A use of bulk high-temperature superconductors (HTSs) for an undulator is attractive since a high magnetic field can be generated at low-temperatures. While potential for generation of the high magnetic field is high, in-situ magnetization of the bulk HTSs for periodic field generation is challenging issue. Recently, we proposed a new type of undulator using bulk high-Tc superconductors (HTS) and a solenoid magnet. The undulator, named Bulk HTSC staggered array undulator (Bulk HTSC SAU), consists of a stacked array of bulk HTSs and copper insulators and a solenoid magnet. A proof of principle experiment at 77 K using liquid nitrogen has been carried out. The estimated performance at about 30 K was estimated using results of property measurements for the HTS used for the Bulk HTSC SAU. The expected undulator peak field reaches to 1.08 T for undulator period length of 9.9 mm for the undulator gap of 4.0 mm. This performance is about 2 times higher than that of existing technologies.

Thermoluminescence (TL) properties of La₂O₃: Dy³⁺, Li⁺, and La₂O₃: Eu³⁺, Li⁺, exposed to 5.12 Gy of beta radiation, and recorded at different heating rates 0.5, 1, 2, 3, 4, and 5 °C s⁻¹ (from Molefe et al., paper 2019), were analyzed and the trap parameters were determined in this study. These parameters include the order of kinetics b, the activation energy E (eV), the frequency factor S (s⁻¹), or the pre-exponential factor S’’ (s⁻¹), and the initial concentration of trapped electrons n_o (cm⁻³). A new non-linear curve fitting technique, based on the general order kinetic equation and the outcomes of Hoogenstraaten’s Method, was established and applied on the TL glow peaks of La₂O₃: Dy³⁺, Li⁺. The fitting technique was evaluated by calculating the R-square and figure of merit (FOM) values. The results revealed that the FOM values are 0.997, which demonstrates an excellent convergence between experimental and fitted curves. A modified technique based on the three-points analysis method was exploited to deconvolute complex TL glow curves of La₂O₃: Eu³⁺, Li⁺, and in turn to determine the trap parameters the method disclosed that each TL glow curve consists of four peaks. The trap parameters of the individual peaks were numerically determined. The fading, as a function of storage temperature and time, from the TL signals of the investigated materials was predicted and discussed based on the calculated trap parameters. The results support the value of the materials for employment in radiation dosimeter applications with a low fading fraction.

Corona discharges in gases exist under several distinctive forms. In this paper, a survey study has been made of ac corona discharge modes generated in some different gases fed in a wire-duct reactor with a constant rate of flowing at atmospheric pressure. The properties of different corona modes are analyzed under some condition transitions from Trichel pulses to a steady glow. In the course of the presented experimental work, numerous apparent contradictions with earlier observations necessitated further study and are given to provide more information on the physical mechanisms of the ac corona discharges. Furthermore, we have gained insight into some new technologies and applications of the environmentally friendly corona and plasma discharges.

Inverse Compton scattering of polarized laser photons by energetic electrons is an excellent method to generate polarized gamma rays. A 100% polarized laser can generate 100% polarized gamma rays, but polarization varies depending on the scattering angle of the gamma rays. In this study, we experimentally measure the spatial polarization distribution of circularly polarized gamma rays using a magnetized iron that can measure the circular polarization of MeV gamma rays. Measurements of the asymmetry of gamma-ray transmission relative to the magnetized iron at each scattering angle clearly show that gamma rays are circularly polarized near the central axis, and they change from circular to linear polarization as the scattering angle increases. A simple way to obtain highly polarized gamma rays is to use a collimator that transmits only the central axis of the gamma rays with such polarization characteristics. Polarized gamma rays are, indeed, generated by ${90}^{\circ }$ collisional inverse Compton scattering between an electron beam and a circularly polarized laser.

The magnetic field of a staggered-array undulator using a bulk high-temperature superconductor is calculated by analytical and numerical methods. Analytical formulas for the undulator field and the solenoid field required to generate the undulator field are derived from a simple two-dimensional model. The analytical calculation shows the degree of dependence of these fields on the undulator parameters, the generation of a high undulator field proportional to the critical current density of the bulk superconductor, and the good tunability of the undulator field over a wide range of values. The numerical calculation is performed in a three-dimensional geometry by two methods: the center field and energy minimization methods. The latter treats the current distribution inside the bulk, whereas the former neglects it as a natural extension of the analytical model. The calculation also reveals the dependence of the fields on the undulator parameters arising from the current distribution. From the comparison with experimental results, we find that the latter method reproduces the experimental results well, which indicates the importance of the current distribution inside the bulk. Therefore, we derive a semiempirical formula for the required solenoid field by modifying the analytical formula using the numerical results so as to include the effect of the current distribution. The semiempirical formula reproduces the numerical result with an error of 3%. Finally, we estimate the magnetic performance of the undulator as an example of using the formulas and values presented in this paper. The estimation shows that an undulator field twice as large as that of the present in-vacuum undulator but with an equal period and gap can be obtained at a temperature of approximately 20\char21{}40 K, and that deflection parameters ($K$ values) of 1 and 2 can be achieved with periods of 5 and 10 mm at approximately 4\char21{}20 K.

The back bombardment (BB) effect limits wide usage of thermionic rf guns. The BB effect induces not only ramping-up of a cathode’s temperature and beam current, but also degradation of cavity voltage and beam energy during a macropulse. This paper presents a comparison of the BB effect for the case of dispenser tungsten-base (DC) and lanthanum hexaboride (${\mathrm{LaB}}_6$) thermionic rf gun cathodes. For each, particle simulation codes are used to simulate the BB effect and electron beam dynamics in a thermionic rf gun cathode. A semiempirical equation is also used to investigate the stopping range and deposited heat power of BB electrons in the cathode material. A numerical simulation method is used to calculate the change of the cathode temperature and current density during a single macropulse. This is done by solving two differential equations for the rf gun cavity equivalent circuit and one-dimensional thermal diffusion equation. High electron emission and small beam size are required for generation of a high-brightness electron beam, and so in this work the emission properties of the cathode are taken into account. Simulations of the BB effect show that, for a pulse of $6\mu \mathrm{s}$ duration, the DC cathode experiences a large change in the temperature compared with ${\mathrm{LaB}}_6$, and a change in current density 6 times higher. Validation of the simulation results is performed using experimental data for beam current beyond the gun exit. The experimental data is well reproduced using the simulation method.