Abstract: Three approaches to the problem of EUV and soft X-ray lasers are being pursued experimentally at the NOVETTE and OMEGA laser facilities. Photoionization pumping of neon gas may lead to a self- terminating population inversion in Ne II at 27 eV, and experiments planned at OMEGA are planned to observe amplified emission. Line radiation may be used to drive an inversion in helium-like or hydrogen- like fluorine and neon at energies between 53.6 and 151 eV. We have carried out an exploratory experimental sequence on NOVETTE designed to test integral laser targets. Experience gained points the way towards a second generation target design and future coincident spectroscopy and integral laser experiments. A third approach involves collisional excitation of 3p leading to a 3p-3s inversion near 68 eV. The scheme was tested at NOVETTE, and a null result obtained, which may be explained by beam bending caused by large index of refraction gradients. Phase correction is proposed as an improvement for the scheme.

Abstract: A systematic formalism for investigating linear electromagnetic perturbations in general magnetic field configurations is developed. The formalism employs the small adiabaticity parameter rho /L0 and is valid for arbitrary frequencies. Here, rho and L0 are, respectively, the Larmor radius and equilibrium scale length. Effects associated with plasma and magnetic field inhomogeneities as well as finite Larmor radii are contained. The specific case of axisymmetric Tokamaks is then considered to illustrate the potential application.

Abstract: Oscillations induced on the profile of a Gaussian CW CO2 laser beam by being transmitted through the TOSCA Tokamak plasma are confined within envelopes whose shapes are correctly predicted by theory, permitting plasma fluctuation intensity and wavelength to be deduced as functions of frequency by a curve fitting procedure. The analysis shows spontaneous density fluctuations integrated across the TOSCA minor diameter to be mainly transverse to the magnetic field, with intensity maxima between 40 and 100 kHz and ne( nu ) varies as nu -2 towards higher frequencies. At 200 kHz n3( nu )/n3 is about 104 times thermal, and the total fluctuation level n3/ne is a few percent. Coherent oscillations near 100 kHz, associated with rotating MHD structure, are occasionally observed. Wavelengths are found to lie between 1 and 6 cm, and correspond to kappa perpendicular to rho i in the range 0.2-2.0, pi i being the ion gyroradius for the prevailing plasma conditions.

Abstract: Experimental investigations of strong turbulence associated with the radial density gradient of a rotating magnetized plasma column are reported. The experiment is designed to make Taylor's hypothesis effective, in order to allow a simple interpretation of measured frequency spectra in terms of wavenumber spectra. The spectral index of the turbulent potential fluctuations is determined and the variation of the spectral intensity is investigated for varying magnetic fields. The results compare favourably with theoretical predictions. The importance of distinguishing subranges in the turbulent spectrum is demonstrated. Some aspects of the relative diffusion of a test-cloud of charged particles released in the turbulent field are discussed.

Abstract: The improved theoretical analysis of Fraunhofer-diffraction method as a new means to measure the frequency, wavenumber, intensity and even spatial position and propagating direction of plasma waves is presented. It is further, experimentally verified and the measuring accuracies are ascertained by measurements in a microwave region, of ion-acoustic waves in a DC discharge. Successes of introducing the practically important conditions into theoretical analysis have made it possible to establish this method as a standard and powerful diagnostic technique for measurements of plasma waves and turbulences in various plasmas such as in Tokamaks.

Abstract: The effect of a finite frequency on the dispersion relation of low-frequency surface waves propagating on a magnetized plasma-vacuum interface is investigated. It is shown that two distinct modes exist depending on the sign of the wavenumber perpendicular to both the magnetic field direction and the normal to the surface, which may be related to the fast and ion-cyclotron body waves. The damping of these waves due to resonance absorption is calculated, and it is shown that the fast surface wave is undamped if its frequency is higher than the ion-cyclotron frequency.

Abstract: For pt.I see ibid., vol.25, no.6, p.665 (1983). The authors review various methods for obtaining an expression for the ponderomotive force on a magnetized plasma; these methods are based on a fluid, kinetic, or a stress-tensor approach. They propose a new method which employs a fluid-dielectric model of the plasma; this method seems to be simple and generally applicable. They first of all calculate an expression for nonstationary waves in an isotropic plasma and find agreement with earlier results. They then derive an expression for the ponderomotive force in a magnetized plasma for the case of stationary waves and compare their result with earlier attempts to obtain such an expression.

Abstract: Magnetic field fluctuations have been studied in the ETA-BETA II experiment as a function of density, time and radius The spectral analysis of the measured fluctuations has shown that the higher frequency portion of the spectrum (>50 kHz) is more sensitive to the density variation, whereas the lower frequency portion ( approximately 10 kHz) shows a radial profile which, especially at later times during the discharge, resembles the characteristic shape of MHD resistive modes Radial correlation lengths of several centimeters are found In general the amplitude of the fluctuations increases at lower densities and is larger toward the end of the discharge and in the outer plasma region These trends may be correlated with the typical variation of the streaming parameter However, the lower frequency fluctuations, in particular, can be interpreted as MHD instabilities which can produce large distortion of the magnetic surfaces leading to island formation and overlapping resulting in stochastic behaviour of the magnetic field lines in a relevant radial extent ( approximately=1 cm) of the outer plasma regions

Abstract: A new method based on the laser-induced fluorescence method has been developed to measure the spatial electron density distribution in plasmas. The local electron density can be determined by observing the intensity ratio of the laser- to the collision-induced fluorescence. A spatial electron density distribution of a helium plasma (Te approximately 6 eV, ne:1011-12 cm-3) has been determined by observing the He(31P to 21S) laser-induced fluorescence and the He(31D to 21P) collision-induced fluorescence resulting from the He(31P to 31D) process due to collisions with electrons. The comparison of the result with that of a conventional method proves this new method is of practical use in the space-resolved measurements of plasma electron density.

Abstract: The absorption of magnetoacoustic modes at the spatial Alfven resonance of Tokamak plasmas is investigated within the context of an ideal MHD model which includes finite omega / omega ci effects. It is found that these effects can dramatically modify the pure MHD picture of the resonant absorptiometry and the spectrum of global eigenmodes of the Alfven wave. Implications for the interpretation of recent experimental results are discussed.

Abstract: A review of the experiments associated with laser-driven implosions is presented. These experiments include actual implosion experiments and experiments which simulate particular aspects of laser-driven implosions. Exploding pusher and isentropic implosion experiments are treated separately. Where possible a comparison of the data to analytic or computer simulation calculations is made. Exploding pusher analytic theory is shown to be qualitatively correct, and the analytic models of ablation are compared to experiment. Current isentropic experiments, however, appear to be dominated by hot electron effects. It is shown that most of the experiments which have been reported do not display a strong dependence on laser wavelength, and this result is predicted by theory. An analysis which is intended to display the effects of hot electron preheat does demonstrate a dependence of implosion data on wavelength. It is also shown that some topics, such as transport and implosion stability, require much more experimental and theoretical effort. The conclusion reached is that long wavelength lasers may require more than 10 MJ to ignite a target.

Abstract: Corrections for the systematic errors associated with the measurements of electron cyclotron emission from DITE Tokamak using a Michelson interferometer are considered under the following headings. (a) Finite optical depth an isotropic reflection model is developed leading to a line-integral expression for the emission intensity which depends on the optical depth and the wall reflection coefficient. (b) Finite density and refraction: the error due to the distortion of the instrument antenna pattern is calculated from results of ray-tracing computations. (c) Relativistic resonance layer width: an expression is derived for the corresponding spatial error for emission perpendicular to the magnetic field. (d) Magnetic field corrections: an expression for the spatial error due to the poloidal and diamagnetic field contributions is given and its effect on the observed Shafranov shift is investigated. (e) Frequency response: the general principles of quasi-optics are applied to the Michelson interferometer demonstrating that a small-aperture blackbody oven may be used to calibrate the system. (f) Spatial resolution of the viewing optics: the equivalence of lens optics and waveguide antenna is shown both theoretically and experimentally and expressions are given for the resolution perpendicular to the viewing axis. (g) Frequency resolution: it is shown that the resolution of a Michelson interferometer can be better than that suggested by application of the Rayleigh criterion. These corrections are applied to experimental emission spectra and the derived electron temperature profiles compared with laser scattering measurements in a discharge where the plasma equilibrium is changing. The Shafranov shift of the corresponding temperature surfaces is shown to be in good agreement with that expected for the magnetic flux surfaces. Using the wall reflection model, the electron density profile is derived from the emission profile of the third harmonic cyclotron frequency.

Abstract: Experiments with 200 kW of applied electron cyclotron heating (ECH) power have demonstrated electron temperatures of about 1 keV in the ELMO Bumpy Torus-Scale (EBT-S) device. Electron densities are in the range of (0.5-1.5)*1018 m-3 and increase as the square root of the applied ECH power. A potential well is present, and its depth in V closely follows the electron temperature expressed in electron volts. Only low charge states of impurities are found, and Zeff approximately=1.0. Data from the electrons can be compared with simple scaling laws when scale lengths are held constant. These comparisons indicate that electron densities, temperatures, and confinement times scale according to neoclassical expectations.

Abstract: The authors examine the relative merits of laser induced fluorescence scattering at the Lyman-alpha and Balmer-alpha wavelengths for the measurement of both the spatial distribution and absolute magnitude of neutral hydrogen densities in fusion plasmas. The enhancements of the fluorescence signals for present and for saturation laser intensities are determined and signal to noise ratios are presented for a range of fusion plasma conditions. Details of the interpretation of the fluorescence signals, and the limitations, at the two wavelengths are discussed. In the hotter regions of the plasma, Balmer-alpha fluorescence scattering allows the measurement of neutral densities as low as 107 cm-3, whereas present intensities from Lyman-alpha sources permit fluorescence measurements only for neutral hydrogen densities approaching 1010 cm-3. Also presented is a technique for the spatial measurement of the electron number density based upon fluorescence scattering on the Balmer transitions, this process not being possible at Lyman-alpha for the range of electron densities in magnetically contained fusion plasmas. This may have applications in regions of the plasma otherwise difficult to diagnose, for example, near divertors and limiters.

Abstract: A general model is adopted with the magnetic piston perfectly coupled to the imploding plasma. The work done by the piston in moving from initial radius r0 to equilibrium radius rp is equated to the enthalpy of the plasma column at rp. This, together with pressure balance, suffices to produce an expression for the pinch ratio dependent only on gamma , the specific heat ratio of the pinched plasma. For a constant current, constant length pinch with gamma =5/3 a pinch ratio of 0.29 is predicted. For the pinch phase of a gamma =5/3 plasma focus treated as a constant current pinch having a length which increases with decreasing radius, a pinch ratio of 0.14 is predicted. These compare well with experimentally observed values.

Abstract: Experimental results are presented on localized MHD disturbances in a plasma contained in a uniform magnetic field. The disturbances were generated by small antennae and observations were made downstream with magnetic probes to determine the extent to which the wave packet would be guided by the magnetic field. The acoustic wave was found to be strongly localized along field lines, the shear AlfvCn wave was less strongly localized and the fast Alfven wave was not localized, in agreement with theoretical expectations.

Abstract: The authors derive for the case of a magnetized plasma the analogues of the Zakharov equations for an isotropic plasma. They discuss the linearized dispersion relations following from these equations.

Abstract: The enhancement of the ponderomotive potential near gyroresonance is investigated both experimentally and theoretically. Due to nonadiabaticity the maximum value of the ponderomotive potential is limited by the transit time of the particle through the r.f. field structure. The results have important implications for isotope separation and r.f. plugging of fusion plasmas.

Abstract: It is demonstrated that a spontaneously excited ionization wave in a small radius positive column is suppressed resonantly by an externally launched wave at some discrete frequencies. Waves whose frequency is not equal to these discrete frequencies have only a small effect of suppression. Results suggesting a feedback effect through the column are shown. It has been found that asynchronous quenching as described by van der Pol's equation should be modified. Also, the energy relation between the wave deviates from that given by van der Pol's relation. These characteristics are explained by considering nonlinearities of ionization rate and loss factor in Pekarek's equation.

Abstract: The current driven by electron cyclotron resonance heating in a Tokamak is shown to depend strongly on the poloidal angle at which the power is absorbed. This dependence arises because the ratio of passing to trapped electrons varies around each flux surface. A Fokker-Planck treatment is used to obtain the current as a function of poloidal angle, wave phase velocity and inverse aspect ratio. The effect offers the possibility of experimentally demonstrating the existence of trapped electrons in a Tokamak.

Abstract: High power ECH (utilizing a 28-GHz gyrotron at power levels up to 200 kW, cw) and fast-wave ICH (in the frequency range 15-30 MHz at power levels up to 20 kW, cw) experiments on EBT-Scale (EBT-S) have yielded Te approximately 1.1 keV, n approximately 1-2*1018 m-3, and tau E approximately 6 ms. The ring and core loss rates scale as predicted by the neoclassical theory, and the plasma parameters have the predicted values for the densities, temperatures, and confinement times reachable in this small plasma radius (10 cm) device at low field (1.0 T). In addition, the following observations were made: (1) the stable operating window is larger at high power levels, (2) a substantial increase in energetic ion tails (Ti>100 eV) and a doubling of the ring electron stored energy (beta) were seen at the highest ICH power levels, and (3) a significant increase in core density and stabilization of hot electron modes was possible with gas puffing.

Abstract: The plasma electron density fluctuation spectrum can be obtained from the measurement of the phase fluctuation spectrum of a probing electromagnetic wave measured some distance from the plasma. If the mean square fluctuation of the probing beam is much less than unity and the observer-plasma distance is well within the Fresnel distance of the irregularities, a direct relationship exists between the density and phase spectra. As an example of this procedure, an experiment is described which uses a probing beam wavelength of 2 mm to measure the density irregularities. It is then proposed that a suitable wavelength for the present large toroidal plasma devices is in the 10 mu m region.

Abstract: Toroidal and poloidal plasma rotation are measured in a high beta Tokamak device by studying the Doppler shift of the 4686 AA He II line. The toroidal flow motion is in the same direction as the plasma current at an average velocity of 1.6*106 cm s-1, a small fraction of the ion thermal speed. The poloidal flow follows the ion diamagnetic direction, also at an average speed of 1.6*106 cm-1. In view of certain ordering parameters, the toroidal flow is compared with the predictions of neoclassical transport theory in the collisional regime. For the poloidal motion, however, it is likely that an (Er*B)/B2 drift in a positive radial electric field, approaching a stable ambipolar state (Stringer, 1970) is responsible. Mechanisms for the time evolution of the rotation are also examined. The radial electric field responsible for the (Er*B)/B2 drift is determined from the theory using the measured poloidal velocity.

Abstract: The efficiency of current drive by X-mode electron cyclotron waves is calculated using the weakly relativistic resonance condition in a full Fokker-Planck treatment which includes electron-electron collisions. For suprathermal resonant electrons the values obtained are less by a factor (Z + 5)/Z than those predicted by the Lorentz gas model. However, this relationship is found not to hold for resonant parallel velocities less than the thermal velocity. A ray tracing code, incorporating the calculated current drive efficiencies, has been used to study the relativistic corrections for X-mode second harmonic waves injected from the low field side into a Tokamak the size of DITE.

Abstract: A beam of potassium plasma of 1012 cm-3 density from a continuous magnetoplasma-dynamic arc source has been propagated into a magnetic mirror device in a direction transverse to the magnetic field. A self induced polarization and E*B drift of the beam was observed. The plasma filled the magnetic mirror to a density of 1012 cm-3 when insulating end plugs were used. The density was slightly reduced if the mirror ratio was reduced to unity and was reduced to 1011 cm-3 if the end plugs were made conducting thus shorting the electric field. The temperature of the trapped plasma corresponded to approximately two thirds of the energy in the initial motion of the beam. These results are discussed qualitatively in terms of the polarization drift model of Schmidt (1960). The possible application of this injection technique to tandem mirrors is discussed briefly.

Abstract: The physics of radio-frequency current drive for steady-state Tokamak operation has been studied in the context of a conceptual small Tokamak, called the RST. Two distinctively different schemes of current drive by using RF waves have been discussed. In the first, a wave travelling in the toroidal direction damps on the electrons, thereby transferring momentum to the electrons, creating a current; typical of this category is Landau damping of traveling lower hybrid waves. The second general category is called 'enhanced bootstrap' current, in which RF waves may be used to enhance the cross-field particle diffusion above the neoclassical rate, thereby producing significant enhancement of the plasma bootstrap current at reduced plasma pressure.

Abstract: Observations of the current-driven electrostatic ion cyclotron instability, both at Te/Ti=1 and Te/Ti>>1, show that as the normalized wave number, kperpendicular to rho i is varied, different modes (m=1, 2, 3...) become successively the most unstable mode. The calculated values of kperpendicular to rho i at which the cross-over from one mode to the next occurs are in reasonable agreement with the observed values provided that the local density gradient is taken into account.

Abstract: The present understanding (May 1983) of current drive by lower hybrid waves in Tokamak plasmas is reviewed with particular stress on the theory. First, the classical model of Fisch and its variants are discussed in light of recent experimental data. It is argued that these simple models do not account for most of the features of the results obtained. Next, effects of runaways on current generation are considered. It is shown that runaways, resulting from a residual ohmic electric field, may play an important role. Further, the mechanism of runaway-current sustainment, as proposed by LIU et al. (1982b) is re-examined. It is shown that, for a realistic range of parameters, this mechanism does not allow a significant current to be sustained. Finally, some results of a recently-developed numerical code, which include the evolving electron distribution function, ray tracing and transport, are briefly noted. It is concluded that none of the existing theories can be used to interpret satisfactorily all the experimental observations.

Abstract: Auxiliary heating experiments are continuing on both PLT and PDX. PLT has increased the available ICRF power delivered to the plasma to 3 MW for the 42 MHz system and to 1.6 MW for the 25 MHz system. Deuteron and electron heating are observed in the minority 3He (Td approximately 2.8 keV, Te approximately 2.2 keV) and H (Td approximately 2 keV, Te approximately 2.2 keV) heating regimes. In addition, ion heating has been observed in the second harmonic regime (Teff=2/3 (Eh)=3.3 keV). Recent auxiliary heating of low q(