Spurious oscillations in klystrons due to returning electrons from the collector into the drift tube were observed and studied at KEK. Simulations of returning electrons using EGS4 Monte Carlo method have been performed. And the oscillation conditions are described in this paper.
The Self Stimulated Undulator Klystron (SSUK) and its possible applications in the Particle Accelerator Physics, incoherent Self-Stimulated Undulator Radiation Sources (SSUR) and Free-Electron Lasers (FEL) are discussed.
The optical klystron enhancement to self-amplified spontaneous emission (SASE) free electron lasers (FELs) is studied in theory and in simulations. In contrast to a seeded FEL, the optical klystron gain in a SASE FEL is not sensitive to any phase mismatch between the radiation and the microbunched electron beam. The FEL performance with the addition of four optical klystrons located at the undulator long breaks in the Linac Coherent Light Source (LCLS) shows significant improvement if the uncorrelated energy spread at the undulator entrance can be controlled to a very small level. In addition, FEL saturation at shorter x-ray wavelengths (around 1.0 AA) within the LCLS undulator length becomes possible. We also discuss the application of the optical klystron in a compact x-ray FEL design that employs relatively low electron beam energy together with a short-period undulator.
A klystron beam focusing system using permanent magnets, which increases reliability in comparison with electromagnet focusing system, is reported. A prototype model has been designed and fabricated for a 1.3 GHz, 800 kW klystron for evaluation of the feasibility of the focusing system with permanent magnets. In order to decrease the production cost and to mitigate complex tuning processes of the magnetic field, anisotropic ferrite magnet is adopted as the magnetic material. As the result of a power test, 798 kW peak output power was successfully achieved with the prototype focusing system. Considering a power consumption of the electromagnet focusing system, the required wall-plug power to produce nominal 800 kW output power with the permanent magnet system is less than that with electromagnet. However, the power conversion efficiency of the klystron with the permanent magnet system was found to be limited by transverse multipole magnetic fields. By decreasing transverse multipole magnetic field components, especially the dipole and the quadrupole, the power conversion efficiency would approach to that with electromagnets.
The High Intensity Neutrino Source (HINS) Six-Cavity Test has demonstrated the use of high power RF vector modulators to control multiple RF cavities driven by a single high power klystron to accelerate a non-relativistic beam. Installation of 6 cavities in the existing HINS beamline has been completed and beam measurements have started. We present data showing the energy stability of the 7 mA proton beam accelerated through the six cavities from 2.5 MeV to 3.4 MeV.
Advanced technical solution for the design of a low perveance electron gun with a high quality beam dedicated to high power Ka-band klystrons is presented in this paper. The proposed electron gun can be used to feed linear accelerating structures at 36 GHz with an estimated input power of 20 MW, thus achieving an effective accelerating electric field in the (100-150) MV/m range. additionally, in the framework of the Compact Light XLS project, a short Ka-band accelerating structure providing an integrated voltage of at least 15 MV, has been proposed for bunch-phase linearization. For the klystron, a very small beam dimension is needed and the presented electron gun responds to this requirement. An estimate of the rotational velocity at beam edge indicates that the diamagnetic field due to rotational currents are small compared to the longitudinal volume. A detailed analysis of how this is arrived at, by compression of the beam, rotation in the magnetic field, and analysis of the subsequently generated diamagnetic field has been discussed.