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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.

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.

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Disruptive instabilities in PLT have been analysed by using an array of surface barrier X-ray detectors viewing the plasma cross-section along 20 chords. A wide variety of phenomena has been observed. A system of classification has been attempted, based upon: (1) the severity of the disruption, (2) the dominant precursor oscillations, and (3) the location of the onset of the disruption. Minor disruptions, in which the disruption does not appear at the location of the island of the precursor oscillation, have been observed, sometimes accompanied by seemingly independent higher-frequency oscillations of different helicity localized near the point of the disruption. Major disruptions exhibit flatter central q-profiles, slowing of the oscillations, asymmetry with respect to the centre of the discharge, and a correlation with high-Z impurity radiation.

This structure disappears with increasing electron temperature and is ascribed to weak n*2 satellites, such as a_, and to n = 3 satellites, respectively. Table I Experimental and theoretical wavelengths are listed in ACKNOWLEDGMENTS

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Eu x-ray spectra of heliumlike titanium, Tixxr, from Tokamak Fusion Test Reactor (TFTR) plasmas have been observed with a high-resolution crystal spectrometer and have been used as a diagnostic of central plasma parameters. The data allow detailed comparison with recent theoretical predictions for the Tixxr heliumlike lines and the associated satellite spectrum in the wavelength 0 range from 2.6000 to 2.6400 A. Improved values for the excitation rate coefficients of the Tixxl resonance linc, the intercombination lines, and the forbidden line, and new theoretical results on the wavelengths and transition probabilities for berylliumlike satellites due to transitions of the type 1s 2lnl'-1s2p2l"nl"' with n =2 -4 have been calculated. These data complement the theory given in an earlier paper [F. Bely-Dubau et al. , Phys. Rev. A 26, 3459 (1982)]. The experimental data are in excellent agreement with the theoretical predictions for the entire satellite spectrum. For plasmas with electron temperatures, T" in the range from 1.2 to 1.8 keV, there is also good general agreement between theory and experiment for the heliumlike lines of TixxI. The observed intensity ratios of the intercombination and forbidden lines to the resonance line are, however, larger than the predicted values by as much as an order of magnitude for electron temperatures T, & 1.2 keV. The enhancement of these lines is correlated with the abundance of lithiumlike titanium. The experimental data indicate that still other atomic processes, in addition to those considered by the theory, are important for the excitation of these lines. The experimental results are documented to stimu-0 late further analysis. The observed wavelengths agree to within an uncertainty of 0.5 mA with predictions from calculations which include relativistic and radiative corrections up to the third order in a. The central ion temperature and the central toroidal rotation velocity of TFTR plasmas with ohmic and neutral beam heating were obtained from Doppler measurements of the Ti xxr resonance line. %wavelength shifts of the apparent resonance line profile due to unresolved dielectronic satellites, which can be important corrections to Doppler-shift measurements of plasma rotation velocities, have been determined as a function of the ion and electron temperatures and the fitting limits. Results on the electron temperature and the relative charge-state density of lithiumlike and heliumlike titanium were derived from the satellite spectrum and have been interpreted with plasma modeling. These results are of interest for the determination of the ionization equilibrium and the impurity transport.