1. Design Requirements/Issues Source/Injector Performance -successful run of 135 pC -DC photocathode gun: cathode lifetime >600 C; GaAs wafer > 2 kC Delivery of appropriate beam to FEL - transverse/longitudinal matching to wiggler -beam quality preservation (space charge, other wakefield/collective effects, CSR) Energy Recovery -transverse/longitudinal matching, acceptance (momentum spread ~10%) -space charge, BBU, FEL/RF interaction Solution – layout of Demo and Upgrade in facility vault Demo Upgrade three module linac quad telescopes match into/out of recirculator Bates end-loops FODO backleg transport to FEL insertion FEL insertion Longitudinal phase space management similar to that in Demo: DRIVER ACCELERATOR DESIGN FOR THE 10 KW UPGRADE OF THE JEFFERSON LAB IR FEL D. Douglas, S. V. Benson, G. A. Krafft, R. Li, L. Merminga, and B. C. Yunn Thomas Jefferson National Accelerator Facility, 12000 Jefferson Avenue, Newport News, VA 23606 ABSTRACT * An upgrade of the Jefferson Lab IR FEL is now under construction. It will provide 10 kW output light power in a wavelength range of 2–10  m. The FEL will be driven by a modest sized 80–210 MeV, 10 mA energy-recovering CW superconducting linac. Stringent phase space requirements at the wiggler, low beam energy, and high beam current subject the design to numerous constraints. These are imposed by the need for both transverse and longitudinal phase space management, the potential impact of collective phenomena (space charge, wakefields, beam break-up, and coherent synchrotron radiation), and interactions between the FEL and the accelerator RF system. This report addresses these issues and presents an accelerator design solution meeting the requirements imposed by physical phenomena and operational necessities. Project Summary The US Navy has provided 9.3 M$ initial funding for an upgrade of the Jefferson Lab IR Demo FEL from 1 to 10 kW. The Upgrade will be an evolutionary derivative of the Demo – a wiggler-driven optical cavity resonator producing low micropulse energy but high average power through use of an energy-recovering SRF linear accelerator driver operating at high repetition rate. Construction activities have begun; follow-on funding is anticipated in 2001, with Upgrade beam operations starting early in FY2002. Upgrade Path – Increase output power by at least 10  via Higher beam power -Current: 10 MeV/5 mA injector  10 MeV/10 mA injector(2  ) -Energy: 35-48 MeV linac (1 cryomodule)  80-210 MeV linac (3 cryomodules)(4  ) FEL enhancements -FEL extraction efficiency ½%  1%(2  ) -Wiggler-driven concentric optical cavity  optical klystron driven R 5 cavity Geometric accommodation (reuse of existing vault) - FEL insertion following linac (CSR)  FEL insertion in backleg TOTAL: 16  Parameter Set – Demo and Upgrade * Text of paper THC03 is available on-line at http://www.jlab.org/~douglas/FELupgrade/masterindex.html Performance Lattice design/analysis underway; design requirements (matching, acceptance) can be met -Example: energy compression during energy recovery using octupole correction of lattice torsion Longitudinal phase space octupoles off octupoles on PARMELA simulations/Demo measurements certify 135 pC operation Preliminary study indicates BBU thresholds exceed anticipated operating currents Initial CSR simulation (1-D longitudinal wake model) suggests emittance goals readily met Acknowledgments This work was supported by the U. S. Navy, the Commonwealth of Virginia, and the U. S. Department of Energy under contract number DE-AC05-84-ER40150. ParameterDemo NominalUpgrade DesignAchieved (7/2000) Energy (MeV)35-4880-21020-48 I ave (mA)5105 Q bunch (pC)60135 FEL repetition rate (MHz)18.75-754.69-7518.75-75 Bunch  l (psec) 0.40.20.4 @ 60 pC I peak (A)6027060 A   p/p ¼%½% ¼% @ 60 pC ~¼% @ 135 pC  N (mm-mrad) <13<30 5-10 @ 60 pC ~25 @ 135 pC  FEL ½%1%>1%  E full after FEL 5%10%>6-8% linac FELarc FEL lattice functions