A. W. Ali

REVA University

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R. Fedosejevs

University of Alberta

Mianzhen Mo

SLAC National Accelerator Laboratory

S. Fourmaux

Institut National de la Recherche Scientifique

J. C. Kieffer

Institut National de la Recherche Scientifique

Philippe Lassonde

Institut National de la Recherche Scientifique

S. P. Slinker

United States Naval Research Laboratory

Ying Y. Tsui

University of Alberta

J. A. Chakera

Raja Ramanna Centre for Advanced Technology

P. E. Masson-Laborde

CEA Paris-Saclay

W. Rozmus

University of Alberta

Cooperative Institutions

United States Naval Research Laboratory

Naval Research Laboratory Plasma Physics Division

University of Alberta

University of Maryland, College Park

Lawrence Livermore National Laboratory

Princeton University

K Lab (United States)

University of California, Los Angeles

Institut National de la Recherche Scientifique

University of British Columbia

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A continuous kilohertz Cu Kα source produced by submillijoule femtosecond laser pulses for phase contrast imaging

Applied Physics Letters (2008)

J. A. Chakera A. W. Ali Ying Y. Tsui R. Fedosejevs

We report a continuously operated Cu Kα x-ray source produced by a commercial kilohertz submillijoule femtosecond laser system. The source has an x-ray conversion of ∼4×10−5 into Kα line emission at 8.05 keV. The microplasma x-ray source has a size of 8 μm (full width at half maximum) produced by focusing 260 μJ laser pulses on a moving Cu-wire target. An average photon flux of ∼1.1×109 photons/sr/s is obtained using the above laser pulses. The source has been used to record phase contrast images of test samples. This compact x-ray source can serve as a low cost operating system for phase contrast imaging in clinical applications.

Microplasma

10.1063/1.3046727

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Citations (24)

Dependence of the Electron Energy Distribution on the Vibrational Temperature in the Electrically Excited N2

H. C. Chen A. W. Ali A. V. Phelps

Abstract : The effects of the vibrational excitation and deexcitation of nitrogen molecules in an electrical discharge on the electron energy distributions and transport coefficients are investigated theoretically. The electrons collide with vibrationally excited molecules either gain or lose energy which results in the redistribution of the electron energy. The distribution function is calculated numerically by solving the Boltzmann equation, using a complete set of elastic momentum transfer and inelastic cross sections. The presence of vibrationally excited molecules which collide and exchange energy with the electrons has a strong effect on the electron energy distribution function. This effect is demonstrated for various vibrational temperatures. The energy distributions are calculated at the ratio of electric field to gas density E/N which ranges from 10(-16) to 20 x 10(-16) V cm2 . Generally, as the vibrational temperature increases, the electrons become richer in the high-energy tail of the distribution function.

Boltzmann distribution

10.21236/ada476586

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Towards shorter wavelength lasers and breaking the 1000 angstrom barrier. 2: Bound continuum emission

nrl (1974)

A. W. Ali

Angstrom

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NRL Compact Accelerator Theory Studies

nrl (1990)

R. F. Hubbard A. W. Ali Glenn Joyce J. Krall F. Mako

Abstract : NRL compact accelerator theory studies in support of the Spiral Line Induction Accelerator (SLIA) and the Recirculating Linear Accelerator (RLA) are summarized in a series of short papers. The first of these papers describes the ELBA three-dimensional beam simulation code, a particle code which has been used to model beam stability and transport in both accelerators. The second paper presents and analytical model for the dangerous three-wave electromagnetic instability and defines parameter regimes for the SLIA where the instability can be completely stabilized. ELBA simulations of the SLIA in the various stability regimes, described by the analytical mode, are described in the next paper. The fourth paper includes additional ELBA simulations of beam transport in the SLIA, demonstrating that high eccentricity equilibria can lead to serious emittance growth. The effects of axisymmetric ion channel motion on beam transport in the RLA are discussed in the next paper. The sixth paper describes ELBA simulations of erosion and off-axis drifts in both straight and curved sections of the RLA. The final paper discusses the various atomic and surface plasma processes which may occur in compact accelerators. Keywords: Compact accelerators, Charged particle beams, Relativistic electron beams, Stellarator fields, Ion focused regime, Emittance growth.

Beam emittance

Particle beam

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Spectroscopic measurements of the laser-HANE plasma. Memorandum report

E. A. McLean J. A. Stamper Hans R. Griem A. W. Ali B. H. Ripin

To simulate HANE phenomena at various altitudes, a pulsed (5 nsec) Nd-laser is focused onto Al or C foil targets surrounded by an ambient gas (N/sub 2/, H/sub 2/) at pressures between 15 m Torr and 5 Torr. Temperatures and densities are derived from side-on, time-resolved and time-integrated measurements of absolute spectral line and continuum intensities emitted from the photoionized region ahead of the blast-wave front, and also in the region behind the blast front.

Torr

Blast wave

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Quasimonoenergetic electron beams from laser wakefield acceleration in pure nitrogen

Applied Physics Letters (2012)

Mianzhen Mo A. W. Ali S. Fourmaux Philippe Lassonde J. C. Kieffer

Quasimonoenergetic electron beams with maximum energy >0.5 GeV and 2 mrad divergence have been generated in pure nitrogen gas via wakefield acceleration with 80 TW, 30 fs laser pulses. Long low energy tail features were typically observed due to continuous ionization injection. The measured peak electron energy decreased with the plasma density, agreeing with the predicted scaling for electrons. The experiments showed a threshold electron density of 3×1018cm-3 for self-trapping. Our experiments suggest that pure Nitrogen is a potential candidate gas to achieve GeV monoenergetic electrons using the ionization induced injection scheme for laser wakefield acceleration.

Plasma acceleration

10.1063/1.3685464

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Citations (42)

Parametric investigation of laser wakefield acceleration versus F-number of focusing optics

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE (2009)

Navid Vafaei-Najafabadi A. W. Ali J. A. Chakera R. Fedosejevs Ying Y. Tsui

Laser wakefield acceleration is a growing area of research with the promise of generating high energy, low divergence, and short duration electron bunches from tabletop scale accelerators. To date, electron beams with maximum energy of 1 GeV with 2.5% energy spread have been generated using a 3cm plasma channel [1] . However in order to advance the maximum energy of electron beams beyond this limit, better understanding of the physics and effect of different parameters on the interaction are essential. In this paper we report on our parametric studies of wakefield electron acceleration using the 10TW chirped pulse amplified laser system at the Advanced Laser Light Source (ALLS), Montreal. Laser pulses with energies of ~210 mJ at 33fs were focused using a short (f/6) and a long focal length (f/12) off axis parabola onto 2mm supersonic helium and nitrogen gas jets at different pressures. Nitrogen with electron densities of up to 2×10 20 cm -3 and helium densities up to 5×10 19 were used. Beams with energies of tens of MeV were observed using the short focal length parabola and beams with energies of several MeV were observed using the long focal length parabola. We also found that electron beams are more easily generated with higher levels of prepulse, consistent with previous reports of prepulse generated guiding channels in the plasma[5].

Rayleigh length

Parabola

Plasma acceleration

10.1117/12.839825

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Citations (1)

Characterization of laser wakefield generated betatron X-ray radiation using grazing incidence mirror reflection

The European Physical Journal D (2014)

Mianzhen Mo S. Fourmaux A. W. Ali Philippe Lassonde Jean-Claude Kieffer

Betatron

Transition radiation

Reflection

10.1140/epjd/e2014-50346-5

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Citations (4)

Electron Energy Deposition in Atomic Nitrogen

Ronald D. Taylor S. P. Slinker A. W. Ali

Abstract : A discrete, time-dependent energy deposition model is used to study high-energy electron-beam (100 eV to 10 MeV) deposition in atomic nitrogen. Both time-dependent and steady-state secondary electron distributions are computed. The loss function, mean energies per electron-ion air production (DELTA W), production efficiencies, and yield functions are presented for a wide range of energies.The latest experimental and theoretical cross section are used in the model which predicts DELTA W is approximately 31 eV for a wide range of beam energies and background ionization fractions.

Deposition

10.21236/ada185423

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Low-Energy Electron Impact Rate Coefficients for Some Atmospheric Species.

A. W. Ali A. D. Anderson

Abstract : Low-energy electron impact excitation and ionization rate coefficients, relevant to ionospheric species, are calculated using measured or calculated cross sections. (Author)

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