V. V. Myalton

Dynamics of the Current Distribution in a Discharge of the PF-3 Plasma Focus Facility

In this paper, results are presented from studies of the dynamics of the plasma-current sheath and current distribution in the PF-3 facility, one of the largest plasma focus machines in the world. The experiments were done at input energy of W = 290 kJ and discharge current of I ~ 2 MA, with the chamber being stationary filled with the working gas. The current sheath parameters were measured with absolutely calibrated magnetic probes installed at different distances from the system axis and at different heights above the anode plane. The possibility is demonstrated of the formation of closed current loops due to the development of shunting breakdowns in the insulator region. The maximum residual plasma density at which the electrode gap remains magnetically self-insulated is estimated.

Spectroscopic measurements of the parameters of the helium plasma jets generated in the plasma focus discharge at the PF-3 facility

The spectroscopic technique used to measure the parameters of the plasma jets generated in the plasma focus discharge and those of the plasma of the immobile gas through which these jets propagate is described. The time evolution of the intensities and shapes of spectral lines in experiments carried out with helium at the PF-3 facility was studied by means of electron-optical streak cameras. The plasma electron temperature, T ≈ 4–5 eV, was determined from the intensity ratio of two spectral lines, one of which (λ1 = 5876 Å) belongs to neutral helium, while the other (λ2 = 4686 Å), to hydrogen-like helium ions. The plasma density at different time instants was determined from the Stark broadening of these lines in the electric fields of different nature. The plasma density is found to vary from 4 × 1014 to 2 × 1017 cm−3.

Study of the interrelation between the electrotechnical parameters of the plasma focus discharge circuit and the plasma compression dynamics on the PF-3 and PF-1000 facilities

The main stages of the plasma current sheath (PCS) dynamics on two plasma focus (PF) facilities with different geometries of the electrode system, PF-3 (Filippov type) and PF-1000 (Mather type), were studied by analyzing the results of the current and voltage measurements. Some dynamic characteristics, such as the PCS velocity in the acceleration phase in the Mather-type facility (PF-1000), the moment at which the PCS reaches the anode end, and the plasma velocity in the radial stage of plasma compression in the PF-3 Filippov-type facility, were determined from the time dependence of the inductance of the discharge circuit with a dynamic plasma load. The energy characteristics of the discharge circuit of the compressing PCS were studied for different working gases (deuterium, argon, and neon) at initial pressures of 1.5–3 Torr in discharges with energies of 0.3–0.6 MJ. In experiments with deuterium, correlation between the neutron yield and the electromagnetic energy deposited directly in the compressed PCS was investigated.

Study of Plasma Flows Generated in Plasma Focus Discharge in Different Regimes of Working Gas Filling

Results are presented from experimental studies of the plasma flows generated in the KPF-4 Phoenix Mather-type plasma focus device (Sukhum Physical Technical Institute). In order to study how the formation and dynamics of the plasma flow depend on the initial distribution of the working gas, a system of pulsed gas puffing into the discharge volume was developed. The system allows one to create profiled gas distributions, including those with a reduced gas density in the region of plasma flow propagation. Results of measurements of the magnetic field, flow profile, and flow deceleration dynamics at different initial distributions of the gas pressure are presented.

Features of the Application of the Magnetic-probe Method for Diagnostics of High-temperature Plasma

Some aspects of the applicability of the magnetic-probe technique in high-power pulsed discharges are analyzed. The influence of an electron beam and an intense X-ray yield of (~1 TW/cm2), which result from the compression of high-current plasma in the interelectrode gap of a Z-pinch discharge, on the correctness of measurements using magnetic-field probes was studied. We considered the use of multilayer shells as a method for protecting the sensing element of a magnetic probe. The results of experimental testing of probes of a new design in experiments with wire assemblies on the Angara-5-1 facility at discharge currents of up to 4 MA are presented. Experiments on the Angara-5-1, PF-3, and PF-1000 high-power electrophysical facilities show the effect of the shape and material of the probe shell on the perturbation of plasma that flows around a probe and, as a consequence, on the accuracy of the magnetic-field measurements.

INVESTIGATION OF FORMING PLASMA FLOW GENERATED IN PLASMA FOCUS DISCHARGE

На плазменном фокусе ПФ-3 методами скоростной фоторегистрации исследована стадия формирования пинча, являющегося источником аксиального плазменного потока. Основной упор был сделан на регистрацию начального момента генерации потока. Комбинация нескольких щелевых развёрток, размещаемых в различных направлениях и на различном удалении от плоскости анода, позволила воссоздать пространственную картину формирования аксиальных потоков вещества. Обнаружены потоки вещества, распространяющиеся быстрее (1,310 см/с), чем плазма, вытесняемая по оси магнитным поршнем (0,510 см/с). Вероятнее всего, именно эти потоки вещества наблюдаются на значительном удалении от анода в виде компактных джетов.

PARAMETERS OF THE PLASMA STREAMS FROM THE PLASMA FOCUS IN EXPERIMENTS ON THE PF-3 FACILITY

Представлены оптические спектральные методики и результаты измерения температуры и концентрации плазмы в аксиальных струях, полученные в рамках экспериментов по лабораторному моделированию динамики астрофизических джетов, проводящихся на установке ПФ-3. Концентрация плазмы определялась по форме штарковских контуров спектральных линий, ионизационная температура — по отношению интенсивности спектральных линий атомов и ионов или по степени ионизации. Приведены значения концентрации и температуры плазмы струй из разных газов — водорода, гелия и неона на расстояниях 35 и 65 см от плазменного фокуса.

Dynamics of the plasma current sheath in plasma focus discharges in different gases

The shape of the plasma current sheath (PCS) in the final stage of its radial compression, the dynamics of pinching, and the subsequent pinch decay in plasma focus (PF) discharges in different gases are studied using an improved multichannel system of electron-optical plasma photography and a newly elaborated synchronization system. The PCS structure in discharges in heavy gases (Ne, Ar) is found to differ significantly from that in discharges in hydrogen and deuterium. The influence of a heavy gas (Хе) additive to hydrogen and deuterium on the structure and compression dynamics of the PCS is investigated.