37,506 research outputs found
Beam Extraction and Transport
This chapter gives an introduction to low-energy beam transport systems, and
discusses the typically used magnetostatic elements (solenoid, dipoles and
quadrupoles) and electrostatic elements (einzel lens, dipoles and quadrupoles).
The ion beam emittance, beam space-charge effects and the physics of ion source
extraction are introduced. Typical computer codes for analysing and designing
ion optical systems are mentioned, and the trajectory tracking method most
often used for extraction simulations is described in more detail.Comment: presented at the CERN Accelerator School CAS 2012: Ion Sources,
Senec, 29 May - 8 June 201
Multidimensional simulations of magnetic field amplification and electron acceleration to near-energy equipartition with ions by a mildly relativistic quasi-parallel plasma collision
The energetic electromagnetic eruptions observed during the prompt phase of
gamma-ray bursts are attributed to synchrotron emissions. The internal shocks
moving through the ultrarelativistic jet, which is ejected by an imploding
supermassive star, are the likely source of this radiation. Synchrotron
emissions at the observed strength require the simultaneous presence of
powerful magnetic fields and highly relativistic electrons. We explore with one
and three-dimensional relativistic particle-in-cell simulations the transition
layer of a shock, that evolves out of the collision of two plasma clouds at a
speed 0.9c and in the presence of a quasi-parallel magnetic field. The cloud
densities vary by a factor of 10. The number densities of ions and electrons in
each cloud, which have the mass ratio 250, are equal. The peak Lorentz factor
of the electrons is determined in the 1D simulation, as well as the orientation
and the strength of the magnetic field at the boundary of the two colliding
clouds. The relativistic masses of the electrons and ions close to the shock
transition layer are comparable as in previous work. The 3D simulation shows
rapid and strong plasma filamentation behind the transient precursor. The
magnetic field component orthogonal to the initial field direction is amplified
in both simulations to values that exceed those expected from the shock
compression by over an order of magnitude. The forming shock is
quasi-perpendicular due to this amplification. The simultaneous presence of
highly relativistic electrons and strong magnetic fields will give rise to
significant synchrotron emissions.Comment: 8 pages, 5 figures. This work was presented at 21st International
Conference on Numerical Simulation of Plasmas (ICNSP'09). Accepted for
publication IEEE Trans. on Plasma Scienc
ASCOT: solving the kinetic equation of minority particle species in tokamak plasmas
A comprehensive description of methods, suitable for solving the kinetic
equation for fast ions and impurity species in tokamak plasmas using Monte
Carlo approach, is presented. The described methods include Hamiltonian
orbit-following in particle and guiding center phase space, test particle or
guiding center solution of the kinetic equation applying stochastic
differential equations in the presence of Coulomb collisions, neoclassical
tearing modes and Alfv\'en eigenmodes as electromagnetic perturbations relevant
to fast ions, together with plasma flow and atomic reactions relevant to
impurity studies. Applying the methods, a complete reimplementation of the
well-established minority species code ASCOT is carried out as a response both
to the increase in computing power during the last twenty years and to the
weakly structured growth of the code, which has made implementation of
additional models impractical. Also, a benchmark between the previous code and
the reimplementation is accomplished, showing good agreement between the codes.Comment: 13 pages, 9 figures, submitted to Computer Physics Communication
Advances in the physics studies for the JT-60SA tokamak exploitation and research plan
JT-60SA, the largest tokamak that will operate before ITER, has been designed and built jointly by Japan and Europe, and is due to start operation in 2020. Its main missions are to support ITER exploitation and to contribute to the demonstration fusion reactor machine and scenario design. Peculiar properties of JT-60SA are its capability to produce long-pulse, high-Ăź, and highly shaped plasmas. The preparation of the JT-60SA Research Plan, plasma scenarios, and exploitation are producing physics results that are not only relevant to future JT-60SA experiments, but often constitute original contributions to plasma physics and fusion research. Results of this kind are presented in this paper, in particular in the areas of fast ion physics, high-beta plasma properties and control, and non-linear edge localised mode stability studies.Postprint (published version
Coronal Electron Confinement by Double Layers
In observations of flare-heated electrons in the solar corona, a longstanding
problem is the unexplained prolonged lifetime of the electrons compared to
their transit time across the source. This suggests confinement. Recent
particle-in-cell (PIC) simulations, which explored the transport of
pre-accelerated hot electrons through ambient cold plasma, showed that the
formation of a highly localized electrostatic potential drop, in the form of a
double layer (DL), significantly inhibited the transport of hot electrons (T.C.
Li, J.F. Drake, and M. Swisdak, 2012, ApJ, 757, 20). The effectiveness of
confinement by a DL is linked to the strength of the DL as defined by its
potential drop. In this work, we investigate the scaling of the DL strength
with the hot electron temperature by PIC simulations, and find a linear
scaling. We demonstrate that the strength is limited by the formation of
parallel shocks. Based on this, we analytically determine the maximum DL
strength, and find also a linear scaling with the hot electron temperature. The
DL strength obtained from the analytic calculation is comparable to that from
the simulations. At the maximum strength, the DL is capable of confining a
significant fraction of hot electrons in the source
Simulation of guiding of multiply charged projectiles through insulating capillaries
Recent experiments have demonstrated that highly charged ions can be guided
through insulating nanocapillaries along the direction of the capillary axis
for a surprisingly wide range of injection angles. Even more surprisingly, the
transmitted particles remain predominantly in their initial charge state, thus
opening the pathway to the construction of novel ion-optical elements without
electric feedthroughs. We present a theoretical treatment of this
self-organized guiding process. We develop a classical trajectory transport
theory that relates the microscopic charge-up with macroscopic material
properties. Transmission coefficients, angular spread of transmitted particles,
and discharge characteristics of the target are investigated. Partial agreement
with experiment is found
Optimization of a charge-state analyzer for ECRIS beams
A detailed experimental and simulation study of the extraction of a 24 keV
He-ion beam from an ECR ion source and the subsequent beam transport through an
analyzing magnet is presented. We find that such a slow ion beam is very
sensitive to space-charge forces, but also that the neutralization of the
beam's space charge by secondary electrons is virtually complete for beam
currents up to at least 0.5 mA. The beam emittance directly behind the
extraction system is 65 pi mm mrad and is determined by the fact that the ion
beam is extracted in the strong magnetic fringe field of the ion source. The
relatively large emittance of the beam and its non-paraxiality lead, in
combination with a relatively small magnet gap, to significant beam losses and
a five-fold increase of the effective beam emittance during its transport
through the analyzing magnet. The calculated beam profile and phase-space
distributions in the image plane of the analyzing magnet agree well with
measurements. The kinematic and magnet aberrations have been studied using the
calculated second-order transfer map of the analyzing magnet, with which we can
reproduce the phase-space distributions of the ion beam behind the analyzing
magnet. Using the transfer map and trajectory calculations we have worked out
an aberration compensation scheme based on the addition of compensating
hexapole components to the main dipole field by modifying the shape of the
poles. The simulations predict that by compensating the kinematic and geometric
aberrations in this way and enlarging the pole gap the overall beam transport
efficiency can be increased from 16 to 45%
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