Pinch plasmas as intense EUV sources for laboratory applications

Compact pinch plasma devices are intense sources of pulsed EUV radiation with output energies of several joules per pulse in single lines. Their spectrum peaks in a wavelength range where conventional x-ray tubes provide poor intensity. With correct optimization, both continuous radiation or line radiation with / > 1000 can be produced for broadband and narrowband applications, respectively. Because of their low cost and their compact size, pinch plasmas seem well suited to supplement research activities based on synchrotron radiation.In this paper, pinch plasma sources developed for x-ray lithography and x-ray microscopy are described. Their emission characteristics are optimized with regard to specific requirements given by the particular application and are compared to laser produced plasmas. The lithography source is compatible with the electron storage ring printing process with respect to its spectrum and enables full-depth exposures in 1-m-thick 60 mJ cm^-2 sensitivity resist at resolution below 0.2 m within 10 minutes. The source for microscopy applications enables flash imaging of biological specimens with suboptical resolution (0.1–0.2 m) at nanosecond exposure times. In addition, the averaged plasma parameters meet the requirements for an EUV laser medium. The nitrogen 2–3 transition is especially promising for achieving amplified spontaneous emission of hydrogen-like or helium-like ions excited by three-body or charge exchange recombination.     

Evolution on Z-pinch in argon-filled capillary

A capillary plasma Z-pinch as an alternative active medium of soft X-ray lasers was studied experimentally and theoretically. The theoretical analysis was based on the self-consistent solution of the so called snow-plow model of plasma pinch together with feeding double-resonance circuit. The calculated development of the current as well as the evaluated pinch time are in good agreement with the measured ones. The experimental pinch time was evaluated from the time-resolved measurement of broad band soft X-ray emission.     

Gas-puff Z-pinch experiment

The fast linear Z-pinch was experimentally investigated using a high-current pulse generator (10·8 F, 5–10 kJ, 150–250 kA) and pulse injection of argon and neon. Measured electrical characteristics of the discharge (current shape and risetime, inductance) and calculated dynamic parameters of plasma implosion (accelerated mass, radial plasma velocity) are presented. X-ray diagnostics with temporal resolution (vacuum X-ray diodes, semiconductor detectors) were utilized. The temperature and the density of pinch plasma (T_e 50 eV, n_e 1·4 × 10²⁶ m^–3) as well as its other parameters (size, lifetime) were estimated. Total energy emitted by the pinch in ultra-soft X-ray region (hv<1 keV) during 200 ns pulse achieves 125 J/4.The author is grateful to P. unka for stimulating discussions and also to V. ****Piffi and J. Rau for their help concerning X-ray detectors.     

Application of a Double－Wollaston－prism Laser Differential Interferometer in Plasma Focus

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Plasma excitations in the superconducting state of two-band layered superconductors

We investigate the low-frequency plasma modes polarized in the c-direction in two-band layered superconductors. The dynamic dielectric function (ω,q) is derived at T=0, using the generalized random-phase-approximation which is consistent with the Hartree–Fock single-particle states. It is shown that the dielectric function has two zero-points which correspond to the longitudinal plasma modes in two-band layered superconductors.     

Thermodynamic Properties of the Two-Dimensional Two-Component Plasma

The model under consideration is a two-dimensional two-component plasma, stable against collapse for the dimensionless coupling constant <2. The combination of a technique of renormalized Mayer expansion with the mapping onto the sine-Gordon theory provides the full thermodynamics of the plasma in the whole stability range of . The explicit forms of the density–fugacity relationship and of the specific heat (at constant volume) per particle are presented.     

Plasma effects in picosecond-femtosecond UV laser ablation of polymers

Laser ablation of polyimide (PI) and polymethyl-methacrylate (PMMA) at 248 nm with pulse lengths ranging from 200 fs to 200 ps was investigated. The measured ablation rates show minima for pulse lengths of about 5 ps (PMMA) or 50 ps (PI).The reflected fraction of the ablating laser pulse was measured as a function of the pulse length. In the case of PMMA maximum reflectance corresponds to a minimum ablation rate.This behavior can be explained by a dynamic plasma reflection model: A fast build up of a dense plasma is followed by high obscuration for a brief transition time and a self-regulating opacity for the rest of the pulse. This model of plasma mediated ablation leads to a ^1/4-dependence of the ablation rate at fixed fluence, which fits very well to the measured data, in particular if an extension to nanosecond ablation data of PI and PMMA is considered. PACS 52.50.Jm; 61.80.Ba; 42.65.Re     

D-D neutron yield in the 125 J dense plasma focus Nanofocus

We present here a very small transportable dense plasma focus with 125 J of energy able to be used mainly as an intense fast neutron source. The aim of this work was to design, construct and experimentally study a very compact nuclear fusion apparatus, at the lower energy limit, useful for multiple applications, such as soil humidity measurements, inspection of several materials metallic inclusions, medical neutron-therapies, etc. Besides, the possibility of using the same device as X-rays emitter has been explored. In a narrow range of deuterium filling pressure around 1 mbar, peaked Rogowski dips are observed. Correspondingly, strong neutron and hard X-ray pulses are measured. The neutron pulses last, in average, 50 ns, being about 10⁶ the amount of neutrons per pulse. The performance of this device has shown to be higher than any other plasma focus apparatus, compar ed on the empirical scaling law of neutron yield vs. pinch current.Received: 29 April 2003, Published online: 5 August 2003PACS: 52.58.Lq Z-pinches, plasma focus and other pinch devices - 52.70.Ds Electric and magnetic measurements - 52.70.Nc Particle measurements     

Plasma channel formation in nitrogen upon electron beam injection

A theoretical study is performed of plasma channel formation and current neutralization upon injection of a high current electron beam into nitrogen under high pressure (p 70 torr). The complex ion formation and recombination mechanism is considered together with its effect on the parameters of the plasma formed and the dynamics of beam current neutralization. Analytical expressions are obtained for the densities of simple and complex ions in the limiting cases and numerical calculations are carried out by computer for a more general case. It is shown that in nitrogen at a pressure of 70 torr when complex ions are considered the plasma channel conductivity decreases by approximately 35–40%.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 59–65, December, 1990.     

Generation of Plasma Wave at Pump-Wave Frequency and Second Harmonic Generation at Ultrarelativistic Laser Power

In this paper, the influence of ponderomotive and relativistic nonlinearities on the filamentation of an ultraintense laser pulse is investigated in three dimensions within the paraxial ray approximations. Generation of electron plasma wave (EPW) structure at pump-wave frequency and the second harmonic generation in these filamentary structures are reported. The generation of the plasma wave is due to intensity gradient (in the transverse direction of the laser beam in filamentary structure) and density gradient (due to ponderomotive-force effect). For typical laser–plasma parameters: The $hbox{laser intensity} = 2.5timesbreak 10^{20} hbox{W/cm}^{2}$; the $hbox{particles density} = 1.9 times 10^{19} hbox{cm}^{-3}$; and it is found that the maximum intensity of EPW is in the range of $2.0 times 10^{13} hbox{W}/hbox{cm}^{2}$. Interaction of the plasma wave with the incident laser beam leads to second harmonic generation, and the yield comes out to be $approx! 2.1 times 10^{-7}$.      

Plasma in open magnetic trap injected from independent UHF source

The properties of plasma injected into the open magnetic trap of uniform field from an independent UHF source have been investigated. It is established that a rather quiescent plasma with control density within the range of 2×10⁸–2×10¹² cm^–3 and temperature 2–3 eV is accumulated in the trap. It turned out that plasma lifetime in the trap is determined by a classical mechanism of particle escape at the expense of collisions, at fixed value of magnetic field in the trap it is not practically changed with the variation of neutral gas pressure and reaches the maximum value 4×10^–3 s at magnetic field strength in the trap equal 1600 Oe. Besides, the experimental data are analyzed on the basis of balance equations.     

On the Focussing and Transmission Properties of Electron Beam in High Power Microwave Sources Filled with Plasma

Based on the electron movement principles the beam paraxial trajectory and space trajectory equation in drifting space filled with plasma are given in this paper. The space is divided into two areas( and , contains ₁ and ₂), the behavior of electrons in these areas is studied. The equations are theoretically or numerically solved, the focussing and transmission properties are studied and some parameters affecting these properties are discussed in detail. The relativistic effect is also taken into account. The study shows that with plasma filled the beam can be focused efficiently and transmitted with high quality by optimally choosing the plasma filling fraction and the voltage.Plasma microwave electronics stemmed from 1949, however, it developed rapidly in recent years. In the process of high power microwave study, plasma is more and more introduced into microwave source. Because of the neutralization effect of plasma, the beam can transmit with high quality, even under weak or without magnetic field, it can propagate through drifting tube or slow wave structure by its self magnetic focusing force^[1–2]. By making full use of this property, microwave devices without magnetic field system can be made, this leads to a decrease in volume and weight of the device. Some experiments show that this kind of device can promote the output power and efficiency obviously. However, because of the presence of plasma, the beam's behavior changes greatly compared to those under vacuum condition. It is important to study the properties of the beam in drifting space or slow wave structure filled with plasma for the development of the device.     

Stability assessment and operating parameter optimization on experimental results in very small plasma focus,using sensitivity analysis

Regarding the importance of stability in small-scale plasma focus devices for producing the repeatable and strength pinching, a sensitivity analysis approach has been used for applicability in design parameters optimization of an actually very low energy device (84 nF, 48 nH, 8–9.5 kV, ～2.7–3.7 J). To optimize the devices functional specification, four different coaxial electrode configurations have been studied, scanning an argon gas pressure range from 0.6 to 1.5 mbar via the charging voltage variation study from 8.3 to 9.3 kV. The strength and efficient pinching was observed for the tapered anode configuration, over an expanded operating pressure range of 0.6 to 1.5 mbar. The analysis results showed that the most sensitive of the pinch voltage was associated with $0.88\pm 0.8\text{mbar}$ argon gas pressure and 8.3–8.5 kV charging voltage, respectively, as the optimum operating parameters. From the viewpoint of stability assessment of the device, it was observed that the least variation in stable operation of the device was for a charging voltage range of 8.3 to 8.7 kV in an operating pressure range from 0.6 to 1.1 mbar.     

Investigation of Plasma Parameters in a Magnetoplasma Compressor

The article presents the results of experimental investigations that were carried out at the Center for Science and Technology Development in Belgrade (Yugoslavia) and pertained to the plasma streams generated by a gasdischarge magnetoplasma compressor (MPC). The integral characteristics of the discharge, the dynamic parameters of a compression flux, and the concentration of the plasma electrons in the magnetoplasma compressor have been determined. The distinguishing features of the discharge afterglow from the volume of a vacuum chamber for a long time after the termination of the discharge current have been investigated.     

Experimental Study of the Plasma Cathode Electron Gun

The high-power microwave devices with plasma-filled have been unique properties. One of the major problems associated with plasma-filled microwave sources is that ions from the plasma drift toward the gun regions of the tube. This bombardment is particularly dangerous for the gun,where high-energy ion impacts can damage The cathode surface and degrade its electron emission capabilities. One of the techniques investigated to mitigate this issue is to replace the material cathode with plasma cathode. A unique plasma cathode electron gun are investigated in detail experimentally in this paper. The PCE-gun has been operated at pulser voltage up to 8KV,discharge current up to 166A,and pulse lengths of up to 60s.     

Large-Distance Behavior of Particle Correlations in the Two-Dimensional Two-Component Plasma

The model under consideration is a two-dimensional two-component plasma, i.e., a continuous system of two species of pointlike particles of opposite charges ±1, interacting through the logarithmic Coulomb interaction. Using the exact results for the form-factors of an equivalent Euclidean sine-Gordon theory, we derive the large-distance behavior of the pair correlation functions between charged particles. This asymptotic behavior is checked on a few lower orders of its -expansion ( is the inverse temperature) around the Debye–Hückel limit 0, and at the free-fermion point =2 at which the collapse of positive-negative pairs of charges occurs.     

Plasma laser with convective gas flow

A system for convective gas flow through the active zone of a plasma laser is considered. Expressions are obtained for the energy rating of the active zone at which convective flow ensures the required thermal regime. The kinetics of a helium-strontium plasma produced by high-energy particles is analyzed. The threshold values of the energy rating at which gain is ~chieved on the transition Sr II(s(1/2)Sr II (5P_1/2) ( = 4305 Å) are obtained. The calculations have shown that convective gas flow can ensure the required heat removal even at energy ratings substantially exceeding the threshold values.Translated from Trudy Fizicheskogo Instituta im. P. N. Lebedeva, Vol. 120, pp. 75–84, 1980.     

A Sum Rule for the Two-Dimensional Two-Component Plasma

In a two-dimensional, two-component plasma, the second moment of the density correlation function has the simple value {12[1–(/4)]²}^–1, where is the dimensionless coupling constant. This result is derived by using analogies with critical systems.     

The three-phase theory for plasma focus devices

A simplified theory for preliminary design of plasma focus devices that starts at the breakdown phase is proposed. For best focus, it is shown that the model can be used to predict the values of the inner and outer electrode radius, inner electrode length, gas pressure, and charging voltage that give minimum possible pinch radius. The theoretical results agree with experimental observations. The model shows that of these parameters, inner electrode length, inner and outer electrode radii play a significant role. An optimum pinch radius ratio of 0.05 to 0.40 was realized. Test results show that the focus strength is dependent on the breakdown conditions via the initial and final velocities of the current sheath during the radial collapse phase and the axial rundown phase. The final axial velocity determines the initial inward radial velocity. Results for a test design are presented     

Plasma frequency of the electron gas in layered structures

The plasma frequency of a complete degenerate electron gas in the layered model of Visscher and Falicov is calculated by means of both the Bohm-Pines canonical transformation method and the equation-of-motion method in the RPA. The dispersion equation for plasmons is obtained in a finite system ofn planes with both the cyclic condition and free ends. It is shown that the thermodynamic limit (n) of the plasma frequency is independent of the boundary conditions. The previous results obtained by various authors in different ways are shown to be certain limits of our result.