Z-Pinch at extreme energies: Nanofocus of less than 1J. Plasma Focus of 400 J. Gas embedded Z-pinch operating at MA

The work presented in this thesis is in relation with an experimental study developed in three different pulsed plasma generators. Two of them were already operating in the plasma laboratory of the Chilean Nuclear Energy Commission (CCHEN ) at the beginning of this thesis and they are: a) plasma focus PF-40OJ ((880nF, 30kV, 120kA, 400J, 300ns maximum current, dl/dt4x1011 A/s) which is one of the first plasma focus devices at low energy that produces neutron pulses of fusion and b) the pulsed power generator SPEED-2 (4.1μF equivalent capacity, 300 kV, 4 MA in short circuit, 187 kJ, 400 ns at maximum current, dl/dt∼1013 A/s) designed to operate in a plasma focus configuration. The third experiment corresponds to a plasma focus device at energy lower than 1J (Nanofocus), which was designed, constructed and characterized during the development of this thesis. The performed work can be summarized in two general aspects: the experimental study of the scaling in plasma focus devices at low energy and the development of a linear Z-pinch configuration using the SPEED-2 generator. In this last situation, a mechanism of preionization was developed in order to create a gas embedded Z-pinch discharge (Deuterium in the case of our experiment) that was conveniently coupled to the electrical characteristics of the generator. In every experiment, the plasma properties were studied (density, dynamics, size, radiation emission) and they reported the state of it. In the plasma focus device PF-40OJ, the electronic density was characterized for discharges in H2 by using optical refractive techniques, measuring density values in the pinch ∼1025m-3, similar to those reported in plasma focus devices at higher energies. The anisotropy was measured in the distribution of the intensity in the neutron emission for discharges in D2 using track detector techniques CR-39. A distribution for the neutron flux characterized by an isotropic contribution of 57.5% and also by other anisotropic of 42.5% of the total production of neutrons is obtained with this technique. Finally, the average energy and the spectral distribution of neutrons at 900 from the axis of the pinch were measured by using the time of flight technique and an array of photomultipliers where it is possible to observe a maximum in the distribution around 2.5 MeV and a second diffused peak around 2.8 MeV. The Nanofocus device was electrically characterized. The plasma dynamics was studied by means of ultrafast photography in the visible spectrum reporting the formation of a dynamic coaxial discharge (plasma focus type) which is characterized by the formation and subsequent breaking of plasma column over the anode. The emission of radiation was studied by means of X-rays detection techniques with and without time resolution. From the signals of the photomultiplier, x-ray emission starts in the moment of the electrical break, and the maximum emission is previous to the moment of maximum current. An effective energy for radiation of 4.2keV is obtained from the detection technique with photography film and stepped filters. In the gas embedded Z-pinch experiment, a couple of conical electrodes were used to determine a preferential area of electrical break in the gas and then to form the discharge channel. The information of the channel structure, the same as its electronic density, was obtained using refractive optical techniques. A singularity was observed near to the cathode with a electronic density of the order of 4x1024m-3 immersed in a plasma column of density of the order of 1x1024m-3. For those discharges where the formation of the plasma channel was well defined, it is possible to observe compression of the column and 3He detectors give signals corresponding up to 5 x 105 neutrons per pulse. Moreover, macroscopic instabilities are not observed during the time in which the discharge is studied by means of optical diagnosis. With this, it is obtained that times of stability in the discharge are higher to those reported in this type of pinch discharge