Electrostatic acceleration, schematic

Figure 2. (a) Schematic representation of electrostatic acceleration, (b) Schematic representation of acceleration by an oscillating electric field. Arrow lengths indicate the strength and direction of the acceleration that electrons undergo at different points in the RF phase. 

Schematic pictures of single-ended and two-stage configurations of electrostatic accelerators...

Figure 2 Schematic of the accelerator mass spectrometer at the Centre for AMS at Lawrence Livermore National Laboratory. Negative ions from a muiti-sampie ion source are separated by a low-energy mass spectrometer, accelerated to 6 MeV in an electrostatic accelerator, converted to positive ions by passage through a foil stripper, and accelerated again. Quadruply charged carbon atomic ions (30 MeV kinetic energy) are focused by quadrupole lenses and resolved by high-energy mass spectrometers, followed by velocity selection and identification of charge state in an ionization detector.

It is easiest to discuss the electron optics of a TEM instrument by addressing the instrument from top to bottom. Refer again to the schematic in F ure la. At the top of the TEM column is an electron source or gun. An electrostatic lens is used to accelerate electrons emitted by the filament to a h potential (typically 100-1,000 kV) and to focus the electrons to a cross-over just above the anode (the diameter of the cross-over image can be from 0.5 to 30 Mm, depending on the type of gun ). The electrons at the cross-over image of the filament are delivered to the specimen by the next set of lenses on the column, the condensers. 

In Eq. (48), y is the coefficient of surface tension, g is gravitational acceleration and Apm is the difference in mass densities between the aqueous and organic liquids. The interface position z = (r) and the deflection t(r) = — of the interface from its unperturbed position are shown schematically in Fig. 6. Nondimensionalization of Eq. (48) leads to two dimensionless groups that relate electrostatic and gravitational stresses to surface tension. These groups are called the electrostatic and gravitational bond numbers, and are given by [25]... 

The mixture of molecular ion and fragments is accelerated to specific velocities using an electric field and then separated on the basis of their different masses by deflection in a magnetic or electrostatic field. Only the cations are detected and a mass spectrum is a plot of mass-to-charge ratio (w/z) on the x-axis against the number of ions (relative abundance, RA, %) on the y-axis. A schematic of the components of a mass spectrometer is shown in Fig. 30.2 and an example of a line-graph-type mass spectrum in Fig. 30.3. 

Figure 1 Schematic depictions of electrostatic (a) and oscillating electromagnetic (b) fields for charged particle acceleration.

FIGURE 14.2 Schematic layout of a 14C accelerator mass spectrometer with 500kV double stage Pelletron accelerators. (Courtesy of National Electrostatics Corporation, Middleton, WI.)... 

Figure 16.6 A simplified schematic of a time of flight spectrometer and the principle of the ion reflector (reflectron). (1) sample and sample holder (2) MALDI ionization device by pulsed laser bombardment (3 and (3 ) ions are formed between a repeUer plate and an extraction grid (PD 5000V) then accelerated by an other grid (4) control grid (5) microchannel collector plate (6) signal output. Below, a reflectron, which is essentially an electrostatic mirror that is used to time-focus ions of the same mass but which have initially different energies. The widths of the peaks are of the order of 10 and the resolution ranges between 15 to 20 000.

A detailed description of the interacting beams apparatus used in the present work can be found elsewhere [12], In short, positive ions are extracted from a plasma-type ion source and accelerated to beam energies that can be varied between 2.5 and 5 keV. Negative ions are produced in the beam by double sequential charge exchange in a cesium vapor. A pair of electrostatic quadrupole deflectors (QD1, QD2) is used to direct the negative ion beam into and out of the path of the laser beams, as shown schematically in Fig. 2. The ion-laser interaction region is defined... 

Schematically shown in Fig. 5 is the preparation of an enzyme mimic for the hydrolysis of ester 6 by molecular imprinting. Phosphonate 5 is an analog of the transition state for the alkaline hydrolysis of Ester 4. It was used as a template for polymerization with two equivalents of the binding-site monomer iVJV -diethyl-4-vinyl-benzamidine. Amidinium groups were chosen, because they can interact electrostatically with the side carboxyl-ate group as well as with the anionic transition state of the alkaline hydrolysis, thus achieving substrate recognition and transition-state stabilization. Polymerization of the preassembled binding-site monomer with the template (Fig. 5A) followed by template removal (Fig. 5B) leaves a cavity that acts as transition-state receptor for the ester substrate (Fig. 5C). The imprinted polymer accelerates the hydrolysis of 6 more than 100-fold compared to the reaction at the same pH in buffer solution without the polymer. The reaction kinetics is of the Michaelis-Menten type. A polymer obtained with amidinium benzoate as a control, with a statistical distribution of amidinium groups, is ca. one order of magnitude less active in the hydrolysis of 6.

Fig. 4.36 Schematic of the reflective beam blocker setup. Ions are produced in a pulsed discharge and accelerated to 7 keV. A gold mirror is placed in the beam path to illuminate the fast moving ion packet with a 10 Hz IR laser pulse. A set of electrostatic electrodes is used to bump the ion beam over the reflective beam blocker. On the way to the ion detector the ion beam enters an electrostatic ion beam trap (EIBT) dedicated to photoelectron-photofragment coincidence (PPG) experiments [493]...

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