The nuclear-pumped laser program at the Institute for Technical Physics at Chelyabinsk- 70 is described. Work has primarily concentrated on rare gas and metal vapor lasers.

The time and wavelength dependencies of luminescence resulted from 11 low-lying Cd II levels in He-Cd medium excited by 252Cf fission fragments have been measured in the temperature range from 553 to 669 K and various buffer gas pressures (1.5–5 atm). The method used is based upon applying multichannel coincidence technique and single-photon spectrometry. The lifetime, pumping rate, and luminescence spectral line width data obtained for 325- and 441.6-nm transitions have been used to estimate lasing characteristics of He-Cd medium under optimal conditions.

We present the cross section for the ejection of electrons from helium and argon by 252Cf fission fragments, differential in the ejected electron energy. The electron energy ranges from 10 to 1,500 eV. The experimentally obtained cross sections are compared with calculations in the framework of Gryzinski&s theory and Gerjuoy&s theory. The results of the energy loss partitioning are presented. It is demonstrated that there is reasonable agreement between Gerjuoy&s theory and experiment.

A fission fragment-pumped Ar-Xe laser at 2.48 ¼m is reported. A threshold level of 3 × 107 thermal neutrons/cm2s was found with a 0.01% laser efficiency. The mechanism associated with temperature effects on laser performance is identified.

Spectral-luminescent properties of the Nd3+-activated laser liquid based upon POCl3-SnCI4 upon excitation by-products of nuclear reactions have been researched. It was concluded that the main luminescence characteristics such as T, Δλ, and λmax depend slightly upon the way of the medium excitation. It was obtained that the pumping efficiency δ of the upper working level is directly proportional to the activator ions' concentration and almost independent of the uranyl presence in the liquid. The measured values t, Δλ, λmax, and δ were used for the estimates of some parameters of nuclear-pumped lasers based upon phosphorus oxychloride. The effect of the Nd3+ ions laser action from the 4F3/2 level to the 4I11/2 level (λ = 1,050 nm) in aprotic liquids POCI3-SnCl4 in the presence of uranium by flashlamp pumping has been obtained.

The luminescence spectra of dense inert gas mixtures with iodine vapors excited by α-particles of 238Pu and 239Pu sources were investigated from 200 to 1,000 nm. In luminescence spectra of He-I2, Ar-I2, and Kr-I2 mixtures besides atomic lines corresponding to (np-ns) transitions of inert gas atom (n = 4 and 5 for Ar and Kr, respectively) there exist 288-, 320-, 342-, and 500-nm iodine molecular bands. The 342-nm (D&3II2g - A&3II2u) band has the highest intensity in these spectra and the highest intensity in the Kr-I2mixture. The measured bandwidth of the 342-nm band is equal to 24 A (full width at half maximum). In the Xe-I2 spectrum, the 342-nm band does not exist but the 253-nm Xel* excimer band has the highest intensity in it. The measured bandwidth of the 253-nm band equals 27 Å.

Heavy-ion accelerators can provide various beams from protons to uranium ions with energies ranging from a few keV/u to more than 1 GeV/u. The Munich Tandem van de Graaff accelerator has been used for most of the experiments described in this article. It can provide continuous or pulsed beams of almost all elements with particle energies of about 3.5 MeV/u. The pulse width is typically 2 ns. Maximum DC-beam currents of the order of 10 μA can be obtained, for example, for 32S ions. When the beam is focused to a beam spot of about 3 mm diameter, the flux of the ions is comparable to the flux of fission fragments used for nuclear-pumped lasers. Ion beam pumping is therefore well suited for model experiments of nuclear-pumped lasers. Technical aspects of ion beam-pumped lasers are discussed and the results of the lasers that have thus far been pumped by this method aresummarized. As ion beams are available either continuous or at high-pulse repetition rates ranging from tens of kHz to MHz, detailed spectroscopic and time-resolved studies of the emission of light induced by heavy-ion excitation of the target material can easily be performed. Experiments in which the emission by rare gas excimers and line radiation from atoms and ions has been studied are described. Lifetime measurements of excited levels at different target densities were used to measure collisional rate constants.

The emission of the third continuum of argon in the wavelength range between 175 and 250 nm and the vacuum ultraviolet emission of neon (λ < 100 nm) has been studied by timeresolved optical spectroscopy. The target gases at pressures between 2 and 100 kPa were excited with a pulsed beam of 100 MeV 32S9+ ions from the Munich Tandem van de Graaf accelerator. Wavelength spectra recorded in different time windows after the 2-ns beam pulses show that two different components contribute to the third continuum of argon. A radiative lifetime of 5.71 ± 0.08 ns for the Ar22+ molecule and a rate coefficient k3 = (1.46 ± 0.12) x 10-30 cm6/s for the reaction Ar2+ + 2Ar → Ar22+ + Ar were obtained from the pressure dependence of time spectra at a wavelength of 190 nm. From time- and pressure-dependent studies of the third continuum emission of neon at a wavelength of 99 nm, rate coefficients k2 = (3.6 ± 0.3) x 10-13 cm3/s for the bimolecular reaction Ne2+ + Ne→ 2Ne+ and k3 = (2.84 ± 0.09) X 10-31 cm6/s for the termolecular reaction Ne2+ + 2Ne → Ne22+ + Ne were determined.

The possibility of heavy-ion beam-pumped ion lasers is demonstrated by observation of optical gain on the 476.5-nm Ar II 4p–4s ion laser transition in argon gas excited by 2.5–ns pulses of 110–MeV 32S ions with repetition rates up to 156 kHz. The particle energy per pulse was about 20 μJ. The projectiles were stopped in the target at pressures between 5 and 35 kPa. The beam from an argon ion probe laser operated at 476.5 nm was used to determine gain amplitude and time structure from a measured transient increase of the probe laser intensity when target excitation by the ion beam was present. The maximum gain observed was (0.5 ± 0.1) x 10-3 at a target gas pressure of 5 kPa. The optical gain observed in argon is consistent with calculations based upon an analysis of spectroscopic studies of rare gas targets excited by heavy-ion beams.

In an earlier preliminary design study, we proposed a novel nuclear-pumped laser-driven (NPL) inertial confinement fusion (ICF) power reactor that represents an important variation on the “neutron feedback” concept for ICF. This NPL-driven ICF concept also included an advanced, DT-seeded, D3He-fueled pellet and magnetic protection of the first wall of the reactor chamber. Advantages that were demonstrated for this approach included increased efficiency for laser-to-target energy coupling, increased efficiency for thermalto-electric energy conversion, and reduced neutron activation and waste. The coupling efficiency is enhanced because a nuclear-pumped flashlamp is directly pumped by fission fragments from uranium micropellets within the lamp medium. The thermal conversion efficiency is greater because a large fraction of the ICF pellet&s fusion yield is in charged Finally, the fraction of the fusion yield carried by neutrons is significantly reduced in comparison with pure D-T-fueled pellets; thus, neutron-induced activity in the first wall is decreased and safety is increased. The initial study indicated these factors could result in a required driver energy of 5 MJ (vice 10 MJ currently projected) and a pellet gain of only 50 (vice 100 currently projected) for a feasible l,000-MWe power reactor operating with approximately six pellets per second. The current study includes a refined analysis of an NPL-driven ICF power reactor of this type. A cylindrical design for the fission/NPL blanket is selected as a “natural” geometry for pumping the NPL. Required enrichments and criticalities are then predicted for the multiplication of the fusion neutron yield needed to pump the NPL. Based upon these results, we report a more detailed parametric study of the efficiencies for converting neutron, X-ray, and plasma yields from advanced ICF pellets into electrical and optical energy flows required in this concept. We also examined breeding tritium in a lithium blanket layer. Results from these studies help define topics and parameter spaces for further research on this unique reactor concept.

The control of the extracted beam quality of a nuclear-pumped laser is a major issue. One possible control method involves changing the spatial power deposition profile, which is a function of the gas pressure and the pumping mechanism. Thus, we proposed a combined He-3 and wall coating (e.g., B-10 or U-235) technique. Then, the pump power deposition profile can be adjusted by varying the He-3 partial pressure. To examine this technique, measurements are being performed with an in-core cell by imaging the radiation-induced fluorescence onto a linear diode array located some distance from the cell. Results from these measurements are presented and other related issues such as gas dynamics, index of refraction effects, and efficient beam extraction from a large-volume cavity are discussed.

A practical, visible nuclear-pumped laser (NPL) has been sought at the University of Illinois and other laboratories for a number of years. Yet, the results from successful visible NPLs to date have not been fully satisfactory, e.g., the threshold pumping power is too high for conventional applications. Progress in recent studies of 3He-Ne-H2 as a candidate NPL operating in the visible region at 585.3 nm on the 2P1,-1S2 Ne transition is described. We obtained lasing on the above transition for 3He-Ne-H2 concentrations of 1,140, 588, and 412 torr, respectively, with the laser cavity placed in the beamport of the University of Illinois TRIGA reactor. The threshold thermal neutron flux is 1014 n/cm2-s, corresponding to a threshold pumping power of 5 W/cm3.

Lasing in atomic iodine pumped with incoherent, nuclear-stimulated XeBr* fluorescence is reported. These experiments represent the first demonstration of a nuclear flashlamppumped laser of any type. The fluorescence of XeBr* under nuclear pumping is also discussed.

The first demonstration of a nuclear-pumped laser (NPL) dates back to the mid-1970s while theoretical studies started earlier. This history will be briefly reviewed, followed by a discussion of the present status of various NPL concepts. Both physics and engineering issues are noted. Most attention has been given to gaseous media due to problems associated with radiation damage in liquid- and solid-state media. Various pumping methods, ranging from direct pumping of the laser medium to the use of nuclear-pumped flashlamps, will be discussed. Recent experimental results on pumping of O2(1Δ), the first demonstration of a nuclear-pumped flashlamp-driven laser XeBr*-I, and the new 3He-Ne-H2 NPL will be presented. Potential applications and corresponding NPL requirements, e.g., the long delay time requirements for an inertial fusion driver based upon NPLs, will be reviewed.

A new scheme for a large-scale solid-state laser system for inertial confinement fusion application is proposed. Double-pass amplifiers composed of a large number of Nd:glass rods and flash lamps between them are used together with phase-conjugation cells and output stimulated Brillouin scattering pulse compressors. The results of the preliminary experimental tests are presented, and the advantages of the proposed scheme are discussed.

We report experiments that were carried out at the inductive storage machine GIT-4 with wire arrays. The tungsten wire array parameters were the following: the mass per centimeter was equal to 370 μg/cm, the length was 4 cm, and the initial radius was 0.2 cm. When the wire array current was 1.5 MA, the rise time was 100 ns and the total radiation energy was 50 kJ at the 80–100–kJ energy transferred to the wire array.

We have studied experimentally the beam-plasma two-stream dissipative collisional instability of relativistic electron beams (REB) injected into plasma produced by interaction of REB with neutral nitrogen. The gas pressure ranged from 0.02 to 8 Torr. REB (T = 100 μs, E = 300 keV, 7 = 3–15 A) were injected into gas through a pulsed foilless valve. An external magnetic field was not used. A description of the experimental setup and that of applied diagnostics are presented. In some of the experiments the inner walls of a metallic interaction chamber were covered with microwave-absorbent material. We present the experimental dependence of the critical current of two-stream instability on gas pressure and beam penetration length. We have also measured the distribution of microwave emission along the beam axis. The influence of plasma self-radiation on the instability was observed and is attributed to a feedback. A possible mechanism of the feedback is discussed.

An experiment on Al-Cu impedance-match targets, carried out at the Shenguang highpower laser facility, is described. The shock adiabat of Cu in the pressure region 0.4- 0.8 TPa, measured experimentally, is close to the extrapolated results of the data at lower pressure obtained with a high-explosive loading facility and also is in agreement with the data at high pressure measured in the underground nuclear test environment.