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Electron beam pinching is a common physical phenomenon in the working process of high-current electron beam diodes. The radial collapse velocity (Va) of the beam is an important index to determine the beam pinching and the working characteristics of the diode. The current research methods are based on optical diagnosis and theoretical estimation formulas for a specific diode. The radial collapse velocity of Qiangguang-I accelerator’s tight-pinched short γ diode can be obtained by the following three methods in this paper: 1) a theoretical formula, which is used to calculate the radial collapse velocity on the basis of the existing research results, and can very quickly determine the pinching situation because in this case this formula just needs a diode pinching current; 2) the method of calculating Va, which is established based on particle-in-cell simulation. The simulation model includes the anode ion current, thus can simulate the pinching of electron beam more precisely; 3) a method of calculating Va, which is given by measuring the pinch center offset and the γ-ray PIN waveform, because the Qiangguang-I γ diode is inconvenient for optical diagnosis. The radial collapse velocities obtained by the above three methods are 8.43, 8.70 and 7.89 cm2/ns respectively, and the relative difference among the three methods is < 10%. The third method obtains a slightly smaller value because the ion current assumed in the theory and simulation is H+. The ion current composition in the actual diode is complex, the diffusion speed is slower, then the radial collapse velocity is smaller. Compared with the typical Va value (2–4 cm2/ns) of the Gamble II accelerator diode given by the Blaugrund team, the Va value of the short γ diode of the Qiangguang-I accelerator is nearly doubled. The diode on Qiangguang-I, which works after a plasma opening switch (POS), has a very short rising time (less than 10 ns), and pinches quickly. In contrast, the rising time of the Gamble II accelerator diode is about 40 ns, which is different from the working status of the Qiangguang-I diode. This paper provides a new way to study the radial collapse velocity of high-current diodes.

Pulsed high-energy fluence X-ray source is based on the “Flash II” accelerator. It can be used to carry out effect vulnerability and sensitivity test of unit level system generated electromagnetic pulse (SGEMP). The energy fluence of pulsed hard X-ray is a main parameter of the equipment beam. At present, theoretical calculation method is widely used. Energy fluence can be calculated according to the dose, energy spectrum and energy absorption coefficient of each energy segment.The principle measuring energy fluence of pulsed hard X-ray by total absorption method is introduced. The photoelectric cell with lutetium silicate (LSO) scintillator is selected as a core component of the detection system, and the measurement system is developed. It is composed of scintillation detector, LSO scintillator, dimmer film, photon collimator, visible light shielding material, power supply and signal collecting system. The conversion coefficient between the incident photon energy and the waveform parameter is calibrated by a standard X-ray source. The energy fluence measurement experiment is carried out with the high-energy beam source of the “Flash II” accelerator as an experimental platform. In order to meet the requirements of the effect test experiments, the series diode structure is used in the accelerator for forming a high strength and large area uniform X-ray source. In the experiment, the LiF TLD is located in the front of the phototube and used to monitor the dose. According to the measured waveform, the actual energy of the incident photons is calculated. Combined with the receiving area of incident photons, the energy fluence of pulsed hard X-ray is calculated. The average measured value is 35.9 mJ/cm2 in 5 consecutive experiments. Energy fluence calculated from the measured dose and energy spectrum is 39.8 mJ/cm2. The results of the two methods are compared.It can be found that the experimental result is about 9.8% smaller than the theoretical value. The reasons are as follows. According to the law of exponential decay of rays in matter, in fact, the scintillator cannot absorb all the rays, and some of the rays can penetrate through, the energy of these rays cannot be detected, and thus giving rise to small experimental value. Due to the limited energy point of quasi-monoenergetic source, the sensitivity under the mean photon energy is taken as the sensitivity of the detector, and therefore there is a certain degree of uncertainty. The successful application of the measurement technology provides a good experimental method for the following similar research, and can also provide a reference for X-ray intensity analysis.

University of Technology Sydney. Faculty of Engineering and Information Technology. Quantum mechanics is nonlocal, which makes it different from classical mechanics. Quantum information and quantum computation is a promising frontier science which is based on quantum mechanics. The nonlocality of quantum mechanics is the fundamental reason that many quantum information processing tasks have significant advantages over their classical counterparts. In this dissertation, we study three aspects of quantum nonlocality, which include the quantitative relationship between entanglement and nonlocality, the quantification of genuine tripartite nonlocality and the distribution of nonlocal quantum resources. To be specific, • We investigate the quantitative relationship between entanglement and nonlocality of bipartite quantum systems. We start by exploiting the condition that the nonlocality of two different two-qubit states can be optimally examined by a same nonlocality test setting. Via numerical simulation, we find that the nonlocality of a generic two-qubit state is upper bounded by a function of the corresponding entanglement. Further, we give an analytical proof for the upper bound and find the class of two-qubit states that can reach the upper bound. • We analyze the quantification of genuine tripartite nonlocality of a generic three-qubit state. We find a method to solve the problem for a special class of three-qubit states which include not only pure states but also mixed states. Applying the method, we drive analytical results for the genuine tripartite nonlocality of generalized GHZ states, generalized Werner states and two class of mixed states with special correlation matrices. • We investigate the distribution of nonlocal quantum resources. To distribute bipartite nonlocal quantum resources, we design an efficient quantum repeater scheme, which not only achieves the optimal transmission rate but also consumes less resources of local operations and classical communication, for the case of general pure states of two-qubit system. We also analyze the case of bipartite pure states of arbitrary dimensional quantum system and get an upper bound on the probability of a successful projection operation to produce a maximally nonlocal state. To distribute tripartite nonlocal resources, we propose a simple scenario to generate tripartite nonlocal resources from bipartite nonlocal resources. As examples, we examine the cases that two-qubit Werner states and general two-qubit pure states are prepared as resources, respectively. We get the upper bounds on the genuine tripartite nonlocality that can be generated in the scenario. We also provide the optimal measurement settings to achieve the upper bounds.

This paper presents a method for moderate pulsed X rays produced by a series diode, which can be driven by high voltage pulse to generate intense large-area uniform sub-100-keV X rays. A two stage series diode was designed for Flash-II accelerator and experimentally investigated. A compact support system of floating converter/cathode was invented, the extra cathode is floating electrically and mechanically, by withdrawing three support pins several milliseconds before a diode electrical pulse. A double ring cathode was developed to improve the surface electric field and emission stability. The cathode radii and diode separation gap were optimized to enhance the uniformity of X rays and coincidence of the two diode voltages based on the simulation and theoretical calculation. The experimental results show that the two stage series diode can work stably under 700 kV and 300 kA, the average energy of X rays is 86 keV, and the dose is about 296 rad(Si) over 615 cm2 area with uniformity 2:1 at 5 cm from the last converter. Compared with the single diode, the average X rays' energy reduces from 132 keV to 88 keV, and the proportion of sub-100-keV photons increases from 39% to 69%.

The principle of measuring electron emission threshold of surface area metal electrode is presented. The measurement system of electron emission thresholds of two electrodes is developed. The electron emission characteristics of materials with different roughness degrees or Cr2O3 coating-deposit 40 um are measured in “Chenguang” accelerator. The results show that polishing can suppress electron emission. The higher the roughness degree of material, the lower the electron emission threshold is. Material coated with Cr2O3 has higher electron emission threshold than polished material.

Based on the relativistic Brillouin flow theory, electron current and power loss in loss-front stage of coaxial cylinder vacuum magnetically insulated transmission line (MITL) are deduced under limiting current approximation. Through the particle-in-cell (PIC) model, loss currents and loss powers under different anode voltages are simulated. Simulation and theory results show that the proportions of loss current and loss power to the total current and power decrease when cathode-anode voltage increases. Beyond 4MV, limiting current approximation fits simulation results better than minimum current approximation. At voltages higher than 10 MV, relative error from limiting approximation is under 10%, while it exceeds 50% under minimum current approximation. This work is meaningful for establishing full circuit simulation of MITL system.

In this paper, the interference of wave packets reflected from a stationary boundary and a moving boundary respectively are discussed. The present theory is based on the boundary value problem of classical electrodynamics, especially with the moving boundary which gives rise Doppler effect. Various distinguished interference properties are investigated and a rigorous expression for the velocity measurement of the moving mirror is provided. At the end, the paper points out that many similar and important problems are waiting for us to explore.