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CLIC choke-mode structure CLIC choke-mode structure

CLIC choke-mode structure - PowerPoint Presentation

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CLIC choke-mode structure - PPT Presentation

Hao Zha 2013Oct09 Outlines 1 Chokemode structure design 2 Optimization on RF parameters 3 Experiments 4 Future plan Overview of CDS design Name Description Parameters Manufactory amp ID: 185380

mode choke beam design choke mode design beam wakefield dipole cds load plane parameters results cells mutation optimization irises

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Slide1

CLIC choke-mode structure

Hao Zha2013-Oct-09Slide2

Outlines

1. Choke-mode structure design;2. Optimization on RF parameters;3. Experiments.4. Future planSlide3

Overview of CDS

design

Name

Description

Parameters

Manufactory &

Measurement

CDS-AOriginal design;regular choke;Irises: CLIC-G(0.15m): 20~30 V/pC/m/mmPrototype cells made in CERNCDS-BHOM tuned choke;Wakefield suppression Improve;Irises: CLIC-G(0.15m): 15~20 V/pC/m/mmNoCDS-CNew choke design, Optimized on wakefield suppression;Irises: CLIC-G(0.15m): ~5 V/pC/m/mmη: 24.2%Prototype cells (aluminium) made in Tsinghua.Wakefield tested in AWA.CDS-DNew choke design;Optimized on RF parameters.Irises: a/λ=0.125(0.15m): ~4 V/pC/m/mmη: 26.0%No

NameDescriptionParametersManufactory &MeasurementCDS-AOriginal design;regular choke;Prototype cells made in CERNCDS-BHOM tuned choke;Wakefield suppression Improve;NoCDS-CNew choke design, Optimized on wakefield suppression;Prototype cells (aluminium) made in Tsinghua.Wakefield tested in AWA.CDS-DNew choke design;Optimized on RF parameters.NoSlide4

Equivalent circuit model

For accelerating mode,

ϕ

3

=

π

/2, so z=∞. Then It is fully reflected by choke.

Some HOMs could be also fully (or mostly) reflected.Slide5

Thin-neck choke design

Zc

a

Short load

L

a

section a

Plane CZcb =K*ZcaLbsection bzazbz3Plane D

Plane APlane APlane DPlane C

S

12

K

1

2

3

4

f2

36GHz

49GHz

60GHz

69GHz

T

he joint planes (Plane A and Plane D) are equivalent as impedance transformers

Purpose of thin-neck design:

Increase the 2

nd

fully reflected frequency

Reduce reactance of HOMsSlide6

Matching step

Purpose of matching step design:

Reduce

reactance of

some HOMs.

Compensate residual reflection from the load,

p

ossible to design loads with lower price.Slide7

Dipole detuning

(

~16GHz)

(

~18GHz)

c1

c2

(mm) (GHz) Purpose of dipole detuning: Detune lower band HOMs (one cell).

Provide weak detuning between cells (like DDS).Slide8

Wakefield simulation results

W

(s=0.15m)

WDS

5

CDS-A

20~30+Thin-neck10~17+Matching step7~10+Dipole detuning (CDS-C)5~6CDSWDSFc11Frms45Fworst2520Slide9

RF parameters of CDS-C

HFSS simulation results:

CDS-C

CLIC-G

Iris aperture(

mm)

3.15, 2.35

3.15, 2.35Q(Cu)4895, 53855538, 5738Shunt impedance(MΩ/m)59, 8381, 103Group velocity(%c)1.38, 0.731.65, 0.83Max E-field(MV/m)246235Sc (MW/mm^2)5.725.43Pulse heating(K)23.247.9Peak input power(MW)67.4

60.5Filling time(ns)72.462.2RF-beam efficiency24.2%28.1%Slide10

Optimization on RF parameters

Optimization target : RF-beam efficiency (η), Max surface field (Es, Sc

, Hs).Geometry sizes of irises are the focus points.

Input:

Geometry sizes of irises

Output:

η

, Es, Sc, HsOptimizationSlide11

Genetic algorithm

Lots of geometry variables => Huge searching space.Genetic algorithm

=> find optimum solutions more quickly (actually much more quickly).

Use C++ to implement it.

Fitness

η

, Es, Sc

Individuals Gene: GeometryBorn children (with gene mutation)Higher fitness, more childrenCalculationDiscardedJoin inlowHighRandom initialization

Here we use a simplified way to calculated RF parameters.Slide12

Optimization results (1)

Max population: 400~800Birth rate: 4/iterationIteration: 800

Searching time: 2.5×106

;

CDS-C

CDS-D

CLIC-G

Iris aperture(mm)3.15, 2.353.49, 2.503.15, 2.35Shunt impedance(MΩ/m)59, 8353, 7481, 103Group velocity(%c)1.38, 0.732.00, 0.751.65, 0.83

Bunch population (109)3.724.503.72Max E-field(MV/m)246223235Sc (MW/mm^2)5.725.175.45

Pulse heating(K)

23.2

22.0

47.9

Peak input power

(MW)

67.4

79.3

60.2

Filling time

(ns)

72.4

60.8

62.2

RF-beam efficiency

24.2%

26.0%

28.1%Slide13

Optimization results (2)

Wakefield suppression: 4V/pC/m/mmF

c=1.01; Frms

=3.8;

F

worst

=3

5CDS-CCDS-DSlide14

Radial line experiments

Target: (1) To verify HOMs absorption (S12) in choke-structures; (2) To test the RF load;Reflection S11 can be tested on VNA after calibration (“multi-short load calibration”)

To VNASlide15

Radial line experimentsSlide16

Reflection of RF load

Results are promising;Slide17

HOMs absorption in chokeSlide18

Layout of AWA

G1: Photo cathode + Faraday cup. To study the phonemes of laser trigged RF break down.

G2: Witness beam line, Mg cathode + gun + 1*linac, 15MeV, max 100nC. G3: Drive beam line, Semiconductor cathode + gun + 6*linac, 75MeV; >=100nC, can produce bunch train.Slide19

Set up experiments (1)

GUN

LINAC

Chamber

ICT

ICT

Spectrometer

20GHz oscilloscope, 0~20GHz mixer

1#

2#

3#

4#

oscilloscope

With load

Without loadSlide20

Set up experiments (2)

Chamber

YAG

ICT

Bellows

YAG

Bellows

Be windows:50um thickness;For 14MeV electron beam, ~30% (calculated by Fluka) of the beam can pass it without any scattering.After optimized on beamdynamics:1nC Beam size: ~0.7m,5nC Beam size: ~1.6m,Beam aperture: 5.5mmSlide21

Set up experiments

(3)Slide22

Wakefield measurement results (1)

L

0

10GHz

CABLE

Attenuation

1# 20 dB 2# 20 dB 3# 0 dB 4#0 dB Slide23

Spectrum of signal in cable 4#

Unidentified dipole mode? It may be the 36GHz – 2*10GHz = 16GHz

Fundamental

mode 12GHz

Dipole mode

~16GHz

Unidentified dipole mode?

Dipole mode ~19GHzDipole mode ~23GHzDipole mode ~28GHzSlide24

Wakefield measurement results (2)

L

0

No Mixer

CABLE

Attenuation

1# 30 dB 2# 20 dB 3# 10 dB 4#0 dB Slide25

Spectrum of signal in cable 3#

Dipole mode

at 16GHz and 19GHz

Looks

like the dipole mode

at 50-22=

28GHz

Fundamental mode UnidentifiedQ (@12GHz) = 160~400Q (@16GHz) = 12.5Q (@19GHz) = 15.3Slide26

Future plan

Manufacturing & High power test;Start manufacturing choke-mode cells, 6cells/24cells(Tsinghua

); Single choke-cell for high power test designed (Tsinghua & KEK);

Start to design the compact coupler for choke-mode (

Tsinghua

).

Wakefield test with two beams;

- Two beam line facility (AWA)Further optimization (geometry, load design);Slide27

Thank you!!Slide28

Multi-short calibration

At least 3 different load is needed in the standard calibrationSolve the Inconsistent equations to get more precise network parameters (Least square method).

- y: reflection detected by network analyzer ;

- x

: reflection of radial line at plane A

……Slide29

Genetic representation

There are 3 selections for

genetic representation.The second way

has the best practical results.

For the first and third selections, it is very difficult to put iris parameters of every cell into chromosomes. We just selected some cells (e.g. first, middle and last cell) as chromosome

.

linear fitPolynomial co-efficiencypolynomial fitSlide30

Fitness function

Early convergence is a big problem of GA:

Better solution has more children, and soon it and its posterity will monopolize the whole world.

Fitness = Performance – CompetitionSlide31

Reproduction

Evolution will be aroused in the reproduction by two ways: Mutation

; Crossover (not very suitable in our case).About mutation, we find this way of mutation has a better effect

Sequential

mutation (rather than randomly mutation) + Mutation step becomes gradually smaller (rather than constant)