Beam Deflection Measurements Research Articles

Photothermal probe beam deflection measurement of thermal diffusivity of atmospheric air

We have used a modified photothermal probe beam deflection system with a back pumping configuration for the measurements of the temperature-dependent thermal diffusivity of atmospheric air. The results are consistent and reasonably well agree with the literature values. The measured thermal diffusivity values are the same for the same measuring temperature regardless of the beam offsets and the deflecting surface temperatures. For the gas with known temperature-dependent thermal diffusivity, this method can be used to deduce the temperature of a gas from the measured thermal diffusivity value.

Noncontact photothermal probe beam deflection measurement of thermal diffusivity in an unconfined hot gas

A pulsed CO2 laser beam is used to produce a transient thermal refractive index gradient in a nitrogen gas doped with trace amounts of absorbing Freon 12 at temperatures from 25 to 425 °C. The diffusion of this gradient is probed by a continuous helium-neon laser beam parallel to but displaced from the pulsed beam. The observed defletion signal agrees well with theory, and thermal diffusivity or gas temperature can be derived from the signal.

RF Beam Deflection Measurements and Corrections in the SLC Linac

The requirements of RF acceleration in the SLC Linac to produce high energy beams are complicated by the presence of small transverse RF beam deflections which arise from several sources. These RF deflections place stringent tolerances on the phase and amplitude stability of the klystrons. They also force the use of special magnetic bumps to correct the trajectories of oppositely charged beams that will pass down the linac. If left unabated, RF deflections can limit the performance of the SLC. There are several methods to reduce the deflections. Many measurements of RF deflections have been made in the low energy part of the linac where the beams are most sensitive.

Dynamic concentration of positive ions near the axis of an electron plasma column

A steady-state non-neutral plasma, generated by Penning discharge, is used as a focusing element for MeV ion beams. An almost pure electron plasma column is produced which has nearly constant density (109–1010 cm−3) inside a radius of several millimeters. The background gas is at a pressure of 10−7 torr or less. A model calculation is presented which shows that although orbital damping is negligible, positive ions created by electron-neutral collisions are dynamically concentrated near the axis of the plasma. Light emission by excited ions in the plasma is observed to be brightest in a thin line along the axis. The measured radial profile of relative light intensity is in good agreement with the calculated ion distribution. A radial charge density profile of the plasma, which is inferred from beam deflection measurements, is depressed by several percent near the axis due to positive ions concentrated there.

Determination of the flexural strength and elastic modulus of ice from in situ cantilever-beam tests

From the theory of cantilever beams on an elastic foundation, it is shown that the strength index and modulus index of ice can be determined from measurements of either the failure load or the tip deflection, or both, of in situ cantilever beams tested over a wide enough range of ratio of beam length to beam thickness. Four methods are proposed, two of which do not require the measurement of beam deflection during beam loading, an often difficult task to perform with sufficient reliability, especially in the field. The methods have been applied to available field and laboratory data. The initial results show reasonably consistent estimates of the strength index but a large variation in the predicted values of the modulus index. One preferred method is suggested but its validity and reliability need to be further evaluated by analyzing a sufficient number of field and laboratory tests.

Generation and Storage of SEM or STEM Intensity Profiles on a Multi-Channel Analyzer

Using an SEM for quantitative analysis often requires intensity profiles along a single scan line. These profiles are usually obtained by either: 1) selecting a scan line from the CRT display, switching to Y-modulation and photographing the displayed intensity profile, or 2) scanning the negative of a photograph of the entire CRT display along a line using a microdensitometer. The first method requires additional measurements of the CRT beam deflection to get quantitative information, and thus has limited accuracy. The second method places another interface between the measurement and the detector signal.For SEMs or STEMs equipped for energy dispersive x-ray analysis with a multichannel analyzer (MCA) and minicomputer, modifications can be made to the circuitry to allow digital recording of line scan intensity data directly with the MCA.

Ground state dipole moment of NaH

Measurements and analysis of the electric deflection of a sodium hydride molecular beam is presented. The electric dipole moment of ground state NaH is calculated from measurement of beam deflection. (AIP)

Distribution of atomic momentum in resonance fluorescence

It is shown that the distribution of the momentum transfer to an atom in resonance fluorescence may be easily derived from the angular distribution of spontaneously emitted photons. Some general properties of the momentum distribution are found, and explicit forms of the distribution are derived for several special cases. It is shown that the distribution tends to become Gaussian after a large number n of spontaneous photon emissions, with variance proportional to n, but it is already close to the asymptotic form when n=3. When the appropriate averaging is performed to allow for the velocity spread of the atoms, the derived distributions account for the results of atomic beam deflection measurements, but much of the information about the original distributions is thereby lost. In a standing wave field both stimulated and spontaneous emissions contribute to the atomic momentum, in such a way that the variance of the momentum spread is again proportional to the number n of photon emissions.

Measurement of alkali-metal polarizabilities by deflection of a velocity-selected atomic beam

The electric dipole polarizability of the alkali-metal atoms Na, K, Rb, and Cs are determined by measuring the deflection of a velocity-selected beam by an inhomogeneous electric field. It is shown experimentally that scattering of slower beam atoms by background gas in the apparatus is an important systematic error in measurements of this kind if a beam-velocity selector is not used, and that this scattering is responsible for the discrepancies between different, earlier beam-deflection measurements of polarizability. The polarizability values obtained in this work are $\ensuremath{\alpha}(\mathrm{Na})=24.4\ifmmode\pm\else\textpm\fi{}1.7$ ${\mathrm{\AA{}}}^{3}$, $\ensuremath{\alpha}(\mathrm{K})=45.2\ifmmode\pm\else\textpm\fi{}3.2$ ${\mathrm{\AA{}}}^{3}$, $\ensuremath{\alpha}(\mathrm{Rb})=48.7\ifmmode\pm\else\textpm\fi{}3.4$ ${\mathrm{\AA{}}}^{3}$, and $\ensuremath{\alpha}(\mathrm{Cs})=63.3\ifmmode\pm\else\textpm\fi{}4.6$ ${\mathrm{\AA{}}}^{3}$.

Measuring rotationally symmetric potential profiles with an electron-beam probe

An electron-beam probe has been developed to measure the potential profile of a plasma within a spherical grid structure which was designed to trap charged particles. The potential was obtained from observed deflections of a collimated beam of electrons incident upon the device at selected impact parameters. The beam consisted of conversion electrons of 62.2 and 84.2 keV from a Cd109 source. Deflections of the beam through the plasma were measured relative to the beam trajectory without voltage applied to the grids. A movable detector allowed angular resolution to within 0.08 deg for maximum deflections of 7 deg. The inversion of the nonlinear singular integral relating potential and deflection is accomplished in an iterative manner with appropriate series expansions about the singular points. Simulations using postulated potential profiles show this procedure to give accuracy typically better than 4% with 20 deflection samples. Beam deflection measurements in spherical electrostatic systems without plasma show this probe technique to be very accurate. For a variety of experimentally controlled plasma parameters, no measurable departures from electrostatic potential profiles were observed.

Alkali Polarizabilities by the Atomic Beam Electrostatic Deflection Method

The electric dipole polarizabilities of the alkali atoms have been measured by observing the deflection of a collimated beam of neutral atoms in a two-wire-type inhomogeneous electric field. Beam deflection measurements are taken both for the case when ${s}_{B}$, the deflection of atoms with the most probable velocity in the source, is larger than the detector wire width ${w}_{d}$, and for ${s}_{B}l0.1{w}_{d}$. The results in units of ${10}^{\ensuremath{-}24}$ ${\mathrm{cm}}^{3}$ are: $\ensuremath{\alpha}(\mathrm{Li})=22\ifmmode\pm\else\textpm\fi{}2$, $\ensuremath{\alpha}(\mathrm{Na})=21.5\ifmmode\pm\else\textpm\fi{}2$, $\ensuremath{\alpha}(K)=38\ifmmode\pm\else\textpm\fi{}4$, $\ensuremath{\alpha}(\mathrm{Rb})=38\ifmmode\pm\else\textpm\fi{}4$, and $\ensuremath{\alpha}(\mathrm{Cs})=48\ifmmode\pm\else\textpm\fi{}6$. These values are in reasonable agreement with other recent experimental and theoretical determinations of the alkali polarizabilities.