5 Matching Results

Search Results

Advanced search parameters have been applied.

ENERGY DISTRIBUTION OF TWO-ELECTRON IONIZATION OF HELIUM IN AN INTENSE LASER FIELD.

Description: It is well known that a neutral atom interacting with a strong laser field will ionize at sufficiently high intensity even for photon energies well below the ionization threshold. When the required number of photons becomes very large, this process is best described by the suppression of the Coulomb barrier by the laser's oscillating electric field, allowing the electron to tunnel into the continuum. As the laser intensity is increased, more tightly bound electrons may be successively liberated by this mechanism. Such a sequential multiple ionization, long accepted as a reasonable approach to the formidable problem of a multielectron atom interacting nonperturbatively with an intense electromagnetic field, provides fair estimates of the various charge state appearance intensities while the tunneling rates are in excellent agreement with single ionization yields. However, more accurate measurements revealed systematic and very large deviations from the tunneling rates: near appearance intensity under standard experimental conditions, the observed double ion yield is several orders of magnitude larger than predicted by the sequential rate. It soon became clear that electrons could not be considered as independent and that electron-electron correlation had to be taken into account. Dynamic correlations have been considered in several theories. First qualitatively in the shakeoff model; then empirically through the e-2e cross-section in the quantum/classical three-step model (tunnel ionization, acceleration by the oscillating electric field and e-2e recollision with the ion); recently through the so-called intense field many-body-S-matrix theory and a purely empirical model of collective tunnel ionization. The validity of these ideas has been examined using numerical models. The measurement of total ion yields over a dynamic range exceeding ten orders of magnitude, a major breakthrough made possible by the availability of high-repetition rate lasers at the beginning of the 90's, was for a long time the only quantitative data to confront ...
Date: September 24, 2000
Creator: LAFON,R.; CHALOUPKA,J.L.; SHEEHY,B.; DIMAURO,L.F.; PAUL,P.M.; AGOSTINI,P. et al.
Partner: UNT Libraries Government Documents Department

ENERGY DISTRIBUTION OF TWO-ELECTRON IONIZATION OF HELIUM IN AN INTENSE LASER FIELD.

Description: It is well known that a neutral atom interacting with a strong laser field will ionize at sufficiently high intensity even for photon energies well below the ionization threshold. When the required number of photons becomes very large, this process is best described by the suppression of the Coulomb barrier by the laser's oscillating electric field, allowing the electron to tunnel into the continuum. As the laser intensity is increased, more tightly bound electrons may be successively liberated by this mechanism. Such a sequential multiple ionization, long accepted as a reasonable approach to the formidable problem of a multielectron atom interacting nonperturbatively with an intense electromagnetic field, provides fair estimates of the various charge state appearance intensities while the tunneling rates are in excellent agreement with single ionization yields. However, more accurate measurements revealed systematic and very large deviations from the tunneling rates: near appearance intensity under standard experimental conditions, the observed double ion yield is several orders of magnitude larger than predicted by the sequential rate. It soon became clear that electrons could not be considered as independent and that electron-electron correlation had to be taken into account. Dynamic correlations have been considered in several theories. First qualitatively in the shakeoff model; then empirically through the e-2e cross-section in the quantum/classical three-step model (tunnel ionization, acceleration by the oscillating electric field and e-2e recollision with the ion); recently through the so-called intense field many-body-S-matrix theory and a purely empirical model of collective tunnel ionization. The validity of these ideas has been examined using numerical models. The measurement of total ion yields over a dynamic range exceeding ten orders of magnitude, a major breakthrough made possible by the availability of high-repetition rate lasers at the beginning of the 90's, was for a long time the only quantitative data to confront ...
Date: September 24, 2000
Creator: LAFON,R.; CHALOUPKA,J.L.; SHEEHY,B.; DIMAURO,L.F.; PAUL,P.M.; AGOSTINI,P. et al.
Partner: UNT Libraries Government Documents Department

End stoppering in mirror machines

Description: Like toroidal confinement, confinement by a potential barrier offers the possibility of unlimited Q if the barrier is good enough. For a barrier height PHI, approximately tau approximately equal to tau/sub collision/ exp PHI/T/sub i/. These notes review previous ideas about how to establish a potential barrier at the ends of a mirror machine and we also discuss a different possibility using mirror confinement itself to establish a barrier utilizing the positive ambipolar potential characteristic of mirror machines. One example consists of three mirrors in tandem, the two at the ends having a much smaller volume. Then mirror confinement in the end cells would be used to establish ambipolar barriers that stopper up the ends of the central, large mirror cell. An example is discussed in which, by approximate calculation, it appears that ignition might occur in a center cell 10 to 20 meters long and the overall Q is 5 or more, including the power required to sustain the end cells by neutral injection.
Date: August 24, 1976
Creator: Fowler, T. K.
Partner: UNT Libraries Government Documents Department

Radiation of Electron in the Field of Plane Light Wave

Description: Results of integration of a Lorentz equation for a relativistic electron moving in the field of running, plane, linear polarized electromagnetic wave are presented in the paper. It is shown that electron velocities in the field of the wave are almost periodic functions of time. For calculations of angular spectrum of electron radiation intensity expansion of the electromagnetic field in a wave zone into generalized Fourier series was used. Expressions for the radiation intensity spectrum are presented in the paper. Derived results are illustrated for electron and laser beam parameters of NSC KIPT X-ray generator NESTOR. It is shown that for low intensity of the interacting electromagnetic wave the results of energy and angular spectrum calculations in the frame of classical electrodynamics completely coincide with calculation results produced using quantum electrodynamics. Simultaneously, derived expressions give possibilities to investigate dependence of energy and angular Compton radiation spectrum on phase of interaction and the interacting wave intensity.
Date: February 24, 2006
Creator: Zelinsky, A.; Drebot, I.V.; Grigorev, Yu.N.; Zvonareva, O.D.; /Kharkov, KIPT; Tatchyn, R. et al.
Partner: UNT Libraries Government Documents Department

NSTX Protection And Interlock Systems For Coil And Powers Supply Systems

Description: NSTX at Princeton Plasma Physics Laboratory (PPPL) requires sophisticated plasma positioning control system for stable plasma operation. TF magnetic coils and PF magnetic coils provide electromagnetic fields to position and shape the plasma vertically and horizontally respectively. NSTX utilizes twenty six coil power supplies to establish and initiate electromagnetic fields through the coil system for plasma control. A power protection and interlock system is utilized to detect power system faults and protect the TF coils and PF coils against excessive electromechanical forces, overheating, and over current. Upon detecting any fault condition the power system is restricted, and it is either prevented from initializing or suppressed to de-energize coil power during pulsing. Power fault status is immediately reported to the computer system. This paper describes the design and operation of NSTX's protection and interlocking system and possible future expansion.
Date: September 24, 2009
Creator: X. Zhao, S. Ramakrishnan, J. Lawson, C.Neumeyer, R. Marsala, H. Schneider, Engineering Operations
Partner: UNT Libraries Government Documents Department