 100 4- COMPARISON MAFIA / GDFIDL FOR SIMULATION OF BESSY II CAVITY (3 Circular Waveguides with Coaxial Transition DAMPERS) - STRUCTURE WITHOUT ABSORBING

18 120x COMPARISON MAFIA / GDFIDL FOR SIMULATION OF BESSY II CAVITY (3 Circular Waveguides with Coaxial Transition DAMPERS) - STRUCTURE WITHOUT ABSORBING MATERIAL - 80 MAFIA / F.Marhauser (BESSY) GDFIDL / V.Serrière (E.S.R.F) 60 ReZ [ Ω] Wake on 400 meters and a 4 mm meshing x10 9 Frequency [Hz]

19 ZOOM ON BANDWITH : 0.6 to 1.2 GHz

20 ZOOM ON ON BANDWITH : 1.2 to 1.8 GHz

21 CONCLUSION ON SIMULATION TOOLS AND RESULTS 1) ASPECTS ALREADY DEALED WITH : SIMULATIONS WITH 3 RF SIMULATION SOFTS HAS BEEN DONE :. SUPERFISH : Perfect for optimisation of simple symmetrical Body. HFSS : Adapted for S parameters studies (even including absorbing materials). GDFIDL : Usefull for H.O.M studies of complex Cavities even including ferrite THE MAIN ELEMENTS OF THE CAVITY HAVE BEEN STUDIED GLOBALY : BODY, RIDGE, FERRITE STUDY OF TRANSVERSE H.O.M OPTIMISE THE TILE MODEL AGAIN TO ABSORB SUFFICIENTLY H.O.M WITHOUT THE FUNDAMENTAL ONE (by changing width and gap of the ridge and the length of the waveguide) OBTAIN A FUNDAMENTAL MODE WITH A FREQUENCY CLOSER TO MHz THERMAL STUDY OF THE CAVITY 2) POINTS TO DO :

Status of the HOM Damped Cavity Project

Status of the HOM Damped Cavity Project E. Weihreter / BESSY for the HOM Damped Cavity Collaboration BESSY, Daresbury Lab, DELTA, MaxLab, NTHU Project funded by the EC under contract HPRI-CT-1999-50011