Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 1/36 CLIC_DDS & Test Structure 03.05.2010 V. Khan, A. D’Elia, R. Jones A

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 1/36

CLIC_DDS & Test Structure03.05.2010

V. Khan, A. D’Elia, R. JonesA. Grudiev, W. Wuensch, R. Zennaro


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


Initial designs : CLIC_ DT

Ref: Khan, Jones. Proc. of EPAC08

<a>/λ=0.155 , ∆f = 3.6σ= 3.3 GHz, ∆f/favg= 20 %

Large bandwidth structure

RF breakdown constrains: Not satisfiedBeam dynamics constraints : Satisfied

Ref: Khan, Jones. Proc. Of LIAC08

Small bandwidth structure

<a>/λ=0.102 , ∆f = 3σ= 0.83 GHz, ∆f/favg= 4.5 %

RF breakdown constrains: SatisfiedBeam dynamics constraints : Not satisfied


192 cells8-fold interleaving

Summary of CLIC WS’09 : DDS1_C

24 cellsNo interleaving

192 cells8-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 = 36.92 m

∆f=3.6 σ =2.3 GHz∆f/fc=13%


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 (2nd 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


DDS1_C

Parameters CLIC_DDS1_corrected(8-fold interleaved)

Bunch space (rf cycles/ns) 8/0.67

Limit on wake (V/pC/mm/m) 6.3

Number of bunches 312

Bunch population (109) 4.2

Pin (MW) 74.6

Esur max. (MV/m) 290

Pulse temperature rise (K) 65

RF-beam-eff. 22.5


10ε 5ε

3.33ε 2ε

Circular

Square

Ellipticala)Convexb)Concave

a

b

ε = a/b


a

b

ε = a/bReference line


10ε 5ε

3.33ε

Circular Square

ε=20ε=10

ε=5

Convex ellipticity

Concave ellipticity

Single un-damped cell Iris radius=4.0 mm


Circular Rectangular Elliptical(Convex)

Elliptical(Concave)

ε=10 ε=5 ε=3.33 ε=2.0 ε=1 ε=20 ε=10 ε=5

Facc(GHz) 12.24 12.09 11.98 12.0 11.99 11.98 11.98 11.9911 11.9919 11.9935

Eacc(V/m) 0.43 0.43 0.42 0.43 0.43 0.42 0.42 0.43 0.43 0.42

Hsur max

/Eacc (mA/V)

3.64 4.86 4.71 4.54 4.29 3.75 3 4.94 4.99 5.11

Esur max

/Eacc2.27 2.27 2.33 2.28 2.28 2.33 2.33 2.27 2.27 2.33

Undamped cell with various geometries

Iris radius = 4. 0 mmIris thickness = 4.0 mm


Optimisation scan for DDS2_E

Optimisation of cavity shape for min. H surmax

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


E surmax

Efficiency

∆f _dipole

∆T

Pin

Manifold damped structures3 cell simulations

Optimisation of E surmax , ∆f and efficiency

Optimised parameters for DDS2


b

2b

2bemajor

emajor3.0eminor

Detailed cell geometry : CLIC_DDS2_E

Rc

hr1

2*r2

r2

h1

r1+h+2*r2

r1

a1

a2g=L - t

L a

t= 2*a2

Radius = 0.5 mm

Variable parameters (mm)

Cell #1 Cell#24

a 4.0 2.3

b 11.01 10.039

a2 2.0 0.65

a1 1*a2 2*a2

Rc 6.2 6.8

r2 3.25 2.3

Constant parameters (mm)

All cells

L 8.3316

r1 0.85

h 4.5

h1 1.25

Fillet @ cavity and manifold joint

1.0

Rounding of cavity edge

0.5


DDS1_C

DDS2_E

Parameters DDS1_C DDS2_E Changes for

Shape Circular Elliptical Min. H-field

<Iris thickness> (mm) 2.35 2.65 Min. E-field

Rc 1/24 (mm) 6.2-7.5 6.2-6.8 Critical coupling

Changes : DDS1_C to DDS2_E

DDS1_C

DDS2_E


DDS1_C

DDS2_E


Dipole mode : circuit parameters

DDS1_C

DDS2_E

DDS1_C

DDS2_E

DDS1_C

DDS2_E


a1=4mma24=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


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 increasedProblem : Poor dipole coupling resulting in wake-suppression degradation

DDS2_EDDS2_ER

Rc


Dispersion curves

Light line

Uncoupled 1st mode

Uncoupled manifold mode

Avoided crossing

Uncoupled 2nd mode

Cell # 1

Cell # 24


DDS2_E :Rc=6.2 - 6.8 mm

DDS2_ER : Rc=6.8 mm const


High Power Test: CLIC_DDS_A

It has been decided to build 1st out of 8-fold interleaved structures for High Power Testing


Cell # 1

Cell # 24

CLIC_DDS_ANon interleaved 24 cell structureMotivation: High power testing (71 MW)Uniform manifolds

CLIC_DDS_A


mc=14.45

mr = 2.2Uniform 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


)/(E

ESImagSReS 2

2

cell singleacc

ULureacc_struct

61

c mW

Where S= Poynting vector

Cell # 1

E-field H-field Sc

6.75 W/μm2

40 o K

50 o K

@ 95 MV/mOpposite sides Selected contours


@ 138 MV/m

Cell # 24E-field H-field Sc

220 MV/m

Opposite sides Selected contours


CLIC_DDS_A Parameters

∆a

∆t

∆b


CLIC_DDS_A : Surface fields


CLIC_DDS_A : Fundamental mode properties


CLIC_DDS_A : RF properties

Max. Values

Esur=220 MV/m∆T = 51 KPin= 70.8Eacc_UL=131 MV/mSc=6.75 W/μm2

RF-beam-eff=23.5%

∆T

35*Sc

Esur

Eacc

Pin

Dashed curves : Unloaded conditionSolid curves: Beam loaded condition

CLIC_G Values

Esur=240 MV/m∆T = 51 deg.Pin= 63.8Eacc_UL=128 MV/mSc=5.4 W/μm2

RF-beam-eff=27.7%


CLIC_DDS_A : Dipole mode properties

f0

fxfsyn, fπ



CLIC_DDS_A


Undamped

Damped

Qavg ~1700


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 Matching iris

Mode launcher

First cell

Last cell


11.994 GHz

0.00035

dB 34.5S max11

First matching cell

11.994 GHz

0.000035

dB 44.5S max11

Last matching cell


2

b2b1b1.5

2

b25b24b24.5

In progress : Full structure

mb1 = b1mb24 = b25

ma1ma24a1 a2 a24 a25

mb1 mb24b1.5 b24.5

First matching cell Last matching cell

Mode launcherb2.5

........Mode launcher


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


Initial study

Monopole

Dipole

Sicεr = 10μr = 1tanδ = 0.06mr = 3.2 mmr = 2.0 mm

Iris radius = 4. 0 mmIris thickness = 4.0 mm


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 2010-11


Next in 2010-11 ?

Task May Jun Jul Aug Sept. onwards

Matching end cells In progress

HFSS: Full structure(N+2 cells) simulations

To do

Comparison of results (wakefield)in GdfidL

To do

Mechanical design To do

Fabrication To do

DDS_SiC Schedule to be discussed

CLIC_DDS_B Schedule to be discussed


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.


DDS1 revised simulations with surface approximation 5micron+aspect ratio of 5

Cells esur hsur eacc ttf Eacc*ttf Esur/eaccttf hsur./eaccttf

1 0.67 1.5 0.2748 0.96 0.26 2.54 5.76

5 0.94 2.5(2.7) 0.4963 0.953 0.473 1.987 5.28

9 0.93 2.2(2.3) 0.538 0.946 0.509 1.827 4.32

13 0.94(0.97) 2.2(2.3) 0.5532 0.939 0.519 1.81 4.23

17 0.78 1.7(1.8) 0.4742 0.932 0.442 1.765 3.85

21 0.89 1.88(1.9) 0.5574 0.925 0.516 1.725 3.64

24 0.67(0.72) 1.0 0.3272 0.92 0.3 2.23 3.33


DDS1 : Plain curve ; DDS2 : Curve with dots


DDS2

Cell # 1Rc=6.2

Cell # 1Rc=6.5

Cell # 1Rc=6.8

Cell # 13Rc=6.8

Cell # 13Rc=6.6

Cell # 13Rc=6.5

Cell # 13Rc=6.2


Cell # 24Rc=6.2

Cell # 24Rc=7.2

Cell # 24Rc=7.0

Cell # 24Rc=6.8

Cell # 24Rc=6.6

Cell # 24Rc=6.4

DDS2


Damped Detuned Structure 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


DDS2_HPT structure

Cell Eacc Q R’/Q vg/c Es/Eacc Hsur/Eacc Sc/Eacc2

# (V/m) kΩ/m (%) mA/m W/(x10-4)

1 0.4488 5020 10.179 2.07 2.23 4.9 7.3

2 0.4563 5091 10.649 1.85 2.2 4.82 6.9

5 0.4882 5325 11.723 1.62 2.05 4.5 5.5

9 0.5255 5604 12.899 1.51 1.89 4.15 4.5

13 0.5555 5838 13.952 1.42 1.8 4.0 4.0

17 0.5828 6061 15.049 1.34 1.7 3.75 3.4

21 0.6021 6307 16.416 1.22 1.66 3.5 2.9

23 0.4217 6451 17.411 1.11 1.65 3.3 2.9

24 0.5749 6534 18.130 1.0 1.67 3.3 2.98


ma (mm)

mg

(m

m)

noc=1

4 5 6

4.5

5

5.5

6

6.5

7

-20

-15

-10

-5

ma (mm)

mg

(m

m)

noc=2

4 5 6

4.5

5

5.5

6

6.5

7

-20

-15

-10

-5

ma (mm)

mg

(m

m)

noc=3

4 4.2 4.4 4.6 4.8 5 5.2 5.4 5.6 5.8 6

4.5

5

5.5

6

6.5

7

-40

-30

-20

-10

ma (mm)

mg

(m

m)

noc=1

5 5.2 5.4 5.6 5.8

6.4

6.6

6.8

7

7.2

-20

-15

-10

-5

ma (mm)

mg

(m

m)

noc=2

5.2 5.4 5.6 5.8

6.2

6.4

6.6

6.8

7

7.2

-20

-15

-10

-5

ma (mm)

mg

(m

m)

noc=3

5.2 5.25 5.3 5.35 5.4 5.45

6

6.5

7

-40

-30

-20

-10

common_minimum = ma mg S11 S11 S11 (noc=1) (noc=2) (noc=3) 5.0000 6.3316 -4.7483 -9.9892 -8.3322 5.3000 6.8316 -19.5343 -19.0196 -50.6180 5.5000 7.3316 -12.6941 -10.2416 -6.6752 5.6000 7.3316 -5.7225 -24.0994 -6.4650 5.7000 7.3316 -2.7236 -10.7502 -4.1787

global_min = ma mg S11 S11 S11 (noc=1) (noc=2) (noc=3) 5.3000 6.8316 -19.5343 -19.0196 -50.6180

Contour plots for first cell

common_minimum =

Empty matrix: 0-by-5

global_min =

Empty matrix: 0-by-5

Contour plots for last cell


a1=4mma24=2.3mm

∆f=3.5 σ =2.2 GHz∆f/fc=13%

DDS1_C : Plain curve DDS2_E : Curve with dots


DDS1 : Plain curve ; DDS2 : Curve with dots

Dipole mode : circuit parameters

Documents

Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 1/36 CLIC_DDS & Test Structure 03.05.2010 V. Khan, A. D’Elia, R. Jones A