Effective fields in magnetic colloids and features of their magnetization kinetics

We present results of magnetization and magnetic susceptibility dependence investigations performed for undecane-based ferrofluids with dominant of Brownian relaxation for particles. A robust and effective method of fine particle size characterization is presented. It is based on the core–shell model and the analysis of the dependence of saturation magnetization on particle concentration. A novel advantage method has been used as a straightforward way to determine the concentration dependence of the effective field related to particle interaction that was calculated from the experimentally obtained concentration dependence of low field susceptibility. The computed relationship is compared with the concentration dependences of effective fields derived from several well-known theoretical models. We present some peculiarities of the real part of dynamic magnetic susceptibility on temperature. Investigated features are defined both by the magnetic state of fine particles and by crystallization of carrier at the liquid to a solid phase transition. For the first time, the dependence of the magnetization relaxation time on the colloidal particle concentration and the magnitude of bias DC magnetic field was investigated experimentally. Results are in good agreement with theoretical predictions for moderate concentration and significantly differs for concentration greater 7 vol%. It is concluded that this effect can be related either to the enhanced particle interaction or to the transition of some particles from superparamagnetic to a ferromagnetic state. These predictions are verified through the calculation in terms of Cole–Cole diagrams methods

Dynamics of magnetic fluid drop's shape in rotating and stationary magnetic fields

Abstract A drop of magnetic fluid was experimentally studied in a rotating magnetic field H r with the additional influence of a stationary magnetic field H s : The conditions of a drop break were studied with different values and directions of intensities between rotating and static magnetic fields. The results of the experiment were theoretically well grounded.

Device for electron bunch measurement in the picosecond region

The method of bunch length measurement in picosecond region using circular scanning in RF cavity was developed. Also the same cavity provides bunch length measurement based on analysis of wake fields, excited in the cavity by travelling bunch. Both methods doesn’t need precise synchronization with the beam and were used for investigation of the time response of GaAs photocathode in NEA condition. In this report the description of experimental setup and obtained results are presented

Measurement of Time Response of Laser-Triggered GaAs Photocathode

none12An RF gun with a laser-triggered photocathode is a very attractive as an injector for linear accelerators since it can produce a low-emittance high-current electron beam with originally short pulse length. A GaAs photocathode can generate a polarized electron beam. The time response of GaAs photocathode is very important for RF gun operation if it is comparable with RF period. An experirnental facility has been fabricated to measure the length of electron bunch extracted from GaAs photocathode illuminated by laser pulse of 98 ps (FWHM). The method of hunch length measurement using circular scanning in RF cavity was developed. We use 50 kV DC gun for beam extraction. The minimum measured bunch duration was 106 +/- 20 ps (FWHM) for 4.5. 10^8 electrons per pulse. In this report we describe the experimental setup and obtained results.noneP. V. Logatchev; A. V. Aleksandrov; M. S. Avilov; N. S. Dikansky; A. V. Novokhatski; G. Ciullo; G. Lamanna; B. Yang; R. Calabrese; V. Guidi; P. Lenisa; L. TecchioP. V., Logatchev; A. V., Aleksandrov; M. S., Avilov; N. S., Dikansky; A. V., Novokhatski; Ciullo, Giuseppe; G., Lamanna; B., Yang; Calabrese, Roberto; Guidi, Vincenzo; Lenisa, Paolo; L., Tecchi