WG1 Summary

Lasers

Cathodes

1 / 17

Cathodes

SRF Guns

Joint Sessions

Topics & Speakers I

• Laser Systems– JLab laser: S. Zhang

– Elliptical shaping: Y. Li

– Cornell autocorr. meas: S. Pan

– Xtal pulse stacking @ BNL: T. Rao

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– Xtal pulse stacking @ BNL: T. Rao

• Cathodes– CeB6 (therm.): K. Togawa

– Pb, K2CsSb & Diamond @ BNL: J. Smedley

– Nanostructured: K. Harkay

Topics & Speakers II

• Beam Dynamics – Theory, Simulation– No Stinkin’ Merger: D. Douglas

– DC+Z-bend optimization: X. Dong

– SRF gun dynamics: D. Kayran

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• SRF Gun Design & Development– Fabrication issues: T. Grimm

– HZB Project: T. Kamps

– Wisconsin: R. Legg

– The Many Guns of BNL: A. Burrill

Discussion Groups

• Robert Legg – Operational Issues

• Andrew Burrill – Coupler & HOM Issues

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• John Lewellen – Questions for Contemplation

– thanks to Todd, Bob, Brian for half of the list

Drive Lasers

• Laser power should no longer be an issue

• Operation concerns• rep rate

• pattern

• contrast ratio

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•

• Bunch / pulse shaping is maturing– interesting new techniques

• xtal stretchers

• direct elliptical pulse formation

• Laser architecture: Fiber + bulk xtal proposed

Image courtesy B Dunham

Elliptical (and other) Pulses

0.0

0.5

1.0

I (a

rb.u

nit

s)

P = 12 mm

-30

0

30

r (

µµ µµm

)

P = 2 mm

-30

0

30

P = 3 mm

P = 4 mm

Images courtesy Y Li

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-1 0 1

0.0

0.5

1.0

-1 0 1 -1 0 1 -1 0 1-1 0 1

-20

0

20 a=-4125 fs2

r ( µµ µµ

m)

i (a

rb. u

.)

-20

0

20

a=-2625 fs2

a=1875 fs2

a=-4875 fs2

a=0 fs2

time (ps)

-1 0 1 -1 0 1-1 0 1-1 0 1

t (ps)

Cathodes

• mA-range operation– Alkali cathodes (e.g. Cs2Te)

• High QE in green for 100+ mA operation– Multi-alkali– NEA (Cs:GaAs)

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– NEA (Cs:GaAs)– Cathode heating effects may be a problem?

• Temperature distribution across cathode?

• Designer / Structured– Diamond amplifier– Nanofabricated lattice

Cathode Studies

Beam from Diamond Amplifier Cathode

Image c

ourte

sy J

K2CsSb cathode performance

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Image courtesy J Smedley

Image c

ourte

sy J

Sm

edle

y

Cs2Te (FZD)

1% QE in gun

Image courtesy J Teichert

SRF guns: Current Architectures

Elliptical cell Quarterwave Cavity

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Elliptical cell Quarterwave Cavity

Elliptical-Cell SRF Guns• FZD 1.3 GHz 3.5-cell

– Filter cavity cathode isolation

• Brookhaven 1.3 GHz and 703.75 MHz

Single-cell

– Plug and Choke joint cathode isolationIm

age c

ourte

sy J

Teic

hert

Images courtesy A Burrill

10 / 17

• Peking University

– 100 kV DC Cs2Te “booster cathode”

– 3 ½-cell SRF cavity following gun

• HZB 1.5-cell, 1.3 GHz

Image courtesy K Liu

Image courtesy T Kamps

QW SRF Guns

• BNL– 112 MHz

• Wisconsin– 200 MHz

Image courtesy T Grimm

Ima

ge

co

urte

sy R

Le

gg

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– 200 MHz

– RF short @ cathode

• NPS– 500 MHz

– Shorted line

Image courtesy T Grimm

Ima

ge

co

urte

sy R

Le

gg

Other Gun Architectures & Concepts

• Peking University

– 100 kV DC gun

– 3 ½ cell, 1.3-GHz cavity

• Advanced Energy Systems

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• Advanced Energy Systems

– Reentrant cavity design optimized for power use

– RF power feed along cathode stalk

• SPring-8 SCSS Injector

– Thermionic cathode

– Very good beam emittance (SASE-FEL driver)

Operational Issues Discussion

• Where do you put your

complexity?

• Field emission

– Worse with gradient

– Stray drive laser light

• “Mundane” problems

can be the worst

– “Infrastructure” systems

get little attention

13 / 17

– Stray drive laser light

may exacerbate

• Alignment

– Ions hit cathode center…

– off-axis laser: εn goes

from 3 to 5 µm

• Thermionic cathodes?

– Works well at SCSS

– Worked well at SCA

– Worth an honest effort

Gun Frequency Coax/WG FPC power HOM style

ELBE/ EuroFEL 3.5

cell Gun

1300 MHz coax 10 kW Nb couplers x2

½ cell 1300 Coax

BNL-ERL 703 MHz coax 500 kW x2 Ferrite

Wisconsin 200 MHz Capacitive coax

NPS 500 MHz Capacitive coax

INFN 1300 MHz Capacitive coax

Pb-Nb (DESY) 1300 MHz Capacitive Coax 6 kW Nb couplers x2

4GLS 1.5 cell 1300 MHz Coax (3) 150 kW

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4GLS 1.5 cell 1300 MHz Coax (3) 150 kW

PKU (DC-SRF) 1300 MHz Coax

14

Some Leading Questions…• How do we hold the cathode?

– and keep the RF in the cavity?

• How to protect the cathode in case of arcing?

• What’s so great about cylindrical symmetry?

• If we get the “right” on-axis field, do we care what the outer

wall geometry is?

• What about multi-frequency operation?

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• What about multi-frequency operation?

• What are the pros and cons of a Peking U.-style “DC-booster”

cathode?

… Then the session ended. For next time…

Conclusions

• Phenomenal progress over the past few years

– Drive lasers

– Pulse shaping

– Cathode operation, testing, new concepts

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– Cathode operation, testing, new concepts

– SRF guns are operational

• “Next-generation” SRF guns are being worked

on now!

The Last Question

Where will injectors be in 2011?

17 / 17

Paper Outline

• Abstract & Introduction [Lewellen

]

• Drive lasers & pulse shaping [Rao

& Zhang ]

• Cathodes [ Smedley, Teichert]

– current status

• Operation & implementation

– FZD experience [Teichert ]

– Installation & connection

concerns [Legg ]

• Novel Concepts [Smith &

Jordan]

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– current status

– ongoing issues

• Gun designs & progress [ Burrill]

– elliptical cavities [ Burrill]

– quarter-wave cavities [ Grimm]

– Hybrid designs [Liu ]

– Alternate designs [ Bluem]

Jordan]

• Summary, conclusions, future

work