• S. Kashiwagi, G. Isoyama, R. Kato, N. Noda
  ISIR, Osaka
• K. Tsuchiya, S. Yamamoto
  KEK, Ibaraki

We apply the edge-focusing scheme to the wiggler for FEL and SASE in the far-infrared region at ISIR, Osaka University in order to make the gain length of SASE shorter by keeping the beam size small along the wiggler. As the electron beam energy is 10^-30 MeV and the magnetic field of the wiggler is up to 0.4 T, the natural focusing force in the vertical direction is strong in the wiggler and it is strongly dependent on the electron energy and the wiggler gap. The focusing forces should be compatible to or higher than the strong natural focusing force, equally in the horizontal and vertical directions over the wide range of the electron beam energy and the wiggler gap. In order to meet this requirement, we adopt the strong focusing scheme using the EF wiggler. The wiggler consists of 4 FODO cells in the 1.938 m long (32 periods, period length: 60mm). A focusing element and defocusing element are incorporate with single wiggler periods with edge angles of +5 and -5 degrees, respectively, and they are separated by 3 normal wiggler periods. The strong focusing wiggler has been fabricated and magnetic field has been measured at KEK. We will report results of the magnetic field measurements of the strong focusing wiggler.

• C. Pellegrini
  UCLA, Los Angeles, California

Funding: Work funded by the US Department of Energy, grant 4-444025-PG-57689

We study the use of Radio Frequency electromagnetic waves as undulators for short wavelength FELs and undulator radiation sources. Magnetostatic undulators have a gap much smaller than the period, limiting how short a period we can use. The relation between period and gap can be overcome using electromagnetic waves to produce the force wiggling the electrons. The wave frequency is chosen to optimize the system performance. In the case of centimeters or mm waves a waveguide is used to propagate the field over a long distance. We call an undulator based on a waveguide a TWU. In this paper we show that a TWU using X-band RF is a practical and convenient device for short wavelength FELs, and to produce sub-nanometer undulator radiation circularly or linearly polarized.The recent development of high power X-band microwave sources make it possible today to build TWUs of practical interest. In this paper we will discuss the characteristic of the TWU, how to control the effects of RF power losses in the waveguide walls, and how to optimize a TWU and the associated electron transport system for use in a synchrotron radiation source or FEL.

• P. Craievich, S. Di Mitri
  ELETTRA, Basovizza, Trieste

The FEL project FERMI@ELETTRA will use the existing Linac, upgraded to 1.2 GeV, to produce VUV radiation between 100-10 nm. FEL operations require a high quality beam in terms of the bunch energy spread and emittance. In this paper we present an analytical study based on a continuum model to describe the transverse motion of a single bunch. Such a study allows predicting the emittance growth under the combined influence of short-range transverse wakefields, injection offset, initial emittance and misaligned accelerating sections. We also report a comparison between analytical and numerical (tracking code) results.

• J.W. Lewellen, J. Noonan
  ANL, Argonne, Illinois

Funding: Work supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. W-31-109-ENG-38.

Conventional pi-mode rf photoinjectors typically use magnetic solenoids for emittance compensation. This provides independent focusing strength, but can complicate rf power feed placement, introduce asymmetries (due to coil crossovers), and greatly increase the cost of the photoinjector. Cathode-region focusing can also provide for a form of emittance compensation. Typically this method strongly couples focusing strength to the field gradient on the cathode, however, and also requires altering the longitudinal position of the cathode to change the focusing. We propose a new method for achieving cathode-region variable-strength focusing for emittance compensation. The new method reduces the coupling to the gradient on the cathode, and does not require a change in the longitudinal position of the cathode. Expected performance for an S-band system is similar to conventional solenoid-based designs. This paper presents the results of rf cavity and beam dynamics simulations of the new design.