• S. Sasaki, I. Vasserman
  ANL, Argonne, Illinois

Funding: Supported by the U.S. Dept. of Energy, BES-Office of Science, under Contract W-31-109-ENG-38.

Trajectory straightness through the undulator is critical for the success of the LCLS project. Environmental fields, including the earth’s field, will affect the trajectory. The earth’s field works as an external dipole field and, unless it is shielded or corrected, causes a bend in the electron trajectory through an undulator. We investigated the effects of the earth’s field and an iron plate which might be used as part of a girder. Modeling and calculation were performed using the code RADIA. A model with a large solenoid surrounding a seven-period undulator was used for the simulation. According to the calculations, the vertical component of the earth’s field at the undulator axis is enhanced by the undulator poles by a factor of 2.5. The horizontal on-axis component, however, is well shielded by the undulator poles and falls to less than 3% of its original strength. The effect of an iron plate located 200 mm below the undulator axis is negligibly small, so final Hall probe measurements can be done without the girder in place. However, the magnetic tuning of the undulator field must take into account the amplification of the vertical component of the environmental field in the LCLS tunnel.

• S.-H. Lee, S. Sasaki, I. Vasserman, D.R. Walters
  ANL, Argonne, Illinois
• D.E. Kim
  PAL, Pohang, Kyungbuk

Funding: Work supported by DOE under contract no. W-31-109-Eng-38.

A prototype vacuum chamber is being designed for use in the Linac Coherent Light Source at Stanford Linear Accelerator Center under development at the Advanced Photon Source. The chamber will be fabricated from the austenite stainless steels. In general, the magnetic properties of austenite stainless steels are affected by their compositions, processing methods and physical conditions. Austenite stainless steels are generally regarded as non-magnetic in the annealed condition and not attracted significantly by a magnet. However, cold working or welding will change their magnetic properties. This paper presents measurements use to choose a proper chamber material for LCLS undulator, to examine the fabrication processes, and to investigate the relative magnetic permeabilities of the stainless steels such as 316LN, 20Cb-3, Nitronic 33, Nitronic 40 and 310S. This paper presents the results of fabricating of 3"-long vacuum chambers along with their permeability measurements. In addition, the magnetic field variations with/without vacuum chamber under APS undulator A and numerical studies of magnetic field to the permeability of the flat/cylindrical chambers are presented.