levels which might have a significant role in the light shift of the 22p level due to the 1.06-/im laser field are 6s, 7s, Ad, and 5d. These are far from being resonantly coupled to the 22p level, at least 1700 cm" 1 away. Their relative positions are such that their combined effects are partially cancelled* A rough evaluation showed that under these conditions the 5d level, which is expected to be responsible for the largest effect, contributes to the shift of the 22p level an amount of approximately 3xl0" 3 MHz/ MW-cm' 2 . This is at least 4 orders of magnitude less than the measured shift, and is thus completely negligible, With respect to the shift Lv g of the ground state, since it cannot be measured alone the best procedure is to calculate it as carefully and precisely possible. A calculation based on Fig. 1 has been carried out. 6 The result is &v g = -26.3 MHz/MW-cm" 2 . The dashed line in Fig. 3 corresponds to the sum of the two calculated shifts Ai/ e + Ay g , whereas the straight line corresponds to a least-squares fit on the measured shifts. Agreement between experimental and theoretical results is satisfactory.To conclude, this experiment provides clear evidence for the shift of a Rydberg level, due to an intense and strongly nonresonant em field. It is of interest to note that in a pure quantum treat-PACS numbers: 52.55.Gb, 52.35.Py On the PDX tokamak, large-amplitude magnetohydrodynamic (MHD) fluctuations have been observed during plasma heating by injection of high-ment, radiative corrections can be interpreted as the sum of spontaneous and stimulated radiative corrections. The net effect of spontaneous radiative corrections due to vacuum fluctuations is well known to be responsible for the Lamb shift. In the same spirit, the light shifts which have been studied in our experiment can perhaps be viewed as resulting from the stimulated radiative corrections induced by an intense and nonresonant em field.We thank Professor CI. Cohen-Tannoudji for many helpful discussions concerning both the experiment and its interpretation. We are indebted to Dr. M. Aymar and Dr. M. Crance for their calculation of the shift of the ground state.Strong magnetohydrodynamic activity has been observed in PDX neutral-be am-heated discharges. It occurs for fi T q^ 0.045 and is associated with a significant loss of fast ions and a drop in neutron emission. As much as 20%~-40% of the beam heating power may be lost. The instability occurs in repetitive bursts of oscillations of ^ 1 msec duration at 1-6-msec intervals. The magnetohydrodynamic activity has been dubbed the "fishbone instability" from its characteristic signature on the Mirnov coils.

A detailed description of the time behaviour of a hydrogen discharge in the ST-Tokamak is based on measured radial electron temperature and density profiles at 12 different times, together with measurements of the Ohmic-heating current and voltage, the temporal, spatial, and spectral distributions of hydrogen light, the ion temperatures, and impurity concentrations. Early in the discharge the electron temperature profiles show evidence of a skin effect that develops on a time-scale of several milliseconds into a peaked profile of about 2.2 keV maximum. Thereafter the peak temperature stops growing and develops into a flat plateau, the width of which appears to be determined by the Kruskal-Shafranov limit. The average particle confinement time scales with , and reaches a maximum of 13-14 ms. The power balance is dominated by electron loss and re-cycling, rather than ion loss or radiation. The recycling process at the aperture limiter appears to involve sufficiently energetic neutral atoms to provide a fairly flat radial source function for particles, and hence to influence directly the development of the radial distribution of power input and energy balance.

A study is made of the spectral distribution of the soft X-ray emission produced by the thermal part of the electron velocity distribution in the ST Tokamak. The slopes of the spectra are in good agreement with the prediction from laser measurement of electron temperature if radial profile effects are taken into account. The absolute intensity is a factor 5 to 100 larger than is expected for hydrogen bremsstrahlung. This enhancement can be quantitatively accounted for by recombination radiation from oxygen and heavy-metal impurities. The enhancement factor ζ was measured at different radii, in order to study the impurity distribution in the tokamak. These, as well as other experiments, in which high-Z gases (Xe, Kr, A) were pulsed into the discharge, indicated that, within the measuring accuracy, Zeff does not vary substantially with radius.

Toroidal plasma rotation in the Princeton Large Torus, PLT, has been measured for various plasma and neutral beam injection conditions. Measurements of the plasma rotational velocities were made from Doppler shifts of appropriate spectral lines and include data from both hydrogen and deuterium beams and co-and counter-injection at several electron densities. Without injection, a small but consistent toroidal rotation exists in a direction opposite to the plasma current (counter-direction) in the plasma center but parallel to the current (co-direction) in the plasma periphery. Using these measured velocities and the plasma density and temperature gradients, radial electron fields can be determined from theory, giving E r » 40 V/cm near tne plasma center and E r » 10 V/cm near the plasma edge. Insertion of a local, 2.5 percent magnetic well produced no observable effect on the beam driven rotation. Modeling of the time evolution and radial distribution of the rotation allows one to deduce an effective viscosi..; of the order of (1-5) x 10 4 cm 2 /sec.

Fusion neutron emission of 1.5 × 1014 neutrons · s−1 and 2 × 1013 neutrons/pulse has been observed for PLT deuterium discharges with up to 2.5 MW of deuterium neutral-beam injection. The neutron time evolution and magnitude are consistent with theoretical calculations of the fusion reactions caused by energetic injected ions which are confined and slow down classically. The factor-of-two accuracy in the absolute neutron calibration is the major uncertainty in the comparison with theory. Neutron sawtooth oscillations (⪅ 3%) are observed which can also be explained classically.

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This work supported by the U.S. Department of Erfsrgy Contract No. DE-AC02-76-CHO-3073. Reproduction, trans-? Fatten, publfcatlon, use and disposal, ]n Mhole or In z part, by or for the United States Government Is permitted.