S. L. Nedoseev

Study of the plasma in a preformed Z-pinch constriction

The development of a preformed constriction in cylindrical agar-agar loads at currents of up to 3 MA is studied experimentally. The loads 3–5 mm in diameter have a mass density of 0.1 g/cm3 and are filled with different materials. Due to the implosion of the constriction to a minimum size of 40–70 µm, a hot dense plasma (with the electron density ne=1022 cm−3, electron temperature Te=0.8–1.5 keV, and ion temperature Ti=3–12 keV) is produced. It is found that the ion temperature substantially exceeds the electron temperature. The lifetime of the high-temperature plasma determined from the FWHM of a soft X radiation (SXR) pulse is shorter than 5 ns, the radiation power of photons with energies of ≥1 keV is higher than 0.5×1010 W, and their total energy attains 50 J. High-speed photography in the VUV, SXR, and optical spectral regions indicates the protracted generation of the high-temperature plasma. Calculations by the two-dimensional ideal MHD model of the Z-pinch show that the most important consequence of the protracted plasma generation in the constriction region is that the current is intercepted by a freshly produced plasma. In the course of plasma generation, the current near the axis inside the region of radius 50 µm is at most one-half of the total current. After the plasma generation comes to an end, almost the entire current is concentrated in this region for several nanoseconds; this process is accompanied by a sharp increase in the plasma temperature.

Formation of hot spots in the plasma of a Z-pinch produced from low-density deuterated polyethylene

Results are presented from experimental studies of the plasma formation dynamics in a Z-pinch produced from a cylindrical microporous agar-agar load. The experiments were performed on the S-300 facility at a current of 2 MA and current rise time of 100 ns. To enhance the energy concentration, a deuterated polyethylene neck with a mass density of 50–75 μg/cm3 and diameter of 1–2 mm was made in the central part of the load. The spatiotemporal characteristics of the Z-pinch were studied using an optical streak camera and fast frame photography in the optical and soft X-ray spectral ranges. X-ray emission was detected using semiconductor and vacuum diodes, and neutron emission was studied by means of the time-of-flight method. It is found that, in the course of continuous plasma production, hot spots with a diameter of 100 μm form in the pinch plasma. The hot spots emit short soft X-ray pulses with a duration of 2–4 ns, as well as neutron pulses with an average neutron energy of about 2.45 MeV. The maximum neutron yield was found to be 4.5 × 109 neutrons per shot. The scenario of hot spot formation is adequately described by two-dimensional MHD simulations.

Measurements of neutron emission from a Z-pinch constriction

Results are presented from measurements of neutron emission generated during discharges with current amplitudes of up to 3 MA and a current rise time of ∼100 ns through profiled loads 10 mm in height and 4–5 mm in diameter. The experiments were performed with the S-300 eight-module high-power generator. To enhance the effect of energy accumulation, a≤1-mm-diameter neck was made in the central region of the load. An agar-agar foam of mass density 0.1 g/cm3 with an additive of deuterated polyethylene was used as a plasma-forming material. The formation of a hot plasma in the Z-pinch constriction was accompanied by the emission of soft X-ray (E = 1–10 keV), hard X-ray (E ≥ 30 keV), and neutron pulses with a minimum pulse duration of ≤10 ns. The neutron energy measured by the time-of-flight technique in three directions relative to the load axis (0°, 90°, and 180°) was found to be 2.5 ± 0.3 MeV, which corresponds to the dd reaction. The total neutral yield during the development of one constriction with a characteristic size of 100 μm attained 108 neutrons per pulse.

Peculiarities of Wire Array Implosion

The results of the experiments on Z‐pinch produced from wire arrays performed on the facility Angara‐5‐1 are presented. The models of liner implosion, i.e. prolonged plasma production have found their confirmation. Estimation based on our experimental data show that W wire cores are heterogeneous. The velocity of core expansion is determined by energy deposited at the first nanoseconds after current start. The effect of the inner array on the current distribution in the region between the arrays has been revealed. The «lost mass » was measured at initial radius of array at the moment of X‐ray pulse maximum.

X-Ray Radiation Characteristics of Nested-Wire Array Implosion in Sino-Russian Joint Z-pinch Experiments on Angara-5-1

X-ray radiation characteristics of nested wire array implosions were investigated in the Sino-Russian joint Z-Pinch experiments on Angara-5-1 facility with a load current of 2.5 ~ 3.6 MA. The experimental results indicate that an X-ray power-platform prior to the main peak and a less intensive sub-peak after the main peak in the X-ray power waveform exist for the nested wire array implosions, and the radiation process is relatively faster than that in the case of single array. Laser shadowgraph of the imploding plasma suggests that the prior power-platform is a result of the collision of the inner-outer plasma layers. The faster radiation process of nested array implosion can be explained by analysing the corresponding result of the time-resolved one-dimensional imaging system, which demonstrates a better axial imploding uniformity and synchronization. The sub-peak after the main peak is proposed to be a result of the later-time additional implosion of plasma.

Dense Z-pinch neck development dynamics investigation on S-300 generator

The experimental investigations of neck development dynamics in the Z-pinch with 0.1 g/cm/sup 3/ density were carried out on an 8-module pulsed power generator, the S-300 (4 MA, 100 ns). The objective of these experiments was a study for the possibility of obtaining plasmas with extra-high parameters in the Z-pinch neck region, corresponding to the fusion ignition conditions.

Investigations into radiating Z-pinches and the “Baikal” project

In SRC RF TRINITI the physics of radiating Z pinches for application as a source of x-ray for ICF target ignition are under investigation. Simultaneously the works on a designing the module of the generator “Baikal” [1] which should deliver the current pulse up to 50 MA as a driver for radiating Z pinch are designed by co-operation of the RRC the Kurchatov Institute, the SRC RF TRINITI, the SUE NIIFA and RFNC VNIITF. Experiments for study of the wire array compression are conducted on the largest in Russia laboratory source of pulsed electric power “Angara-5-1” installation.

Radiating heterogeneous Z-pinch 2-D compression dynamics

The constriction development dynamics in dense heterogeneous profiled Z-pinches was studied on an 8-module powerful current generator, the S-300 at current up toI=3 MA with a rise time τ=70 ns. The Z-pinch energy concentration effect was provided by using axially — inhomogeneous loads, of 10 mm in height, consisted of two identical axially placed cylinders, with cylindrical insertion between them, but which had lower linear mass. For plasma formation the agar-agar foam with 1⋎100 mg/cm3 density was used and which was added by radiating mixture (Cu, Cl, K) and deuterated substance (CD2). For plasma parameter diagnostics and X-ray and neutron radiation measurements the following set of diagnosties: X-ray spectroscopy of highly ionized species of ions in the quanta energy range of 1⋎10 keV, integral and very short time frame and streak camera photography in X-ray and optical spectral ranges, neutron integral and time of flight measurements, X-ray radiation registration in the range of 0.4⋎100 keV, and laser probing was used. The impact of radiation cooling on 2-D plasma compression dynamics was studied.