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Title: Measuring and Analyzing Transverse Low-Energy Ion Beam Emittances*

Abstract

The transverse emittance of an ion beam describes its transverse size as the particles are transported from a source to a target. It allows for predicting beam losses in limiting apertures and the beam focus size at the target. Various definitions and issues are discussed. The most common and emerging measuring techniques are presented, including their advantages. Several methods of emittance data analysis, their accuracy and trustworthiness, are discussed.

Authors:
 [1]
  1. ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Spallation Neutron Source (SNS)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
969768
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Conference
Resource Relation:
Conference: 17th International Workshop on ECR Ion Sources and Their Applications, Lanzhou, China, 20060917, 20060921
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; BEAM EMITTANCE; DATA ANALYSIS; ION BEAMS; BEAM DYNAMICS; MEASURING METHODS; ion beams; ion beam transport; ion beam emittance; ion beam diagnostics; emittance analysis

Citation Formats

Stockli, Martin P. Measuring and Analyzing Transverse Low-Energy Ion Beam Emittances*. United States: N. p., 2007. Web.
Stockli, Martin P. Measuring and Analyzing Transverse Low-Energy Ion Beam Emittances*. United States.
Stockli, Martin P. Mon . "Measuring and Analyzing Transverse Low-Energy Ion Beam Emittances*". United States. doi:.
@article{osti_969768,
title = {Measuring and Analyzing Transverse Low-Energy Ion Beam Emittances*},
author = {Stockli, Martin P},
abstractNote = {The transverse emittance of an ion beam describes its transverse size as the particles are transported from a source to a target. It allows for predicting beam losses in limiting apertures and the beam focus size at the target. Various definitions and issues are discussed. The most common and emerging measuring techniques are presented, including their advantages. Several methods of emittance data analysis, their accuracy and trustworthiness, are discussed.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}

Conference:
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  • In our previous work, we investigated the use of ion beam deposition (IBD) to grow epitaxial films at temperatures lower than those used in thermal processing (less than 500/sup 0/C). Presently, we have applied IBD to the growth of dense (6.4 x 10/sup 22/ atom/cm/sup 3/) silicon dioxide thin films at 400/sup 0/C. Through these experiments we have found several clues to the microscopic processes leading to the formation of thin film phases by low energy ions. Using Monte-Carlo simulations, we have found that low energy collision cascades in silicon have unique features such as a high probability of relocationmore » events that refill vacancies as they are created. Our results show that the combination of a low defect density in low energy collision cascades with the high mobility of interstitials in covalent materials can be used to athermally generate atomic displacements tha can lead to ordering. These displacements can lead to epitaxial ordering at substrate temperatures below the minimum temperature necessary for molecular beam epitaxy (550/sup 0/C). It can also lead to the formation of high quality silicon dioxide at temperatures well below that of thermal oxidation in silicon (i.e. <850/sup 0/C). A growth model which we derive from these observations provides a fundamental understanding of how atomic collisions can be used to induce epitaxy or compound formation at low temperatures.« less
  • A visual diagnostic technique has been developed to monitor and study ion beam structure shape and size along a transport line. In this technique, a commercially available fluorescent screen is utilized in conjunction with a video camera. This visual representation of the beam structure is digitized and enhanced through use of false-color coding and displayed on a TV monitor for on-line viewing. Digitized information is stored for further off-line processing (e.g., extraction of beam profiles). An optional wire grid placed upstream of the fluor screen adds the capability of transverse emittance (or angular spread) measurement to this technique. This diagnosticmore » allows real-time observation of the beam response to parameter changes (e.g., evolution of the beam structure, shifts in the beam intensity at various spatial locations within the beam perimeter, and shifts in the beam center and position). 3 refs., 5 figs.« less
  • A low-energy ion beam deposition system has been developed at Oak Ridge National Laboratory and has been applied successfully to the growth of epitaxial films at low temperatures for a number of different elements. The deposition system utilizes the ion source and optics of a commercial ion implantation accelerator. The 35 keV mass- and energy-analyzed ion beam from the accelerator is decelerated in a four-element electrostatic lens assembly to energies between 10 and 500 eV for direct deposition onto a target under UHV conditions. Current densities on the order of 10 ..mu..A/cm/sup 2/ are achieved with good uniformity over amore » 1.4 cm diameter spot. The completed films are characterized by Rutherford backscattering, ion channeling, cross-section transmission electron microscopy, and x-ray diffraction. The effects of substrate temperature, ion energy, and substrate cleaning have been studied. Epitaxial overlayers which show good minimum yields by ion channeling (3 to 4%) have been produced at temperatures as low as 375/sup 0/C for Si on Si(100) and 250/sup 0/C for Ge on Ge(100) at growth rates that exceed the solid-phase epitaxy rates at these temperatures by more than an order of magnitude.« less
  • The steady states associated with transverse injection of low-energy electrons into the region occupied by an ion beam are studied in a one-dimensional formulation. It is shown that the behavior in steady state is determined by the ratio of the injection current density to the critical current density. When the ratio is greater than unity a regime develops in which sheaths form at the walls. The magnitude of the critical current density is found for the cases in which the ion beam fills the chamber partly or completely. The dynamics of the neutralization process and the prospects for realizing themore » steady states found theoretically are studied by means of numerical simulation using the particle technique. 4 refs., 4 figs.« less