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
2 / 17
– 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
3 / 17
• 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
4 / 17
• 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
5 / 17
•
• 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
6 / 17
-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)
7 / 17
– 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
8 / 17
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
9 / 17
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
11 / 17
– 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
12 / 17
• 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
14 / 17
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?
15 / 17
• 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
16 / 17
– 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]
18 / 17
– 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