esources summary t. kamps, c. hernandez-garcia fls 2012 workshop 05.03.2012 – 09.03.2012...

FLS 2012 | Intro to WG eSources | Thorsten Kamps | [email protected] 1

eSources Summary

T. Kamps, C. Hernandez-GarciaFLS 2012 Workshop

05.03.2012 – 09.03.2012

03.05.2012


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


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


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


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


Photocathodes/Drive Lasers and Beam Current Goals(FELs and ERLs as SRR), D. Dowell et al., NIM A 622

03.05.2012


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


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


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


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


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


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

esources summary t. kamps, c. hernandez-garcia fls 2012 workshop 05.03.2012 – 09.03.2012...

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