The wiggler consists of magnet system with alternate magnetic polarity and is set in the straight section of a storage ring. It produces synchrotron radiation independently of the normal bending magnets. With the progress of the study on utilization of synchrotron radiation, the wiggler has become an important device as a high intensity light source which attracted attention of researchers. For the past decade, many wigglers have been constructed in several countries. As the operational experience are accumulated, the beam-dynamical problems with the wiggler became gradually clear. In the recent storage rings which are dedicated to the synchrotron radiation use, the main parameters are chosen so as to obtain the optimum spectrum of the wiggler radiation. In this description, at first some results derived from wiggler theory are reviewed briefly, which are useful for the wiggler magnet design, then the characteristics of the periodic magnet-field are described and finally some wigglers (mainly with the superconducting magnets) in operation in the world are surveyed.
The maximum operating current in a superconducting composite of a superconducting magnet, can not be increased up to the critical current of the superconducting filaments, because of the need to have a stable performance of the magnet. In relation to this, some researchers have reported that an insulating coating on a superconductor is very effective in raising the recovery current and that there is an optimum thickness for a coating material to increase the recovery current, Such an effect seems to be of importance in thermal design of superconducting magnet, but only a few related works seem to have been reported on this problem. In particular, the real effects of surface coating on boiling heat transfer to liquid helium have not been clarified because the boiling characteristics have not been discussed based on the real surface temperature of coated surface. Thus, in the present study, boiling experiments on a circular flat plate were conducted to study the real influence of surface coatings on the pool boiling heat transfer to saturated liquid helium at atmospheric pressure. The coating material, its thickness and surface inclination were the parameters of interest in these experiments. Polytetrafluorethylene and stainless steel were chosen as the coating materials because their thermal properties are known, Experimental data obtained in the present study show the following results. A low thermal conducting coating shifts the nucleate boiling curve to a higher region of superheat. Its degree depends not only on surface inclination but also on coating material. On the other hand, film boiling curve is not affected by surface coating and is determined only by surface inclination. Critical heat flux (CHF), which decreases with increasing the angle of inclination from facing upward to facing downward orientation, is slightly increased as the coating thickness increases. As the coating thickness increases, the minimum-heat-flux (MHF) and the degrees of superheat at the CHF and MHF points become larger respectively, and they approach the respective asymptotic values determined by the thermal properties of the coating material. Using the experimental data obtained in this study, a nondimensional relation, which describes universally the influence of coating thickness on the MHF and the degrees of superheat at the CHF and MHF points, was derived. Further, the aforementioned asymptotic values of the degree of superheat at the MHF point was correlated to the thermal properties of the liquid and the surface material. Based on the above experimental results and the concept of cold-end recovery, the influence of the coating thickness on the maximum operating current was estimated. The results show that the maximum operating current can be increased by a thin insulating coating. They also show, that the current gained reaches the maxima at a certain coating thickness, thus it will be necessary to enhance the nucleate boiling heat transfer on a coated surface to realize a large improvement in the maximum operating current.
An extensometer capable of use for tensile tests down to 4K was designed and constructed, in which the elongation of specimen was measured as bending strain of U-shaped thin beam by resistance strain gauges. As the gauge factor was temperature-dependent, a resistance thermometer was also installed on this device to measure the temperature while testing. The calibration was performed at low temperatures by using a simple apparatus in which a displacement was applied by a precision micrometer. The performance characteristics are summarized as follows: (1) The sensitivity increases monotonically by 6% of its room temperature value of 524μ strain/mm as the temperature is lowered to 4K. (2) The deviations from the linear relation of output strain vs. displacement are within 5μm in the displacement range up to 5mm. (3) The zero-drift is observed in the whole temperature range tested, but its rate to the temperature variation does not exceed the amount of 0.9μm/K.
The carbon glass resistance thermometers (CGRT) shows an unstable drift by heat cycles. Since we were looking for a more stable element of thermometer for cryogenic and high magnetic field environments, we selected amorphous silicon as a substitute for CGRT. The resistance of many amorphous samples were measured at 4K, at 77K, and at 300K. We eventually found an amorphous silicon (Si-H) alloy whose the sensitivity below 77K was comparable to that of the germanium resistance thermometer with little magnetic field influence.
A superconducting power cable is one of the promising ways for transmitting huge electric power effectively in the future. We proposed the new superconducting cable design with a similar electrical insulation structure to the conventional extruded polyethylene cable in order to exploit the excellent electrical insulation capability of polyethylene at cryogenic temperature. Electrical insulation of the cryogenic liquid transfer tube is required for the long term voltage test of the cable, since the cryogenic liquid has to be supplied from the coolant container of the earthed potential to the high voltage cable. The coaxial glass insulated transfer tube with vacuum thermal insulation has been developed for handy transport of cryogenic liquid between apparatuses at different electrical potentials. The fundamental electrical characteristics of the glass insulated transfer tube were investigated. Furthermore, this newly developed transfer tube has been incorporated into the superconducting power cable system with success.
We have fabricated cooling system for a laboratory scale superconducting magnet. An electromotive valve for liquid He and liquid N2 discharge device have been developed for this system. The system performed that the magnet was automatically immersed by liquid He after pre-cooling down by liquid N2.