eSources Summary
T. Kamps, C. Hernandez-Garcia
FLS 2012 Workshop
05.03.2012 – 09.03.2012
03.05.2012
FLS 2012 | Intro to WG eSources | Thorsten Kamps | [email protected]
1
Questions and themes which came up during the
workshop
• Do we need a common metric to compare emittance
performance of machines, helping us to understand if
a particular solution is applicable? The 2/3 of charge
emittance, rms emittance, slice emittance of lasing
slice,…
• What to we need to do to get the SRF gun working
within the parameter space required for future light
sources? How can we approach performance levels
already achieved with DC and NCRF guns.
03.05.2012
FLS 2012 | Intro to WG eSources | Thorsten Kamps | [email protected]
2
What people expecting from the working group
• What are the specs of different type of light sources and how
can we meet them?
• How can we break the present limits on beam brightness?
• What is the state-of-the-art right now?
• What issues and troubles do groups have and how can my issues
and troubles be solved? Mainly operational issues connected to
cathodes, field emission in DC and RF guns, dark current.
• What simulation tools are required to build better sources?
• How can we bring the SRF gun system to high average current
and high brightness
• Cathodes, cathodes, cathodes and more cathodes.
• How to measure extreme beam parameters from the electron
source, from the wanted and unwanted beam.
• How to reduce cost of system and operation.
03.05.2012
FLS 2012 | Intro to WG eSources | Thorsten Kamps | [email protected]
3
Is there a better way to summarize requirements on the
electron beam from the injector
• Where does the injector end? Is it enough to produce an
ultra-bright beam or do we need to care about degradation
in the following beamline.
• For FEL type sources: Is the 6D peak brightness and pulse
length of the X-ray pulse is the figure of merit?
• We could produce a bright 6D phase space volume and
adapt to the required beam parameters.
• The other axis on the performance plot could be the either
the average current (repetition rate) or bunch charge.
• Combine this in a three-axis plot with 6D brightness vs.
average current and charge/pulse.
• Don’t forget stability and reliabitlity.
03.05.2012
FLS 2012 | Intro to WG eSources | Thorsten Kamps | [email protected]
4
Other requirements ERL as SRR and FELs have on
electron sources
• ERLs can drive free electron laser (FEL) and storage ring
replacement (SRR) type light sources.
• FEL users expect slight shot-to-shot variations and look
for peak brightness and pulse length.
• SRR users expect storage ring like stability (top-up) and
look for average brightness and pulse length. There is
small subgroup of users demanding high flux.
• We need consistent metric of parameters.
03.05.2012
FLS 2012 | Intro to WG eSources | Thorsten Kamps | [email protected]
5
Photocathodes/Drive Lasers and Beam Current Goals
(FELs and ERLs as SRR), D. Dowell et al., NIM A 622
03.05.2012
FLS 2012 | Intro to WG eSources | Thorsten Kamps | [email protected]
6
Other themes raised during discussion
• Collaborate to use make efficient use or ressources. Do
not duplicate experiments.
• Get people from other fields (surface science,
chemistry, users) on board to better understand
photoemission and robustness.
03.05.2012
FLS 2012 | Intro to WG eSources | Thorsten Kamps | [email protected]
7
Tuesday – State of the art and status of current projects
with NCRF and SRF guns
• Mikhail reported on the results of experimental optimization of
an L-Band NCRF photoinjector for FLASH/XFEL facility
• The group reports emittance values for a range of bunch
charges from 20 pC to 2 nC.
• Key issues solved recently were the RF phase stability and
longitudinal laser pulse shape optimization.
• John Corlett introduced the current status of the APEX facility,
highly reentrant (QWR) 187 MHz cavity for CW operation. Focus
on photoemission studies with CsK2Sb, Cs2Te and diamond
amplifier cathodes. Lots of collaborations with Cornell, ANL,
INFN Milano, BNL.
• The cavity is now at LBL and RF conditioned. At nominal field
level of 19.5 MV/m dark current is 8 uA. Next step is setup of
diagnostics beamline.
03.05.2012
FLS 2012 | Intro to WG eSources | Thorsten Kamps | [email protected]
8
NCRF guns continued
• Boris Militsyn introduced EBTF/CLARA facility. Main
goals is to reach performance limits for NCRF S-Band
gun with metallic photocathodes for ultra-short
electron pulse production. Potential driver for an FEL
class source.
• Gun takes on the 2.6 cell S-Band design of Alpha-X, the
accelerator is optimized for velocity bunching.
• Close collaboration with local surface science lab on
site.
03.05.2012
FLS 2012 | Intro to WG eSources | Thorsten Kamps | [email protected]
9
Status of SRF guns for FEL applications
• Bob Legg reported on recent results for the WiFEL SRF
QWR 199.6 MHz gun. Main goal is to drive a CW FEL facility
with ultra-short pulses generated in the blow-out mode.
Needs high peak field on cathode. Planning with a load lock
to use metallic and semiconductor cathodes. Plug design
from ELBE SRF gun.
• Lots collaboration with industry, Niowave and Danfysik,
and JLAB
• Cavity was successfully cold-tested at Niowave and is now
at Wisconsin. Setup of electron diagnostics and
cryomodule assembly is next.
• Use capabilities of Aladdin synchrotron radiation source for
material research in ultra-low thermal emittance
photocathodes.
03.05.2012
FLS 2012 | Intro to WG eSources | Thorsten Kamps | [email protected]
10
Status of SRF guns for FEL applications
• Jochen Teichert reported of status and future plans for the
elliptical 3.5 cell 1.3 GHz SRF gun serving multiple user
modes at ELBE (IR FEL, Thomson scattering, neutron and
positron production).
• Present cavity is now since 2007 in operation and showed
no Q degradation with NC photocathode present in cavity
volume.
• Did lots of measurements of long. and trans. slice
parameters using zero phasing and ELBE. Issues with dark
current and multipacting. Attempt to counteract MP with
DC bias and plan to use with TiN coating.
• New cavity, produced by JLAB, showed excellent
performance (Epk of 43 MV/m and Qo exceeding
1*10^10).
03.05.2012
FLS 2012 | Intro to WG eSources | Thorsten Kamps | [email protected]
11
Joint session with ERL on ERL class electron sources, DC
and SRF guns for high average current
• Andrew Burrill shed light on the requirements on ERL class
electron sources and introduced us to parameters of
exisiting and planned gun systems.
• Communicate required and achieved longitudinal
emittance performance to complete gun performance
table by D. Dowell.
• Brief discussion on what cathode lifetime is. Operational
cathode lifetime describes conservation and decay of beam
current delivered by the cathode/drive laser combo.
• Field emission one of the main limitations in DC and SRF
guns alike.
03.05.2012
FLS 2012 | Intro to WG eSources | Thorsten Kamps | [email protected]
12