Nuclear-pumped Lasers Research Articles

Labs drive the arms race

The conviction of laboratory managers that high technology can provide safety and national security in a dangerous world and that technological solutions are paramount over political solutions has been a major driving force in perpetuating the nuclear arms race. The credo in the laboratories appears to be that there are never enough designs of nuclear weapons for deterrence so that there is always a need to develop such new ideas as the nuclear-pumped X-ray laser as a defense against energy missiles. The author outlines several alternative steps, including the ratification and reaffirmation of arms control treaties, negotiations, and a halt to the Star Wars program. A central point is to stop nuclear weapons testing. 7 references.

Ozone dosimetry for calibration of power deposition in nuclear pumped lasers

Ozone yield from the irradiation of O2–SF6 mixtures has been utilized for calibration of power deposition in boron-10 coated tubes used in nuclear pumped laser experiments. Laser experiments using such tubes have previously relied solely on theoretical calculations. Results obtained from an O2–SF6 dosimeter show reasonable agreement with recent theoretical calculations and, because of its simplicity and accuracy, the use of this dosimeter is proposed for calibration of nuclear pumped laser sources.

Nuclear-reactor pumped lasers excited by ion-ion neutralization

A class of nuclear pumped lasers (excited by reactor-produced thermal neutrons) in which the laser levels are populated by negative ion-positive ion neutralization is proposed and an analysis of two particular systems, 3He/N2O/O2 and 3He/N2O/N2, is performed. Laser action is predicted in atomic oxygen and nitrogen as a result of O−-O+ and O−-N+ neutralizations. The source of negative ions is dissociative attachment to N2O. A threshold neutron flux of ≊1015cm−2 s−1, peak power of >500 W/cm2, and a fission power to laser power conversion efficiency of ≊0.4% may be possible in these systems. This is as a result of efficient utilization of the large thermal electron density in the attachment process, and the highly selective nature of the ion-ion neutralization in producing product-excited states.

Design, construction, and testing of a nuclear-pumping facility at the University of Missouri Research Reactor

An intense effort to design, construct, and test a nuclear-pumping facility (NPF) has been completed at the University of Missouri-Columbia (UMC). The NPF has a flow capability similar to that of the now defunct Brookhaven Chemonuclear In-Pile Research Loop, plus the optical capability to monitor light output from the irradiation chamber. Both features make the UMC NPF a unique research loop usable for a wide variety of projects including radiation chemistry, fluorescence studies, photochemistry, dual media nuclear-pumped lasers, and direct nuclear-pumped lasers. Initial tests of the facility included a demonstration of 40.0 ft3/h flow rates (pump limited), and a spectral scan of N2 and He. The latter test represents a first effort in obtaining nuclear-pumped gas spectra from a high-power steady-state reactor such as the University of Missouri Research Reactor (MURR). Results indicate that observed spontaneous emission mainly comes from the first negative spectral series in N2+ (B2Σ+u →x2Σ+g) and from He*2 electronic transitions.

Dynamics of the Nuclear and Electrically Pumped 1.45-μm Atomic Carbon Laser in Mixtures of Helium + CO And Helium + CO2

The first successful modeling of an impurity-type nuclear pumped laser (NPL) (i.e., one that employs trace densities of the lasing species in a noble gas buffer), atomic carbon at 1.45 ..mu..m, was achieved. Such NPLs are important due to their low flux threshold and quasi-steady-state oscillation. The atomic carbon NPL is unique in that time delays up to 5 ms are observed between the laser signal and the excitation pulse in helium + CO/sub 2/ mixtures while no delay is observed in helium + CO. Using a kinetic model in conjunction with an experimental program, we show that this difference in delay arises from slow dissociation of CO/sub 2/ to form CO. Significantly, the model also successfully simulates electrical pumping of He-CO or CO/sub 2/ mixtures.

Analysis of the UF6-Xe Direct Nuclear-Pumped Laser

The quenching role of UF6 in noble gas nuclear-pumped lasers is examined. Detailed results are presented for the He-UF6-Xe system. These results indicate that depletion of the atomic ion is the mechanism responsible for the observed behavior. Based on this, it is concluded that UF6 is not compatible with noble gas lasers. In ad- dition to identifying the quenching role of UF 6, some key rates whose rate constants are not known are iden- tified. 235U(n,ff)FF reaction and to deduce from that the quenching role of UF6. Although the experiment employed an Ar-Xe-UF 6 mixture, detailed calculations are carried for a He-Xe-UF 6 mixture. This is because more kinetic data are available for He; moreover, the pumping mechanism is not expected to depend on the buffer gas as long as it is a noble gas with ionization and excitation potentials higher than those for Xe. It will be assumed that He is the dominant substance in the system and, as such, is initially excited and ionized by fission fragments. The energy stored in the excited and ionized states of He is then trans- ferred to the lasing material by charge transfer and Penning ionization. For noble gas lasers,3'4 recombination of the atomic ion yields the upper laser level, while recombination of the molecular ion yields the lower laser level. Thus, there is an optimum noble gas concentration for which the power output is maximum. Two possible mechanisms may be advanced for interpreting the termination of lasing observed in the experiments of Ref. 2. The first assumes that electron attachment is the dominant mechanism, while the second is based on the depletion of the atomic ion as a result of neutralizatio n of Xe + by UF^ and F ~ . The calculations indicate that the mechanism depends, to a large extent, on the neutralization rate of UF4+ and UF^ for which no measurements are available. For the case where the neutralization rate is comparable to rates involving complex ions,5 the results were not consistent with available ex- periment. However, when lower rates were assumed, the results were consistent with the observation of Ref. 2. Calculations using the lower rate indicate that depletion of the atomic ion is the mechanism responsible for quenching.

Kinetics of a CO 2 Nuclear Pumped Laser

D IRECT nuclear pumping was demonstrated at a number of laboratories using molecular and atomic systems with one notable exception, i.e., CO2. This work is being undertaken with the objective of explaining the mystery surrounding the direct nuclear pumping of CO2. To achieve this objective, a detailed kinetic model which incorporates all important reactions in a He-N2-CO2 mixture is formulated. The results show that for mixtures typical of those employed in electric discharge systems, the gain coefficients are such that lasing is not expected to take place. Moreover, for conditions representative of current nuclear-pumped laser experiments, concentrations of CO2 in the 1-3% range are optimum.

Characteristics of a UF6-H2/HF nuclear-pumped laser

Nuclear pumped lasers are characterized by high-threshold neutron fluxes and low gain. This is due primarily to the fact that the fissile gas, which has the largest partial pressure and hence has the largest fraction of fission energy deposited in it, is not the lasing species. The closer the fissile gas can be coupled to the actual lasing process, the more efficient the laser will be. In this paper, a model for a potential new nuclear-pumped HF laser is presented. Using a 235UF6-H2 gas mixture, a peak gain of about 50%/m and a threshold neutron flux of <1014/cm2 s are predicted. Recommendations are made concerning optimum use of the new system.

Nuclear-pumped cw lasing of the 3He-Ne system

The gain for the 6328-Å laser line for the nuclear excited He-Ne system has been measured for 300 Torr pressure at thermal neutron flux levels from 2×107 to 1×1014 n/cm2 sec. In order to estimate small:signal gain, the gain was also measured as a function of input intensity. For demonstration of feasibility of cw operation of nuclear pumped lasers, a cavity was operated and lasing was observed. Although the laser output was small, we conclude that lasing in a cw mode has been achieved with He-Ne using moderate neutron flux levels.

Recherche d'un effet laser dans le melange HeCo 2 irradie par le reacteur caliban : Groupe Plasma d'Origine Nucléaire

A preliminary experiment on nuclear pumped lasers has been performed with a fast burst reactor (“Caliban”, France). A high-intensity infra-red radiation issued by a HeCo 2 mixture has been observed during the active ionization stage of the mixture.

Distribution functions in plasmas generated by a volume source of fission fragments

The role played by fission fragments and electron distribution functions in nuclear pumped lasers is considered and procedures for their calculations are outlined. The calculations are illustrated for a 3He–Xe mixture where fission is provided by the 3He(n,p) 3H reaction. Because the dominant ion in the system depends on the Xe fraction, the distribution functions cannot be determined without the simultaneous consideration of a detailed kinetic model. As is the case for wall sources of fission fragments, the resulting plasmas are essentially thermal but the electron distribution functions are non-Maxwellian.

Direct Nuclear Pumping by a Volume Source of Fission Fragments

A detailed kinetic model is presented for the analysis of nuclear pumped lasers when the pumping is a result of a volume source of fission fragments. The results of the model are employed to study a He-3 - Xe laser. For the range of pressures, neutron fluxes and mixtures considered, the gain and power calculations are in good agreement with experiment. Moreover, based on these calculations, it appears that the collisional recombination is the dominant pumping mechanism for 7p-7s transitions while direct excitation is the dominant pumping mechanism for the 5d-6p transitions.

Direct Nuclear-Pumped Lasers Using the 3He(n,p)3H Reaction

A description is presented of experimental results concerning a specific class of direct nuclear-pumped lasers classified as 'volumetric nuclear lasers'. In the considered laser system a fissioning gas, He-3, is mixed with the lasing gas to form a homogeneous mixture, resulting in uniform volume excitation. In typical volumetric nuclear lasers a fast-burst reactor is used as a source of neutrons which penetrate a polyethylene moderator. Here the fast neutrons are thermalized. After thermalization, neutrons scatter into the laser cell. Nuclear reactions produce a proton of 0.56 MeV and a tritium ion of 0.19. These ions produce secondary electrons which pump the laser medium creating a population inversion. The results reported demonstrate direct nuclear pumping of He-3-Ar, Xe, Kr, and Cl with the considered system.

Power density in direct nuclear-pumped 3He lasers

The interaction of neutron beams with 3He gas is of interest for nuclear pumped lasers. The effects of spectral dependence of the neutron beam, neutron attenuation in the gas-filled laser tube, and transport of the charged-particle 3He(n,p)3H reaction products are treated in detail. An expression for the energy density as a function of position within the tube, tube radius, operating pressure, and neutron fluence is given. The maximum energy density within the optical cavity is achieved when the tube radius a (cm) is given by a=3.26/P where P (atm) is the operating pressure. The variation of radius by 50% above and below optimum will change the energy density at most by 10%, although performance degrades quickly for radii outside this range. If the optimum tube radius is used for each operating pressure, then the power density on the centerline (kW/cm3) is given as ξCL=9.3×10−18Pf0 in a thermal neutron environment of f0 (n/cm2 sec).

Power deposition in He from the volumetric 3He(n,p)3H reaction

Calculations are presented in this paper which show the amount of power that can be expected to be deposited in 3He for typical direct nuclear-pumped (DNP) lasers presently in use. The calculations were performed taking into consideration the cylindrical geometry of the system, the depletion of the thermal flux across the tube cross section, and the energy loss of the protons to the cell walls. If a laser efficiency of 1% is assumed, the results indicate a steady-state laser output of 12.5 kW from a volume of 152.6 cm3 or 82 W/cm3 can be achieved.

A helium-mercury direct nuclear pumped laser

A 6150-Å He-Hg laser, pumped solely by the 1n (10B,α) 7Li nuclear reaction, has been achieved using the Sandia SPRII reactor. The optimum conditions for lasing were 600 Torr total pressure with 2.5 mTorr Hg partial pressure, with a threshold for lasing of ∼1016 n/cm2 sec. This is the first visible-wavelength laser having nuclear energy as its only source of excitation.

Observations on the Luminescence ofα-AI2O3(Synthetic Sapphire) in a Reactor Environment

Optical components made of α-Al2O3 (synthetic sapphire) are used in optical systems (nuclear-pumped lasers, fission cells, etc.) to operate in a reactor in-core environment. Absorption and luminesc...

Nuclear-pumped 3He-Ar laser excited by the 3He(n,p)3H reaction

A volumetric direct nuclear-pumped laser has been achieved for the first time by using the 3He(n,p)3H reaction to excite a 3He-Ar laser. Lasing was achieved at 1.79 μ in Ar I at total pressures ranging from 200 to 700 Torr with 10% Ar, demonstrating stable high-pressure lasing. Laser energy output increased with both increasing total pressure and thermal neutron flux.

Transversely excited submillimeter-wave waveguide laser

Gaseous core reactors and nuclear pumped lasers have the potentials of space propulsion at exhaust jet velocities up to 50,000 m/sec, space power at 1 kg/kW specific mass, power transmission via laser beams over astronomical distances and beneficial applications on Earth.The energization of lasers directly by nuclear reactions has recently been achieved. In experiments conducted jointly by the University of Florida and the Los Alamos Scientific Laboratory, New Mexico, a helium-xenon laser was directly pumped by fission fragments. The obtained laser wavelength was 3.5 μm. A group of researchers at the Sandia Corporation in Albuquerque, New Mexico, was successful in energizing a carbon monoxide laser by fission fragments at wavelengths in the 5-μm band. At the University of Illinois lasing was achieved at wavelengths of 8629 Å and 9393 Å in a neon-nitrogen mixture. A program of gaseous core reactor research is underway with experiments being conducted at the Los Alamos Scientific Laboratory in New Mexico, USA. The program utilizes a beryllium moderator-reflector, forming a cylindrical cavity of 1 m diameter and 1 m length. This system and associated control system hardware, uses components from the previous ROVER nuclear rocket program. Various configurations of canisters containing enriched gaseous uraniumhexafluoride fuel are inserted into the reactor cavity for research on neutronics and nuclear induced optical radiation.Critical mass, control swing and the effects of poison were measured by simulating enriched uranium hexafluoride fuel with uranium foils, which were placed in homogenous and inhomogeneous distributions in the cavity. Critical mass was determined at about 6 kg 93% enriched 235 uranium. A uranium hexafluoride canister system was built for safe operation in the reactor cavity and for physics measurements and observations at nuclear criticality.It is anticipated that this work will result in the demonstration of principles of a new type of nuclear power reactor, and of laser power output from such a reactor.

Direct nuclear pumped (DNP) lasers

We consider the single-mode Maxwell-Bloch equations describing a Doppler-broadening ring laser. For different parameter ranges this system undergoes period-doubling, intermittency, and two-frequency routes to chaos as a single parameter (e.g., detuning) is varied, as has been observed in recent experiments with He-Ne and He-Xe lasers.