• G.I. Cancelo, B. Chase, M.A. Davidsaver
  Fermilab, Batavia
• V. Ayvazyan, M.K. Grecki, S. Simrock
  DESY, Hamburg
• J. Carwardine
  ANL, Argonne
• T. Matsumoto, S. Michizono
  KEK, Ibaraki

Funding: *Work supported by Fermi Research Alliance, LLC. under ContractNo. DE-AC02-07CH11359 with the United States Department of Energy.

In September 2008 the DESY-FLASH accelerator was run with up to 550, 3 nano-coulomb bunches at 5 Hz repetition rate. This test is part of a longer term study aimed at validating ILC parameters by operation as close as possible to ILC beam currents and RF gradients. The present paper reports on the analysis that has been done in order to understand the RF control system performance during this test. Actual klystron power requirements and beam stability are evaluated with heavy beam loading conditions. Results include suggested improvements for upcoming tests in 2009

• N.J. Walker, V. Ayvazyan, L. Froehlich, M.K. Grecki, S. Schreiber
  DESY, Hamburg
• J. Carwardine
  ANL, Argonne
• B. Chase, M.A. Davidsaver
  Fermilab, Batavia
• T. Matsumoto, S. Michizono
  KEK, Ibaraki

Funding: Work at Argonne supported by U.S. Department of Energy, Office of Science, office of Basic Energy, Sciences, under Contract No. DE-AC02-06CH11357

XFEL and ILC both intend to accelerate long beam pulses of a few thousand bunches and high average current. It is expected that the superconducting accelerating cavities will eventually be operated close to their respective gradient limits as they are pushed to higher energies. In addition, a relative energy stability of <10^-4 must be maintained across all bunches. These parameters will ultimately push the limits of several sub systems including the low-level rf control, which must properly compensate for the heavy beam loading while avoiding problems from running the cavities close to their quench limits. An international collaboration led by DESY has begun a program of study to demonstrate such ILC-like conditions at FLASH, which serves as a prototype for both XFEL and ILC. The objective is to achieve reliable operation with pulses of 2400 3-nC bunches spaced by 330 ns (a current of 9 mA) while meeting the required energy stability and while operating accelerating cavities close to their quench limits. Other goals include measurement of cryoload from HOM heating and evaluation of rf power overhead for the ILC. The paper will describe the program and report recent results.