The experimental characteristics of divertor detachment in the JET tokamak with the Mark I pumped divertor are presented for Ohmic, L-mode and ELMy H-mode experiments with the main emphasis on discharges with deuterium fuelling only. The range over which divertor detachment is observed for the various regimes as well as the influence of divertor configuration, direction of the toroidal field, divertor target material and active pumping on detachment will be described. The observed detachment characteristics such as the existence of a considerable electron pressure drop along the field lines in the scrape-off layer, and the compatibility of the decrease in plasma flux to the divertor plate with the observed increase of neutral pressure and the D α emission from the divertor region will be examined in the light of existing results from analytical and numerical models for plasma detachment. Finally, a method to evaluate the degree and window of detachment is proposed and all the observations of the JET Mark I divertor experiments summarised in the light of this new quantitative definition of divertor detachment.

The laser generation d ultrasound in solids is reviewed with particular emphasis on the application of this unique ultrasonic source. Three regimes for the generation of ultrasound in solids using lasers in the visible near infrared wavelength region exist: thermoelastic, plasma and constrained surface source regimes. The mechanism for ultrasonic generation in each of these regimes is given. Recent experimental investigations into laser-generated unrasound are also described, including a description d a different mechanism for the generation of ultrasound in solids using a COn laser. Finally, the many applications of lasergenerated ultrasound are reviewed. These applications range from nondestructive testing to the determination of candle flame parameters. Possible future applications are also outlined.

Analysis of the edge plasma fluctuation in several confinement devices reveals the self-similar character of the fluctuations through the presence of long-range time correlations. These results show that the tail of the autocorrelation function decays as a power law for time lags longer than the decorrelation time and as long as times on the order of the particle diffusion time. The algebraic decay of the longrange time correlations is consistent with plasma transport characterized by self-organized criticality.

Frequency spectra of fluctuations of the ion saturation current, floating potential, and turbulent transport measured in the plasma edge of different fusion devices (tokamaks and stellarators) have been compared. All of the spectra show the same behavior over the whole frequency range investigated, which supports universality of plasma turbulence or turbulent transport. The results obtained are an indication of edge-plasma turbulence evolving into a critical state, independent of the size and plasma characteristics of the device. [S0031-9007(99)09024-9] PACS numbers: 52.55. 52.25.Gj, 52.40.Hf Many systems display universal characteristics whose experimental determination has led to insights furthering the understanding of their dynamics. An example of such a system is fluid turbulence [1]. In 1941, Kolmogorov showed that two-dimensional systems display features in spatial scales ͑k͒ leading to the well known k 25͞3 and k 23 regimes in 2D turbulence. Another broader group of dynamical systems are those thought to be described by the concept of self-organized criticality (SOC). These nonequilibrium systems often evolve naturally towards a state that is nearly critical [2,3]. The nature of this self-organized criticality may account for scale invariant phenomena in nature such as 1͞f noise [4] and fractal (self-similar) structures [5]. In SOC systems, the Fourier spectra are expected to be nearly 1͞f for a given range of frequencies. This behavior arises from the existence and random superposition of avalanches. It has been argued theoretically that transport processes in magnetically confined plasmas have some of the characteristics of self-organized critical systems [6][7][8]. Some such processes are the scaling of transport coefficients, the response to plasma perturbations [9], and the self-similar character of the electrostatic fluctuations at the plasma edge [10].The self-similar nature of fluctuations is an indication of the existence of long-range time correlations. These are characterized by algebraic "tails" (i.e., decay at large lags) of the autocorrelation function. A comparative analysis of edge fluctuations among different magnetic confinement devices gives a Hurst exponent varying between H 0.64 and 0.74 [10]. The narrow range of variation of H is an indication of the similarity of the low frequency range of the spectrum among these devices. In this Letter, we take a step further in this research and explore the properties of the complete frequency spectra of edge plasma fluctuations and turbulent transport in different tokamaks and stellarators.Even in complex systems that exhibit scale invariant fluctuations, one expects the distribution of avalanches to show finite size scaling. In a sand pile, the size of the pile, L, and the probability of dropping sand are the basic parameters of the running sand pile dynamics. Consequently, the spectral distribution, P, will depend on frequency, v, and the size of the pile, L. Techniques of finite-size scaling have been applied to interpret the data. The si...

The rescaled range analysis techniques are used to investigate long-range dependence in plasma edge fluctuations [Mandelbrot and Wallis, Water Resources Res. 4, 909 (1969)]. This technology has been applied to data from several confinement devices such as tokamaks, stellarators, and reversed-field pinch. The results reveal the self-similar character of the electrostatic fluctuations at the plasma edge with self-similarity parameters ranging from 0.62 to 0.72. These results show that the tail of the autocorrelation function decays as a power law for time lags longer than the decorrelation time and as long as times of the order of the confinement time. In cold plasma devices (Te<1 eV at the core), there is no evidence of algebraic tails in the autocorrelation function. Some other characteristic features of the autocorrelation function and power spectrum have been investigated. All of these features are consistent with plasma transport as characterized by self-organized criticality.