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Energetic Ions in Present-Day Tokamaks
Published in Sergei Sharapov, Energetic Particles in Tokamak Plasmas, 2021
The hot ions of different energies transfer their energy to thermal ions and electrons at different proportions via Coulomb collisions. If the energy of hot ions is less than a critical value determined by Ecrit=14.8AfTe(∑iniZi2/neAi)2/3,
Elementary Processes of Charged Species in Plasma
Published in Alexander Fridman, Lawrence A. Kennedy, Plasma Physics and Engineering, 2021
Alexander Fridman, Lawrence A. Kennedy
Electron–electron, electron–ion, and ion-ion scattering processes are the so-called Coulomb collisions. While their cross sections are quite large with respect to those of collisions with neutral partners, these are relatively infrequent processes in discharges with a low degree of ionization. An important feature of the Coulomb collisions is a strong dependence of their cross sections on the kinetic energy of colliding particles. This effect can be demonstrated by a simple analysis, illustrated in Figure 2.3. Here, two particles have the same charge and for simplicity, one collision partner is considered at rest. Scattering takes place if the Coulomb interaction energy (order of U ~ q2/b, where b is the impact parameter) is approximately equal to the kinetic energy ε of a collision partner. Then, the impact parameter b ~ q2/ε, and the reaction cross section σ can be estimated as πb2 and σε~πq4/ε2
Recent Trends in Plasma Chemistry and Spectroscopy Diagnostics
Published in Tanmoy Chakraborty, Lalita Ledwani, Research Methodology in Chemical Sciences, 2017
Example: Let us take a low-temperature, low-density, weakly ionized plasma for industrial applications. By low temperature, we mean “cold” plasma with a gas temperature normally ranging from 300°K and 600°K, by low density, we mean plasmas with neutral gas number densities of approximately 1013–1016 molecules cm−3 (pressure between ~0.1 and 103 Pa), and by weakly ionized, we mean degree of ionization lies between 10−6 and 10−1.19 At very low ionization level (<10−3), neutral collision dominates. On the other hand, for a few percent ionization, the Coulomb collisions dominate over collisions with neutrals in any plasma.20
Core-Pedestal Plasma Configurations in Advanced Tokamaks
Published in Fusion Science and Technology, 2023
Ehab Hassan, C. E. Kessel, J. M. Park, W. R. Elwasif, R. E. Whitfield, K. Kim, P. B. Snyder, D. B. Batchelor, D. E. Bernholdt, M. R. Cianciosa, D. L. Green, K. J. H. Law
The injected neutral atoms (usually isotopes of hydrogen or helium) into the plasma initially travel in straight lines through the tokamak plasma unaffected by the background fields. Once these particles get ionized during multiple collision processes with the plasma species, such as charge exchange and ionization by ions and electrons, each energetic ion develops an orbit around the magnetic flux depending on their energy, angle of injection, and target energy absorption location at the central region of the plasma. Hence, these injected ions lose their energy to heat the plasma constituents by slowing down through Coulomb collisions initially with electrons and then with ions as their energy decreases.74 The neutral beam provides efficient current drive in the gap between the central deposition of ion-cyclotron heating at the magnetic axis and the deepest penetration depth of the LH waves and HCs. In addition to basic steering of the neutral beam through the vacuum vessel and into the plasma, the ion source/accelerator can be divided into subregions with each of them aiming toward a different location at the core of the plasma, which gives the flexibility to drive either a locally concentrated or a broadly spread current profile over a range of 0 < < 0.6 (Ref. 71).
Microscopic and hydrodynamic impact energy transfer from nanoplasma electrons to ions in exploding clusters
Published in Molecular Physics, 2018
The SEID procedure developed by us for EIET simulations was applied to clusters with fixed ionic charges (Section 2). This procedure was used to calculate the EIET contribution in the experimentally available clusters (H+)N, (He2+)N and (Ne8+), and in the model systems of (He+)N, (Ne+)N and (Ne4+)N clusters. The clusters listed above fall into two categories, resulting in two different classes of collisions, which are driven by distinct electron-ion interactions: (i) (H+)N and (He2)N clusters contain bare nuclei so that the electron-ion potentials are attractive and purely Coulomb (over distances exceeding ∼10−13cm). In this case, the electron-ion collisions, which are specified by a Coulomb interaction at short distances, will be referred to as ‘Coulomb collisions’. (ii) Ions of the (He+)N, (Ne+)N, (Ne4+)N and (Ne8+)N clusters contain ionic cores with radii (in the range of Å) which are somewhat smaller than the neutral atom radii. When the collisions are elastic, the electron-ion, like the electron-atom, potentials may be considered as being strongly repulsive at distances smaller than the atom (ion) radius [33], remaining attractive and Coulomb-like at larger distances. We shall refer to the electron-ion collisions in this case as ‘repulsive collisions’. It is important to note that our EIET simulation procedure (Section 3) is applicable for both Coulomb and repulsive collisions.
Multiscale modelling and splitting approaches for fluids composed of Coulomb-interacting particles
Published in Mathematical and Computer Modelling of Dynamical Systems, 2018
In the experiments, we use particles, which are Ar ions. For the transport step, the particles are globally transported by the Newtonian transport equation and controlled by an external electrical field. For the collision step, the particles interact locally by Coulomb collisions. In the collision step, we choose each particle of the 100 particles as a test particle and use the average of the other particles as the field particle.