In particle physics, Rutherford scattering is the elastic scattering of charged particles by the Coulomb interaction. It is a physical phenomenon explained by Ernest Rutherford in 1911 that led to the development of the planetary Rutherford model of the atom and eventually the Bohr model. Rutherford scattering was first referred to as Coulomb scattering because it relies only upon the static electric (Coulomb) potential, and the minimum distance between particles is set entirely by this potential. The classical Rutherford scattering process of alpha particles against gold nuclei is an example of "elastic scattering" because neither the alpha particles nor the gold nuclei are internally excited. The Rutherford formula (see below) further neglects the recoil kinetic energy of the massive target nucleus.
The initial discovery was made by Hans Geiger and Ernest Marsden in 1909 when they performed the gold foil experiment in collaboration with Rutherford, in which they fired a beam of alpha particles (helium nuclei) at foils of gold leaf only a few atoms thick. At the time of the experiment, the atom was thought to be analogous to a plum pudding (as proposed by J. J. Thomson), with the negatively-charged electrons (the plums) studded throughout a positive spherical matrix (the pudding). If the plum-pudding model were correct, the positive "pudding", being more spread out than in the correct model of a concentrated nucleus, would not be able to exert such large coulombic forces, and the alpha particles should only be deflected by small angles as they pass through.
However, the intriguing results showed that around 1 in 20,000 alpha particles were deflected by very large angles (over 90°), while the rest passed through with little deflection. From this, Rutherford concluded that the majority of the mass was concentrated in a minute, positively-charged region (the nucleus) surrounded by electrons. When a (positive) alpha particle approached sufficiently close to the nucleus, it was repelled strongly enough to rebound at high angles.
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In particle physics, Rutherford scattering is the elastic scattering of charged particles by the Coulomb interaction. It is a physical phenomenon explained by Ernest Rutherford in 1911 that led to the development of the planetary Rutherford model of the atom and eventually the Bohr model. Rutherford scattering was first referred to as Coulomb scattering because it relies only upon the static electric (Coulomb) potential, and the minimum distance between particles is set entirely by this potential.
Scattering is a term used in physics to describe a wide range of physical processes where moving particles or radiation of some form, such as light or sound, are forced to deviate from a straight trajectory by localized non-uniformities (including particles and radiation) in the medium through which they pass. In conventional use, this also includes deviation of reflected radiation from the angle predicted by the law of reflection.
The Rutherford model was devised by the New Zealand-born physicist Ernest Rutherford to describe an atom. Rutherford directed the Geiger–Marsden experiment in 1909, which suggested, upon Rutherford's 1911 analysis, that J. J. Thomson's plum pudding model of the atom was incorrect. Rutherford's new model for the atom, based on the experimental results, contained new features of a relatively high central charge concentrated into a very small volume in comparison to the rest of the atom and with this central volume containing most of the atom's mass.
Solid State Physics IV provides a materials and experimental technique oriented introduction to the electronic and magnetic
properties of strongly correlated electron systems. Established knowledge is
Presentation of particle properties, their symmetries and interactions.
Introduction to quantum electrodynamics and to the Feynman rules.
This advanced theoretical course introduces students to basic concepts in wave scattering theory, with a focus on scattering matrix theory and its applications, in particular in photonics.
Delves into plasmonics fundamentals, covering the Drude model, scattering by small particles, plasmonic metals, resonant nanoparticles, and experimental observations.
Delves into non-equilibrium electron-phonon interactions, energy conversion, and transport regimes.
Explores electron-proton elastic scattering, form factors, and the implications of the proton's finite size.
Neoclassical tearing modes (NTMs), magnetic islands located at rational q surfaces, are an important class of resistive magnetohydrodynamics (MHD) instabilities in tokamak plasmas, with q the safety factor. NTMs are one of the main constraints of the achievable plasma pressure by increasing the local radial transport and NTMs can lead to plasma disruptions. It is therefore crucial to understand the physics of NTMs and ensure their reliable control.This thesis explores the physics and control of NTMs, by means of dedicated experiments in the TCV tokamak and interpretative simulations with the modified Rutherford equation (MRE), a model widely used in interpreting island width evolutions. Triggerless NTMs originating from unstable tearing modes (TMs, stability index Δ′>0) and saturating under the effects of the perturbed bootstrap current are the main focus of this thesis.In TCV, triggerless NTMs are reproducibly observed in low-density discharges with strong near-axis electron cyclotron current drive (ECCD), providing an excellent opportunity of studying these modes. Instead of direct computations of Δ′, a model for Δ′ is developed based on extensive experiments and interpretative simulations. This model facilitates the clarification of the complete evolution of triggerless NTMs, from onset as TMs to saturation as NTMs. Our Δ′ model also explains an unexpected density dependence of the onset of NTMs, where NTMs only occur with a certain range of density that broadens with increasing near-axis ECCD power and with lower plasma current. The density range is found to result from the density and plasma current dependence of the stability of ohmic plasmas and the density dependence of ECCD efficiency.Given its high localization and flexibility, off-axis ECH/ECCD will be used for NTM control in future tokamaks. Comprehensive experimental and numerical studies of the dynamics of NTMs are carried out in this thesis, concerning both the stabilization of existing NTMs and the prevention of NTMs by means of preemptive off-axis ECCD. It is shown and predicted that the prevention of NTMs is much more efficient than NTM stabilization in terms of EC power. Interpretative simulations of the complex set of experiments constrain well the coefficients in the MRE and quantify NTM evolutions. The prevention effects from off-axis ECCD are found to result from local ECH/ECCD instead of a change of Δ′.A key element of a reliable real-time (RT) control of NTMs is the alignment of EC beams with the target mode location. A small sinusoidal sweeping of the deposition location of EC beams around the target location proves to be effective for both NTM stabilization and prevention, making it a promising technique. Integrated control of NTMs, plasma pressure and model-estimated q profiles is demonstrated on TCV, including advanced plasma state reconstruction, monitoring, supervision and actuator management. A RT-capable MRE module, based on our validated MRE, is developed for the first time and tested by extensive offline simulations for TCV and AUG. It provides a more intelligent physics-based NTM controller, aware of the EC power it requires to stabilize or prevent a given NTM. The information from the RT-MRE is also valuable for RT actuator allocations and decision-making in view of the overall integrated control, in particular for future long-pulse tokamaks like ITER and DEMO.