MaRIE ( Ma tter- R adiation I nteractions in E xtremes)

1. Proposed LANL Beam Experiments(in Support of MaRIE) Bruce CarlstenLos Alamos National LaboratoryFuture Directions for Accelerator R&D at FermilabMay 12, 2009

2. MaRIE(Matter-RadiationInteractionsinExtremes) • The Multi-probe Diagnostic Hall will provide unprecedented probes of matter. • X-ray scattering capability at high energy and high repetition frequency with simultaneous proton imaging. • The Fission and Fusion Materials Facility will create extreme radiation fluxes. • Unique in-situ diagnostics and irradiation environments comparable to best planned facilities. • The M4 Facility dedicated to making, measuring, and modeling materials will translate discovery to solution. • Comprehensive, integrated resource for controlling matter, with national security science infrastructure. LANSCE Accelerator

3. Electron Injector Linear Accelerator Bunch Compressor Undulator X-rays Beam Electron Beam Dump Original MaRIE 50-keV XFEL Baseline Concept Probably wouldn’t work – ISR leads to energy spread

4. Current thinking – 20 GeV XFEL • Use series of flat-beam transforms (FBT) and emittance exchanges (EEX) to decrease transverse emittance at the expense of longitudinal emittance • Prebunch electron beam before wiggler • less stringent demand on emittance (so lower energy is okay) • reduces incoherent radiation problem • smoother output pulse • can use much shorter wiggler • Much less expensive accelerator and will fit on our mesa

5. Baseline Design Strategy Beam energy is chosen because of two constraints: • The choice for beam energy (g) is dominated by the beam emittance, not wiggler period (which can go down to 1 cm) • If we can reduce the emittance enough and use a 2-cm wiggler period, the beam energy would drop to 20 GeV. • Strategy: • Prebunch beam to violate constraint • Use FBT/EEX to minimize emittance

6. What We Are Thinking For New Baseline Design Overview: beam energy: 20 GeV rf frequency: 2.856 GHz bunch charge in accelerator: 500 pC bunch charge at wiggler: 250 pC bunch length: 80 fsec wiggler length: 20 m transverse emittance: 0.15 mm Linac: field gradient: 50 MV/m cavity/klystron number: 217 cavity length: 1.84 m cells per cavity: 53 peak klystron power: 100 MW

7. Emittance Budget End at wiggler with prebunched 1/4 nC at 20 GeV ex < 0.15 mm mrad ey < 0.15 mm mrad ez < 100 mm mrad Start with injector with ½ nC ex ~ 0.7 mm mrad ey ~ 0.7 mm mrad ez ~ 1.4 mm mrad Somewhere in between the normalized longitudinal emittance starts growing linear with energy due to wakefields this comes from 0.01% energy spread and 80 fs at 20 GeV wakefield for 1 nC, 4 ps, 1.3 GHz cell

8. What We Are Thinking For New Baseline Design 2-cm period wiggler S-band linac to 20 GeV S-band linac to 1 GeV Prebunch stage Emittance manipulation stage EEX 2: L=0 mm ex ~ 100 mm ey~ 0.14 mm ez~ 0.14 mm EEX 3: L=0 mm ex ~ 0.14 mm ey~ 0.14 mm ez~ 100 mm 0.25 nC (prebunched) FBT 1: L=0 mm ex ~ 70 mm ey~ 0.007 mm ez~ 1.4 mm FBT 2: L=2 mm ex ~ 35 mm ey~ 0.014 mm ez~ 1.4 mm EEX 1: L=2 mm ex ~ 1.4 mm ey~ 0.014 mm ez~ 35 mm FBT 3: L=0 mm ex ~ 0.14 mm ey~ 0.14 mm ez~ 35 mm 500 kV DC injector or AFEL copy or CTF3 copy 0.50 nC, L=35 mm ex ~ 0.7 mm ey~ 0.7 mm ez~ 1.4 mm

9. Not As Easy As We Would Like • Three technical “issues” • FBT only for round to flat so far – previous slide has more complicated FBT behavior • Need to pass angular momentum through EEX • Prebunching at ¼ Angstrom not yet credible • Need extension of FBT to arbitrary sub-set of phase space • Need to understand how to do the 6-D transform – think we are better off using the FBT and EEX, but maybe better off constructing a new solution for the transfer matrix • We think immersing EEX in weak solenoid field may lead to solution • May have long prebunching EEX at 2.5 Angstrom or longer wavelength

10. FBT Extension is Numerically Promising Cuts in final vertical emittance, not horizontal emittance

11. Prebuncher May Be Problematic • SLAC colleagues like to point out ISR in a bend coupled with the R56 from the final dipole leads to this axial smearing: • which leads to very small angles for sub-Angstrom bunching • Two ways out – degree-angle doglegs with optically long drifts or prebunch at a very high subharmonic (or both) • CSR effect too, there is an optimum in here somewhere but it will take effort to find it • What about microbunching in an EEX? Is it a better idea for compression?

12. EEX Prebuncher Idea Constraint for masking requires a negative drift somewhere

13. EEX Prebuncher Idea Two options – either S1 or S2 can be negative

14. Beam Physics Issues • Can we really pass angular momentum through EEX? • Massaging beam with quads for multiple FBTs • What energy do the wakefields dominate the longitudinal emittance? Will be exceed our longitudinal emittance budget? • CSR through EEX – better or worse than for a chicane? • Do we need even number of EEX stages? • What is the right trade between amount of beam loss in mask (ie bunching amplitude) and emittance for smaller bunch charges? What is the optimum prebunching wavelength? • Is there enough time for PWA technology to mature?

15. Why Would Fermilab Be Interested? • HEP synergy - lower emittance increases LC luminosity • Historical ownership of FBT and EEX technologies • 750/1500 MeV linac can make a very nice 150/50 nm FEL, good opportunity for materials science user facility • Motivated LANL partner – we would want to support NML with personnel and funding for experiments

16. Specifics of Proposed Experiments • We propose that the NML look like the MaRIE XFEL front end • Demonstrate various FBT variants – nonsymmetric initial beam • Demonstrate coupled FBT/EEX designs • Extend demonstration prebunching in EEX to UV, DUV, XUV wavelengths • Understand FEL performance from prebunching at subharmonics • Build an XUV FEL with emittance manipulation stage and prebuncher