Development of Dielectric-Based Wakefield Power Extractors

Chunguang Jing1,2, W. Gai1, A. Kanareykin2,

Igor Syratchev, CERN

1. High Energy Physics Division, ANL

2. Euclid Techlabs LLC

April. 2010* Now with National Light Source, BNL

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Contents

Introduction 7.8GHz Dielectric-Based Power

Extractor--- design, fabrication, and test. 26GHz Dielectric-Based Power

Extractor--- design, fabrication, and test. Proposed 12GHz Dielectric-Based

Power Extractor (for CLIC) Summary

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Dielectric-lined Waveguide to Slow the Wave

Electric Field Vectors (TM01)

•Pros: simplicity of fabrication

potentially higher breakdown threshold

low surface field enhancement

Easy deflecting mode damping

•Cons: Multipactor

Er/Ez=a/

Dielectric loaded waveguide can slow the RF wave for acceleration like the conventional disk-loaded waveguide. Low-loss dielectric materials bring promise to this kind of structure.

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7.8GHz Dielectric-Based Wakefield Power Extractor*

Two related journal publications: 1) F. Gao, et al, PR ST-AB, 11, 041301 (2008); 2) F. Gao, et al. IEEE Trans. NS, 56, 3, JUNE (2009) 1492-1497.

*Prototype structure without transverse mode damping. It is to demonstrate the concept.

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7.8GHz Dielectric-Based Wakefield Power Extractor----design

Geometric and accelerating parameters value

ID / OD of dielectric tube 12.04mm /22.34 mm

Dielectric constant 4.6

Length of dielectric tubes 266 mm

Synchronous frequency of TM01 mode 7.8 GHz

Group velocity 0.23c

R/Q of TM01mode 6090(/m )

Q of TM01mode

Generated rf power (AWA beam:Tb=769ps,z=1.5~2mm)

2745

11MW/10nC per bunch

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mode launcherinside

DL deceleration waveguide

TM01-TE10 coupler

rf output port

Insertion loss Reflection

7.8GHz Dielectric-Based Wakefield Power Extractor----fabrication & bench test

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7.8GHz Dielectric-Based Wakefield Power Extractor----beam test (I): setup

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A UV laser pulse is split into two trains, each consisting eight micropulses spaced by 2T.

e- bunch train generated:i). 16 bunches, Tb = 769ps, qmax = 4.8nCii). 16 bunches, Tb = 1.54ns, qmax = 4.9nCiii). 4 bunches, Tb = 769ps, qmax = 26.5nC

7.8GHz Dielectric-Based Wakefield Power Extractor----beam test (II): e-bunch train generation

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15ns rf pulse generated, Pmax = 2.4MW @ qmax = 4.8nC.

7.8GHz Dielectric-Based Wakefield Power Extractor----beam test (III): 1-16 bunches, Tb=769ps

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30ns rf pulse generated, Pmax = 1MW @ qmax = 4.9nC.

7.8GHz Dielectric-Based Wakefield Power Extractor----beam test (IV): 16 bunches, Tb=1.54ns

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7.5ns rf pulse generated, Pmax = 44MW @ qmax = 26.5nC.

7.8GHz Dielectric-Based Wakefield Power Extractor----beam test (V): 4 bunches, Tb=769ps

44MW generated40MW extracted

f - GHz t - ns

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26GHz Dielectric-Based Wakefield Power Extractor

----by Euclid Techlabs, supported by DoE SBIR program

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26GHz Dielectric-Based Wakefield Power Extractor----design

Geometric and accelerating parameters value

ID / OD of dielectric tube 7 mm /9.068 mm

Dielectric constant 6.64

Length of dielectric tubes 300 mm

Synchronous frequency of TM01 mode 26 GHz

Group velocity 0.25c/0.42c

R/Q of TM01 mode 9788(/m )

Q of TM01mode

Generated rf power (AWA Beam)

295037MW/10nC per bunch

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*20nC, single bunch, bunch length 1.5mm.

*16, 20nC bunch train, steady output power of 148 MW and 56 MV/m peak gradient. The energy loss is 5.7 MeV for the last bunch in the bunch train .

26GHz Dielectric-Based Wakefield Power Extractor----power estimation

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26GHz Dielectric-Based Wakefield Power Extractor----fabrication

SiC based 26GHz UHV rf load 26GHz UHV rf power detector

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Load

Rf probe

LO=14.576GHz

11.424GHz BPF (228MHz BW)

16GHz scope

26GHz Dielectric-Based Wakefield Power Extractor----beam test (I): setup

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26GHz Dielectric-Based Wakefield Power Extractor----beam test (II): 16 bunches, Tb=769ps

Down-converted rf Trace

11.44+14.576=26.016 GHz

SiC based Rf load behaves well.

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26GHz Dielectric-Based Wakefield Power Extractor----beam test (III): 4 bunches, Tb=769ps

11.44+14.576=26.016 GHz

Background noise to the scope

Down-converted rf Trace

SiC based Rf load behaves well.

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Number is the percentage of charge transmission out of the structure, which indicates the BBU appears when charge goes high.

Theoretically, 9nC29.6MW, 24.8MV/m; 17MW was measured (bunch length effect, coupler loss, etc)

26GHz Dielectric-Based Wakefield Power Extractor----beam test (IV): charge sweeping, 4 bunches, Tb=769ps

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Transverse Damping---- to improve the high current beam transportation

TM01 mode (axial current only)

HEM11 mode (azimuthal current included)

TM01 mode Ez HEM11 mode Ez

SiCCopperDielectricsVacuum

by Euclid Techlabs, supported by DoE SBIR program

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Proposed 12GHz Dielectric-Based Wakefield Power Extractor

----submitted to DoE 2010 SBIR program by Euclid Techlabs

In collaboration with CERN (Igor Syratchev)

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12GHz Quartz-Based Power Extractor Using CLIC Parameters:

σz=1mm, Q=8.4nC, Tb=83ps

Freq 11.994GHz

Effective Length 23cm

Beam channel 23mm

Thickness of the dielectric tube 2.582mm

Dielectric const. 3.75(Quartz)

Loss tangent (@10GHz) 6*10^-5

Q 7318

R/Q 2.171k/m

Vg 0.4846c

Peak surface Gradient Ell=12.65MV/m; E=18.28MV/m

Steady Power 142MW

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-The ceramic part is installed into the separate copper tube. The other compact piece integrates the choke and the matching grove and could be the part of the flange to be connected tothe coupler.- Between the two, one can foresee the EB welding or another flange. With this approach the system cab be easily dismantled and the pieces recycled.- For later the slot can be equipped with damping material (for the HOM) and to be used for the vacuum pumping of the entire volume.- By design, the system is rather insensitive to the fabrication/installation errors (slot width, position of ceramic and etc.)- For the fabrication, it looks inexpensive.

Preliminary Design of a 12GHz Quartz-Based Power Extractor

(by Igor Syratchev)

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Current Status

The 1st step is to build a 11.424GHz version DWPE so that we can high power rf test it at SLAC and explore the possible issues.

This work has been applied for 2010 DoE SBIR funding (just funded).

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SUMMARY

Dielectric-based wakefield power extractors have been successfully demonstrated.

Two structures, 7.8GHz and 26GHz, were fabricated and tested. 40MW for 7.8GHz and 20MW for 26GHz were measured.

X-band DWPE is planned to develop soon.