The beginning of an experimental study of a high-current discharge in a vacuum with a duration of less than 100 ns initiated by laser plasma is reported. Measurements of the discharge current, neutron output, and ion fluxes by collector technique are given. When the discharge current reaches 40 kA, dips of up to 30

The article presents the results of modeling a diode accelerator for neutron generation with a laser deuteron source and a system for suppressing electronic conductivity by magnetic fields. Variants of the formation of an insulating magnetic field by annular permanent magnets and a spiral electrodynamic line are considered. The possibility of implementing an effective pulsed neutron generator based on such an accelerator is shown. The results of the conducted computer and physical experiments allow us to expect record values of the neutron energy price to be achieved using the T(d,n)4He nuclear reaction.

The article considers an in-situ method potential for establishing the surface distribution of tritium in the first wall of a fusion reactor using neutron tomography. The method includes the formation of a pulse-periodic flux of accelerated deuterons bombarding the studied surface of the first reactor wall following its saturation with tritium, generation of a fast neutron field according to T (d, n)4He reaction, measurement of neutron fluence at given spatial points, and reconstruction of the spatial tritium distribution according to measurement data. An algorithm for such a reconstruction is presented based on an approximate solution to the inverse Fredholm problem.

We present the simulation results of a diode accelerator for generating neutrons with a laser source of deuterons and a system for suppressing electronic conductivity by the pulsed magnetic field of a spiral line. The possibility of implementing an effective pulsed neutron generator based on the accelerator is shown. The results of computer and physical experiments allow us to hope for the possibility of creating a sealed accelerating tube with output parameters above 10 10 n/pulse as a result of T (d, n) 4 He nuclear reactions. A possible design for such an accelerating tube is proposed, and the technological feasibility of its implementation is substantiated.

A method of restoring the neutron field generated by a vacuum accelerating tube with a metal–tritium target of a complex configuration is proposed. The method uses the data from neutron measurements on a disassembling vacuum bench with a small deuterium target. The method provides radiation safety. Specific examples of its application in the process of investigating ion diodes developed at the National Research Nuclear University MEPhI are presented.

Two technological schemes are considered, as well as the possibilities of their implementation for the manufacture of sealed accelerator tubes based on diodes with magnetic isolation Schematic designs of tubes under development with a laser source of deuterons and an electronic conductivity suppression system are presented. To do this, a sufficiently heat-resistant permanent magnet is included in the vacuum volume of the first tube. Another design of the tube contains a pulsed system for suppressing electronic conductivity using a pulsed magnetic field created by a conical spiral placed inside the tube.

The collective acceleration of laser plasma ions in a rapidly increasing magnetic field (108 T/s) excited by a powerful current pulse in a low-inductive conical spiral expanding in the direction of plasma acceleration has been studied. A mathematical model and an algorithm for calculating the radial Br and axial Bz components of the magnetic field in the approximation of a conical spiral by a system of rings of variable radius are proposed to analyze the factors affecting the efficiency of such acceleration. Based on computer modeling and an experimental variation of magnetic-field excitation parameters, the regime of effective ion acceleration is obtained. With the help of time-of-flight collector measurements, the velocities of ions whose atomic mass differs by two orders of magnitude are determined. The maximum velocity of both light ions (lithium) and heavy ions (lead) exceeds 106 m/s, and the corresponding energy for lead ions is ~1 MeV. The efficiency of collective acceleration with the direct acceleration of laser plasma ions in a high-current high-voltage diode with magnetic insulation is compared.

The collective acceleration of laser plasma ions in a magnetic field generated by a powerful fast-growing current pulse in a low-inductive conical spiral is studied. The velocity of ions for a number of elements which significantly differ in atomic weight are obtained on the basis of collector measurements. The maximum velocity of both light (lithium) and heavy (lead) ions exceed the value of 10 8 cm/s; for ions of lead, the corresponding energy amounts to a value of ∼1 MeV. A mathematical model of ion acceleration is proposed and simulation results are compared with the experiment.

Based on experimental and computer simulation the acceleration of deuterons from laser plasma in a strong non-stationary magnetic field was studied. The possibility of reaching an energy of ∼100 keV, corresponding to the effective course of the nuclear reactions D (d, n) 3He and T (d, n) 4He, was demonstrated. YAG: Nd3+ laser (W ≤ 0.85 J, τ ≈ 10 ns) was used in the experiment with focusing laser radiation on a deuterated polyethylene target. The high voltage pulse generator with a conical spiral coil was used to generate a high-speed magnetic field (2·107 T/s). A mathematical model of the process is proposed. According to this model, the acceleration of a laser plasma is analyzed by means of a computer. The algorithm is based on a numerical solution of the system of Newton-Lorentz equations.

The scheme proposed is meant for the generation of thermonuclear neutrons in a pulsed plasma trap with magneticinertial confinement of plasma. A high-temperature plasma region, which mainly produces neutrons, is formed in the center due to the interaction of two counter-axial streams of deuterons and heavy jets of hydrogen, injected perpendicular to the axis of the trap. The evaluation showed that the fusion mechanism of generation of neutrons dominates the direct interaction of the "beam-plasma". INTRODUCTION A scheme for generating thermonuclear neutrons in a pulse trap with magnetic and inertial plasma containment is proposed. A high-temperature region of plasma wherein neutrons are mostly generated is formed in the center due to the interaction of two countercurrent axial deuteron streams and a stream of heavy hydrogen injected perpendicular to the trap axis. Figure 1 demonstrates a variant of the said scheme for neutron generation with a heavy hydrogen isotope injector. Figure 1: Scheme of the thermonuclear neutron generator (1 − diode accelerator anode; 2 − its cathode; 3 − focusing coils; 4 − magnetic trap). The injection of heavy hydrogen can be carried out using several methods. One of the variants of realization of a pulse heavy hydrogen isotope injector may be a laser ion source with a plasma-forming target saturated with heavy hydrogen, with a conical cavity, the axis of which is directed to the center of the magnetic trap. In order to provide laser radiation feed to the gun, a hermetic optical window is designed in the casing of the device. Another variant for realization of a pulse heavy hydrogen isotope injector may be a pulse plasma accelerator, e.g. of the "rail gun" type. In order to accelerate the plasma heating process at energy transfer from the accelerated protons to electrons, the device may further contain a generator of a gas stream with a high number in the Periodic Table (e.g. xenon or iodine vapors). Thereby, the electron concentration in the trap may be increased by about 2 orders of magnitude. The principle of generator operation The control unit transmits a signal to start the pulse deuterium and/or tritium isotope injector, and the stream of these isotopes is formed directed to the magnetic trap. The time of continuous generation of the heavy hydrogen isotopes stream is about several milliseconds. Simultaneously with the injection start, the start of the pulse current generator and the formation of the magnetic field in the generator working volume are carried out. Several decades of nanoseconds prior to the achievement of the maximum value of the magnetic field induction, the start of the high voltage pulse generator is carried out; it may be designed, e.g. basing on the Blumlein line or the Arkadiev-Marx scheme. The amplitude and duration of the high voltage pulse U(t) should thus be in the ranges of (0.5-1) MV and (50-100) ns correspondingly. The authors have developed such a pulse voltage source, allowing a repetitively pulsed mode of operation with a frequency of up to 10 Hz [1]. At the cathode surface, as well as at the metallic inserts on the shells of the focusing coils, a strong electric field is formed providing for conditions for effective emission of electrons accelerated to the anode and oscillating in the region adjacent to it, forming a virtual cathode. Under the effect of electron bombardment of the anode electrode, the following processes occur: heating of the anode, desorption of heavy hydrogen from the saturation region, formation of anode plasma, extraction of hydrogen nuclides from the plasma and acceleration of nuclides to the direction of the virtual cathode formed in the focusing coil region, to the direction of the magnetic trap. Both diode systems thus function in the reflective triode mode [2]. CALCULATION-THEORETICAL MODEL From the solution of the self-matching Poisson equation, the following formula is obtained for a possible approximated dependence of the total current of protons dissipated in je ct io n la se r vacuum pumping ___________________________________________ † email address isaev@lenta.ru 9th International Particle Accelerator Conference IPAC2018, Vancouver, BC, Canada JACoW Publishing ISBN: 978-3-95450-184-7 doi:10.18429/JACoW-IPAC2018-TUPAL042 TUPAL042 1100 Co nt en tf ro m th is w or k m ay be us ed un de rt he te rm so ft he CC BY 3. 0 lic en ce (© 20 18 ). A ny di str ib ut io n of th is w or k m us tm ai nt ai n at tri bu tio n to th e au th or (s ), tit le of th e w or k, pu bl ish er ,a nd D O I. 04 Hadron Accelerators T28 Neutron Sources in the plasma inside the magnetic trap and providing for its heating: wherein and are the radii of the anode and cathode spherical sectors, correspondingly, IA is the Alfven current, m, M are electron and proton weights, correspondingly, e is the elementary electric charge, c is light speed, , d is the distance between the magnetic trap coils, a is the coil radius. According to the outlined schemes, the coils of the magnetic trap and the coils of the proton focusing system creating the total magnetic field are fed with current pulses I1,2(t), correspondingly, which may be approximated by sinewaves with the amplitudes wherein C is the value of the accumulated capacity in the pulse current source circuit, L1,2 are coil inductivities. In order to provide for the magnetic localization of the accelerated protons in the trap volume in the lateral direction, it is necessary for the maximum Larmor deuteron radius in the trap to be not higher than the coil diameter: wherein e is the elementary electric charge, and the formula is the amplitude of the magnetic field induction in the center of the trap ( is the magnetic constant, w1 is the number of threads in the coil). Figure 2 demonstrates the calculated family of the magnetic field amplitude distribution over the device symmetry axis – The computer analysis has shown that the maxima closest to the center are achieved at the locations of the magnetic trap coils: 2 / 3 2 2 / 3 2 1 1 0 м 1 ) 1 4 ( ) 1 4 ( 1 2a μ ) 5 . 0 , (      p p I w d p B B , and the distant maxima correspond to the locations of the focusing coils: . μ ) , ( 2 2 0 м 2    R I w D p B B Figure 2: Calculated family of the magnetic field amplitude distribution over the device symmetry axis. In order for all the protons accelerated in the diodes to enter the trap, the following condition should be met: which follows from the adiabatic invariability of the relation of the kinetic energy of the lateral proton movement to the magnetic field induction [3]. The calculation has shown that for effective generator operation, the following conditions should be imposed upon its parameters: When the accelerated protons enter the inner region of the magnetic trap, they are dissipated and decelerated in the hydrogen isotope stream from the injector, forming hightemperature plasma due to heating of the electron component with subsequent thermolization. The deceleration process is described by the following differential equation: wherein F(T) is the dependence of the energetic proton losses in plasma per the length unit to kinetic energy, V(t) is the velocity of the accelerated protons in the trap. The computer analysis has shown that the time of pumping of energy of the accelerated proton stream to plasma formed in the magnetic trap is ~10-2 ms. In such a long period of time, the process of deuteron stream formation itself in the diode system may be regarded as almost instant. , ) ) 1 ( ]( ) 1 ( 1 [ ) ( 86 . 1 ) ( 2 2 ) ( 1 1 4 / 1 2 2 / 1 2 2          mc t eU k A k A u du p p R R R M m I t I

Computer simulation of electrons from explosive emission acceleration and X-ray quantum generation in pulse coaxial diode system with interior anode, which is used in accelerating tube of compact X-ray generator [1] with Tesla transformer as high voltage source, was done. The results obtained allow us to choose accelerating tube diode system geometry for different running modes. Comparison of numerical results with experimental data of dose rate dependence on the distance from vacuum tube anode and energy at first circuit Tesla transformer was fulfilled.

The report deals with the design and the operation features of the coaxial deuteron accelerator, in which a symmetrical ion triode circuit is used to limit electronic emission from the surface of neutron-forming targets and accelerating cathode electrodes. The basis of the construction design is two external cathodes, between which a hollow vacuum-arc source of deuterons is located which plays the role of a partially transparent anode. A high coefficient of anode transparency which is necessary for effective suppression of the electron current is obtained by using an ion-optical system consisting of magnetic and immersion lenses. As a result of computer simulation, performed with taking into account a numerical analysis of the dynamics of electrons, the geometry and dimensions of the accelerating triode system have been optimized. Moreover, for an accelerating voltage with the amplitude of 150 kV and a pulse-repetition rate of 25 Hz, the predicted average neutron flux can reach 10(10) neutrons per second.

This paper examines the model of acceleration of the laser plasma, containing ions of heavy hydrogen, by a rapidly growing magnetic field for neutron generation. The calculation results for the acceleration of a laser plasma bunch at the time of its formation are presented. The calculations were carried out for a toroidal plasma bunch formed by a focused laser pulse into a thin ring of radius r on the surface of a solid target containing deuterium and displaced relative to the geometric center of the annular conductor at the distance z towards the laser. The proposed model is quite general in nature, since any azimuthally symmetric plasma formation can be represented as a set of similar toroidal enlarged plasma particles.

This paper presents the new experimental results concerning acceleration of deuterium ions extracted from laser plasma in the rapid-growing nonuniform magnetic field in order to initiate the nuclear reactions D(d, n)3He and T(d, n)4He. For obtaining of laser plasma a Nd: YAG laser (λ = 1,06 μm) that generates in Q-switched mode the radiation pulses with the energy W ≤ 0,85 J and duration of τ ≈ 10 ns was used. Rapid-growing magnetic field was created with the discharge of Arkadyev-Marx pulsed-voltage generator to conical coil with the inductance of 0,65 μΗ. At characteristic discharge time of 30 ns, the rate of magnetic field growth achieved 2·107 T/s. Ion velocity was determined with the time-of-flight technique. During the experiment on deuterium plasma an ion flux velocity of ∼3 · 108 cm/s was obtained, which corresponds to the deuteron energy of ∼100 keV. Herewith, for target power density of ∼5·1011 W/cm2 obtaining of up to 1015 of accelerated deuterons and up to 108 of neutrons per a pulse is expected.

A multistage generator of high-voltage pulses with a scroll geometry of spark switches, which is produced according to the Marx scheme, is presented. The device is designed for a small pulsed neutron source and makes it possible to obtain accelerating-voltage pulses with amplitudes of up to 450 kV at a stored energy of up to 50 J and a load current of up to 1.5 kA.

The results of new studies on the production of accelerated deuteron fluxes in a small ion diode with pulsed magnetic insulation of electrons have been presented. A plasma anode of the diode has been formed under the action of a 1.06 μm laser radiation with a pulse duration of 10 ns, a pulse energy of up to 1 J, and a power density on the target of 5 × 1015 W m–2. An accelerating voltage of up to 300 kV has been created using an Arkad’ev–Marx pulsed voltage generator with a stored energy of 50 J and a repetition rate of 1 Hz. A magnetic field of higher than 0.6 T for insulating electrons has been formed by a current pulse of the first cascade of the generator in a spiral line before a conical cascade. Stable deuteron acceleration to 300 keV with a current of up to 1.5 kA and a pulse duration of 0.3 μs has been achieved.