A new design of a galvanic sensor of pulsed X-ray radiation is proposed, which is a flat electric capacitor with a window in one metal lining and a solid dielectric made of the single crystal sapphire with a thickness of 200-300 µm inside. The influence of the surface roughness of the sapphire in the window area on the galvanic linear sensor of X-ray radiation has been established. Tests have shown that with ultra-smooth polishing of the sapphire plate working surface in the window area to a roughness of Rq≤ 0.2 nm, it is possible to provide the galvanic linear detection of X-rays with an energy in the range of 0.1-1 keV and a power density of 1-2 MW•cm-2 with a sensor response time of about 8 ns. Sensors of this type can be used in studies of inertial nuclear fusion processes

A new design of a galvanic sensor of pulsed X-ray radiation is proposed, which is a flat electric capacitor with a window in one metal lining and a solid dielectric made of a single-crystal sapphire with a thickness of 200-300 μm inside. The influence of the surface roughness of the sapphire in the window area on the galvanic linear sensor of X-ray radiation has been established. Tests have shown that, with ultra-smooth polishing of the sapphire plate working surface in the window area to a roughness of R q ≤ 0.2 nm, it is possible to provide the galvanic linear detection of X-rays with an energy in the range of 0.1-1 keV and power density of 1-2 MW· cm -2 with a sensor response time of about 8 ns. Sensors of this type can be used in studies of inertial nuclear fusion processes. Keywords: X-ray radiation, galvanic sensor, sapphire, dielectric, flat capacitor.

The phenomena occurring in dielectrics (Al2O3 and SiO2) in the field of high-power soft X-ray radiation are investigated. Experimental studies are carried out at the Angara-5-1 facility, which allows a pulsed radiation power density of the source up to 5 MW/cm2 at the location of the examined samples. It is revealed that charge carriers are generated in the surface layer of the irradiated dielectric, which causes current generation in a circuit including the dielectric. A necessary condition for current generation is the presence of “hot” electrons, which provide surface conductivity. A mathematical model is proposed to describe the process of current generation in dielectrics during exposure to high-power pulsed X-ray radiation. The model is based on the joint solution of the kinetic equations for X-ray photons, photoelectrons, conduction electrons and holes in the valence band and self-consistent Maxwell’s equations. In Maxwell’s equations, instead of the external current of secondary charge carriers, the radiation conduction current is used.

The high sensitivity of traditional diagnostic methods hinders their application in inertial confinement fusion with the pulsed radiation power of target plasma being as high as 1013–1014 W. Different methods of attenuating the incident radiation flux either alter its characteristics or are too complicated. The results of tests of a new detector, where quartz glass is used as a sensing element, at the Angara-5-1 facility are presented. It is demonstrated experimentally that the detector sensitivity is ~2 V/(MW cm 2 ) and the time resolution is ~1 ns. The mechanism of formation of the response signal, where the temperature of electrons produced under irradiation plays a significant part, is discussed.

ДИЭЛЕКТРИЧЕСКИЙ ДЕТЕКТОР ИНТЕНСИВНЫХ ПОТОКОВ РЕНТГЕНОВСКОГО ИЗЛУЧЕНИЯИ.А

An X-ray detector with a dielectric (KU1 optical glass) used as a sensitive element is described. Operation of the detector is based on the discovered effect of electric-field generation in a dielectric under exposure to radiation. The measurements were taken at the Angara-5-1 facility, at which the radiation source is megaampere Z-pinch plasma. It is shown that when the radiation power incident on the detector is approximately 1 MW/cm2, the detector response is a few volts with a time resolution of 1–2 ns. This effect is thought to be caused by “hot” electrons induced by radiation in the dielectric. The estimates for these experimental conditions are presented.

ГАЗОВЫЙ Х-ПИНЧ: МОДЕЛИРОВАНИЕ И РЕАЛИЗАЦИЯИ

Исследуется эффект, наблюдающийся при взаимодействии электромагнитного излучения (энергия квантов 25-1000 eV) с диэлектриком, имеющим металлическое покрытие. Источником излучения служил мегаамперный Z-пинч. Измерения, проведенные с образцами оптического стекла, показали, что под действием излучения (мощность ~106 W/сm2) в электрической цепи, включающей металлизированный диэлектрик, возникает ток. Авторы считают, что причиной данного гальванического эффекта является генерация в диэлектрике горячих" электронов.

The effect observed upon interaction between the electromagnetic radiation with quantum energy of 25–1000 eV and a dielectric with metal coating is investigated. The radiation source was a megampere Z-pinch. Measurements performed on optical glass samples showed that radiation with a power of ~106 W/cm2 in the electric circuit switching on the metalized dielectric induces the current. It is shown that the observed galvanic effect originates from the generation of hot electrons in the dielectric.

The plasma pinch on the basis of a gas jet with special density distribution is described. The gas jet was produced by means of a pulse gas valve with a nozzle that was capable of forming a gas flow with a maximum density in the center of the discharge gap. The diagnostic techniques involved measurements of the discharge current and the pinch voltage, the size of the radiation area and the X-ray intensity. The experiments with different gases (Ar, Ne and N2) showed that as a result of the discharge at this gas distribution the hot plasma area of “point” form (its typical size is 100 μm and lifetime 3–5 ns) arises in the middle of the discharge gap. This area is the X-ray source of energy of quanta 50–5000 eV. The radiation spectrum depends on the gas type. The experimental results are presented.

The results of a study of a radiating Z-pinch with a profiled initial gas-density distribution over the z axis are presented. The gas distribution with the density maximum and transverse-size minimum at the discharge-gap center is formed by a pulsed gas valve with a specially designed nozzle. The parameters of X-ray radiation are measured for pinches formed in gaseous neon at currents of up to 200 kA. The experimentally selected gas density ensures the formation of a region with a typical size of less than 1 mm at the discharge-gap center. This region emits X-ray radiation in the keV photon-energy range in a time of less than 5 ns. Prospects for the development of an X-ray source based on this mechanism are discussed.

We discuss the possibility of creation of soft x-rays sources with small spatial and temporal extent based on the high-current discharge in a supersonic gas jet, instead of commonly used X- pinch technique which implies the use of some wire configurations. The construction and parameters of the nozzle providing a gas density configuration similar to the wire X-pinch is proposed. The MHD modeling of the implosion of such a configuration is performed, as well as the modeling of the emitted x-ray spectra. Some experimental results are also presented.

A multielectrode vacuum photoemission detector for X-ray tomography of plasmas at the ITER facility is described. The detector characteristics have been investigated with an X-ray source. The spectral response of the detector to X-ray photons with energies of 3–30 keV has been determined. The spatial and angular dependences of the X-ray detection efficiency are presented. The useful signal of the ITER facility has been estimated.

A vacuum photoemission detector designed for plasma tomography in X rays on the ITER facility is described. Such detectors allow X rays to be detected in the presence of intense neutron and γ-photon fluxes. The results of tests of a prototype of this detector on a 60Co source of γ rays, its calibration using radiation from an X-ray tube, and tests of its serviceability on the T-10 facility are presented. The values of the valid signal and the signal-to-noise ratio are assessed for the parameters of the ITER facility. Selecting the number of detectors and their arrangement on the ITER facility to ensure the required spatial resolution of the diagnostics is considered.