What is an Energy Recovery Linac and Why is there one in your Future?

What is an Energy Recovery Linac and Why is there one in your Future? Sol M. Gruner CHESS, Physics Dept. Cornell University Ithaca, NY 14853 Outline 1. Who needs another synchrotron source? 2. What is an ERL? How is it different? 3. ERL properties 4. Differences between ERLs and XFELs SRI2001_ERLworkshp.doc

Growth in Synchrotron Radiation Science CHESS 1975 1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 3000 2500 2000 1500 1000 500 0 INSPEC: Synchrotron Radiation (not astronomy) 3000 2500 2000 1500 1000 Protein Data Bank: Deposits / year 500 0 Number of Publications 1975 1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 Number of PDB Deposits

Facts of Life Europe without Russia, with roughly same size research community as U.S.: o 12 rings 1.5 GeV in various stages o 2 rings (Diamond, Soleil) planned o Ambitions for others U.S. has 5. Worldwide, ~ 70 rings are in various stages. Demand continues to grow. Nonexpert communities are largely untapped in o Environmental science o Imaging o Much of engineering o Arts (e.g., archaeometry) o Etc. The question is not if a new U.S. SR source is needed, but when and how many? SR sources are expensive (> $200M) and have long lead times (5-10 years). SRI2001_ERLworkshp.doc

Given the Facts of Life, prudent to ask: What are the limitations of storage rings? Are there cost or science effective alternatives? SRI2001_ERLworkshp.doc

Ideal SR source wish list 1. High average & peak brilliance (phot/s/0.1% bw/mrad 2 /mm 2 ) brightness (phot/s/0.1% bw/mrad 2 ) flux (phot/s/0.1% bw) 2. Flexible pulse structure programmable pulse trains pulse lengths from 1 fs to 0.1 ns 3. Source cross-sectional area small size shape as desired very sharp edges 4. Flexible operation infinite lifetime robust, stable readily changed from one mode to next modular, independence of parts SRI2001_ERLworkshp.doc

Some Fundamentals Flux: F n [ph/s/0.1% bw] = 1.431x10 14 N u Q n I[A], N u = # periods Q n = parameter (~1) dependent upon Deflection parameter I = current. Brilliance: Photon flux/unit transverse phase space volume. 2 2 Fn B ph/s/0.1% bw/mm / mr =. 2 (2 π) ε ε Peak Brilliance: Photons/pulse (F p = F n /f) in 6-D phase space, including longitudinal direction. 2 ˆ Fp 2.35 B B = =, 2π ε ε ε 2π τ f ( ) 3 Coherent Flux: x y E τ = pulse length; f = pulse freq. 2 8 λ[å] 2 2 Fc [ph / s / 0.1%] = 10 B [ph / s / 0.1% / mm / mr ] 2 Photon Degeneracy: # photons/pulse both transversely and longitudinally coherent. D 3 ˆ 2 2 [ph /s / 0.1% / mm / mr ] 1.2 10 24 δ = B x y λ[å] Thus, I, εε, τ are of fundamental importance. x y. \\Bio5th\people\SOL\VUES\ANL ERL talk\aps ERL.doc

Transverse effects of magnetic focusing, SR & RF equilibrium emittance after ~10 4 revolutions. Longitudinal effects of phase focusing, stochastic SR emission & energy loss, and RF equilibrium bunch length Interparticle effects (e.g., Touschek effect) & population of tails of cross-sectional distribution Limit current, lifetime. SRI2001_ERLworkshp.doc

Important Conclusions: 1. Equilibrium dynamics determine Minimum emittance Minimum bunch length Shape, wings of bunch Fill decay Max current i.e., essentially all the factors of importance for synchrotron radiation!! 2. The equilibration times are long, typically thousands of revolutions around ring. SRI2001_ERLworkshp.doc

\\Bio5th\people\SOL\VUES\ANL ERL talk\aps ERL.doc

ERL Concept Works! CHESS 48 MeV 5 ma Average IR Power 1720 W Average current 5 ma Electron energy 48 MeV Wavelength range 3-6.2 µm Charge per pulse >60 pc Pulse length 0.4-1.7 ps Repetition frequency up to 74.85 MHz Energy recovery efficiency 99.97%

ERL: Source Size and Pulse Length CHESS ESRF 6 GeV @ 200 ma ε x = 4 nm mrad ε y = 0.01 nm mrad ERL 5 GeV @ 100 / 10 ma ε x = ε y = 0.2 / 0.02 nm mrad ERL (w/ compression) ERL (no compression) ESRF t

Basic Comparison on Machine Issues ERL and Storage Rings CHESS Storage Ring bunches differ hor. & vert. ring limits bunch lengths energy stored lattice limits emittances long time const. low flex. ERL round or flat bunches ring doesn t limit bunch lengths energy recycled injector limits emittances short time const flex. ESRF 350-500 m

Basic Comparison on Machine Issues ERL and XFEL CHESS ERL linac driven undulator low bunch charge single pass energy recycled high rep-rate simultaneous beamlines XFEL linac driven long undulator high bunch charge single pass self-amplified spont. emission low rep-rate multiplexed beamlines 350-500 m

Flow of the SRI2001 Workshop CHESS Energy Recovery Linac Sources of Synchrotron Radiation D. Bilderback, S. Gruner, C-C. Kao & G. Williams Introduction Tutorials on essential technologies ERL & related projects at various labs

ERL Team CHESS I. Bazarov, S. Belomestnykh, D. Bilderback, K. Finkelstein, E. Fontes, S. Gray, S. Gruner, R. Helmeke, H. Padamsee, J. Rigers, Q. Shen, R. Talman, M. Tigner CHESS & Laboratory for Nuclear Studies, Cornell University G. Krafft, L. Merminga, C. Sinclair Thomas Jefferson National Accelerator Facility