Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36 CLIC_DDS & Test Structure V. Khan, A. D’Elia, R. Jones A. Grudiev, W. Wuensch, R. Zennaro

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36 Overview Initial designs: CLIC_DT DDS design: DDS1_C Modified DDS: DDS2_E Test Structure: CLIC_DDS_A Next : 1) CLIC_DDS_B ? 2) DDS_SiC

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36 Initial designs : CLIC_ DT Ref: Khan, Jones. Proc. of EPAC08 /λ=0.155, ∆f = 3.6σ= 3.3 GHz, ∆f/favg= 20 % Large bandwidth structure RF breakdown constrains: Not satisfied Beam dynamics constraints : Satisfied Ref: Khan, Jones. Proc. Of LIAC08 Small bandwidth structure /λ=0.102, ∆f = 3σ= 0.83 GHz, ∆f/favg= 4.5 % RF breakdown constrains: Satisfied Beam dynamics constraints : Not satisfied

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN / cells 8-fold interleaving Summary of CLIC WS’09 : DDS1_C 24 cells No interleaving 192 cells 8-fold interleaving Manifold Coupling slot Dipole mode Manifold mode ∆fmin = 65 MHz ∆tmax =15.38 ns ∆s = 4.61 m ∆fmin = 8.12 MHz ∆tmax =123 ns ∆s = m ∆f=3.6 σ =2.3 GHz ∆f/fc=13%

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36 Shortcomings of DDS1_C High surface fields : It does not satisfy RF breakdown constraints (results consistent in various ver. of HFSS and CST microwave studio) Solution* : Major change in cavity shape : circular to elliptical [*] R. Zennaro & A. D’Elia Use of surface approximation (2 nd ord. soln.) for meshing the geometry for accurate simulation results rather than volume mesh Suggestions from CERN collaborators* Problems encountered during post CLIC WS’09 visit No consistency in freq. and fields in different ver. of HFSS and CST microwave studio

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36 DDS1_C ParametersCLIC_DDS1_corrected (8-fold interleaved) Bunch space (rf cycles/ns)8/0.67 Limit on wake (V/pC/mm/m)6.3 Number of bunches312 Bunch population (10 9 )4.2 Pin (MW)74.6 Esur max. (MV/m)290 Pulse temperature rise (K)65 RF-beam-eff.22.5

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36 Circular Square Elliptical a)Convex b)Concave a b ε = a/b

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36 a b ε = a/b Reference line

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36 Circular Square ε=20 ε=10 ε=5 Convex ellipticity Concave ellipticity Single un-damped cell Iris radius=4.0 mm

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36 CircularRectangularElliptical (Convex) Elliptical (Concave) ε=10ε=5ε=3.33ε=2.0ε=1ε=20ε=10ε=5 Facc(GHz) Eacc(V/m) H sur max /Eacc (mA/V) E sur max /Eacc Undamped cell with various geometries Iris radius = 4. 0 mm Iris thickness = 4.0 mm

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36 Optimisation scan for DDS2_E Optimisation of cavity shape for min. H sur max Circular Rectangular ε=10 ε=5 ε=3 ε=2 ε=1 Single undamped cell Iris radius=4.0 mm Optimised parameters for DDS2 Circular cell ε=2 ε=3 Single cell with manifold

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36 E sur max Efficiency ∆f _dipole ∆T P in Manifold damped structures 3 cell simulations Optimisation of E sur max, ∆f and efficiency Optimised parameters for DDS2

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36 Detailed cell geometry : CLIC_DDS2_E RcRc h r1r1 2*r 2 r2r2 h1h1 r 1 +h+2*r 2 r1r1 a1 a2 g=L - t L a t= 2*a2 Radius = 0.5 mm Variable paramete rs (mm) Cell #1Cell#24 a b a a11*a22*a2 Rc r Constant parameters (mm) All cells L r10.85 h4.5 h11.25 cavity and manifold joint 1.0 Rounding of cavity edge 0.5

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36 DDS1_C DDS2_E ParametersDDS1_CDDS2_EChanges for ShapeCircularEllipticalMin. H-field (mm) Min. E-field Rc 1/24 (mm) Critical coupling Changes : DDS1_C to DDS2_E DDS1_C DDS2_E

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36 DDS1_C DDS2_E

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36 Dipole mode : circuit parameters DDS1_C DDS2_E DDS1_C DDS2_E DDS1_C DDS2_E

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36 a 1 =4mm a 24 =2.3mm ∆f=3.5 σ =2.2 GHz ∆f/fc=13% DDS1_C DDS2_E DDS1_C DDS2_E DDS1_C DDS2_E DDS1_C DDS2_E DDS1_C DDS2_E

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36 A. Grudiev & A. D’Elia : Potential final design with all roundings incorporated To move all this part (coupling guide+manifold) up Rounding Change : Rc needs to be increased Problem : Poor dipole coupling resulting in wake-suppression degradation DDS2_E DDS2_ER RcRc

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36 Dispersion curves Light line Uncoupled 1 st mode Uncoupled manifold mode Avoided crossing Uncoupled 2 nd mode Cell # 1 Cell # 24

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36 DDS2_E :Rc= mm DDS2_ER : Rc=6.8 mm const

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36 High Power Test: CLIC_DDS_A It has been decided to build 1 st out of 8-fold interleaved structures for High Power Testing

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36 Cell # 1 Cell # 24 CLIC_DDS_A Non interleaved 24 cell structure Motivation: High power testing (71 MW) Uniform manifolds CLIC_DDS_A

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36 mc=14.45 mr = 2.2 Uniform manifold throughout the structure : Mechanical ease Manifold geometry for CLIC_DDS_A Rc=6.8 Dimensions are in mm Cell 1 Cell 24 mc = 14.45mm mc = 15mm mc = 14.45mm mc = 15mm

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36 Where S= Poynting vect or Cell # 1 E-fieldH-field Sc 6.75 W/μm 2 40 o K 50 o 95 MV/m Opposite sides Selected contours

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN MV/m Cell # 24 E-fieldH-field Sc 220 MV/m Opposite sidesSelected contours

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36 CLIC_DDS_A Parameters ∆a ∆t ∆b

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36 CLIC_DDS_A : Surface fields

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36 CLIC_DDS_A : Fundamental mode properties

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36 CLIC_DDS_A : RF properties Max. Values Esur=220 MV/m ∆T = 51 K Pin= 70.8 Eacc_UL=131 MV/m Sc=6.75 W/μm 2 RF-beam-eff=23.5% ∆T 35*Sc Esur Eacc Pin Dashed curves : Unloaded condition Solid curves: Beam loaded condition CLIC_G Values Esur=240 MV/m ∆T = 51 deg. Pin= 63.8 Eacc_UL=128 MV/m Sc=5.4 W/μm 2 RF-beam-eff=27.7%

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36 CLIC_DDS_A : Dipole mode properties f0 fx fsyn, fπ

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36 24 cells No interleaving CLIC_DDS_A 24 cells No interleaving Undamped Damped Q avg ~1700

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36 Matching cell design procedure ma = mg Two options Vary ma and mb : very small room to vary mb vary ma and mg mb Matching cell Mode launcher Regular cell Matching cell N=1-3 Regular iris Matching iris Mode launcher

First cell

Last cell

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN / GHz First matching cell GHz Last matching cell

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36 In progress : Full structure mb1 = b1 mb24 = b25 ma1 ma24 a1a2a24a25 mb1 mb24 b1.5 b24.5 First matching cellLast matching cell Mode launcher b Mode launcher

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36 Potential design for DDS_SiC Motivation : Better damping DDS3 Geometry : SiC running through manifolds Possible advantage(s) : 1) Relaxed tolerances 2) Short coupling slots → reduced ∆T Possible disadvantage : Need to think about locating BPM’s

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36 Initial study Monopole Dipole Sic εr = 10 μr = 1 tanδ = 0.06 mr = 3.2 mm r = 2.0 mm Iris radius = 4. 0 mm Iris thickness = 4.0 mm

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36 Summary DDS1_C : Adequate damping but high surface fields DDS2_E : Surface fields within acceptable limits but damping is relatively poor but still acceptable CLIC_DDS_A : First out of 8 structures of DDS2_E, RF design is done and will be built in

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36 Next in ? TaskMayJunJulAugSept. onwards Matching end cellsIn progress HFSS: Full structure (N+2 cells) simulations To do Comparison of results (wakefield)in GdfidL To do Mechanical designTo do FabricationTo do DDS_SiCSchedule to be discussed CLIC_DDS_BSchedule to be discussed

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36 Acknowledgements Thanks to Igor Syratchev for suggesting to look into DDS_SiC We acknowledge all our collaborators from CERN, KEK and SLAC for providing all the necessary information and many-many useful suggestions.

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36 DDS1 revised simulations with surface approximation 5micron+aspect ratio of 5 CellsesurhsureaccttfEacc*ttfEsur/eaccttfhsur./eaccttf (2.7) (2.3) (0.97)2.2(2.3) (1.8) (1.9) (0.72)

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36 DDS1 : Plain curve ; DDS2 : Curve with dots

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36 DDS2 Cell # 1 Rc=6.2 Cell # 1 Rc=6.5 Cell # 1 Rc=6.8 Cell # 13 Rc=6.8 Cell # 13 Rc=6.6 Cell # 13 Rc=6.5 Cell # 13 Rc=6.2

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36 Cell # 24 Rc=6.2 Cell # 24 Rc=7.2 Cell # 24 Rc=7.0 Cell # 24 Rc=6.8 Cell # 24 Rc=6.6 Cell # 24 Rc=6.4 DDS2

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36 D amped D etuned S tructure overview Gaussian distribution of cell parameters is chosen in this (CLIC_DDS) structures which causes wakefield to decay in nearly Gaussian fashion for short time scale (few nsec) Limited number of cells (N=24) in a structure (poor sampling of a Gaussian) leads to recoherence of the wake (t=1/∆fmin) Recoherence of the wake is suppressed by coupling out the higher order modes using a waveguide like structures i.e. manifolds running parallel to the accelerating cells Interleaving neighbouring structure frequencies can be envisaged to improve the wake suppression

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36 DDS2_HPT structure CellEaccQR’/Qvg/cEs/EaccHsur/EaccSc/Eacc 2 #(V/m)kΩ/m(%)mA/mW/(x10 -4 )

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36

common_minimum = ma mg S11 S11 S11 (noc=1) (noc=2) (noc=3) global_min = ma mg S11 S11 S11 (noc=1) (noc=2) (noc=3) Contour plots for first cell

common_minimum = Empty matrix: 0-by- 5 global_min = Empty matrix: 0-by- 5 Contour plots for last cell

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36 a 1 =4mm a 24 =2.3mm ∆f=3.5 σ =2.2 GHz ∆f/fc=13% DDS1_C : Plain curve DDS2_E : Curve with dots

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN /36 DDS1 : Plain curve ; DDS2 : Curve with dots Dipole mode : circuit parameters