Possible use of a gasdynamic-piston device to excite short-wave lasing

Abstract

POSSIBLE USE OF A GASDYNAMIC-PISTON DEVICE TO EXCITE SHORT-WAVE LASING V. S. Zuev and L. D. Mikheev This article is a revision of an earlier preprint [30] and deals with a device described in [28]. A distinguishing feature of this device is that it can produce a considerable amount of gas compressed to 2500 atm at a temperature 3.5 kK. Argon (atomic weight 40) compressed in such a device has a density 0.35 g/cm 3 (disregarding possible deviation of the gas from ideal). A device by Yu. N. Ryabinin for adiabatic compression of gases is mentioned in [10]. Gas was compressed by a flying piston a hundredfold to 10,000 atm and heated adiabatically to temperatures on the order of 9 kK. Comparison of the parameters of the device described in [28], on the one hand, and the device of [10], on the other, shows the gas densities to be of the same order, approximately 250 times larger than under normal conditions. We demonstrate below a rare opportunity realizable in a gas stream from a high-pressure vessel in which the gas density is so high. We shall consider below possible applications of a piston device, but naturally only some of them. We examine the supersonic gas streams and the shock waves produced when they are braked. These streams and these shock waves will be discussed in turn from the standpoint of the feasibility of exciting short-wave lasing by pbotopumping inert gases. Coherent radiation can be excited ahead of a shock-wave front by radiation from the front of the shock wave. Such a phenomenon is observed when perfluoralkyliodides (CnF2n+lI) or xenon difluoride (XeF 2) or carbon oxysulfide (COS) is added to the main gas as an impurity. Details of the experiments are given for the first case in [1, 2], for the second in [3, 4], and for the third in [5]. The possibility of generating coherent vacuum ultraviolet (VUV) radiation (172 nm) ahead of a shock wave by optically pumping xenon molecules was considered in [6]. Radiating shock waves were excited in the experiments of [1-5] by emergence of a detonation wave from a solid explosive in contact with the gas. The use of explosives to excite shock waves in gases of normal density is widely used in practice. Detonation of an explosive charge weighing I-2 kg is feasible under laboratory conditions [7, 8, 9]. It is important in what follows that motion of a shock wave excited by detonation of an explosive is supersonic in the laboratory frame. An immobile shock wave can be produced, however, if supersonic gas is made to flow into the explosive blast. Supersonic gas flows are produced when gas escapes into vacuum (more precisely speaking, into a low-pressure gas) from a high-pressure vessel [10, 11]. Before proceeding to calculate the parameters of jets from the high-pressure vessel of dynamic piston device, let us determine, by way of orientation, the energy reserve in a gas at 2500 arm pressure and 3.5 kK temperature. We have in mind inert gases -- helium, neon, argon, krypton, and xenon. The internal energy of an ideal gas per unit mass is 2 c = (1) y(y - 1) ' where c 2 is the square of speed of sound and ~/= Cp/C v is the adiabatic exponent. Using the tables of [7] for the state parameters of inert gases (shock-adiabat tables) for a temperature 10 kK and higher and for a density 4 and more times that under normal conditions, we conclude that He, Ne, Ar, Kr, and Xe at T <_ 10 kK and p < 160 atm have ~/= 5/3, which is typical of a monatomic gas. At a temperature decreasing from 10 kK and a pressure raised to 2500 atm the temperature-induced ionization of the gases is even less noticeable (the degree of ionization decreases when the temperature is lowered and when the density is increased [10]), so that we can regard "/= 5/3 as highly accurate (actually the tables of [7] contain no data for p = 2500 atm and T = 3.5 kK). It is not clear at present to what extent ideal gases at p = 2500 atm and T = 3.5 kK can be regarded as ideal. That is to say, how accurately they can be described by the equation of state of an ideal gas Translated from preprint No. 18, 1992 of the Lebedev Physics Institute, Russian Academy of Sciences, Moscow, Russia. 62 0270-2010/92/1401-0062512.50 9 Plenum Publishing Corporation