Neutral beam penetration

Only a small fraction of the particles needed to fuel the plasma will be injected from external sources, like gas puff, neutral beams or pellets. The majority enters the plasma via recycling from divertor plates, baffles, limiters and wall. This motivates investigations about the actual recycling mechanisms. In particular, the velocities of the hydrogen particles are of interest in view of the penetration depth, and they are closely connected to the recycling mechanisms. 

In the case of XPS, the surface sensitivity is characterized by the mean free-path length of the photoelectrons of a few nanometers that applies for up to 10 atomic layers. On the other hand, LIES occurs when a beam of low electron energy (from 100 eV up to 1 keV) is applied to the surface, and the energy of the elastically scattered ions is analyzed later. The surface sensitivity is largely enhanced because of the large ion neutralization that penetrates into the bulk of the sample. Only the top layer is able to respond to this signal. 

In the SIMS a primary noble gas atom or ion (e.g. Ar°, Ar+, Xe°, Xe+) beam is bombarded on the sample in ultra-high vacuum, penetrating to a depth of 30-100 A. The kinetic energy of the particle is assumed to dissipate via a collision cascade process, which causes the emission of electrons, neutral species and secondary ions, the yields of which vary with polymer surface composition and obviates the possibility of quantitative SIMS informa-... 

Multicharged ions coexist with neutral species in plasmas produced by high-frequency photons, or when a current of neutral atoms is injected into a magnetically confined plasma. The degree of penetration of a neutral hydrogen beam is very dependent upon charge-transfer processes of the type... 

Principles and Characteristics The twin techniques of secondary neutral mass spectrometry (or sputtered neutral mass spectrometry, SNMS) and SIMS, which share bombardment of the sample surface with a focused primary ion beam (Ar+, Cs+, Ga+, O2) of sufficiently high ion energy (some keV), are among the most powerful surface analytical techniques for compositional characterisation of surfaces. As in SIMS, in SNMS the implanted primary ions penetrate into the solid surface to different depths (1-10 nm) and transfer their kinetic energy as a function of the sample material, primary ion energy and mass. Whereas SIMS detects the directly emitted secondary ions, in SNMS the secondary sputtered ions are suppressed by a... 

More recently, low-energy ion scattering spectroscopy (LEISS) has been used to elucidate the surface coverage of the monolayer supported and bulk vanadium and molybdenum oxide-based catalysts under in situ thermal treatments [2]. In LEISS, a beam of ions (typically, He+) with a certain energy (0.1 to 10 keV) scatters elastically from the outermost layer of atoms since the ions that penetrates the solid are neutralized [1]. 

Ion-Scattering Spectroscopy (ISS). ISS utilizes low energy (0.1-3 KeV) inert gas ions as the incident beam." A fraction of these ions undergo collisions with surface atoms and are backscattered with some loss of energy. Back-scattering will only occur from atoms at the surface, since ion neutralization occurs for incident ions that penetrate beyond the first layer. 

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