Author: Nanbu, K.
Paper Title Page
MOPPP010 Investigation of CSR Effect for Femtosecond Electron Bunches in an Isochronous Accumulator Ring 589
  • N.Y. Huang, H. Hama, F. Hinode, S. Kashiwagi, M. Kawai, T. Muto, I. Nagasawa, K. Nanbu, Y. Shibasaki, K. Takahashi
    Tohoku University, Research Center for Electron Photon Science, Sendai, Japan
  Coherent synchrotron radiation (CSR) from a novel isochronous ring is a candidate for light source that provides THz radiation with high average flux. A compact isochronous accumulator ring (IAR) for the maximum beam energy of 54 MeV has been designed so as to eliminate the 0th order momentum compaction factor, and the 1st order of it is mostly compensated. In addition, the path length deviation due to betatron motion is mostly compensated in a cell. Though there is no RF cavity in IAR, the injected beam may circulate for certain number of turns. Multi experimental stations can be allocated like synchrotron radiation facilities. However, it has been well known that instability due to the CSR wake field is an issue for the beam stability in the ring operated at low alpha mode. Therefore, a study for effects of the CSR wake on the bunch length and shape in IAR has been in progress. It has turned out that the maximum longitudinal field strength created by CSR would be ~ 0.15 MV/m for the case of 100 fs Gaussian bunch, which is considerably an intense field. To protect the bunch shape from the CSR wake, further study is definitely required.  
MOPPP036 Progress in Reducing the Back-bombardment Effect in the ITC-RF gun for t-ACTS Project at Tohoku University 643
  • X. Li, H. Hama, F. Hinode, S. Kashiwagi, M. Kawai, T. Muto, K. Nanbu, Y. Tanaka
    Tohoku University, Research Center for Electron Photon Science, Sendai, Japan
  • F. Miyahara
    KEK, Ibaraki, Japan
  An ITC (independently tunable cells) thermionic RF gun* has been developed to produce sub-picosecond electron pulses as part of the injector for coherent terahertz radiation at Tohoku University. Both experiments and simulations have shown that the back-bombardment (B.B.) effect on the LaB6 cathode is a serious issue for option. A numerical model has been developed to evaluate the temperature increase of the cathode due to B.B. in which a 2D equation for heat conduction is solved by taking the back-streaming electrons into account. Using this model we have studied the possibility of suppressing the B.B. by employing dipole field and optimization of the cathode radius, compared with experimental data. Other methods and the prospect of the RF gun will also be reported.
* H. Hama et al., New J. Phys. 8 (2006) 292
MOPPP074 Magnetic Field Measurement for a THz Undulator Using the Vibrating Wire Method 732
  • S. Kashiwagi, H. Hama, F. Hinode, M. Kawai, X. Li, T. Muto, K. Nanbu, Y. Tanaka
    Tohoku University, Research Center for Electron Photon Science, Sendai, Japan
  Funding: This work is supported by the Ministry of Education, Science, Sports and Culture, Grant-in-Aid for Scientific Research (S), Contract #20226003.
We constructed the undulator that is a basically a Halbach planer type for a generation of intense coherent terahertz radiation from the very short electron bunch. The period length of the undulator and the number of periods are 100 mm and 25, respectively. Its maximum magnetic field is 0.41 T and the K-value is 3.82 with 54 mm gap. The vibrating wire method is studied to measure the periodic magnetic field of the undulator. By measuring amplitudes and phases of standing waves excited on the wire by the Lorentz force between AC current and magnetic field, we can reconstruct the magnetic field distribution along the wire. The theoretical analysis has been performed for the THz undulator and derived a relation between a reproducibility of undulator field and the number of the harmonic mode to use for the reconstruction. A model experiment was demonstrated using 20cm wire and one pair of permanent magnet block. The theoretical study and the results of model experiment using the vibrating wire method will be shown in this conference.