- Challenges and Solutions - Matthias Liepe Cornell University CORNELL Matthias Liepe 12/12/2003 - 1 - U N I V E R S I T Y
• ERL Light Source: Why? • The Cornell ERL: An Overview – Prototype – 5 GeV SR Source • SC RF in the Cornell ERL Injector - Challenges and Solutions - • SC RF in the Cornell ERL Main Linac - Challenges and Solutions - • Outlook and Summary CORNELL Matthias Liepe 12/12/2003 - 2 - U N I V E R S I T Y
Today's Workhorse Light Sources: Storage Rings Today's Workhorse Light Sources: Storage Rings • 1 st generation parasitic SR on high energy physics storage rings • 2 nd generation dedicated bending magnet sources, designed for high flux SR • 3 rd generation Some rings use dedicated undulator sources optimized for brilliance, using high current, low superconducting RF emittance Storage ring light sourses give: • Repetition rate • Stability • High flux, brilliance – average/peak CORNELL Matthias Liepe 12/12/2003 - 3 - U N I V E R S I T Y
Synchrotron Radiation at Cornell Synchrotron Radiation at Cornell 1952: 1 st accurate measurement of synchrotron radiation power by Dale � Corson with the Cornell 300MeV synchrotron. 1953: 1 st measurement of the synchrotron radiation spectrum by Paul � Hartman with the Cornell 300MeV synchrotron. Worlds 1 st synchrotron radiation beam line (Cornell 230MeV synch.) � 1961: 1 st measurement of radiation polarization by Peter Joos with the � Cornell 1.1GeV synchrotron. 1978: X-Ray facility CHESS is being build at CESR � 2003: 1 st Nobel prize with CESR data goes to R.MacKinnon � Dale Corson Cornell’s 8 th president Roderick MacKinnon CORNELL Matthias Liepe 12/12/2003 - 4 - U N I V E R S I T Y
More Users… … More Users Historical Growth of Synchrotron Protein structures in Protein Publications Worldwide: ISI data 1968 to Data Bank (Mostly from SR) 2002, Keyword: “synchrotron” (from G. Margaritondo) CORNELL Matthias Liepe 12/12/2003 - 5 - U N I V E R S I T Y
… More Demands: What do we need in the future? More Demands: What do we need in the future? … 1. High average and high peak • Brilliance (photons/s/0.1% bw/mrad 2 /mm 2 ) • Flux (photons/s/0.1% bw) 2. Coherence 3. Flexible pulse structure • Programmable pulse trains (interval, bunch size) • Adjustable pulse lengths down to the femtosecond regime 3. Small x-ray source size of desired shape, e.g. circular 4. Flexibility of source operation • No fill decay • Stability & robustness • Easily upgraded FEL ERL CORNELL Matthias Liepe 12/12/2003 - 6 - U N I V E R S I T Y
Important Beam Parameters: Important Beam Parameters: A Wish List A Wish List Low emittance Low emittance Long undulator Low energy spread Low energy spread • Decreasing the Short bunches Short bunches electron beam emittance down to • High spectral • High spectral diffraction limit brilliance SR sources brilliance SR sources B ∝ 1/ ε x ε y τ • High coherence • High coherence fraction: fraction: p c = λ 2 /(4 π ) 2 ε x ε y High flux High flux High beam current High beam current F ∝ I beam CORNELL Matthias Liepe 12/12/2003 - 7 - U N I V E R S I T Y
How do we get these Beam Parameters? How do we get these Beam Parameters? Limits of Storage Rings Limits of Storage Rings • Electron beam emittance, bunch profile and energy spread in a storage ring is determined by equilibrium between radiation damping and two main diffusion processes: - quantum fluctuation of the SR and - the intrabeam scattering. ⇒ There is no (affordable) way to decrease the horizontal emittance in storage ring ε x < 10 -10 m·rad and energy spread σ Ε /E < 10 -3 . • Beam lifetime limits bunch length to about 10 ps. Too long for many dynamic processes. • Technology well developed. Theoretical limits are being approached. • Time structure cannot be tailored to user needs. • Fills are necessary, intensity is not constant. ⇒ Equilibrium dynamics determines almost all the parameters on our wish list! CORNELL Matthias Liepe 12/12/2003 - 8 - U N I V E R S I T Y
How do we get these Beam Parameters? How do we get these Beam Parameters? The Alternative: Linacs The Alternative: Linacs • Injectors can be built with very brilliant e- beams and linacs can accelerate with very low emittance growth (if we do it right). - Emittance & pulse length determined by injector. - Single pass non equilibrium device. - Easy upgrade path: Better e - source gives higher brilliance. - Due to adiabatic damping an emittance ε ~ 10 -11 m·rad and energy spread σ E /E ~ 10 -4 is possible for energies E > 5 GeV. - Potential for ultra high brilliance. • Complete flexibility of bunch timing. • No fill decay, constant intensity. • Electron bunches dumped after single pass. CORNELL Matthias Liepe 12/12/2003 - 9 - U N I V E R S I T Y
The Alternative: Linacs The Alternative: Linacs Small Beam Size, Coherence, Short Bunches Small Beam Size, Coherence, Short Bunches 5 GeV storage ring ERL 5GeV@100mA Factor 100 more coherent flux for ERL 3 rd SR ERL for same x-rays, or provide coherence for harder x-rays coherent coherent 16ps 100fs 2ps CORNELL Matthias Liepe 12/12/2003 - 10 - U N I V E R S I T Y
Linac Light Source: X- -Rays Studies in New Regimes Rays Studies in New Regimes Linac Light Source: X Short pulses, high brilliance: Short pulses, high brilliance: High coherent fraction: High coherent fraction: f rep = MHz … GHz plots from Q. Shen CORNELL Matthias Liepe 12/12/2003 - 11 - U N I V E R S I T Y
Linac Light Source: X- -Rays Studies in New Regimes Rays Studies in New Regimes Linac Light Source: X � Smaller beams lead to better spatial resolution (currently sub mm) ERL: 100 to 1000 times smaller area � Smaller emittance leads to high brilliance. ERL: 10 to 1000 more brilliance. 3-D Studies of Structure � Shorter bunches allows much higher time resolution. ERL: 100 times shorter bunches 3D Tomograph of Cells Insect Breathing G. Schneider, LBNL Field museum of Chicago & APS, Argonne National Lab. CORNELL Matthias Liepe 12/12/2003 - 12 - U N I V E R S I T Y
Linac Light Sources: How to get high currents? Linac Light Sources: How to get high currents? • High photon flux ⇒ need high current • But: With a simple linac you’d go broke!! • Example: 5 GeV * 100 mA = 500 MW ⇒ The energy of the spent beam has to be recaptured for the new beam. CORNELL Matthias Liepe 12/12/2003 - 13 - U N I V E R S I T Y
Previous Energy Recovery Machines Leonardo da Vinci (1452-1519) CORNELL Matthias Liepe 12/12/2003 - 14 - U N I V E R S I T Y
Linac Light Sources: How to get high currents? Linac Light Sources: How to get high currents? The Energy- -Recovery Recovery- -Linac Linac The Energy Solution: Use energy recovery. First proposed by M. Tigner in 1965. 65. Solution: Use energy recovery. First proposed by M. Tigner in 19 • Re-use energy of beam after SR generation. • Recirculate beam and pass it through the linac a second time, but 180 deg. out of phase to decelerate beam. • ⇒ ⇒ “ “Energy Storage Ring Energy Storage Ring” ” but not but not “ “Beam Storage Ring Beam Storage Ring” ”. . • CORNELL Matthias Liepe 12/12/2003 - 15 - U N I V E R S I T Y
ERLs: What is the trick? ERLs: What is the trick? 3. SR generation with low emittance beam 6. dump beam: 2. acceleration low dump energy, e t a less radioactivity l u n o c i t y r a m g r i r e c e l a e n e c e e R e e b d s u . 5 . - 4 e r o t : n o m i t c a e e j b n h I s . e 1 r f CORNELL Matthias Liepe 12/12/2003 - 16 - U N I V E R S I T Y
ERLs Worldwide (FEL- -ERLs and SR ERLs and SR- -ERLs) ERLs) ERLs Worldwide (FEL 1960 1970 M. Tigner, 1965 1980 SCA, Stanford, 1986 1990 S-DALINAC, 1990 Cornell ERL 2000 IR FEL Jlab, 1999 LUX (LBL) JAERI, 2002 PERL (NSLS) 4 GLS (Daresbury) KEK … CORNELL Matthias Liepe 12/12/2003 - 17 - U N I V E R S I T Y
ERL Linacs: Why Superconducting Cavities? ERL Linacs: Why Superconducting Cavities? SRF linacs can deliver beams of superior quality: • Smaller emittance (lower impedance) ⇒ higher brilliance • Better RF control and stability ⇒ lower energy spread • CW operation at high gradient ⇒ flexibility in pulse train, lower impedance, cost saving In addition, SRF gives • Higher power conversion efficiency • ERL option (very low wall losses) ⇒ high beam current, high flux CORNELL Matthias Liepe 12/12/2003 - 18 - U N I V E R S I T Y
ERL @ Cornell ERL @ Cornell CORNELL Matthias Liepe 12/12/2003 - 19 - U N I V E R S I T Y
Cornell ERL Light Source Cornell ERL Light Source 5 GeV, 100 mA 5 GeV, 100 mA Neither an electron source, nor an injector system, nor an ERL has ever been built for the required large beam powers and small transverse and longitudinal emittances. � A prototype at Cornell should verify the functionality. 5 GeV CORNELL Matthias Liepe 12/12/2003 - 20 - U N I V E R S I T Y
Cornell ERL: Phase 1, the Prototype Cornell ERL: Phase 1, the Prototype 100 mA Gun Dump 100 MeV, 100 mA 100 MeV, 100 mA 5 MeV Injector 100 MeV Main linac Buncher Bates bends 30m s.c. injector linac s.c. main linac CORNELL Matthias Liepe 12/12/2003 - 21 - U N I V E R S I T Y
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