Bulletin of the American Physical Society
70th Annual Gaseous Electronics Conference
Volume 62, Number 10
Monday–Friday, November 6–10, 2017; Pittsburgh, Pennsylvania
Session FT3: Heavy Particle Collisions |
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Chair: Larry Viehland, Chatham University Room: Oakmont Junior Ballroom |
Tuesday, November 7, 2017 1:30PM - 2:00PM |
FT3.00001: New type of asymmetries in two-center interferences observed in ion-molecular collisions Invited Speaker: Dr. Shaofeng Zhang In ion-atom collisions, the atomic version of double-slit experiments has been proposed by using two atomic centers as the double slits [1]. Recently, various two-center interference effects have been observed in different reaction channels such as ionization [2], capture [3], and the dissociative ionization [4]. These studies significantly advanced our knowledge of the double-slit interference in elastic processes. However, almost all studies so far focused on the interference effects rising from homo-diatomic molecules. Recently, we experimentally studied the interference effects in double capture collisions of $He^{2+}$ on the hetero-diatomic molecule CO where the molecule played the role of an asymmetric `double-slit', and the interference effects were examined in the molecular orientation spectra. It was found that, different from the homo-DM, the angular distributions of the hetero-DM present significant asymmetry. Such asymmetry of the interference pattern suggests certain phase of the ion collision processes has been mapped to the double-slit phase term. Therefore, atomic "double-slit" interference can be exploited to experimentally extract the phase information of ion collision processes and, furthermore, the methodology can be potentially used to manipulate the ion collision interactions. In this conference, we will report on such phenomena and the detailed analysis of the phase. References [1] T. F. Tuan and E. Gerjuoy, 1960 Phys. Rev.117756 [2] N. Stolterfoht et al. 2001 Phys. Rev. Lett. 87023201 [3] L. P. H. Schmidt et al. 2008 Phys. Rev. Lett. 101 173202 [4] S. F. Zhang et al. 2014 Phys. Rev. Lett. 112023201 [Preview Abstract] |
Tuesday, November 7, 2017 2:00PM - 2:30PM |
FT3.00002: The effect of projectile wave packet width on the fully differential ionization cross sections Invited Speaker: Ladislau Nagy In the last years a debate arose concerning the effect of the projectile coherence on the fully differential ionization cross sections in ion-atom impact. Some experimental data show, that the measured cross sections depend on the coherence width of the wave packet associated to the projectile. However, other experiments did not reveal such an effect. The goal of the present paper is to perform a systematic study on the dependence of the cross section on the coherence properties of the projectile. In the theory of atomic collisions there are two alternative ways in describing the ionization by fast ion projectiles. The impact parameter (or the semiclassical) model, assumes a classical trajectory of the projectile, and treats with quantum mechanics only the electrons. The other model, based on quantum scattering theory, includes also the projectile into the quantum system. In this model usually it is assumed that the projectile wave packet in momentum space is sufficiently well peaked about its mean momentum, and a plane wave with infinite coherence width is associated to the projectile. In the present model we have assigned to the projectile a wave packet with a Gaussian profile characterized by a finite coherence width. The position of the wave packet's centre is obtained on the basis of classical scattering. The scattering amplitude is calculated as an inverse Fourier transform of the impact parameter dependent probability amplitude, weighted by the Gaussian profile of the projectile. We study the dependence of the cross sections on the wave packet's width for the ionization of helium by fast ions (100 MeV/amu C$^{6+}$ and 3 MeV protons). The results of our calculations support the importance of the projectile coherence effects in fully differential cross section measurements. [Preview Abstract] |
Tuesday, November 7, 2017 2:30PM - 2:45PM |
FT3.00003: Student Excellence Award Finalist: Fully Differential Study of Capture with Vibrational Dissociation in p $+$ H$_{\mathrm{2}}$ Collisions Basu Lamichhane, Thusitha Arthanayaka, Juan Remolina, Ahmad Hasan, Marcelo Ciappina, Francisco Navarrete, Raul Barrachina, Ramazi Lomsadze, Michael Schulz In recent years, the important role of the projectile coherence properties has been confirmed in several studies on ion-atom scattering processes. In the present study, we used such coherence effects as a tool to sensitively study the few- body dynamics of the scattering process. To this end, a kinematically complete experiment on dissociative capture in 75 Kev p $+$ H$_{\mathrm{2}}$ collisions was performed. Fully differential cross-sections (FDCS) were extracted for a kinetic energy release of 1 eV and for two different molecular orientations as a function of scattering angle. The experiment was performed with a coherent and incoherent projectile beam. The coherent to incoherent FDCS ratios, which represents the interference term, revealed two different types of interference, single- and two-center interference. In the latter an unexpected phase shift of $\pi $ was found in the pronounced oscillations observed in the interference term. This phase shift will be discussed in context of data reported by other groups for other processes in similar collision systems. [Preview Abstract] |
Tuesday, November 7, 2017 2:45PM - 3:00PM |
FT3.00004: Controlled charge exchange between alkaline earth metals and their ions Robin Cote We theoretically investigate the prospects of realizing controlled charge exchange via magnetic Feshbach resonances in cold and ultracold collisions of atoms and ions. In particular, we focus on near-resonant charge exchange in heteroisotopic combinations of alkaline earth metals. We focus our discussion on Be + Be$^+$ and Ca + Ca$^+$. Alkaline-earth elements exhibit favorable electronic and hyperfine structure. The quantum scattering calculations are performed for a range of initial states and experimentally attainable magnetic fields in coupled-channel Feshbach projection formalism, where higher-order corrections such as the mass-polarization term are explicitely included. In addition, we predict a number of magnetic Feshbach resonances for different heteronuclear isotopic combinations of the listed and related alkaline earth elements. Our results imply that near-resonant charge-exchange could be used to control charge diffusion and mobility in cold samples. [Preview Abstract] |
Tuesday, November 7, 2017 3:00PM - 3:15PM |
FT3.00005: Charged Particle Dynamics using the Path Integral Technique A L Harris, T A Saxton, Z Temple We present a theoretical and computational technique for calculating time dependent wave functions using the path integral method. Unlike other methods, we calculate the quantum mechanical time evolution operator numerically exactly and use it to time evolve an initial state wave function. To demonstrate the success and accuracy of the method, we present numerical results for simple one-dimensional systems, such as the harmonic oscillator and a particle moving under a constant force. We show that our numerical results agree with the known analytical answers. One of the primary advantages of the path integral method is that it will work better for more massive particles. We test this idea by comparing results for both an electron and a proton, and show that the calculation is much more efficient for heavier particles. This property makes the path integral method ideal for the future study of heavy-ion atomic collisions. [Preview Abstract] |
Tuesday, November 7, 2017 3:15PM - 3:30PM |
FT3.00006: Testing A Dual-anode Miniature Electron Beam Ion Trap For The Production Of Highly Charged Ions Aung Naing, Joseph Tan In addition to the central role that highly charged ions (HCI) play in the study of radiative and collisional processes occurring in laboratory and astrophysical plasmas, recent theoretical studies indicate that certain HCI, such as Pr$^{\mathrm{9+}}$ and Nd$^{\mathrm{10+}}$, are potentially useful for interesting applications, such as the development of next-generation atomic clocks, quantum information, or the search for variation in the fine-structure constant [1]. Highly charged ions can be produced in an electron beam ion source/trap (EBIS/T) with a strong magnetic field (\textasciitilde 3 T). However, lower magnetic fields are more suitable for abundantly producing the proposed candidate ions with ionization thresholds ranging from 100 eV to 2000 eV. We are developing a room-temperature miniature EBIT (mini-EBIT) for improving the production of such ions. A dual-anode design is suited to the lower electron beam energy compatible with the production of such ions by compensating for the space charge effects. This work presents new features in the design and the construction of the mini-EBIT. Progress on the production of HCI in the mini-EBIT is presented. \underline {Reference} [1] M. Safronova, \textit{et al.}, PRL \textbf{113}, 030801 (2014) [Preview Abstract] |
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