J. J. Ewing

Optical pulse compressor systems for laser fusion

The advantages and limitations of combined backward wave Raman pulse compression and pulse stacking for inertial fusion applications are discussed. A description of the major technological limitations which drive the designs of large (200 kJ) systems and some nominal systems parameters for a terawatt prototype stacker-compressor laser system are given. It is shown that aviable short wavelength laser fusion driver employing this concept can be expected to provide an overall power multiplication of 50 with a total systems efficiency of over 3 percent.

High efficiency XeCl laser with spiker and magnetic isolation

High efficiency x‐ray preionized discharge XeCl laser excitation has been achieved by combining spiker/sustainer excitation techniques with a simple and reliable magnetic isolator. The troublesome rail‐gap switch has been eliminated by using the laser discharge itself as the switch. An efficiency of 4% with 2.7 J optical energy was demonstrated.

Multidimensional modeling of transverse avalanche laser discharges: Applications to the HgBr laser

Geometrical considerations are important with respect to the stability and efficiency of avalanche electric discharge lasers. Parameters such as the electrode contours and the distribution of preionization electrons affect excitation rates through the relative values of the local electric field, local depletion of initial species, and through the response of the discharge circuitry to spatially dependent conditions within the plasma. Constriction of the discharge and subsequent impedance mismatch of the discharge to the pulse forming line result from these spatial nonuniformities. In this paper geometrical effects in the mercury bromide electric discharge laser are examined by comparing the results from a multidimensional discharge and kinetics model with experimental observations. The code models electron and heavy particle kinetics and laser intensity in time and one spatial dimension: parallel to the electrodes and perpendicular to the optical axis. Quantities whose spatial dependence is perpendicular ...

Efficient narrowband electron beam pumped KrF laser for pulse-compression studies

A 25‐J, 50‐ns laser pumped by opposed electron beams is described. Experiments with this device demonstrated a 9% intrinsic laser efficiency at power deposition rates of about 1 MW/cm3. Parasitic control and narrowband output required for Raman‐compression experiments were demonstrated by injection locking the laser. Experiments showing an angle‐encoded extraction of energy from the medium (pulse stacking) with three pulses using a high‐gain three‐pass amplifier configuration are also described. The device utilizes triggering schemes of very low jitter suitable for synchronization to other components for optical pulse‐compression experiments.

Microdischarges for use as microthrusters: modelling and scaling

Microsatellites with masses of tens of kilograms require only hundreds of micronewtons of thrust for station keeping and attitude control. Microdischarges (MDs) offer a compact way of generating such thrusts without using complex propulsion systems. In this paper, results from computational investigations of MDs sustained in Ar with tens of Torr back pressure are discussed with emphasis on conversion of discharge power into gas heating which can then be expanded in a nozzle to generate thrust. Typical cylindrical geometries have diameters of a few hundred micrometres and lengths of a few millimetres. We found that the gas temperature can exceed 1000 K for power densities of tens of kilowatts per cubic centimetre at back (upstream) pressures of tens of Torr. The nozzle length and location of the discharge in the MD channel are important from a gas dynamics viewpoint and so influence the incremental thrust (above that of the cold flow). Confining the discharge in the nozzle typically increases the peak gas temperature and the flow velocity, thereby potentially improving the performance of a MD used as a microthruster.

Future Developments and Applications of KrF Laser-Fusion Systems

The development of KrF lasers has proceeded from the small lasers invented in 1975 to the 10-kJ large amplifier module at Los Alamos National Laboratory. The future KrF laser-fusion drivers required for inertial confinement fusion (ICF) development and commercial applications, starting with single-main-amplifier laser systems in the 100- to 300-kJ range, through multimegajoule single-pulse target demonstration facilities, to repetitively pulsed drivers for electric power plants are examined. Two different types of KrF lasers are currently being analyzed as potential laser-fusion drivers: large electron-beam (e-beam)-pumped amplifiers using pure optical multiplexing for pulse compression and small e-beam sustained discharge lasers using a hybrid pulse compression technique. Both types of KrF lasers appear able to satisfy all of the requirements for commercial-applications ICF drivers, including cost, efficiency, pulse shaping, energy scaling, repetition rate, reliability, and target coupling. The KrF drive...

Cr:LiSAF thin slab zigzag laser

We report on a Cr:LiSAF zigzag thin slab laser in which single-pulse output energy of 1.8 J was achieved at a record specific energy output of 1.5 J/cm/sup 3/ of Cr:LiSAF. A Cr:LiSAF laser model was developed which, when compared with data, gives good agreement with energy and temporal laser output measurements. The device is in a configuration which can be scaled to high average power.

Modeling of Microdischarges for Use in Microthrusters

Summary form only given. Microdischarges having characteristic dimensions of 100s of mum at pressures of 10s to 100s of torr are being investigated for use as sources of thrust for small satellites. These devices are capable of generating up to mN of thrust using non-contaminating propellants such as rare gases or hydrogen. The class of device of interest includes cylindrical multistage discharges with or without nozzles. The dominant mode of propulsion is by imparting thermal energy to the neutral gas by the discharge. Innovative designs may also take advantage of transfer of momentum from ions to the neutral gas. In this talk, this class of microdischarge will be computationally investigated using a 2-dimensional plasma hydrodynamics model having an unstructured mesh to resolve non-equilibrium electron, ion and neutral transport using fluid equations. Sheath accelerated, beam-like electrons are addressed using a Monte Carlo simulation. A compressible Navier-Stokes module provides the bulk fluid velocities and temperatures. Changes in surface properties are addressed with a surface site-balance model. Results from a parametric investigation of pressure (a few 10s to 100s of torr) and geometry will be discussed for rare gas mixtures with the goal of maximizing the velocity of the exhaust at the exit plane. Velocities of up to 100s m/s have been predicted in the throats of the devices with plasma densities of 1013-1014 cm-3 at pressures of 50 torr with a back pressure of 30 torr

A Parallel Thyratron Pulser with Magnetic Sharpening for Large HgBr Lasers

We report on an electric discharge laser pulser that used three parallel thyratrons to drive a large, meter-long HgBr laser. By placing a magnetic sharpening switch between the thyratrons and the laser load, we were able to generate a 60 kV voltage,Rpike, and a 30 kA, 120 nS long current pulse with a rising front of approximately 1 x 1012 A/S at the laserhead. This led to an optical output exceeding 2 J and an energy transfer efficiency of 1.7 percent.