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This article examines the mechanical design tolerances for the Scorpius injector using a 3-D particle-in-cell (PIC) code. In order to meet its objective as a high-fidelity, multipulse flash X-ray source, the accelerator has requirements for the electron beam in order to minimize the spot size of the beam focused onto a foil target to create high fluence X-rays at energies greater than 10 MeV. The requirements for alignment of the cathode, anode beam pipe, focusing solenoids, and transport solenoids specified using Trak and AMBER are independently verified using a 3-D electrostatic/magnetostatic model of the Scorpius injector, including transverse magnetic field errors that arise from mechanical alignment errors. It is predicted that the injector will meet the performance requirements for radiographic operation and has a design margin to correct for potentially unforeseen operating conditions. [ABSTRACT FROM AUTHOR]

We describe the design, operation, and qualification of a coaxial plasma gun (CPG) in a low-pressure environment with a gas puff inlet. This infrastructure enables a CPG to operate in the deflagration mode followed by snowplow plasma sheath formation. These modes inject radially expanding and axially propagating plasma sheaths into a low-pressure residual background. This manuscript details the pulse power delivery circuit, including automatic logic control of subcircuits. High-speed camera images (12800 frames/s) of the formed plasma elucidate the ionization of an axially propagating plasma. Long-exposure images (1.3 s) capture the full propagation distance of the plasmoid. Rogowski coil current diagnostics elucidate the timing of a self-crowbar discharge that delineates between deflagration and snowplow modes. An empirically determined 50-ms gas puff duration resulted in a maximum plasma propagation distance of $\approx 23$ cm. Shorter durations did not ionize a sufficient amount of gas for elongated axial propagation, whereas longer durations suppressed axial plasma sheath expansion. This type of gas injection CPG device is now qualified for use in CPG experiments that require the snowplow mode and maximum mean free path of fast ions resulting from various plasma heating mechanisms. These include CPG operation within external magnetic fields in which significant plasma propagation distance is required, including solar physics experiments and space propulsion development. [ABSTRACT FROM AUTHOR]

How to design an impact platform that can provide a strong electromagnetic environment for all kinds of precision electronic equipment and experimental reference for strong electromagnetic protection is of great significance. In this article, an electromagnetic coil system that generated a strong magnetic field environment was designed and studied. First, the coil parameters and coil structure were designed. Then, the Comsol finite element software was used to simulate and design the three-component coil. The coil distance and turns were adjusted to make the coil center produce a uniform magnetic field area and meet the strong magnetic field index. Finally, the coil system was built to verify the magnetic field generated by the coil through experiments. This system will be used to simulate the strong magnetic field environment that produces different high precision and may occur in the operating environment of the equipment. It will also be used to provide strong magnetic field impact test support conditions for aerospace, naval vessels, and various types of equipment, so as to find and solve the problem of antistrong magnetic reliability of equipment in the design stage. [ABSTRACT FROM AUTHOR]

Scorpius is a multipulse linear induction accelerator (LIA) under development for flash radiography. Because it has substantially more cells than present LIAs, higher magnetic focusing fields are needed to suppress beam breakup (BBU). Therefore, it is more susceptible to corkscrew motion of the beam, which also depends on beam energy spread and focusing magnet misalignments. For energy spread and alignment tolerances expected for Scorpius, a magnetic tune designed to suppress BBU is shown to produce corkscrew motion within the range that can be controlled through the use of steering dipoles on existing LIAs. A gap-voltage modulation scheme is shown to almost completely eliminate chromatic effects such as corkscrew. [ABSTRACT FROM AUTHOR]

Magnetic nozzles with their contactless feature have opened new grounds for long-distance space travels. For quicker mission completions along with improving system reliability, it becomes necessary to design robust systems that exhibit the ability to confine thrust. A semianalytical numerical method is proposed for rapid and assumption-less calculations of the magnetic field because of a thick coil with rectangular cross section. The method is extended for the proposal of a three-coil setup, where divergence angle of the magnetic field lines is readily controlled in-flight to provide the flexibility to modify the output magnetic thrust and the nozzle’s efficiency. [ABSTRACT FROM AUTHOR]

A concept of SUb-atmospheric Radio-frequency Engine (SURE) designed for the near-space environment is proposed. The antenna wrapping quartz tube consists of two solenoid coils with variable separation distance and is driven by radio frequency power supply (13.56 MHz–1 kW). The discharge involves inductive coupling under each solenoid coil and capacitive coupling between them. This novel scheme can ionize the filling air efficiently for the entire pressure range of 32 ~ 5332 Pa in near space. The formed plasma density and temperature are up to $2.23\times 10^{18}\,\,\textrm {m}^{-3}$ and 2.79 eV, respectively. The influences of separation distance, input power, filling pressure, and the number of solenoid turns on discharge are presented in detail. This air-breathing electric propulsion system has no plasma-facing electrode and does not require an external magnetic field and is, thereby, durable and structurally compact and light. [ABSTRACT FROM AUTHOR]

This article intends to design, simulate, and implement a dummy load coil, a very significant element, in the Loran transmitter system. In order to ensure the impedance matching, the solenoid coil is designed with an inductance range from 200 to 300 $\mu \text{H}$. Analytical and finite-element methods are deployed as the most common practice solutions to calculate and simulate the coil inductance. The results obtained from these two methods are compared, and their accuracy and effectiveness are analyzed based on the experimentally implemented coil. Furthermore, a new method is devised to calculate the inductance of the solenoid coil containing numerous wire strands. [ABSTRACT FROM AUTHOR]

Turkish Accelerator Center (TAC) Proton Accelerator Facility (PAF) is a project proposal that aims to build a megawatt (MW) power proton accelerator in Turkey. The proton source of this project was chosen as a microwave discharge ion source due to its long life time, its high current, and its lower maintenance requirements when compared with other ion source types. A microwave discharge ion source test stand was built to gain experience for TAC PAF and for similar projects requiring high beam current in Turkey. A magnetron with 2.45-GHz frequency, 50-Hz repetition rate, and 150-W fixed power was used to create the hydrogen plasma. Two different electrode systems were experimented: the first design consists of 2-mm radius plasma electrode that extracts beam currents up to 0.75 mA and the second design consists of 4-mm radius plasma electrode that extracts beam currents up to 5.2 mA. [ABSTRACT FROM AUTHOR]

The central solenoid model coil (CSMC) project was launched in the Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP). In order to develop and verify the key techniques and manufacturing process of the full-size central solenoid (CS) coil for the China Fusion Engineering Testing Reactor (CFETR). The CFETR CSMC is designed to be a superconducting magnet of 12 T maximum magnetic field when the running current is 47.65 kA, which consists of two Nb3Sn windings in the internal high field and three Niobium-Titanium (NbTi) windings in the external low field. All the windings of the CSMC are a kind of pancake coil continuously wound one-in-hand by cable-in-conduit conductor (CICC), which are electrically connected in series by ohmic joints. To minimize the heat load of the joints to the cryogenic system, the design resistance of the joint is below 5 $\text{n}\Omega $ in operating conditions. The design of the joint is based on the concept of lap joint. A NbTi-NbTi full-size joint sample has been manufactured and tested. In this article, the design and manufacturing processes of the joint sample are described in detail, and the test results show dc resistance below 5 $\text{n}\Omega $ criterion. [ABSTRACT FROM AUTHOR]

The central solenoid model coil (CSMC) of the China Fusion Engineering Testing Reactor (CFETR) is currently in the manufacturing phase. Once completed, the CSMC will be tested on a testing platform. The testing platform is composed of several subsystems, which are coordinated by a control system to conduct a successful experiment and collect scientific data generated during the experiments. A diagnostic system is employed for the purpose of monitoring the status of a superconducting magnet and triggers the alarm system if an abnormal signal has been detected. The central control system of the CSMC testing platform is called the control data access and communication (CODAC) system. In order to realize the normal data communication between the CODAC system and a subsystem, an experimental physics and industrial control system (EPICS) Channel Access (CA) protocol is needed. [ABSTRACT FROM AUTHOR]

This paper proposed the use of a ringer, a self-switched inductive storage system, for applications involving reluctance accelerators, a kind of electromagnetic launcher, and compatible with applications where portability is a requirement. There will be shown three different useful approximations for the analysis of the ringer, employed as a power source for a reluctance accelerator. First, it described the equations governing the que behavior of an ideal unloaded ringer, and then the equations for the ringer with an uncoupled inductive load, and ultimately a Lagrangian model for the ringer as an inductive power source for a reluctance accelerator, capable to make predictions about the currents through the circuits and the exit speed of the projectile for a given firing. The accuracy of the predictions made with the third approximation, the Lagrangian model, was tested experimentally. [ABSTRACT FROM AUTHOR]

According to the Chinese fusion engineering testing reactor (CFETR) central solenoid model coil (CSMC) properties test requirements, a large cryogenic test platform will be built. The feeder, as one of the important components of the platform, should be studied to afford the much valued help for the basic test facilities. This paper focuses on the feeder structural design and the stress analysis in conditions of different loads. All of the work could not only provide necessary help for building CFETR CSMC test platform but also provide the important service experience of the large cryogenic test platform in the future. [ABSTRACT FROM AUTHOR]

Guiding magnetic field plays a very important role in the efficient operation of the relativistic backward-wave oscillator (RBWO). Generally, magnetic fields are made using solenoid coils extended behind the cathode region to get the desired magnetic field in the beam-microwave interaction region. Large diameter anodes are required to generate a required electron beam with low radial velocity. This paper presents a pulsed solenoid coil design in which the uniform magnetic field extends just up to the cathode and requires a much lesser volume in which the coil has to be kept and has a lower number of turns. This magnetic field coil setup has been tested for 18-A dc coil current to measure the magnetic field profile. A uniformity of 93.5% is achieved within 460 mm length. This coil setup was further tested with an RBWO setup at 550 kV, 7-kA electron beam parameters to generate 1-GW peak microwave power using a 0.55-T magnetic field at 3.28 GHz. [ABSTRACT FROM AUTHOR]

The central solenoid model coil (CSMC), a crucial component of China Fusion Energy Test Reactor, is currently in the design and manufacturing process. CSMC assembly consists of a number of steps such as winding pack, an outer NbTi coil, a middle Nb3Sn coil, an inner Nb3Sn coil, and a preload structure. The highest field of the model coil is 12 T with the maximum change rate of a magnetic field of the conductor is 1.5 T/s. In this paper, length of the cooling channels together with thermal–hydraulic parameters such as inlet pressure, temperature, and mass flow rate are optimized. In addition, thermal–hydraulic analysis for the cooling loop located in the worst condition of the model coil was conducted to recognize the temperature and mass flow rate change over time. The hydraulic model, the material properties, and the heat loads associated with analysis are given, and the results of the analysis are presented. [ABSTRACT FROM AUTHOR]

In order to develop and verify the key manufacturing technologies of the large Nb3Sn superconducting magnet, the central solenoid model coil (CSMC) for China Fusion Engineering Test Reactor is being developed in the Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP), Hefei, China. The design value of the highest magnetic field for CSMC is 12 T, which is made of Nb3Sn and NbTi hybrid superconducting magnets. The key structural parameters of all windings have been determined by the electromagnetic design and optimization of the coil. All the windings of CSMC are a kind of pancake coil wound one in hand by cable-in-conduit conductor; each winding is composed of pancakes (concentric circular turns with turn transitions), pancake joggles, and upper and lower leads. The winding design has been finished including the winding direction analysis, the key bending segments geometry of turn transitions, pancake joggles, and leads transitions. Besides, the new winding production line has come into use and some key forming trials have been conducted. [ABSTRACT FROM AUTHOR]

In order to verify key techniques and manufacturing aspects of the central solenoid (CS) coil of the China fusion engineering test reactor (CFETR), the Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP) plan to develop a CS model coil. The conceptual design of the CS model coil of CFETR has been carried out by ASIPP. The CS model coil shall produce a 12-T peak field in the bore of the magnet. The maximum magnetic field change rate is 1.5 T/s. The designed operating current is 47.65 kA. The CFETR CS model coil structure design mainly includes coil winding design, buffer zone design, preload structure design, coil joints and joint supports design, and liquid helium cooling channels design. This paper presents the conceptual design of CFETR CS model coil structure based on electromagnetic design and optimization. [ABSTRACT FROM AUTHOR]

The dual-axis radiographic hydrodynamic test (DARHT) facility uses bremsstrahlung radiation source spots produced by the focused electron beams from two linear induction accelerators (LIAs) to radiograph large hydrodynamic experiments driven by high explosives. Radiographic resolution is determined by the size of the source spot, and beam emittance is the ultimate limitation to spot size. On the DARHT-II LIA, we measure an emittance higher than predicted by theoretical simulations, and even though this accelerator produces submillimeter source spots, we are exploring ways to improve the emittance. Some of the possible causes for the discrepancy have been investigated using particle-in-cell codes. The simulations establish that the most likely source of emittance growth is a mismatch of the beam to the magnetic transport, which can cause beam halo. [ABSTRACT FROM PUBLISHER]

Testing results of a generator based on the parallel gyromagnetic nonlinear transmission lines with saturated ferrite are presented. Practically identical and stable RF-modulated high-voltage nanosecond pulses were shaped in each of the four channels. The pulse amplitude reaches −175 kV at a modulation depth of RF oscillations to 50% and an effective frequency ~4 GHz. Power in the packet operation mode with a 1-s packet duration at pulse repetition frequencies up to 1000 Hz (in packet) was supplied by a solid-state driver. The electric field strength achieved 250 kV/m at a distance of 3 m from antennas. [ABSTRACT FROM PUBLISHER]

An inductive coil gun is a solenoid surrounding a cylindrical metallic armature (the projectile), both electromagnetically coupled. One or more capacitors discharge a stored voltage quickly through the coil, configuring a kind of RLC circuit, with the pulse-shaped current generating a magnetic field inside the coil that accelerates the projectile. Once the projectile crosses an equilibrium point inside the coil, the existing magnetic field pulls the armature back, therefore reducing the final muzzle velocity and decreasing the efficiency—defined as the ratio between the available capacitor electrostatic versus the slug kinetic energies. This paper describes a system that monitors the armature position inside the coil, with a laser beam, and automatically cuts the current when the projectile reaches the equilibrium point. The system, named current switch circuit, enables higher velocities using the same set of coilgun and projectiles, providing a higher efficiency. [ABSTRACT FROM PUBLISHER]

In this paper, the effect of external magnetic field loaded at the initial period of inertial stretching stage on a jet produced by Ø56-mm shaped charge is evaluated through the depth-of-penetration (DOP) test method. Experimental results are compared with the results obtained under the field loaded at the later inertial stretching stage. A standoff of 650 mm is used in the experiments, in which the shaped charge jet can undergo formation, elongation, breakup, rotation, and drift. The initial energy is provided by a capacitor bank, which is loaded on the solenoid to generate a magnetic field used for coupling with the jet. The external magnetic field loaded at the initial period of inertial stretching stage can enhance the stability of the jet and increase its DOP. The penetration capability of the jet in the above-mentioned condition is increased by 77.4%. [ABSTRACT FROM AUTHOR]

NSTX-U research will offer new insights by studying gas assimilation efficiencies for massive gas injection (MGI) from different poloidal locations using identical gas injection systems. In support of this activity, an electromagnetic MGI valve has been built and tested. The valve operates by repelling two conductive disks due to eddy currents induced on them by a rapidly changing magnetic field created by a pancake disk solenoid positioned beneath the circular disk attached to a piston. The current is driven in opposite directions in the two solenoids, which creates a canceling torque when the valve is operated in an ambient magnetic field, as would be required in a tokamak installation. The valve does not use ferromagnetic materials. Results from the operation of the valve, including tests conducted in 1-T external magnetic fields, are described. The pressure rise in the test chamber is measured directly using a fast time response Baratron gauge. At a plenum pressure of just 1.38 MPa ( \sim 200 psig), the valve injects 27 Pa \cdot \text{m}^{\mathrm {\mathbf {3}}} ( \sim 200$ torr $\cdot $ L) of nitrogen with a pressure rise time of 3 ms. [ABSTRACT FROM AUTHOR]

The central solenoid model coil of China Fusion Engineering Test Reactor consists of two modules: 1) the inner module made of Nb3Sn and 2) the outer module made of NbTi. This paper describes an optimization procedure for the electromagnetic design of the model coil by means of a Fortran code written for this purpose. The target of the optimization was the reduction of the length of the Nb3Sn cable-in-conduit conductor, needed to produce a peak magnetic field of 12 T. The optimization constraints are: 1) the maximum magnetic field on the NbTi module should be lower than 6 T and 2) the unit length of one Nb3Sn conductor should be shorter than 1 km. Based on the electromagnetic optimization, the engineering scheme of the model coil is determined. The feasibility of the engineering scheme is investigated using ANSYS finite element code. Accordingly, a mechanical analysis of the structure under the Lorentz force at 4.5 K is performed. The analysis results indicate that the present design is reasonable and fulfills the design requirements. [ABSTRACT FROM AUTHOR]

Kinetic energy exchange in the longitudinal and transverse directions of a charged particle beam during longitudinal pulse compression is discussed through a compact beam simulator for heavy ion inertial fusion. With the goal of understanding the beam behavior in a compact beam simulator experiment, the evolution of the transverse and longitudinal thermal spreads is evaluated using theoretical estimation and numerical simulation. The multiparticle simulation results show the longitudinal and transverse coupling motions via the space charge effect during the longitudinal pulse compression. The ratio of effective temperatures in the longitudinal and transverse directions derived from numerical results is higher than that evaluated from theoretical estimation. It is implied that the discrepancy is caused by the nonlinear space charge effect during the longitudinal bunch compression. [ABSTRACT FROM PUBLISHER]

Beam dynamics issues were assessed for a new linear induction electron accelerator being designed for multipulse flash radiography of large explosively driven hydrodynamic experiments. Special attention was paid to equilibrium beam transport, possible emittance growth, and beam stability. Especially problematic would be high-frequency beam instabilities that could blur individual radiographic source spots, low-frequency beam motion that could cause pulse-to-pulse spot displacement, and emittance growth that could enlarge the source spots. Beam physics issues were examined through theoretical analysis and computer simulations, including particle-in-cell codes. Beam instabilities investigated included beam breakup, image displacement, diocotron, parametric envelope, ion hose, and the resistive wall instability. Beam corkscrew motion and emittance growth from beam mismatch were also studied. It was concluded that a beam with radiographic quality equivalent to the present accelerators at Los Alamos National Laboratory will result if the same engineering standards and construction details are upheld. [ABSTRACT FROM AUTHOR]

An electron gun is designed for a W-band sheet beam TWT using a planar rectangular cathode working in the space charge limited region. A permanent magnet solenoid focusing system is designed to focus the beam. A pole-piece with a novel multisized (stepped) hole is investigated for stable transport of the beam. The size of the hole in the pole-piece is larger near to the magnets and it is gradually decreased stepwise toward the cathode. The pole-piece with the multisized hole reduces both the transverse magnetic field and magnitude of flux leakage toward the cathode. Simulation results show that the sheet beam transports without significant beam ripple and edge curling under the magnetic field of the designed focusing structure with the pole-piece of multisized hole. The thermal velocity of the electrons is also considered in the simulation. The beam transmission up to 70-mm distance is 98.8% and 97.3%, respectively, for nonthermal and thermal beam under the magnetic field of the designed focusing system. [ABSTRACT FROM PUBLISHER]

Variations in the transient time and in the microwave pulse duration and peak power have been demonstrated for a relativistic subgigawatt $Ka$ -band backward-wave oscillator (BWO) with the slow-wave structure geometry, the accelerating voltage, and the electron beam current remained unchanged. This was done taking into account that the BWO operation mode depends on the starting-current-to-beam-current ratio. Efficient variation of the starting current was attained by changing the beam path in view of a significant difference between the times of the guide pulsed magnetic field diffusion into the electron injection region and beam-wave interaction space. [ABSTRACT FROM PUBLISHER]

To obtain high velocity and high energy conversion efficiency on a synchronous induction coilgun, the armature capture effect which is the inherent characteristic for the synchronous induction coilgun needs to be analyzed. The reason for the armature capture effect is first deduced and analyzed using the lumped element circuit model and then quantificational result is obtained based on the field-circuit coupled model. According to the analytical result, the method to minimize the armature capture effect is proposed from the viewpoint of the magnetic coupling between the driving coil and the armature. Several ways are analyzed through the finite-element simulation. The simulation results show that adjusting the power parameters, such as increasing the capacitance or initial voltage, and decreasing the crowbar resistance, and adjusting the armature parameters, such as decreasing the mass or adopting the solenoid armature, can minimize the armature capture effect and increase the conversion efficiency. These methods are validated through a four-stage induction coilgun. We compare the simulation results with the experimental results and show that by adjusting the armature parameters, we can minimize the armature capture effect. It provides valuable reference for synchronous induction coilgun design. [ABSTRACT FROM PUBLISHER]

It is already several tens of years to a cascade magnetocumulative (MC-1) generator of reproducible magnetic fields of multimegagauss range—a well-known device in megagauss physics. Due to several reasons, it seems to be necessary to recall the history of creation of this physical device, for which capabilities are still unique. First, this could be interesting; second, there is a desire to remind and appreciate contribution and services of the MC-1 generator designers who have left the business; third, this story could help to understand an operation principle and possibilities of the generator to new generation of the megagauss community, convince it that this source of extreme conditions is exceptionally convenient and useful research tool. These ideas suggesting, developing, and examination were carried out in close collaboration with Pavlovskii and Kolokolchikov. [ABSTRACT FROM PUBLISHER]

At the first stage of work related to the production of a generator for generating 20-MG-range magnetic field special attention was paid to learning, updating, and testing magnetocumulative (MC) MC-1 generator numerical models based on MASTER Pro software package aiming to use these models for choosing the most promising generator design. The functionality of a generator and variety of its applications imposes two significant restrictions on a generator HE full mass and the size of the maximum magnetic field volume (basically, diameter). Based on the design-theoretical work, we proposed a design and determined initial parameters for MC-1-generator with the maximum magnetic field >20 MG in the volume with a diameter of no <5 mm and HE mass <50 kg. [ABSTRACT FROM PUBLISHER]

In this paper, a compact high magnetic field facility for cyclotron resonance (CR) investigation in the mid-infrared range is presented. A technology of multiturn coils winding with microcomposite Cu–Nb wire was developed in the Sarov Physics and Technology Institute Norwegian University of Science and Technology Moscow Engineering Physics Institute for the fabrication of compact nondestructive solenoids up to 50 T. An optical scheme and details of experimental techniques of CR measurements are discussed. Two peaks of magnetic absorption at 28 THz were observed in a narrow-gap HgTe/Hg1–xCdxTe heterostructures with quantum wells at 80 K. [ABSTRACT FROM PUBLISHER]

Elimination of the central solenoid would simplify the engineering design of a fusion nuclear science facility and tokamak based devices. The method of transient coaxial helicity injection (CHI) has successfully demonstrated formation of a high-quality closed flux plasma in NSTX and will be used as the front end of the start-up method for a full demonstration of noninductive current start-up, followed by noninductive current ramp-up using neutral beams in the NSTX-U device that is now under construction at the Princeton Plasma Physics Laboratory. CHI is implemented by driving current along open field lines that connect the lower inner and outer divertor plates of a spherical torus. The engineering system requirements and the design of the CHI system on NSTX-U are described. [ABSTRACT FROM PUBLISHER]

It is attractive to use sheet beam vacuum devices to generate high frequency, high-power microwave radiation. In this paper, we present the numerical and experimental studies of a high-power Ka-band sheet electron beam backward wave oscillator (BWO), in which the double-grating rectangular waveguide is used as the slow wave structure (SWS) for its thermal and mechanical robustness. The fundamental mode of this kind of SWS is an antisymmetric mode which has an antisymmetric longitudinal field distribution and will nonsynchronously interact with the electron beam on two sides of the electron channel along the vertical direction. We put forward a method to overcome this trouble in this paper. To drive this BWO, a high-power sheet beam is used with a cross section of 30 mm $\times\,$ 1 mm. A thin graphite cathode is used for its superiority in producing a high current, high-quality electron beam. For an experimental electron beam of 141 kV and 1668 A, the output power of over 46.8 MW at 31.68 GHz is obtained, which corresponds to a beam–wave interaction efficiency of 19.9%. Compared with the conventional hollow beam BWO and the single-grating rectangular waveguide sheet beam BWO, the double-grating sheet beam BWOs efficiency is higher, which indicates that the double-grating sheet beam device is promising for producing millimeter wave radiation with high power and high efficiency. [ABSTRACT FROM PUBLISHER]

The precompression mechanism is a key issue for central solenoid (CS) support structure. The support structure of CS assembly should act a role of withstanding the strong electromagnetic forces. The gap is not allowed between CS modules and the support structure due to the difference of their thermal expansion coefficients after cool down. The support structure should also have the precompression mechanism to cancel this gap. The support structure for CS assembly is designed considering the real procedure to set the precompression mechanism and load the required compression. [ABSTRACT FROM PUBLISHER]

This paper discusses a theoretical and experimental investigation of parameters of plasma [hydrogen (H2) and argon (Ar)] developed in an inductively coupling plasma reactor. The reactor was shaped as a planar chamber inserted between two gaps formed between two separated identical halves of a quasi-closed solenoid cut along its diameter and powered with a 13.56-MHz RF to generate a closed loop of alternating magnetic field crossing the reactor chamber twice. It has been shown that the solution of the Hamilton–Jacobi equation describing motion of a charged particle with the certain momentum in a radial cylindrical wave generated in a gap of the quasi-closed solenoid can be presented as the particle motion along a closed Fig. 8-type trajectory. Simple estimation based on this solution has shown that energy of plasma electrons captured and accelerated in the gap at reasonable power applied to the solenoid should run up to \sim70~eV. Experiments have shown that in the reactor filled with H2 at 6 mtorr and powered, for example, with 2 kW of 13.56-MHz RF, the electrons accelerated in electromagnetic fields were arranged in three distinct populations: 1) electrons of \rm\sim130\-eV energy detected as stable electron flows; 2) certain portion of electrons mentioned in 1) diffused on neutrals and forming in velocity space a layer with thickness \sim6~eV at average energy \sim100~eV; and 3) a small population of cold electrons of \sim20\-eV energy in plasma potential vicinity. It has been shown also that the certain disposition of one of the quasi-closed solenoid halves with respect to the other one leads to the electron energy variation at approximate conservation of their density for all of the electron populations in the range from \sim6 to \sim100~eV. The same effect can be obtained by shift of phase of the RF source powering one of the solenoid halves with respect to the other one. [ABSTRACT FROM AUTHOR]

Stambaugh developed the Peng–Hicks concept of a fusion reactor based on a solid copper center-post spherical tokamak (ST). Using the promising results from the START experiment, they produced a vision for a path to fusion power. This path had two elements such as the ability to produce high fusion gain from an ST and of equal importance, the ability to demonstrate this in a small (and therefore relatively low cost) pilot plant device. In this paper, we review various attempts to pursue this vision, and try to elucidate the reason why success has not yet been achieved. However, we show that the advent of high temperature superconductors may overcome some of the problems, and we suggest a revised version of the small, low entry cost route to fusion power. [ABSTRACT FROM PUBLISHER]

China Fusion Engineering Test Reactor (CFETR) is a tokamak reactor; one design option under the consideration of the China National Integration Design Group employs superconducting magnets. The fusion power is at the range of 50–200 MW and the duty cycle (or burning time) was envisioned as 30%–50%. The plasma current will be 10 MA and the major and minor radii are 5.7 and 1.6 m, respectively. The concept engineering design including the magnet system, vacuum vessel (VV) system, and maintenance method has been carried out in the past years. The toroidal magnetic field strength at R0 is 5 T and the maximum flux swing provided by central solenoid winding will be 160 VS. The main design work, including the electromagnetic analysis of the magnet system, has already been carried out. This paper mainly probes into the VV design and optimization based on three types of maintenance ports. Furthermore, the maintenance method, counted as one of the most important design studies, is presented specifically in this paper. It includes the design of the maintenance ports and the remote handling system design, and so on. The next design stage will mainly include mechanical design, conductor stability, different types of divertor system design, and so on. [ABSTRACT FROM PUBLISHER]

Solenoid has broad applications in power system, power electronics, and pulsed power technology. In this paper, a dispersion method for high-frequency solenoid analysis is put forward. The proposed method can accurately calculate the distributed parameters of the solenoid coils such as self-capacitance and solenoid inductance. The most important point is that the dispersion method can accurately analyze the effects of working frequency and dielectric distribution on the distributed parameters of the high-frequency solenoid, while the traditional static magnetic method is incompetent to do this job. When the solenoid was filled with uniform dielectric, the solenoid inductance had a large monotonic decrement when the working frequency increased. However, when the solenoid was filled with discontinuous dielectrics, the working frequency and the dielectric discontinuity showed strong effects on the solenoid inductance and other distributed parameters. Experimental results demonstrated the dispersion method and its calculation results. [ABSTRACT FROM AUTHOR]

The theoretical premises and experimental results of phase control in high-power microwave oscillators with nanosecond pulse duration are presented. In experiments, two-channel backward wave oscillators (BWOs) for both steady state (100–150 cycles) and super-radiance (SR) mode operation (10–20 cycles) are discussed. For the phase control, the shift of the moment with fastest current rise is provided in the sections of nonlinear transmission lines with axially biased ferrites. The voltage pulse sharpening and shift of group velocity depend on the dc axial magnetic field. In SR mode, two-channel source is capable of producing 2\,\times\,0.3 GW pulses with duration of 2 ns and the center frequency of 10 GHz. The source operates at the repetition rate up to 100 pps with electronic control of the phase in one channel relative to another. The last experiment is carried out using two synchronized compact RADAN-type drivers with two parallel Ka-band BWOs (100 MW, 2 ns, 37 GHz). The controllable shift of interference picture is a proof of the coherency in the aggregated radiation. At the maximum of the pattern in the far zone, the detector indicateds fourfold increase in power density over that measured from single channel. [ABSTRACT FROM AUTHOR]

Some features of neutron emission from dense plasma focus suggest that the participating deuterons have energy in the range of 10^5\ \eV and have a directionality of toroidal motion. Theoretical models of these devices assume that the plasma evolves through a purely irrotational flow and thus fail to predict such solenoidal flow on the scale of the plasma dimensions. Predictions of a relaxation theory are consistent with experimental data [S K H Auluck, Physics of Plasmas, 18, 032508 (2011)], but the assumptions upon which it is based are not compatible with known features of these devices. There is thus no satisfactory theoretical construct which provides the necessity for solenoidal flow in these devices. This paper proposes such theoretical construct, namely, the principle of constrained dynamics, and describes an experiment which provides support for this idea. The experiment consisted of low-inductance self-breaking spark discharge in helium at a pressure \sim100 hPa between two pointed electrodes separated by 30–50-mm distance kept inside a vacuum chamber mounted on a low-inductance high-voltage capacitor. The current derivative signal showed reproducible sharp dips at all of the extrema of the damped sinusoidal discharge. A planar diamagnetic loop centered with and perpendicular to the discharge axis consistently showed a signal representing rate of change of axial magnetic flux. The discharge plasma was very weakly ionized. Its acceleration was constrained by viscous drag of the neutrals, pressure gradient was constrained by heat conduction by neutrals, and at the same time, the axial current density and azimuthal magnetic field were constrained to follow an oscillatory temporal profile. Under these conditions, radial momentum balance equation cannot be satisfied unless the plasma possesses a degree of freedom, which supplies the shortfall in momentum balance. Azimuthal symmetry of the plasma allows azimuthal current density to provide such degree of freedom. A qualitative explanation of observed phenomena is obtained using a simple model. [ABSTRACT FROM PUBLISHER]

A four-beam electron gun has been designed using OPerating environment for Electromagnetic Research and Analysis (OPERA) 3-D to demonstrate the dependence of beam focusing on the thickness and the radial position of anode aperture in a pole piece with reference to the gun axis. The study is important in the sense that focusing the off-axis electron beamlets are a bit difficult with a common focusing system. The OPERA simulated results have been also compared with computer simulation technique simulated results. An example of four-beam electron gun to deliver a total of 428-mA (107 \times 4) current at 6-kV beam voltage has been considered for carrying out the aforementioned study. The four electron beamlets are generated through four individual cathodes, surrounded by electrically isolated four beam focusing electrode and corresponding four individual anodes and a common focusing system. [ABSTRACT FROM PUBLISHER]

The effective 1-s batch of 100-Hz pulse repetition rate mode of an X-band relativistic backward-wave oscillator with a resonance reflector (RBWO-RR) was realized using the “SINUS” pulse-periodic nanosecond accelerator allowing mechanically installed high voltage pulse length of 13 and 42 ns. Magnetic field about of 2 T was produced by two-section solenoid to transport the electron beam along RBWO-RR electrodynamic system. TM01 to TE11 mode converter connected to the oscillator output allowed Gaussian radiation pattern. The microwave oscillator allowed producing the microwave pulse length of 4.7 and 29 ns. The energy of the microwave pulse measured by the X-band aperture calorimeter was 1.4 or 6.3 J corresponding to the mentioned above microwave pulse length of 4.7 or 29 ns, respectively. That allowed estimations of the microwave peak power as high as 280 \pm 30 MW and 210 \pm 20 MW related to the pulse lengths. The efficiency of the oscillator was 23–25%. A possibility of the microwave pulse length fine tuning within 25 to 34 ns range in the “long pulse mode” by changing the solenoid magnetic field configuration was shown. [ABSTRACT FROM PUBLISHER]

KSTAR is a fully superconducting tokamak in operation since 2008 at the National Fusion Research Institute in Korea. All coils are wound using cable-in-conduit conductors and cooled with forced-flow supercritical helium at 4.5 K and 5.5 bar. We consider here the central pair, PF1U/L, of the central solenoid coils; during operation, these coils are subjected to sharp current transients, which induce ac losses in the coil. The thermal hydraulic transient following a trapezoidal current pulse, with a ramp-up to 10 kA at a rate of 1 kA/s and a ramp-down to 0 kA at a rate of 10 kA/s, is simulated here using the 4C code, and the results are compared with the measurements. [ABSTRACT FROM PUBLISHER]

For 60 years, fusion research has been focused on fusion for energy as the ultimate carbon-free solution to the world's energy problems. It is proving a worthy but difficult task. However, it is relatively easy to produce high-energy fusion neutrons. The many potential applications of a 14-MeV neutron source are outlined, and a range of existing designs for such a source, based on a D-T fuelled spherical tokamak (ST), are reviewed. It is shown that the problems of high build and operating costs can be eased by a small device super-compact fusion neutron source (SCFNS) of major radius \sim0.5 m, which although operating at modest plasma performance can provide megawatt-level neutron output. This breakthrough is achieved via the effectiveness of beam-plasma fusion, which becomes dominant in these conditions. Such a device would provide a resolution of the uncertainties in fusion STs (such as start-up, ramp-up, and steady-state operation), be an effective neutron source for research, and be an ideal entry vehicle for development of more powerful neutron sources in the new objective of “fusion for neutrons.” [ABSTRACT FROM PUBLISHER]

A 300-kW 670-GHz gyrotron, operating with a pulsed coil at the fundamental cyclotron harmonic, is designed at the University of Maryland for an application of detecting concealed radioactive materials. The design of a low-spread diode-type magnetron injection gun for this gyrotron is presented. Constraints due to the pulsed coil design and the limitation of maximum electric field at the cathode result in a steep tilting angle of the cathode surface, 74^\circ, along with a Pierce-type focusing section and a high magnetic compression ratio larger than 170. A pitch ratio of 1.34 and a low pitch ratio spread of 2.5% for a cold beam and 9.2% due to emitter surface temperature of 0.1 eV and 1-\mu \m roughness were obtained. The results were benchmarked with three simulation codes: EGUN, TRAK, and MICHELLE. Numerical results were calculated for beam currents up to 19 A, accelerating voltage of 50–90 kV, and magnetic field of 25–30 T. A sensitivity analysis with respect to critical parameters such as the depth of the focusing section and the internal simulation parameters is provided. [ABSTRACT FROM PUBLISHER]

Space-charge neutralization is required to compress and focus a pulsed high-current ion beam on a target for warm dense matter physics or heavy ion fusion experiments. We describe an approach to produce dense plasma in and near the final focusing solenoid through which the ion beam travels, thereby providing an opportunity for the beam to acquire the necessary space-charge compensating electrons. We use a high-current (> 4 kA) pulsed vacuum arc plasma from a ring cathode near the edge of the solenoid. The plasma distribution is characterized by photographic means, by an array of movable Langmuir probes, by a small single probe, and by evaluating Stark broadening of the Balmer H\beta spectral line. The plasma is produced at several cathode spots distributed azimuthally on the ring cathode. It is shown that the plasma is essentially hollow, as determined by the structure of the magnetic field, although the plasma density exceeds 10^14\ \cm^-3 almost everywhere in the volume defined by the solenoid. The plasma is nonuniform and fluctuating. However, since its density exceeds the ion beam density, it is believed that this approach could provide a practical solution to the space-charge neutralization challenge. [ABSTRACT FROM AUTHOR]

This paper presents a flow regulator based on a fast-response giant magnetostrictive actuator (GMA). The finite-element method is adopted for analyzing and optimizing the magnetic circuit structure of the GMA, and the influence of structural parameters on the driving magnetic field uniformity is summarized. Based on the analysis and output demand, a prototype of the GMA driven by a \Phi 5 \times 40\ \mm giant magnetostrictive material rod is made, and a test bench is set. The result shows that the static output displacement is about 47.1 \mu\m. With a flexure hinge working as the displacement amplification structure, the maximum opening displacement of the flow regulator is about 240 \mu\m, and the response time is less than 1 ms. Using nitrogen (\N2) as the working medium, the mass flow rate of the giant magnetostrictive regulator is 12 g/s at 3 MPa. [ABSTRACT FROM AUTHOR]

This paper describes how small permanent magnets embedded in a launch package can be used to locate armature position during launch with greater accuracy than can be achieved by detecting the dipole field of the armature itself. Using this technique, we determined armature position in a medium-caliber launcher to within a millimeter of the value measured with photonic Doppler velocimetry, a precise optical technique. This paper describes the technique and some experimental results. [ABSTRACT FROM AUTHOR]

This paper focused on the verification of the current filament method and the performance comparison of different armatures. Armature has as much influence on the performance of a coil launcher as any other major subsystem. The design of an armature is influenced by a large set of highly coupled parameters. The sleeve armature is a common choice for experiment and analysis of a coil launcher. The current filament method is widely used to analyze the sleeve armature. However, due to skin effect, the current distribution will be inconsistent, and excessive heating will be caused in the sleeve armature. How to use the current filament method accurately should be considered. Another good choice is the solenoid armature, which can make current and temperature distribution uniformly. To verify the current filament method and compare the performance between a sleeve armature and a solenoid armature, several kinds of projectiles were constructed and tested, including a sleeve projectile, a 24-turn copper-ring projectile, a 20-turn wire-ring projectile, and a 20-turn solenoid projectile. Then, 2-D finite-element simulations based on the experiments were taken to further study the problems. It is shown that in the sleeve armature (including multiturn ring armature) most of the induced current tend to distribute unevenly in the armature. Over concentration of the current will cause excessive heat and limit the material, structure, velocity, and efficiency of the sleeve armature. The sleeve armature must be divided into enough number of filaments; otherwise, the current filament method may be invalid. A solenoid armature can solve these problems by distributing the induced current evenly. However, fabrication of the solenoid armature becomes another difficulty. Further analysis of the current density in the solenoid armature shows that the skin effect will work in the wire of the solenoid, but it has little influence on the system performance. A detailed description of the experiments and simulations will be presented in this paper. [ABSTRACT FROM AUTHOR]

Abstract-The efficient operation of high-power microwave (HPM) sources using slow-wave structures (SWSs) in low magnetic field has been an attractive aim pursued by HPM researchers. This paper presents the latest experimental results of an X-band oversized SWS HPM source operating at low guiding magnetic field with both power and efficiency enhancements. Driven by an electron accelerator with diode voltages of 450-900 kV, the generator operated with the output microwave power ranging from 0.5 to 3 GW and the efficiency being kept at about 25%. The optimized magnetic field was in the 0.5-0.75 T range, depending on diode voltages. Without the employment of superconductive-solenoid system, a very stable 100-Hz repetitive operation with 1.5-GW output microwave power was realized in the 1-s-burst mode. [ABSTRACT FROM AUTHOR]

The quality of an ion beam is described by the brightness, which is defined as particle density in phase space (in amperes per square millimeter milliradian). This density should remain constant along the accelerator if normalized with respect to the actual particle velocity. Any degradation of phase space due to nonlinear forces will decrease the quality of the ion beam. For that reason, highest interest should be paid to improve the extraction of an ion beam from the ion source plasma as much as possible, because here, the initial value of brightness is determined. For understanding the process of extraction of an ion beam from a plasma generator and for possible improvements of the extraction system, computer simulation codes are helpful; however, a correct model has to be used. The physical model for ECR ion sources which has been used in this 3-D simulation using KOBRA3-INP will be described. Results of simulation achieved with these boundary conditions are then compared with experimentally obtained results to verify the validity of the applied models. Viewing targets, metal targets coated with KaB, BaF, or CsI, have been used to measure the beam profile. The ion beam profile has been measured behind extraction and behind the first active optical element, a solenoid, which can be used for a further diagnostic measurement: the dynamic beam profile. [ABSTRACT FROM AUTHOR]