No abstract

The differential cross sections for the electron-impact excitation of the lowest triplet states of molecular hydrogen (b 3Σu+, a 3Σg+) have been calculated from threshold to 85 eV impact energy using the Ochkur–Rudge theory. For the X 1Σg+ → b 3Σu+ transition, the relative differential cross sections were measured with a low-energy, high-resolution electron-impact spectrometer from 10° to 80° scattering angle and impact energies of 25, 35, 40, 50, and 60 eV. Theory and experiment are in good agreement for the shape of the differential cross section for energies of 35 eV and above. However, at 25 eV, the theory continues to predict a rather well-developed maximum in the cross section at around 40° while the experimental cross sections are more isotropic. An appreciable contribution to the inelastic scattering in the energy loss region from 11 to 14 eV due to excitation to the a 3Σg+ and/or c 3Πu states is definitely established from the observed angular distributions. A quantitative evaluation of the individual angular behavior of the excitations in this region, however, would require a resolution higher than the presently available one of 0.030 eV.

Abstmct-A laser cell with 2 1 of excitation volume was used to study the electron-beam pumped KIF laser system at excitation rates of 1.8-7.0 MW/cm3. The system was optimized as an oscillator for various mixtures of Ar, Kr, and F2 at total pressures of 1000 and 2500 torr.The resulting optimum conditions gave an intrinsic efficiency (laser energy out/electron-beam energy deposited) of 12 percent for the 1000 torr total pressure mixture with an output energy of 11 J/1. An efficiency of 10 percent with an output of 40 J/1 was obtained for the 2500 torr mixture. The system was then used as an amplifier to measure the extracted power as a function of input power for the two mixtures. The small-signal gain go, the nonsaturable absorption a, and the saturation intensity I, were determined for the two mixtures.Analysis of the data gave go = 16-18 percent/cm, a! = 0.75-1.25 percent/cm, and Z , = 2 MW/cm2 for the 1000 torr mixture andgo = 17-19 percent/cm, a! = 1.0-1.5 percent/cm, and Z , = 9 MW/cm2 for the 2500 torr mix.

DIII-D physics research addresses critical challenges for the operation of ITER and the next generation of fusion energy devices. This is done through a focus on innovations to provide solutions for high performance long pulse operation, coupled with fundamental plasma physics understanding and model validation, to drive scenario development by integrating high performance core and boundary plasmas. Substantial increases in off-axis current drive efficiency from an innovative top launch system for EC power, and in pressure broadening for Alfven eigenmode control from a co-/counter-I p steerable off-axis neutral beam, all improve the prospects for optimization of future long pulse/steady state high performance tokamak operation. Fundamental studies into the modes that drive the evolution of the pedestal pressure profile and electron vs ion heat flux validate predictive models of pedestal recovery after ELMs. Understanding the physics mechanisms of ELM control and density pumpout by 3D magnetic perturbation fields leads to confident predictions for ITER and future devices. Validated modeling of high-Z shattered pellet injection for disruption mitigation, runaway electron dissipation, and techniques for disruption prediction and avoidance including machine learning, give confidence in handling disruptivity for future devices. For the non-nuclear phase of ITER, two actuators are identified to lower the L–H threshold power in hydrogen plasmas. With this physics understanding and suite of capabilities, a high poloidal beta optimized-core scenario with an internal transport barrier that projects nearly to Q = 10 in ITER at ∼8 MA was coupled to a detached divertor, and a near super H-mode optimized-pedestal scenario with co-I p beam injection was coupled to a radiative divertor. The hybrid core scenario was achieved directly, without the need for anomalous current diffusion, using off-axis current drive actuators. Also, a controller to assess proximity to stability limits and regulate β N in the ITER baseline scenario, based on plasma response to probing 3D fields, was demonstrated. Finally, innovative tokamak operation using a negative triangularity shape showed many attractive features for future pilot plant operation.

Experimental differential scattering cross sections for excitation of helium by electron impact from its ground state to its 2 S state are presented at four incident electron energies in the range 26-55. 5 eV for scattering angles between 10' and 70' and at 81.6 eV for scattering angles between 10' and 80 . These differential cross sections are normalized by using previously determined 2 P cross sections and measured 2 S/2 P cross-section ratios. These experimental cross sections and cross-section ratios are compared with results predicted by the Born approximation, the polarized Born approximation, and several other first-order approximations in which direct excitation is calculated in the Born approximation and exchange scattering in various Ochkur-like approximations.Calculations based on these approximations are also compared to the data of other experimenters at energies up to 600 eV. The effect on the small-angle scattering of several nonadiabatic dipole-polarization potentials is examined. For the 34 -81.6-eV energy range, it is shown that the inclusion of polarization is necessary for accurate predictions of the angle dependence of the 2 S cross sections at small angles. Cross sections resulting from the use of analytic self-consistent-field wave functions for both the ground and excited states are presented. They agree well with those obtained from more accurate correlated wave functions.