TY - JOUR
T1 - Enhancement of high-energy electron generation through suppression of Raman backscattering
JF - Europhysics Letters
Y1 - 2004
A1 - Trines, Rmgm
A1 - Kamp, L. P. J.
A1 - Schep, T. J.
A1 - Leemans, W. P.
A1 - Esarey, E. H.
A1 - Sluijter, F. W.
VL - 66
SN - 0295-5075
UR - ://000223064800005
U1 - Fusion Physics
U2 - Computational Plasma Physics
U5 - e65212c7df0b910f0d98521585e35152
ER -
TY - JOUR
T1 - Magnetic fields and plasmas
JF - Fusion Science and Technology
Y1 - 2004
A1 - Schep, T. J.
VL - 45
SN - 1536-1055
UR - ://000220595000006
U1 - Fusion Physics
U2 - Computational Plasma Physics
U5 - 317ac2dd6b774e2b2f149f6e4a7a7b1d
ER -
TY - JOUR
T1 - Multi-scale percolation and scaling laws for anisotropic turbulent diffusion
JF - Physics Letters A
Y1 - 2004
A1 - Bakunin, O. G.
A1 - Schep, T. J.
VL - 322
SN - 0375-9601
UR - ://000189211700015
U1 - Fusion Physics
U2 - Computational Plasma Physics
U5 - 6050995bb6ca669922a5855901542f1c
ER -
TY - JOUR
T1 - On the generation of mean fields by small-scale electron magnetohydrodynamic turbulence
JF - Physics of Plasmas
Y1 - 2004
A1 - Lakhin, V. P.
A1 - Schep, T. J.
VL - 11
SN - 1070-664X
UR - ://000221084400027
U1 - Fusion Physics
U2 - Computational Plasma Physics
U5 - 6db075952afafd3406a0e56f3ff9f81d
ER -
TY - JOUR
T1 - Spectral properties of decaying turbulence in electron magnetohydrodynamics
JF - Physics of Plasmas
Y1 - 2003
A1 - Abdalla, T. M.
A1 - Lakhin, V. P.
A1 - Schep, T. J.
A1 - Westerhof, E.
VL - 10
SN - 1070-664X
UR - ://000184491800006
U1 - Fusion Physics
U2 - Tokamak physics
U5 - f4c3bf4eae7a93e03add50cd7d5ea992
ER -
TY - JOUR
T1 - Guiding center motion
JF - Fusion Science and Technology
Y1 - 2002
A1 - de Blank, H. J.
A1 - Schep, T. J.
VL - 41
SN - 1536-1055
UR - ://000174683300006
U1 - Fusion Physics
U2 - Computational Plasma Physics
U5 - f269b9636b6de944c8ff47cb4aeed3bb
ER -
TY - JOUR
T1 - Electron vortex generation by strong, localized plasma heating
JF - Physics of Plasmas
Y1 - 2001
A1 - Abdalla, T. M.
A1 - Kuvshinov, B. N.
A1 - Schep, T. J.
A1 - Westerhof, E.
AB - The generation of electron vortical structures by strong localized heating is investigated analytically and numerically. The structure formation and its dynamics are described by the model of electron magnetohydrodynamics, extended to include pressure effects. Magnetic structures are generated by the thermal electromotive force that arises due to nonalignment of pressure and density gradients. Their topology is determined by the heating power and the equilibrium density gradient. It is shown that strong localized heating of a nonuniform plasma generates vortical structures that are capable of confining and transporting heat across the plasma. The long term behavior of the structures agrees qualitatively with stationary equilibrium solutions. As these structures survive for rather long times, a filamentary profile of the temperature develops. (C) 2001 American Institute of Physics.
VL - 8
SN - 1070-664X
U5 - 080b8aca40b8a3b75f52c0926ced4b50
ER -
TY - JOUR
T1 - Merging of plasma currents
JF - Physical Review Letters
Y1 - 2001
A1 - Bergmans, J.
A1 - Schep, T. J.
AB - The merging process of current filaments in a strongly magnetized plasma is described. The evolution is calculated using a contour dynamics method, which accurately tracks piecewise constant distributions of the conserved quantities. In the interaction of two screened currents, both develop dipolar vortical flows, bringing the currents together. This is the manifestation of the Lorentz force between aligned currents. Currents will merge into single filaments. Reconnection of the magnetic field takes place, converting the magnetic topology from a figure eight to a circle.
VL - 87
SN - 0031-9007
U5 - a9da177160bf1f2ba8887970786313ec
ER -
TY - JOUR
T1 - Onset of nonlinear regime in beam-plasma interactions
JF - Journal of Physics D-Applied Physics
Y1 - 2001
A1 - Goloviznin, V. V.
A1 - Schep, T. J.
AB - We consider the process of excitation of a strong axisymmetrical plasma wave by a relativistic electron bunch. It is well known that in one-dimensional geometry the excited wave becomes essentially nonlinear when the beam density approaches half the plasma density, and wavebreaking occurs at beam densities higher than that. Such a simple relation, however, does not hold in three dimensions. We find that the total beam current, not only the current density, should exceed a certain threshold for nonlinearity to become visible. Just recently, new developments in accelerator technology have made it possible to produce relativistic electron beams powerful enough to enter this nonlinear regime. We show that a realistic electron bunch from an advanced accelerator can generate in its wake accelerating fields well above 10 GeV m(-1).
VL - 34
SN - 0022-3727
U5 - 8bcc55459e1e6ea4325c24cd5234d5b4
ER -
TY - JOUR
T1 - Modeling the fields of magneto-optical devices, including fringe field effects and higher order multipole contributions, with application to charged particle optics
JF - Physical Review Special Topics-Accelerators and Beams
Y1 - 2001
A1 - Trines, Rmgm
A1 - van Eijndhoven, S. J. L.
A1 - Botman, J. I. M.
A1 - Schep, T. J.
A1 - Hagedoorn, H. L.
AB - A new method for the calculation of the magnetic field of beam guiding elements is presented. The method relates the calculation to measurement data of the magnetic field in a direct way. It can be applied to single beam guiding elements as well as to clusters of elements. The presented description of the magnetic field differs from the classical approach in that it does not rely on power series approximations. It is also both divergence free and curl free, and takes fringe field effects up to any desired order into account. In the field description, pseudodifferential operators described by Bessel functions are used to obtain the various multipole contributions. Magnetic field data on a two-dimensional surface, e.g., a cylindrical surface or median plane, serve as input for the calculation of the three-dimensional magnetic field. A boundary element method is presented to fit the fields to a discrete set of field data, obtained, for instance, from field measurements, on the two-dimensional surface. Relative errors in the field approximation do not exceed the maximal relative errors in the input data. Methods for incorporating the obtained field in both analytical and numerical computation of transfer functions are outlined. Applications include easy calculation of the transfer functions of clusters of beam guiding elements and of generalized field gradients for any multipole contribution up to any order.
VL - 4
SN - 1098-4402
U5 - e8b64714c5284885084eb08d975321dd
ER -
TY - JOUR
T1 - Electron vortices in magnetized plasmas
JF - Physics of Plasmas
Y1 - 2001
A1 - Kuvshinov, B. N.
A1 - Rem, J.
A1 - Schep, T. J.
A1 - Westerhof, E.
AB - This article is devoted to a systematic development of the theory of distributed electron vortices in magnetized plasmas. Such vortices are nonlinear stationary propagating solutions of the model of electron magnetohydrodynamics. Two types of vortices are investigated: two-dimensional dipole and spherical vortices. In both cases dispersion relations are derived and vortex structures are analyzed. The dynamics and stability properties of dipole vortices are investigated numerically. It is found numerically that dipole vortices propagating strictly perpendicular to the magnetic field are always unstable. Obliquely propagating vortices with a single separatrix are found to be stable, while vortices with a double separatrix turn out to be unstable. (C) 2001 American Institute of Physics.
VL - 8
SN - 1070-664X
U5 - 0dbb49d7e12768a6abd792fcb428d636
ER -
TY - JOUR
T1 - Generation of fast electrons by breaking of a laser-induced plasma wave
JF - Physical Review E
Y1 - 2001
A1 - Trines, Rmgm
A1 - Goloviznin, V. V.
A1 - Kamp, L. P. J.
A1 - Schep, T. J.
AB - A one-dimensional model for fast electron generation by an intense, nonevolving laser pulse propagating through an underdense plasma has been developed. Plasma wave breaking is considered to be the dominant mechanism behind this process, and wave breaking both in front of and behind the laser pulse is discussed. Fast electrons emerge as a short bunch, and the electrostatic field of this bunch is shown to limit self-consistently the amount of generated fast electrons.
VL - 63
SN - 1063-651X
U5 - 1773e7deca0e8816b6ff005fa05cbe4f
ER -
TY - JOUR
T1 - Simulation of laser wakefield acceleration of an ultrashort electron bunch
JF - Physical Review E
Y1 - 2001
A1 - Reitsma, A. J. W.
A1 - Goloviznin, V. V.
A1 - Kamp, L. P. J.
A1 - Schep, T. J.
AB - The dynamics of the acceleration of a short electron bunch in a strong plasma wave excited by a laser pulse in a plasma channel is studied both analytically and numerically in slab geometry. ln our simulations, a fully nonlinear, relativistic hydrodynamic description for the plasma wave is combined with particle-in-cell methods for the description of the bunch. Collective self-interactions within:the bunch are fully taken into account. The existence of adiabatic invariants of motion is shown to have important implications for the final beam quality. Similar to the one-dimensional case, the natural evolution of the bunch is shown to lead, under proper initial conditions, to a minimum in the relative energy spread.
VL - 63
SN - 1063-651X
U5 - 3fe66998c97931db111d876c9612281a
ER -
TY - JOUR
T1 - Spectral stability of Alfven filament configurations (vol, 7, pg 2388, 2000)
JF - Physics of Plasmas
Y1 - 2000
A1 - Bergmans, J.
A1 - Kuvshinov, B. N.
A1 - Lakhin, V. P.
A1 - Schep, T. J.
VL - 7
SN - 1070-664X
U5 - 7e9fe537541461580399edc06bb4a27c
ER -
TY - JOUR
T1 - Self-induced transparency and self-induced opacity in laser-plasma interactions
JF - Physics of Plasmas
Y1 - 2000
A1 - Goloviznin, V. V.
A1 - Schep, T. J.
AB - The interaction of a strong electromagnetic wave with a layer of overdense plasma is considered under conditions that allow for self-induced transparency (SIT). In a certain range of the amplitude of the incoming wave, the corresponding nonlinear one-dimensional (1D) set of equations is shown to admit two competing steady-state solutions that satisfy the same boundary conditions. One of those solutions describes just the well-known SIT regime of propagation, the other one corresponds to the full reflection of the incident wave. Their coexistence indicates the possibility of hysteresis-like effects in ultraintense laser interactions with overdense plasmas. 1D Particle-In-Cell simulations confirm analytical results and suggest the dominance of the opaque solution over the entire parameter window where it is possible. Fast longitudinal heating of plasma electrons occurs then in a natural way as a result of the breakup of the opaque solution above some threshold in laser intensity. (C) 2000 American Institute of Physics. [S1070-664X(00)03905-7].
VL - 7
SN - 1070-664X
U5 - 3ee80ae288d148ea812be9fde19d4357
ER -
TY - JOUR
T1 - Drift waves and vortices
JF - Fusion Technology
Y1 - 2000
A1 - Schep, T. J.
AB - Drift waves and drift vortices are low-frequency phenomena that occur in inhomogeneous plasmas embedded in strong magnetic fields. They propagate in the direction perpendicular to the density gradient and to the background magnetic field with phase velocities that are characterized by the diamagnetic velocity. Drift waves and vortices propagate in complementary velocity intervals. Most probably, they play an important role in the anomalous cross-field transport in magnetically confined plasmas. These phenomena can be described by a plasma model in which the electrons and ions are treated as separate fluids that are coupled through the electromagnetic field.
VL - 37
SN - 0748-1896
U5 - 6ec6e7bfec06de25751622f7f5b94a4f
ER -
TY - JOUR
T1 - Guiding center motion
JF - Fusion Technology
Y1 - 2000
A1 - de Blank, H. J.
A1 - Schep, T. J.
AB - The motion of charged particles in slowly varying electromagnetic fields is analyzed. The strength of the magnetic field is such that the gyro-period and the gyro-radius of the particle motion around field lines are the shortest time and length scales of the system. The particle motion is described as the sum of a fast gyro-motion and a slow drift velocity.
VL - 37
SN - 0748-1896
U5 - 13010efad84d15a057e80471833d47f2
ER -
TY - JOUR
T1 - Magnetic fields and plasmas
JF - Fusion Technology
Y1 - 2000
A1 - Schep, T. J.
VL - 37
SN - 0748-1896
U5 - 90834b78c127d5a892394eb3e9cbbd0d
ER -
TY - JOUR
T1 - Spectral stability of Alfven filament configurations
JF - Physics of Plasmas
Y1 - 2000
A1 - Bergmans, J.
A1 - Kuvshinov, B. N.
A1 - Lakhin, V. P.
A1 - Schep, T. J.
AB - The two-fluid plasma equations that describe nonlinear Alfven perturbations have singular solutions in the form of current-vortex filaments. These filaments are analogous to point vortices in ideal hydrodynamics and geostrophic fluids. In this work the spectral (linear) stability of current-vortex filament configurations is analyzed and compared with the results obtained for point vortices in ideal hydrodynamics and the Charney-Hasegawa-Mima equation. We consider single rows, double rows-von Karman streets-and single and double rings of vortices. In all cases the stability picture for the current-vortex filaments is remarkably different from that of the other two models, which can be recovered as limiting cases of the two-fluid Alfven model. New regions of perturbations against which the system is stable are identified and the dependence on physical parameters is described. (C) 2000 American Institute of Physics. [S1070-664X(00)01606-2].
VL - 7
SN - 1070-664X
U5 - 3b4079fcd07ee3760683310161ad488f
ER -
TY - JOUR
T1 - Holtsmark distributions in point-vortex systems
JF - Physical Review Letters
Y1 - 2000
A1 - Kuvshinov, B. N.
A1 - Schep, T. J.
AB - The statistics of uncorrelated point vortices in a plane is studied analytically and numerically. Theoretical distributions are obtained with the general method developed by Holtsmark [Ann. Phys. 58, 577 (1919)] and Chandrasekhar [Rev. Mod. Phys. 15, 1 (1943)]. They are found to agree with the results of numerical tests. Randomly placed Euler vortices have neatly Gaussian velocity distributions and Lorentzian distributions of the velocity difference. Statistics of other types of point vortices is essentially non-Gaussian.
VL - 84
SN - 0031-9007
U5 - d35abda2b9619270c458f8a1a0c34ce5
ER -
TY - JOUR
T1 - Double-periodic arrays of vortices
JF - Physics of Fluids
Y1 - 2000
A1 - Kuvshinov, B. N.
A1 - Schep, T. J.
AB - Analytical solutions to the sinh-Poisson equation are discussed. This equation plays a role in the theory of vortex dynamics [Mallier and Maslowe, Phys. Fluids A 5, 1074 (1993)] and in the discussion of the most probable states of inviscid two-dimensional flows in fluids and plasmas [Montgomery and Joyce, Phys. Fluids 17, 1139 (1974)]. We present a family of double-periodic solutions on a rectangular grid. In limiting cases these solutions reproduce Mallier-Maslowe vortex streets and arrays of Greenhill's point vortices. (C) 2000 American Institute of Physics. [S1070- 6631(00)00912-0].
VL - 12
SN - 1070-6631
U5 - 6f87b7715218f54fa746cef627229eb2
ER -
TY - JOUR
T1 - Fast magnetic and turbulent-wave dynamos in electron magnetohydrodynamics
JF - Physics and Chemistry of the Earth Part a-Solid Earth and Geodesy
Y1 - 2000
A1 - Lakhin, V. P.
A1 - Moiseev, S. S.
A1 - Schep, T. J.
AB - The influence of inertia on the spontaneous amplification of large-scale perturbations by electron magnetohydrodynamic (EMHD) turbulence is studied in a 2 1/2 -dimensional(2 1/2 -D) model. It is shown that electron inertia results in the modification of ct-like effects, which are due to the helicity of the turbulence. Under some conditions no instability of the mean field due to helicity of turbulence will occur. Electron inertia can also change the sign of turbulent viscosity in the equation of the third component of the mean held, making it negative. The possibility is discussed of the generation of 3-D whistlers by 2-D EMHD turbulence due to either helicity or to anisotropy of the turbulence. Unlike the case of 2-D large-scale perturbations, turbulent resistivity is anisotropic and leads to the destabilization of whistler modes, independently of the sign of the resistivity coefficient. (C) 2000 Elsevier Science Ltd. All rights reserved.
VL - 25
SN - 1464-1895
U5 - f3fc0c685d612c571cb79048f01381e6
ER -
TY - JOUR
T1 - Spectral stability of Alfven filament chains
JF - Physica Scripta
Y1 - 2000
A1 - Bergmans, J.
A1 - Kuvshinov, B. N.
A1 - Lakhin, V. P.
A1 - Schep, T. J.
AB - The two-fluid model of nonlinear Alfven perturbations has singular solutions in the form of current-vortex filaments. We investigate analytically and numerically the spectral stability of single and double rows of filaments. Staggered and non-staggered double rows (von Karman streets) are studied. It is shown that in contrast to Euler and geostrophic vortices, single rows of Alfven filaments are stable with respect to short-wavelength perturbations. Both staggered and unstaggered streets can be completely stable within certain ranges of parameters.
VL - T84
SN - 0281-1847
U5 - ca1c8d863450300e62ef32fffba45217
ER -
TY - JOUR
T1 - On self-induced transparency in laser-plasma interactions
JF - Jetp Letters
Y1 - 1999
A1 - Goloviznin, V. V.
A1 - Schep, T. J.
AB - We study fully relativistic nonlinear one-dimensional equations describing steady-state solutions for an electromagnetic wave interacting with a plasma in the self-induced transparency regime. In addition to the well-known solution that corresponds to the transmission of the electromagnetic wave into plasma, another steady-state solution is shown to exist in a certain range of amplitudes of the wave. The latter solution corresponds to total reflection of the incident wave. The coexistence of the two solutions indicates the possibility of hysteretic behavior in the self-induced transparency. (C) 1999 American Institute of Physics. [S0021-3640(99)00619-2].
VL - 70
SN - 0021-3640
U5 - f22cf5f49ad80e48cc30e6e53151f43a
ER -
TY - JOUR
T1 - Current-vortex filaments in magnetized plasmas
JF - Plasma Physics and Controlled Fusion
Y1 - 1999
A1 - Bergmans, J.
A1 - Kuvshinov, B. N.
A1 - Lakhin, V. P.
A1 - Schep, T. J.
A1 - Westerhof, E.
AB - Current-vortex filament solutions to the two-fluid plasma equations that describe drift-Alfven waves are presented. Such filament systems are Hamiltonian. Integrable three and four filament systems are discussed in some detail. A wide variety of orbit topologies exists in the plasma case. Special attention is paid to collapses where all filaments contract to a single point. The differences and extensions with respect to point vortex solutions in two-dimensional (2D) incompressible Euler systems is pointed out.
VL - 41
SN - 0741-3335
U5 - e0e3df9f9021e6ef0f0f5279437bd29f
ER -
TY - JOUR
T1 - Drift-Alfve'n vortices with finite ion gyroradius and electron inertia effects
JF - Physics of Plasmas
Y1 - 1999
A1 - Kuvshinov, B. N.
A1 - Pegoraro, F.
A1 - Rem, J.
A1 - Schep, T. J.
AB - A two-fluid plasma model is used to analyze drift-Alfven vortices in a magnetized, inhomogeneous, warm plasma. This low-beta model retains the effects of finite electron mass and of finite ion gyroradii. The vortices are described by two potentials: the electrostatic potential and one component of the vector potential. The background plasma is assumed to have locally a linear density profile. Solutions in the form of dipoles, which propagate with constant velocity across a strong, uniform magnetic field, are analyzed. A general dispersion relation between the eigenvalues inside and outside the separatrix is derived. The analysis of this dispersion relation and of the spatial vortex structure leads to a general classification of two-potential vortices. Explicit solutions are presented for dipole vortices in the limit of zero electron inertia where finite gyroradius effects are retained and in the limit of cold ions where finite electron mass is taken into account. (C) 1999 American Institute of Physics. [S1070-664X(99)03403-5].
VL - 6
SN - 1070-664X
U5 - 81539a49724cd1753b8fa9ea6eec6803
ER -
TY - JOUR
T1 - Production of direct fusion neutrons during ultra-intense laser-plasma interaction
JF - Journal of Physics D-Applied Physics
Y1 - 1998
A1 - Goloviznin, V. V.
A1 - Schep, T. J.
AB - The plasma response to a picosecond multi-terawatt laser pulse is characterized by several distinctly different time scales. In the present report we consider the plasma's evolution on the slow time scale typical for excitations of the ionic component. A relativistically strong laser pulse (10(18)-10(19) W cm(-2)) is shown to drive, under proper conditions, mega-ampere ion currents with a typical ion energy of 50-150 keV, which covers the region of the resonance peak in the cross section of D-T fusion and, hence, provides an opportunity to initiate nuclear reactions directly in the laser focus.
VL - 31
SN - 0022-3727
U5 - 9d197cd44b4dcf50490a2376d6ba4cf8
ER -
TY - JOUR
T1 - Current-vortex filament model of nonlinear Alfven perturbations in a finite-pressure plasma
JF - Physics of Plasmas
Y1 - 1998
A1 - Lakhin, V. P.
A1 - Schep, T. J.
A1 - Westerhof, E.
AB - A low-beta, two-fluid model is shown to possess solutions in the form of current-vortex filaments. The model can be viewed as that of reduced magnetohydrodynamics, extended with electron inertia, the Hall term and parallel electron pressure. These drift-Alfven filaments are the plasma analogs of point vortices in the two-dimensional Euler and the Charney-Hasegawa-Mima equations. The discrete system has the same global and local invariants as the original, continuous system. In an unbounded plasma, systems of two and three filaments are integrable. When the global linear momenta vanish, the four filament problem is also integrable. Stationary equilibria of a dipole, tripole, and of von Karman streets are presented. The phase-space of two interacting, balanced pairs of filaments is analyzed in detail. New periodic four filament configurations are identified in plasma cases that do not exist in Euler systems. It is also shown that a collapse of the four vortices can occur in a finite time. (C) 1998 American Institute of Physics. [S1070-664X(98)00511-4].
VL - 5
SN - 1070-664X
U5 - 3331d4103454e2f20bc6d2f3ed8ee5ee
ER -
TY - JOUR
T1 - Hamiltonian vortices and reconnection in a magnetized plasma
JF - Journal of Plasma Physics
Y1 - 1998
A1 - Kuvshinov, B. N.
A1 - Lakhin, V. P.
A1 - Pegoraro, F.
A1 - Schep, T. J.
AB - Hamiltonian vortices and reconnection in magnetized plasmas are investigated analytically and numerically using a two-fluid model. The equations are written in the Lagrangian form of three fields that are advected with different velocities. This system can be considered as a generalization and extension of the two-dimensional Euler equation for an ordinary fluid. It is pointed out that these equations allow solutions in. the form of singular current-vortex filaments, drift-Alfven vortices and magnetic islands, and admit collisionless magnetic reconnection where magnetic flux is converted into electron momentum and ion vorticity.
VL - 59
SN - 0022-3778
U5 - 5963e2b65f36a8044c2fe8acc45340cf
ER -
TY - JOUR
T1 - Electron magnetohydrodynamics of magnetized, inhomogeneous plasmas
JF - Physics Letters A
Y1 - 1998
A1 - Kuvshinov, B. N.
A1 - Westerhof, E.
A1 - Schep, T. J.
A1 - Berning, M.
AB - A modified EMHD model is derived that includes the effects of density perturbations and inhomogeneity in a strong magnetic field. Similar to previous EMHD models, the derived equation takes the form of a flux conservation law for a modified vorticity. The modified vorticity is frozen into the current flow. The model unifies whistler and electron gradient waves and generalizes the nonlinear models for these modes. In 2D, the model again reduces to a set of two coupled equations for the vertical magnetic field and the poloidal flux. The scale length in the equation for the vertical held is modified and a drift term is introduced there, whereas the equation for the poloidal flux is not modified with respect to previous 2D models. A noncanonical Hamiltonian representation for the 2D equations is presented. (C) 1998 Elsevier Science B.V.
VL - 241
SN - 0375-9601
U5 - c3a8e8258b12de073bbe0e3754a86a66
ER -
TY - JOUR
T1 - Response to "Comment on 'A mean field prediction of the asymptotic state of decaying 2D turbulence'" Phys. Fluids 10, 1237 (1998)
JF - Physics of Fluids
Y1 - 1998
A1 - Brands, H.
A1 - Stulemeyer, J.
A1 - Pasmanter, R. A.
A1 - Schep, T. J.
VL - 10
SN - 1070-6631
U5 - 66bc8fa44ec2b892b7e6db57ebe1ee68
ER -
TY - JOUR
T1 - Guiding center motion
JF - Fusion Technology
Y1 - 1998
A1 - de Blank, H. J.
A1 - Schep, T. J.
AB - The motion of charged particles in slowly varying electromagnetic fields is analyzed. The strength of the magnetic field is such that the gyro-period and the gyro-radius of the particle motion around field lines are the shortest time and length scales of the system. The particle motion is described as the sum of a fast gyro-motion and a slow drift velocity.
VL - 33
SN - 0748-1896
U5 - 19ef7c41055b8f4be535e29a1504a329
ER -
TY - JOUR
T1 - Magnetic fields and plasmas
JF - Fusion Technology
Y1 - 1998
A1 - Schep, T. J.
VL - 33
SN - 0748-1896
U5 - f26c5769fe3fdb2449a37dac5d90edfe
ER -
TY - JOUR
T1 - A mean field prediction of the asymptotic state of decaying 2D turbulence
JF - Physics of Fluids
Y1 - 1997
A1 - Brands, H.
A1 - Stulemeyer, J.
A1 - Pasmanter, R. A.
A1 - Schep, T. J.
VL - 9
SN - 1070-6631
U5 - 9875cdee8edd1c2607be18993a24e368
ER -
TY - JOUR
T1 - Geometrical approach to fluid models
JF - Physics of Plasmas
Y1 - 1997
A1 - Kuvshinov, B. N.
A1 - Schep, T. J.
AB - Differential geometry based upon the Cartan calculus of differential forms is applied to investigate invariant properties of equations that describe the motion of continuous media. The main feature of this approach is that physical quantities are treated as geometrical objects. The geometrical notion of invariance is introduced in terms of Lie derivatives and a general procedure for the construction of local and integral fluid invariants is presented. The solutions of the equations for invariant fields can be written in terms of Lagrange variables. A generalization of the Hamiltonian formalism for finite-dimensional systems to continuous media is proposed. Analogously to finite-dimensional systems, Hamiltonian fluids are introduced as systems that annihilate an exact two-form. It is shown that Euler and ideal, charged fluids satisfy this local definition of a Hamiltonian structure. A new class of scalar invariants of Hamiltonian fluids is constructed that generalizes the invariants that are related with gauge transformations and with symmetries (Noether). (C) 1997 American Institute of Physics.
VL - 4
SN - 1070-664X
U5 - d67a228d652a7eb5daefc202f5c91aff
ER -
TY - JOUR
T1 - Role of core losses in drift-vortex interactions
JF - Physical Review E
Y1 - 1997
A1 - Westerhof, E.
A1 - Rem, J.
A1 - Schep, T. J.
AB - Dipole drift vortices in the Hasegawa-Mima-Charney equation are studied by means of particle-in-cell (PIC) calculations. Apart from providing an efficient and accurate solution of the equations, PIC provides additional information about the fluid flow such as exchange of fluid between regions interior and exterior to the dipoles. Several cases of perturbed dipoles are studied with particular emphasis on the evolution of the fluid that is initially trapped inside the separatrix of the co-moving stream function of each unperturbed dipole. In particular, the effect of a finite tilt of the dipole axis is analyzed. Here, asymmetric losses from the two dipole halves are found to play a crucial role in the qualitative evolution of the dipole trajectory: dipoles initially moving in the unstable direction are found to reverse their average velocity perpendicular to the density gradient. Very large perturbations are obtained in dipole collisions. Here symmetry of the initial conditions plays an important role: collisions of aligned dipoles appear almost solitonlike, while for nonaligned dipoles the collision at least generates a tilt of the axes of the dipoles, but may also lead to a complete destruction of one of the poles. In all cases a significant loss of initially trapped fluid is demonstrated.
VL - 56
SN - 1063-651X
U5 - c98568933fed6bec691996f99c7362e4
ER -
TY - JOUR
T1 - Guiding center motion
JF - Fusion Technology
Y1 - 1996
A1 - Schep, T. J.
AB - The motion of charged particles in slowly varying electromagnetic fields is analyzed. The magnetic field is supposed to be strong such that the gyro-period and the gyro-radius of the particle motion around field lines are the shortest time and length scale of the system. The particle motion can be described as the sum of a fast gyro-motion and of a slow drift velocity.
VL - 29
SN - 0748-1896
U5 - 746accf9368e338402d0cc94a713add7
ER -
TY - JOUR
T1 - Spectral dynamics of a collective free electron maser
JF - Nuclear Instruments & Methods in Physics Research Section a-Accelerators Spectrometers Detectors and Associated Equipment
Y1 - 1996
A1 - Eecen, P. J.
A1 - Schep, T. J.
A1 - Tulupov, A. V.
AB - A study of the nonlinear spectral dynamics of a Free Electron Maser (FEM) is reported. In the FEM for fusion applications [1], the electron beam is modulated by a step-tapered undulator consisting of two sections with different strengths and lengths. The sections have equal periodicities and are separated by a field-free gap. The microwave beam is guided in a rectangular corrugated waveguide. The electron energy is rather low and the current density is large, therefore, the FEM operates in the collective (Raman) regime. The dynamics of the spectrum is calculated with a code that is based on a multifrequency model in the continuous beam limit with a 3D description of the electron beam. Space-charge forces are included. They strongly influence the behaviour of the generated spectrum. In the saturated regime the gain is still relatively high because of the large outcoupled power fraction. It is discussed that quite robust parameter regions exist, where single-peaked frequency spectra are excited.
VL - 375
SN - 0168-9002
U5 - e50df8877f7a89033a5986de148c6848
ER -
TY - JOUR
T1 - Spectral Dynamics of a Free-Electron Maser with a Step-Tapered Undulator
JF - Physical Review E
Y1 - 1995
A1 - Eecen, P. J.
A1 - Schep, T. J.
A1 - Tulupov, A. V.
AB - The spectral behavior of a high-power, high-gain free-electron maser (FEM) is investigated. The maser has a step-tapered undulator consisting of two sections with different strengths and lengths and equal periodicities. The sections are separated by a field-free gap. The configuration is enclosed within a low quality cavity. The millimeter wave beam is guided within a rectangular corrugated waveguide. The purpose of this undulator setup is to enhance the efficiency at high output power. The associated high gain in the Linear as well as in the nonlinear regime provides a unique oscillator. The spectral dynamics of this device is analyzed with a multipass, multifrequency code. The radiation field of the code is described as a sum over discrete frequency components. The linear gain curve of the step-tapered undulator is not the sum of the curves of two single undulators and has a completely different spectrum. The gain of the FEM is so high that nonlinear interaction occurs within a few passes. In the fully nonlinear regime the gain is still relatively high. The power spectrum evolves towards a state in which the power at the resonance of the second undulator section is suppressed. In the final state, where the frequency spectrum hardly changes from pass to pass, the power spectrum exhibits two peaks at frequencies that are determined by the first section of the undulator. The main peak is related to its resonance frequency, while the second peak is a lower sideband. The dependence of the sideband on the gap length, the relative polarization of both sections, and the reflection coefficient is investigated.
VL - 52
SN - 1063-651X
U5 - fd402955c851029c8c31821ec45a68f7
ER -
TY - JOUR
T1 - Electron Acceleration by Nonlinear Plasma-Waves Excited by a Relativistic Electron Pulse
JF - Journal of Physics D-Applied Physics
Y1 - 1995
A1 - Schep, T. J.
A1 - Tulupov, A. V.
A1 - Bazylev, V. A.
A1 - Goloviznin, V. V.
AB - The excitation of travelling nonlinear Langmuir waves in a plasma by a relativistic electron bunch is considered. The nonlinear excitation is described as relativistic oscillations of the momentum of plasma electrons in effective potentials produced by the bunch and by the perturbation of the electron density of the plasma. The condition for the optimal excitation of the wave yields a relation between the density of the plasma, the density of the bunch and the length of the bunch. Numerical results support the theoretical analysis and demonstrate a deep nonlinear modulation of the electron plasma density and excitation of a large-amplitude longitudinal field at realistic plasma and electron pulse parameters. The back action of the wave field on the bunch is considered. It is shown that sharp peaks develop in its density distribution.
VL - 28
SN - 0022-3727
U5 - 5d996e5119fcd0536c68c062d0e0161d
ER -
TY - JOUR
T1 - The Influence of Hole-Coupling on the Transverse Structure of Intracavity Light-Pulses
JF - Nuclear Instruments & Methods in Physics Research Section a-Accelerators Spectrometers Detectors and Associated Equipment
Y1 - 1995
A1 - van Werkhoven, G. H. C.
A1 - Faatz, B.
A1 - Schep, T. J.
AB - The important issue addressed is the spatial structure of the light pulse inside the cavity of a hole-coupled resonator and the fraction of power lost through the aperture. The radial structure of the radiation is determined by the competition between power loss and scattering at the aperture and by the gain due to the interaction with the electrons. The additional effect of slippage couples the transverse and longitudinal profiles of the light pulse. It is shown that, at the back of the pulse, gain and gain-focussing are dominant. The front of the pulse propagates mainly in vacuum, The on-axis field intensity in this region is reduced by scattering. The influence of these mechanisms on the intra-cavity field structure is analyzed using a model that takes the time-dependent spatial dependence of the optical pulse into account. The phenomena are demonstrated numerically for FEL parameters close to those of FELIX.
VL - 358
SN - 0168-9002
U5 - be7b955d1d2f8610259d6a47985cba53
ER -
TY - JOUR
T1 - Nonlinear Macroscopic Equations for Pulse Evolution in a High-Gain Compton Fel
JF - Nuclear Instruments & Methods in Physics Research Section a-Accelerators Spectrometers Detectors and Associated Equipment
Y1 - 1995
A1 - van Werkhoven, G. H. C.
A1 - Schep, T. J.
AB - The non-linear stage of the interaction between electron and light pulses is considered of a high-gain FEL. It is shown that the non-linear oscillations of the radiation intensity can be described analogously to the bouncing motion of a particle in a time-dependent, anharmonic potential. In case the electrons all have the same energy and bunching factor, the potential is constant in the steady state region of the light pulse. In this region, analytical solutions are in good agreement with the full solution. Using the same approximation also in the trailing edge of the light pulse, it is shown that the model provides a surprisingly good description of the physics involved.
VL - 358
SN - 0168-9002
U5 - 63896a893cf51f9e683b09511f85e655
ER -
TY - JOUR
T1 - Spectral Dynamics of the Fem
JF - Nuclear Instruments & Methods in Physics Research Section a-Accelerators Spectrometers Detectors and Associated Equipment
Y1 - 1995
A1 - Eecen, P. J.
A1 - Tulupov, A. V.
A1 - Schep, T. J.
AB - The FOM Fusion FEM project involves the construction and operation of a 1-MW, 100 ms pulse, rapidly tunable FEM in the 130-250 GHz range for fusion applications. The undulator is a novel step-tapered undulator, consisting of two sections with different strengths and lengths and equal periodicities, and separated by a fieldfree gap. The purpose of this novel proposal is to enhance the efficiency at high output power. The associated high gain in the linear and in the non-linear regime provide a unique oscillator. The spectral dynamics of the high-current FEM with a low-quality cavity is calculated with a multi-pass, multi-frequency code. In this code the electrons are described 3D. The equations in the model are not averaged over a wiggler period. The continuous beam limit is considered. The radiation field is described as a sum over discrete frequencies. The millimeter wave field has the transverse radial dependence of the HE(11)-mode in the rectangular corrugated waveguide. The linear gain curve of the step-tapered undulator has a completely different spectrum than the single undulator. Furthermore the gain of the FEM is so high that non-linear interaction already occurs within a few passes. In the fully non-linear regime the gain is still relatively high and the output power reaches the required high level. Already in an early phase the spectral dynamics is strongly influenced by non-linear competition between the various maser modes. This non-linear mode competition is investigated, in particular the evolution of the sidebands is analized. It is observed that the spectral signal at the resonant frequency of the second undulator is suppressed. This suppression is observed for several gap lengths, Furthermore the spectrum can change with the variation of the gap length from quasi-stable to chaotic.
VL - 358
SN - 0168-9002
U5 - bff291def42f403c06d948a5ba898ac5
ER -
TY - JOUR
T1 - Closure Relations in Macroscopic Fel Equations
JF - Nuclear Instruments & Methods in Physics Research Section a-Accelerators Spectrometers Detectors and Associated Equipment
Y1 - 1994
A1 - van Werkhoven, G. H. C.
A1 - Schep, T. J.
AB - Based upon a macro-electron approach, several closure relations are presented to truncate the hierarchy of moments in macroscopic equations for the electron motion in a Compton FEL. In the non-linear and saturation regime of FEL operation, the optical power predicted by the models is compared with results from a multi-electron simulation code and with results from the literature. An idealized macro-electron model shows that the oscillatory non-linear behaviour is completely determined by the sloshing of energy between the electrons and the wave. A more realistic model which includes the slippage between the pulses, describes the behaviour of the optical power in the linear regime as well as the saturation level and the oscillations in the non-linear regime.
VL - 341
SN - 0168-9002
U5 - b9d1cc4091d1a02b97e46b62069e92d7
ER -
TY - JOUR
T1 - Fels Based on Beam-Plasma Interactions
JF - Nuclear Instruments & Methods in Physics Research Section a-Accelerators Spectrometers Detectors and Associated Equipment
Y1 - 1994
A1 - Bazylev, V. A.
A1 - Schep, T. J.
A1 - Tulupov, A. V.
VL - 341
SN - 0168-9002
U5 - 928b2248d4928b63830a70aafa3cd232
ER -
TY - JOUR
T1 - Investigation of Multifrequency Generation in the Fem
JF - Nuclear Instruments & Methods in Physics Research Section a-Accelerators Spectrometers Detectors and Associated Equipment
Y1 - 1994
A1 - Eecen, P. J.
A1 - Tulupov, A. V.
A1 - Schep, T. J.
AB - The FOM Fusion FEM project involves the construction and operation of a 1-MW, 100 ms pulse, rapid tunable FEM in the 130-250 GHz range for fusion applications. The undulator of the FEM consists of two sections with different strengths and different lengths separated by a gap without undulator field. The design provides arbitrary focussing. Single frequency codes predict a much higher output power for the two-section undulator than for a one-section undulator. However, the different undulator strengths lead to different resonance conditions and therefore, in principle, multiple frequencies can be generated. This problem of multi-frequency generation due to the two-section undulator is under investigation. First results are presented in this paper. The longitudinal mode structure of the FEM is simulated in a multi-pass, multi-frequency code. In this code the electrons are described fully 3D, non-wiggler averaged and in the long pulse limit. AC longitudinal space-charge forces are included. The radiation field is considered to have the known transverse radial dependence of a HE11-mode, due to the rectangular corrugated waveguide of the FEM. A multi-pass calculation in the single-frequency limit is presented, where the field grows into saturation.
VL - 341
SN - 0168-9002
U5 - 00a9a6127d03fc70b623f301dc565773
ER -
TY - JOUR
T1 - Guiding Center Motion
JF - Fusion Technology
Y1 - 1994
A1 - Schep, T. J.
AB - The motion of charged particles in slowly varying electromagnetic fields is analyzed. The magnetic field is supposed to be strong such that the gyro-period and the gyro-radius of the particle motion around field lines are the shortest time and length scale of the system. The particle motion can be described as the sum of a fast gyro-motion and of a slow drift velocity.
VL - 25
SN - 0748-1896
U5 - 65cb08884119c7094e32e62678369bd4
ER -
TY - JOUR
T1 - Magnetic Reconnection
JF - Fusion Technology
Y1 - 1994
A1 - Schep, T. J.
AB - This lecture deals with the concept of magnetic field lines and with the conservation of magnetic flux. In high temperature fusion devices like tokamaks flux conservation can be violated and reconnection can occur at closed magnetic field lines. Reconnection processes lead to changes in the global topology of the magnetic field.
VL - 25
SN - 0748-1896
U5 - 17801b251168e4f1fd223d6458e482b7
ER -
TY - JOUR
T1 - Short-Wavelength Free-Electron Lasers with Periodic Plasma Structures
JF - Journal of Physics D-Applied Physics
Y1 - 1994
A1 - Bazylev, V. A.
A1 - Schep, T. J.
A1 - Tulupov, A. V.
AB - Concepts of compact free-electron lasers that are based on beam-plasma interactions and that operate in the vacuum ultraviolet and x-ray wavelength ranges are discussed. Coherent radiation can not only be produced by periodic transverse motions of an electron beam, but also by its longitudinal motions. In this latter case, coherent transition radiation is generated when an electron beam passes through a structure with a deep periodic modulation of the plasma electron density. A number of structures are considered as short-wavelength radiators: standing Langmuir solitons or collapsing caverns, fast nonlinear longitudinal plasma waves, artificial periodical structures that can be converted into the plasma state by a powerful current generator or by a laser pulse, and periodic z-pinches produced by a thin wire.
VL - 27
SN - 0022-3727
U5 - 033ec5c15bf64f9780dfbbdf4e3e9dd2
ER -
TY - JOUR
T1 - Hamiltonian-Formulation of Low-Frequency, Nonlinear Plasma Dynamics
JF - Physics Letters A
Y1 - 1994
A1 - Kuvshinov, B. N.
A1 - Pegoraro, F.
A1 - Schep, T. J.
AB - In this paper we present a set of equations that governs the linear and nonlinear evolution of plasma phenomena with frequencies below the ion cyclotron and the magneto-sonic and above the ion-acoustic frequencies. Finite electron mass and ion gyroradius effects are taken into account. The spatial scales of the phenomena may range from MI-ID scales down to the inertia electron skin depth. In a high-temperature plasma, this skin depth is smaller than the gyro-radius of a thermal ion. This set describes Alfven and drift vortices, magnetic islands and current sheets. These equations can be cast in (noncanonical) Hamiltonian form. It is shown that infinite sets of conserved quantities (Casimirs) exist that reduce to the Casimirs of 2-D reduced MHD in the appropriate limit. Sufficient conditions for stability are discussed on the basis of the second variation, at constant Casimirs, of the Hamiltonian functional.
VL - 191
SN - 0375-9601
U5 - 265f87ad6407df5d0b8d32bbf5b6e8e6
ER -
TY - JOUR
T1 - Investigation of 3d Effects on Fel Operation
JF - Nuclear Instruments & Methods in Physics Research Section a-Accelerators Spectrometers Detectors and Associated Equipment
Y1 - 1993
A1 - van Werkhoven, G. H. C.
A1 - Faatz, B.
A1 - Schep, T. J.
AB - An investigation is made of 3D effects on FEL operation by comparing the 3D simulation code TDA with a 1 1/2D model. In the latter model, the full spatial dependence of the radiation field is taken into account, whereas the electrons are treated as moving in a 1D, density-averaged ponderomotive potential. Three dimensional effects like a radial beam profile, emittance and betatron oscillations are investigated. For FELIX parameters, the 1 1/2D model is in good agreement with TDA.
VL - 331
SN - 0168-9002
U5 - 834a8023c5a6da3a5afa2fdd0d3ae9be
ER -
TY - RPRT
T1 - Periodic structures in plasma for electron acceleration and free electron lasers
Y1 - 1993
A1 - Bazylev, V. A.
A1 - Schep, T. J.
A1 - Tulupov, A. V.
KW - Plasma physics
PB - FOM Rijnhuizen
CY - Nieuwegein, Netherlands
U5 - 7bd134dfc0f3760bb10644b301055e76
ER -
TY - JOUR
T1 - Theory of the M = 1 Kink Mode in Toroidal Plasma
JF - Physics of Fluids B-Plasma Physics
Y1 - 1991
A1 - de Blank, H. J.
A1 - Schep, T. J.
AB - The energy principle of ideal magnetohydrodynamics (MHD) is used to study the ideal MHD stability of the m = 1 internal kink mode in a toroidal plasma. The equilibrium configurations that are considered allow for a broad region where the safety factor q is close to unity. This region may extend to the magnetic axis, or may be a singular layer. The minimization of the energy functional yields an implicit equation for the growth rate that can be solved by simple numerical means. The examples that are treated numerically retain the essential features of experimentally expected q profiles. The growth rate depends very sensitively on the q profile close to unity and increases with the width of the q almost-equal-to 1 layer. The highest values are of the order of the inverse aspect ratio epsilon divided by the poloidal Alfven time. Nonmonotonic profiles with q > 1 on axis are more unstable than monotonic q profiles with q < 1. In the latter case, the mode tends to be localized in the q almost-equal-to 1 region instead of in the center.
VL - 3
SN - 0899-8221
U5 - 6a74cc12ef98064f89db461870db38b7
ER -
TY - JOUR
T1 - Theory of Resistive Modes in the Ballooning Representation
JF - Plasma Physics and Controlled Fusion
Y1 - 1986
A1 - Pegoraro, F.
A1 - Schep, T. J.
VL - 28
SN - 0741-3335
U5 - a4dbc7bcabe77b3988ff70b42406a0cb
ER -