Extraction induced emittance growth for negative ion sources

Nonlinear emittance growth produced by ion extraction is considered by a 3-D analysis in a Vlasov-Poisson-Boltzmann formulation. Phenomena considered include: presheath effects, including electron depletion, electron sheath accumulation (for large transverse magnetic fields), nonlinear sheath fields (obtained by a self-consistent solution with an assumed quasi-equilibrium positive ion distribution and at least one Vlasov distribution), nonlinear fringe fields produced by the accelerator-extractor itself obtained self-consistently with item 3 above, nonlinear space charge of the beam itself, and beam in conjunction with extracted electrons. For specific volume negative ion source configurations, an investigation of the contribution of aberrations caused by an electron trap and electron accumulation in the extraction sheath are studied. Either of these effects can contribute significantly to the beam emittance, possibly dominating the contribution of the negative ion temperature in the source. 2 refs., 10 figs

Separation of beam and electrons in the spallation neutron source H{sup -} ion source

The Spallation Neutron Source (SNS) requires an ion source producing an H{sup {minus}} beam with a peak current of 35mA at a 6.2 percent duty factor. For the design of this ion source, extracted electrons must be transported and dumped without adversely affecting the H{sup {minus}} beam optics. Two issues are considered: (1) electron containment transport and controlled removal; and (2) first-order H{sup {minus}} beam steering. For electron containment, various magnetic, geometric and electrode biasing configurations are analyzed. A kinetic description for the negative ions and electrons is employed with self-consistent fields obtained from a steady-state solution to Poisson`s equation. Guiding center electron trajectories are used when the gyroradius is sufficiently small. The magnetic fields used to control the transport of the electrons and the asymmetric sheath produced by the gyrating electrons steer the ion beam. Scenarios for correcting this steering by split acceleration and focusing electrodes will be considered in some detail

Separation of beam and electrons in the spallation neutron source H{sup {minus}} ion source

The Spallation Neutron Source (SNS) requires an ion source producing an H{sup {minus}} beam with a peak current of 35 mA at a 6.2% duty factor. For the design of this ion source, extracted electrons must be transported and dumped without adversely affecting the H{sup {minus}} beam optics. Two issues are considered: (1) electron containment transport and controlled removal; and (2) first-order H{sup {minus}} beam steering. For electron containment, various magnetic, geometric and electrode biasing configurations are analyzed. A kinetic description for the negative ions and electrons is employed with self-consistent fields obtained from a steady-state solution to Poisson`s equation. Guiding center electron trajectories are used when the gyroradius is sufficiently small. The magnetic fields used to control the transport of the electrons and the asymmetric sheath produced by the gyrating electrons steer the ion beam. Scenarios for correcting this steering by split acceleration and focusing electrodes will be considered in some detail

Density, actidity, and conductivity measurements of uranyl nitrate/nitric acid solutions

Conductivity, density, and acidity (pH) measurements were made on a series of uranyl nitrate solutions under conditions closely simulating the process used to load weak acid resins in the preparation of the HTGR recycle fuel particle. To relate these parameters to the uranium and nitrate concentrations of the solutions, a least-squares fit of the experimental data and mathematical expressions resulting from computer curve-fitting techniques was made. Measurements were made on solutions having concentrations of 0.05 to 1.27 M uranium, 0.1 to 2.0 M nitrate, and NO/sub 3//U ratios from 1.56 to 2.3. These measurements were made at 25, 30, 40, 50, and 75/sup 0/C. From these experiments, the necessary data were obtained to write two computer programs which can be used to predict or calculate uranium and nitrate concentrations of the process solutions and which will allow control of the process to be exercised in the particle preparation

Electrostatic ion thruster optics calculations

Two- and three-dimensional ion thruster optical calculations including both source and exhaust plasmas are performed. These calculations include both a self-consistent ion source extraction plasma sheath and an explicit computation of the primary ion optics including sheath and electrode induced aberrations. A study determining the effects of beam space charge, accelerator geometry, and properties of the downstream plasma sheath on the position of the electrostatic potential saddle point near the extractor electrode is made. Results of the electron blocking potential barrier height as a function of electrode thickness and secondary plasma processes are described

Beam dynamics of a liquid metal ion source

RMS emittance growth of liquid metal ion sources is studied. Processes included are nonlinear expansion through extractor and accelerator fringe fields, nonlinear beam space charge, plasma effects near needle, and waves (either ion-acoustic or space charge limited as considered by V.I. Dudnikov). This investigation consists of 2-D analysis of appropriate Vlasov-Poisson equations in both steady-state and time-dependent formulations. Various geometries will be considered such as some used by G. Alton of ORNL. 2 refs., 7 figs