Bulletin of the American Physical Society
APS April Meeting 2017
Volume 62, Number 1
Saturday–Tuesday, January 28–31, 2017; Washington, DC
Session J3: Beams |
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Sponsoring Units: DPB Room: Maryland C |
Sunday, January 29, 2017 10:45AM - 10:57AM |
J3.00001: Describing Polarization States of Photon Vortices Andrei Afanasev, Dartagnan Howell Electromagnetic waves with large values of Orbital Angular Momentum (OAM) along their direction of propagation were demonstrated in a broad range wavelengths, from radio to optical. Photons with large OAM, or "twisted photons" can be generated with higher energies in helical undulators or via Compton backscattering. Description of the polarization states of such photons will be a subject of this talk. In particular, we consider representing twisted-photon polarization with Poincare sphere, Majorana sphere, and Dalitz plots, and discuss advantages for each approach. [Preview Abstract] |
Sunday, January 29, 2017 10:57AM - 11:09AM |
J3.00002: Interaction of Photon Vortex Beams with Atomic Matter Maria Solyanik, Andrei Afanasev, Carl E. Carlson In our work we consider helical Bessel beams' (BB's) propagation and interaction with isotropic matter. Dynamical properties of the beams with non-zero orbital angular momentum (OAM), which are determined by spatial degrees of freedom and polarization, modify the fundamental processes in light-matter interactions. Circular dichroism of BBs propagating in hydrogen gas was considered within the frame of studying the vortex beams' attenuation due to photoabsorption in hydrogen gas. In this case, the phenomenon is due to the topology of the wave front, contrary to the zero OAM case, when the change in polarization state is due to matter inhomogeneity. The effect of circular dichroism has been predicted by calculating the beam ellipticity evolution when traversing an isotropic target. According to our results, the BBs' transverse ellipticity profile has a structure of concentric circular maxima which correspond to minima of the intensity. The characteristic polarization singularity arises on the beam axis as the result of interaction with matter. It is shown, that even for the case of the paraxial approximation the effect of circular dichroism takes place. These signatures can be used for theoretical and experimental analysis of the interactions of optical vortices with atomic matter. [Preview Abstract] |
Sunday, January 29, 2017 11:09AM - 11:21AM |
J3.00003: Compact Photon Source for Polarized Target Experiments Gabriel Niculescu, Bogdan Wojtsekhowski High energy photon beams are one of the tools of choice in nuclear and particle physics. However, most of the current techniques used for producing such beams have substantial drawbacks that limit their usefulness (low intensity, large beam size, mixed electron-photon beams). In this presentation we will outline the design of a Compact Photon Source (CPS) capable of providing narrow (\textasciitilde 1mm) untagged photon beams of an intensity suitable for carrying out polarized target experiments. Compared with existing technology the CPS will provide a substantial (10-100) increase in the figure-of-merit. While optimized for a Wide Angle Compton Scattering experiment proposed at JLab, the source described here can be used in a variety of photon-induced physics experiments as well as for industrial applications. [Preview Abstract] |
Sunday, January 29, 2017 11:21AM - 11:33AM |
J3.00004: Synchrotron Light Sources in Developing Countries Herman Winick, Piero Pianetta The more than 50 light sources now in operation around the world include facilities in Brazil, Korea, and Taiwan which started their programs in the 1980's when they were developing countries. They came on line in the 1990's and have since trained hundreds of graduate students locally, without sending them abroad and losing many of them. They have also attracted dozens of mid-career diaspora scientists to return. Their growing user communities have demanded more advanced facilities, leading to the funding of higher performance new light sources that are now coming into operation. Light sources in the developing world now include the following: \textbf{SESAME} in the Middle East which is scheduled to start research in 2017 (\underline {www.sesame.org}); \textbf{The African Light Source}, in the planning stage (\underline {www.africanlightsource.org}); and \textbf{The Mexican Light Source}, in the planning stage (\underline {http://www.aps.org/units/fip/newsletters/201509/mexico.cfm}). See: http://wpj.sagepub.com/content/32/4/92.full.pdf$+$html; http://www.lightsources.org/press-release/2015/11/20/grenoble-resolutions-mark-historical-step-towards-african-light-source. [Preview Abstract] |
Sunday, January 29, 2017 11:33AM - 11:45AM |
J3.00005: THz generation from elliptically-focused two-color laser pulses at 1 kHz Yungjun Yoo, Donghoon Kuk, Zheqiang Zhong, Ki-Yong Kim We have generated high-power terahertz (THz) radiation by elliptical focusing of two-color femtosecond laser pulses in air at a 1-kHz repetition rate. Elliptical focusing produces a 2-dimensional plasma sheet, emitting two diverging THz radiation lobes in the far field. Such radiation is collimated and refocused by a combination of cylindrical and off-axis parabolic mirrors. Here the distances between the 2-D plasma sheet, cylindrical mirror, and off-axis parabolic mirror are carefully adjusted to minimize the THz spot size at the refocus. The refocused THz field strength is estimated by measuring the THz energy, beam spot size, and waveform. Here an uncooled microbolometer camera with real-time lock-in imaging is used to monitor and measure the focused THz beam profiles with a high signal-to-noise ratio at a broad range of THz (1\textasciitilde 40 THz) frequencies. High-pressure gas (N2 and Ar) jets puffed in air are also tested as laser targets to boost the output THz energy even further. [Preview Abstract] |
Sunday, January 29, 2017 11:45AM - 11:57AM |
J3.00006: Measurement of Frequency, Temperature, RF Field Dependence of Surface Resistance of Superconductors Using a Half Wave Cavity HyeKyoung Park, Jean Delayen A theory of surface resistance of superconductor was rigorously formulated by Bardeen, Cooper, Schrieffer more than 50 years ago. Since then the accelerator community has been used the theory as a guideline to improve the surface resistance of the superconducting cavity. It has been observed that the surface resistance is dependent on frequency, temperature and rf field strength, and surface preparation. To verify these dependences, a well-controlled study is required. Although many different types of cavities have been tested, the typical superconducting cavities are built for specific frequencies of their application. They do not provide data other than at its own frequency. A superconducting half wave cavity is a cavity that enables us to collect the surface resistance data across frequencies of interest for particle accelerators and evaluate preparation techniques. This paper will present the design of the half wave cavity, its electromagnetic mode characteristics and experimental results. [Preview Abstract] |
Sunday, January 29, 2017 11:57AM - 12:09PM |
J3.00007: MeV electron acceleration at 1 kHz with \textless 10 mJ laser pulses Fatholah Salehi, Andy Goers, George Hine, Linus Feder, Donghoon Kuk, Bo Miao, Daniel Woodbury, Ki-Yong Kim, Howard Milchberg We demonstrate laser driven acceleration of electrons to MeV-scale energies at 1kHz repetition rate using \textless 10mJ pulses focused on near-critical density He and H$_{\mathrm{2}}$ gas jets. Using the H$_{\mathrm{2}}$ gas jet, electron acceleration to \textasciitilde 0.5MeV in \textasciitilde 10fC bunches was observed with laser pulse energy as low as 1.3mJ. Increasing the pulse energy to 10mJ, we measure \textasciitilde 1pC charge bunches with \textgreater 1MeV energy for both He and H$_{\mathrm{2\thinspace }}$gas jets. Such a high repetition rate, high flux ultrafast source has immediate application to time resolved probing of matter for scientific, medical, or security applications, either using the electrons directly or using a high-Z foil converter to generate ultrafast .$\gamma $-rays. [Preview Abstract] |
Sunday, January 29, 2017 12:09PM - 12:21PM |
J3.00008: The status of MICE Ao Liu Muon beams of low emittance provide the basis for the intense, well characterised neutrino beams of the Neutrino Factory and for lepton-antilepton collisions at energies of up to several TeV at the Muon Collider. The international Muon Ionization Cooling Experiment (MICE) will demonstrate ionization cooling, the technique by which it is proposed to reduce the phase-space volume occupied by the muon beam. MICE is being constructed in a series of Steps. The configuration currently in operation at the Rutherford Appleton Laboratory is optimised for the study the properties of liquid hydrogen and lithium hydride that affect cooling. The results that have recently been submitted for publication will be described along with preliminary results from the MICE study of the effect of liquid hydrogen and lithium hydride on the muon beam. The plans for data taking in the present configuration will be described together with a summary of the status of preparation of the final experimental configuration by which MICE will demonstrate the principle of ionization cooling. [Preview Abstract] |
Sunday, January 29, 2017 12:21PM - 12:33PM |
J3.00009: Detailed Modeling of Physical Processes in Electron Sources for Accelerator Applications Oksana Chubenko, Andrei Afanasev At present, electron sources are essential in a wide range of applications -- from common technical use to exploring the nature of matter. Depending on the application requirements, different methods and materials are used to generate electrons. State-of-the-art accelerator applications set a number of often-conflicting requirements for electron sources (e.g., quantum efficiency vs. polarization, current density vs. lifetime, etc). Development of advanced electron sources includes modeling and design of cathodes, material growth, fabrication of cathodes, and cathode testing. The detailed simulation and modeling of physical processes is required in order to shed light on the exact mechanisms of electron emission and to develop new-generation electron sources with optimized efficiency. The purpose of the present work is to study physical processes in advanced electron sources and develop scientific tools, which could be used to predict electron emission from novel nano-structured materials. In particular, the area of interest includes bulk/superlattice gallium arsenide (bulk/SL GaAs) photo-emitters and nitrogen-incorporated ultrananocrystalline diamond ((N)UNCD) photo/field-emitters. [Preview Abstract] |
Sunday, January 29, 2017 12:33PM - 12:45PM |
J3.00010: IED Countermeasures James Ziegler After the Iraq war started in 2003, within 15 months over 60{\%} of the US casualties were being caused by a weapon that had never been significant in previous conflicts: the Improvised Explosive Device (\textbf{\textit{IED}}). These are explosive mines that are mostly concealed at night near roads, and then detonated the next day when combatant vehicles are driven by. This talk will discuss the history of IEDs, and then concentrate on the use of IEDs in Iraq. The \textbf{\textit{political decisions}} that may have led to the high fatality rate in Iraq will be outlined. Of note, contrasting political decisions in Afghanistan led to IED's causing fewer than 20{\%} of the casualties there, although the number of IED's exceeded that in Iraq. Because of the terrible consequences in Iraq, with no effective available remedy, \textbf{\textit{IED Countermeasures}} was proposed as ideal for student engineering research projects. Over five years, student work to develop a technology for ``\textbf{\textit{Remote IED Deactivation without Detonation}}'' will be outlined (they were very successful !). They used high power beams of RF, electrons, protons and neutrons to attempt deactivation at a 100' distance. The final IED Neutralizer was very successfully field tested. \textbf{\textit{(This talk will contain graphic videos, and is not for the squeamish.)}} [Preview Abstract] |
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