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A single stage 1-MV prototype induction voltage cavity has been tested detailedly. Low-voltage principle experiments with injection currents of several kiloampere, and high-voltage experiments with feed pulses up to 800 kV/150 kA have been conducted. The major objective of the principle experiments is to measure the feed current symmetry. With the cavity fed by a single current, azimuthal distributions of feed currents under several typical azimuthal line configurations are measured. Meanwhile, the influence of the current asymmetry on cavity equivalent inductance is analyzed. With the cavity fed by double currents, the effects of asynchronous feed currents on current symmetry and current addition efficiency are investigated experimentally. When the cavity is single-point driven by high-power pulses, the insulator stack made of three different dielectrics is tested. The results show that the final flashover voltage of the two newly developed materials is slightly higher than that of the common PMMA.

A novel trigger method based on an internal brick and azimuthal line in cavities is presented for Linear Transformer Drivers (LTD). The triggered brick is similar as the other normal bricks in cavities, which has the same charge voltage and the switch gas pressure. When the switch in triggered brick is closed by an external pulse, a high voltage pulse is produced and transmitted to other bricks along an azimuthal line installed in the middle insulator of cavities. Therefore, one external trigger pulse is enough for a 1 MA LTD cavity. This novel trigger manner has been applied successfully in 800 kA cavity with 36 bricks. Based on this novel trigger manner, a trigger method is proposed for a LTD module with multi-stage cavities stacked in series. Only several upstream cavities are triggered by external trigger pulses, and the residual cavities are triggered by the high pulses produced from the particular-location of upstream cavities. This trigger method will greatly simplify the requirements of trigger system, which has a promising application for future 60-MA LTD accelerator.

A two-dimensional, three-temperature radiation magneto-hydrodynamics model is applied to the investigation of evolutional trends in x-ray radiation power, energy, peak plasma temperature and density as functions of drive current rise-time and initial load density distribution by using the typical experimental parameters of tungsten wire-array Z-pinch on the Qiangguang-I generator. The numerical results show that as the drive current rise-time is shortened, x-ray radiation peak power, energy, peak plasma density and peak ion temperature increase approximately linearly, but among them the x-ray radiation peak power increases more quickly. As the initial plasma density distribution in the radial direction becomes gradually flattened, the peak radiation power and the peak ion-temperature almost exponentially increase, while the radiation energy and the peak plasma density change only a little. The main effect of shortening drive current rise-time is to enhance compression of plasma and the effect of flattening initial load density distribution in the radial direction is to raise the plasma temperature. Both of the approaches elevate the x-ray peak radiation power.

Radiation simulation utilizing plasma radiation sources (PRS) generates a large number of undesirable debris, which may damage the expensive diagnosing detectors. An ultra fast shutter (UFS) driven by pulsed high current can erect a physical barrier to the slowly moving debris after allowing the passage of x-ray photons. The UFS consists of a pair of thin metal foils twisting the parallel axes in a Nylon cassette, compressed with an outer magnetic field, generated from a fast capacitor bank, discharging into a single turn loop. A typical capacitor bank is of 7.5 μF charging voltages varying from 30 kV to 45 kV, with corresponding currents of approximately 90 kA to 140 kA and discharging current periods of approximately 13.1 μs. A shutter closing time as fast as 38 microseconds has been obtained with an aluminium foil thickness of 100 micrometers and a cross-sectional area of 15 mm by 20 mm. The design, construction and the expressions of the valve-closing time of the UFS are presented along with the measured results of valve-closing velocities.

The preliminary experimental results of the generation and diagnostics of high-power ion beams of FLASH II accelerator are reported. The high-power ion beams presently are being produced in a pinched diode. The method for enhancing the ratio of ion to electron current is to increase the electron residing time by pinching the electron flow. Furthermore, electron beam pinching can be combined with electron reflexing to achieve ion beams with even higher efficiency and intensity. The anode plasma is generated by anode foil bombarded with electron and anode foil surface flashover. In recent experiments on FLASH II accelerator, ion beams have been produced with a current of 160 kA and an energy of 500 keV corresponding to an ion beam peak power of about 80 GW. The ion number and current of high power ion beams were determined by monitoring delayed radioactivity from nuclear reactions induced in a 12C target by the proton beams. The prompt γ-rays and diode bremsstrahlung x-rays were measured with a PIN semi-conductor detector and a plastic scintillator detector. The current density distribution of ion beam were measured with a biased ion collector array. The ion beams were also recorded with a CR-39 detector.

Numerical computation based on a zero-dimensional thin-plasma-shell model has been carried out to study the scaling of the maximum kinetic energy per unit length, the current amplitude and the compression ratio for the imploding Z-pinch liner driven by peaked current pulses. A dimensionless scaling constant of 0.9 with an error less than 10{%} is extracted at the optimal choice of the current and liner parameters. Deviation of the chosen experimental parameter from the optimal exerts a minor influence on the kinetic energy for wider-shaped and slower-decaying pulses, but the influence becomes significant for narrower-shaped and faster-decaying pulses. The computation is in reasonable agreement with experimental data from the Z, Saturn, Blackjack 5 and Qiangguang-I liners.

The density, drift velocity and reproducibility of the plasma produced by a cable plasma gun array have been measured with a charge collector array. The plasma is used to prefill a coaxial plasma-opening switch with a conducting time approaching 0.4 μs. The reproducibility of the plasma source in subsequent shots is better than 5%. Near the gun nozzle and the opposite electrode, the plasma density amounts to 1015cm-3, which is 2 times to 3 times that in the gap between the two coaxial electrodes. A plasma drift velocity of about 2.4 cm/μs is observed from the time of flight of the charged particles. Both plasma density and drift velocity increase almost linearly with the rise in charge voltage.

Imploding plasma liners in the Z-pinch scheme have been demonstrated to be capable of producing high power radiation in the soft x-ray waveband owing to the conversion of the kinetic energy of imploding liner into thermal energy which in turn is converted into x-ray energy. To obtain largest x-ray power for a certain pulsed-power driving-source, the liner should gain a kinetic energy as great as possible, which imposes an optimal scaling upon the operating parameters of liner in terms of getting largest kinetic energy. This work exposes, by means of numerical calculations based on zero-dimensional quasi-plasma-shell model, the large variation of the scaling factor, which connects the parameters of the initial linear and the driving current, with different driving current waveforms. Also solved in the work is the optimal scaling factor in the sense of producing maximum kinetic energy. Calculations show that maximum kinetic energy is obtained at the current maximum or a little time later. These results are in reasonable agreement with several experiments and will be of help to the design and experimental adjustment of Z-pinch liners.

A series of experiments has been carried out on Qiang-guang I generator to study the dynamics of krypton gas-puff Z-pinches. The generator was operated at a peak current of 1.5 MA with a rise-time of 80 ns. The specific linear mass of gas liner was about 20 μg/cm in these experiments. In the diagnostic system, a four-frame x-ray framing camera and a pinhole camera were employed. A novel feature of this camera is that it can give time-resolved x-ray images with four frames and energy-resolved x-ray images with two different filters and an array of 8 pinholes integrated into one compact assemble. As a typical experimental result, an averaged radial imploding velocity of 157 km/s over 14 ns near the late phase of implosion was measured from the time-resolved x-ray images. From the time-integrated x-ray image an averaged radial convergence of 0.072 times of the original size was measured. An averaged radial expansion velocity was 130 km/s and the maximum radial convergence of 0.04 times of the original size were measured from the time-resolved x-ray images. The dominant axial wavelengths of instabilities in the plasma were between 1 and 2 mm. The change in average photons energy was observed from energy spectrum- and time-resolved x-ray images.

The linear multi-core pulse transformer is an important primary driving source used in pulsed power apparatus for the production of dense plasma owing to its compact, relatively low-cost and easy-to-handle characteristics. The evaluation of the magnetic saturation of the transformer cores is essential to the transformer design, because the energy transfer efficiency of the transformer will degrade significantly after magnetic saturation. This work proposes analytical formulas of the criterion of magnetic saturation for the cores when the transformer drives practical loads. Furthermore, an electric circuit model based on a dependent source treatment for simulating the electric behavior of the cores related to their nonlinear magnetization is developed using the initial magnetization curve of the cores. The numerical simulation with the model is used to evaluate the validity of the criterion. Both the criterion and the model are found to be in agreement with the experimental data.

Kr gas-puff Z-pinch experiment performed recently on Qiang-guang I pulsed power generator is reported. The generator has a 1.5 MA current with a pulse width of 100 ns. The total x-ray energy as well as its spectrum has been obtained, and the average power of x-ray radiation in 50-700 eV measured by XRDs is 2 TW. The generator configuration, gas-puff load assembly and diagnostic system for the experiments are described.

The nonaxisymmetrical magnetic insulation would occur due to the disalignment of inner electrodes in long magnetically insulated transmission lines, or the nonuniform distributions of injected currents in induction cavities of magnetically insulated induction voltage adders (MIVA). The electron sheath profile is a very important parameter to characterize the nonaxisymmetrical magnetic insulation. In the past, the three-dimensional particle in cell simulation was usually used to determine the electron sheath profile, which is extremely time-consuming and inefficient. In this paper, a fast and efficient calculation method is proposed. The classical one-dimensional Creedon theory of the magnetic insulation equilibrium is generalized to a two-dimensional plane of (r, ) via introducing a parameter defined as the azimuthal mode number. Two-dimensional Creedon is developed to model the asymmetric magnetic insulation of the MIVA. Provided the azimuthal distributions of magnetic flux density on the cathode, which is in proportion to the cathode current, the two-dimensional Creedon model is numerically solved. A numerical solution method to calculate the electron sheath profile is proposed, and then the calculation error is also given. As the azimuthal distribution of magnetic flux density on the cathode meets a cosine function, the profile of the electron sheath is approximate to the Gauss function. As the nonuniform portion of cathode current increases, the electron sheath becomes more eccentric, and the calculation error is also much larger.

The magnetically-insulated induction voltage adder (MIVA) is a pulsed-power accelerator widely used in the X-ray flash radiography and -ray radiation simulation. The operating impedance of magnetically-insulated transmission line (MITL) on the secondary side of MIVA will produce significant influence on the power coupling between the pulsed-power driving source and the terminal load. Therefore, optimizing the secondary impedance of MIVA to maximize the electrical-power or radiated output of load is critical for the design of MIVA facility. According to whether the MITL operating impedance is smaller than the load impedance, MIVAs can be divided into two different types, i.e., the impedance-matched case and impedance undermatched case. For the impedance-matched MIVA, because the MITL of MIVA operates at the minimal current point or self-limited flow, the output of MIVA just depends on the MITL operating impedance and is independent of load. Correspondingly, the circuit analysis is relatively easy. However, for MIVA with impedance undermatched load, the analysis method is more complicated. Based on the classical Creedon theory of the magnetic insulation equilibrium and the sheath electron re-trapping theory, a circuit method is established for MIVA with impedance under-matched load. The analysis process consists of two steps. Firstly, the working point of the forward magnetic insulation wave is solved by the minimal current theory on the assumption that the MIVA is terminated by impedance-matched load. Then, the actual operating point after the re-trapping wave has passed is solved, in which the characteristic impedance of the re-trapping wave is treated as a vacuum impedance. And the relationship between the output parameters of MIVA, e.g., the output voltage, the cathode and anode current, and the electrical power, and the undermatched extent of load is obtained numerically. Based on the analysis method, a method to optimize the secondary impedance of MIVA with ten-stage cavities stacked in series to drive X-ray radiographic diodes is developed. This optimization method aims at maximizing the radiated X-ray dose rate of the diode loads on the assumption that only the cathode current is available for the X-ray radiographic diode. The optimization secondary impedance, Zop*, varying with the scaling factor, , is achieved, where is the power exponent between the dose rate and the diode voltage (Ḋ Ud). is usually determined by the diode type, geometrical structure, and operating characteristics. It is found that the optimization secondary impedance Zop* decays exponentially with the increase of value , i.e., the increase of the diode-voltage-dependent degree of the radiated X-ray dose rate. And the larger the load impedance, the larger the value of Zop* is. The circuit analysis method and the impedance optimization method developed in this paper are specially useful for the applications of MIVA in the flash radiographic fields.

A coaxial multi-gap multi-channel spark switch with stainless-steel-spring ring gap electrodes is designed and investigated. The switch is triggered by a pulse applied to the cylindrical electrode outside the discharging channel through a parasitic capacitance coupling. The jitter of the switch is reduced by several short-distance gas gaps in series, and its inductance is reduced by a multi-channel discharge on account of the inductance isolation between the coils of the spring ring electrode. The experimental results indicate that the switch is of low inductance (15-30 nH), low jitter (~3 ns), and stable breakdown performance.

Experiments have been conducted on a plasma opening switch (POS) test-bed to investigate the influence of cathode materials made of aluminum, stainless steel, molybdenum and tungsten on opening performance for conduction time up to 3 microseconds, conduction current up to 100 kA. Remarkably different opening characteristics have been shown for these materials, with tungsten being of the best opening performance.

The electrical explosion of single wire occurs in many application fields, such as wire-array Z-pinch, synthesis of the nanopowder, high-intensity magnetic field source, etc. The initial stage of the electrical explosion of single wire has a critical influence on the stagnation and X-ray yield in the wire-array Z-pinch. The impressive result of X-ray yield from wire-array Z-pinch is a major motivation to promote the research in this field. Although numerous studies have been carried out to gain a deep insight into the physics of the electrical explosion of single wire, more experimental investigations are necessary to optimize the energy deposition and expansion rate. It is important to investigate the characteristics of the electrical explosion of single wire under the negative polarity pulsed-current, which is adopted in many Z-pinch facilities. In this paper, the electrical explosion of aluminum wire under negative polarity pulsed-current in vacuum is investigated. In the present experiments, the light emission is measured by the photomultiplier and streak camera. A laser probe EKSPLA-PL2251C (30 ps, 532 nm) is adopted to perform the shadowgraphy, schlieren and interferometry diagnostics. The radial knife-edge schlieren scheme is employed to translate the regions with plasma refractivity and gas-type refractivity. The interferometry is constructed based on Mach-Zehnder interferometer. The shadowgram, schlieren image and interferogram are recorded by Canon cameras. The typical waveforms of the voltage, current and light emission from the electrical explosion of 15 m-diameter, 2 cm-long aluminum wire are derived. The energy deposition at the instant of voltage collapse is about 2.4 eV/atom (vaporization energy is about 4 eV/atom). In order to increase the energy deposited into the wire, the 15 m-diameter, 2 cm-long aluminum wire with 2 m polyimide coating is exploded with the same electrical parameters. The energy deposition in the coated wire is about 5 eV/atom. From the shadowgram of the electrical explosion of uncoated aluminum wire, the expansion velocity of the high-density region can be estimated to be about 2.2 km/s. However, the expansion velocity of the high-density region of the polyimide-coated aluminum wire is about 5 km/s. The schlieren images show that the wire is exploded into a binary structure, i.e., a high-density core surrounded by the low-density corona. It should be noted that the energy deposition in the coated wire is larger than the vaporization energy, indicating that the aluminum wire is totally in gaseous state. Thus, the plasma region in the schlieren image of electrical explosion of coated wire is not distinct. The core-corona structure is depressed by the insulating coatings to a certain extent. The configuration of the parallel wire is adopted to estimate the expansion velocity of the plasma shell. The expansion velocity of the low-density plasma is about 5.8 km/s. Two-dimensional distribution of the phase shift is derived through the interferogram. The central part of the gas-type material with a radius of 0.1 cm exhibits a large positive phase shift, while the peripheral plasma shows a small negative phase shift. The three-dimensional atomic density distribution is reconstructed in the gas-type distribution area in which the contribution of electrons is negligible. In our experiments, the energy deposition of the electrical explosion of uncoated wire ranges from 2 to 4 eV/atom. This may be caused by the initial conditions of the wire surface and the connection between the wire and electrode. Further research should be carried out for a better understanding of this phenomenon.

The uniformity of intense relativistic electron beams under a converging magnetic guide field is studied experimentally in this paper. In the experiments, fluence calorimeter and x-ray pinhole photograph were used to measure the beam uniformity. The experimental results show that the externally applied magnetic flux density at the cathode and the shape of cathode face have considerable influence on the beam uniformity. The beam uniformity better than 80% is obtained over an area of 200 cm2 when the externally applied magnetic flux density at the cathode is about 0.6 T and the cathode face is concave to a depth of 1.5 mm, relative to the cathode edge.

The magnetic compression of intense relativistic electron beams under a converging magnetic guide field is studied theoretically and experimentally in this paper. A code to evaluate the compressed-beam transport is set up. Calculations of the beam energy fraction transmitted through magnetic mirror are in good agreement with experimental data.