Time-of-flight analysis of neutrals from a plasma as a diagnostic for the ion velocity distribution

In a plasma energy is transferred from ions to neutrals by elastic collisions and charge exchange. By measuring the velocity distribution of the fast neutrals with a time-of-flight spectrometer, one gets very detailed information on the ion velocity distributio

Design of elastomer O-ring vacuum seals

Elastomer O-rings were developed in hydraulics, but design criteria from this field are not suitable in high vacuum technique. In the literature, information on O-ring vacuum seals is normally given in the form of tabulated recipes for groove dimensions. Measurements of the mechanical properties (shown in figures) of O-ring enable us to extend these recipes to a general criterion for high vacuum sealing: a contact pressure at the rubber-metal interface of 13 kg/cm2. Design of seals using free rings between flat flanges and seals using rings confined in grooves of rectangular and triangular section is treated. Figures and tables of design parameters are given. Correct design in the case of stretched rings is discussed. Important secondary results include the required compression force and the maximum allowed gap (if required) between mating flanges. Figures deal with these parameters. The influence of tolerances is treated too in the given examples.</p

A uniform temperature 400°C oven for UHV bake-out

An inexpensive and simple, but sturdy 400°C oven is heated with four 3 kW hot air guns. Due to their plug-in nature, a single set of hot air guns can be used for a number of ovens. The 1500 l/min flow of turbulent hot air keeps the UHV system at a uniform temperature during the bake-out.</p

Velocity distribution and angular distribution of molecular beams from multichannel arrays

Three stainless-steel multichannel arrays with channels of 16, 50, and 140 μm diameter have been investigated experimentally. The whole flow pattern is measured, including the angular dependence of the velocity distribution. All measurements concern the opaque mode, with λ≤L and λ≥α, where λ is the mean free path in the source and α and L are the radius and length of the channel, respectively. The results are compared with the predictions for free molecular flow in the same channel, as a function of the reduced source density n*=L/λ. The peaking factor is 30% lower than predicted by the Giordmaine-Wang model. At angles cursive-theta sign larger than the half-width-half-maximum cursive-theta sign1/2 the angular distribution is not perturbed by the opaque conditions; for cursive-theta sign<cursive-theta sign1/2 it levels off to a lower peaking factor due to operation in the opaque mode. The center-line beam shows an increasing loss of slow molecules for increasing n*. At n*=10 the gain in mean translational energy is 15%, much larger than predicted by the model of Olander. The deformation of the velocity distribution decreases with increasing angle, and for cursive-theta sign≳cursive-theta sign1/2 the molecules again have an unperturbed Maxwell-Boltzmann distribution

Accurate (0.25 mrad) perpendicular alignment of a continuous-wave single-mode dye laser beam and an atomic beam

Two simple methods are described for an accurate perpendicular alignment of a laser beam and an atomic beam, which is required for a velocity independent, i.e., Doppler-free interaction, of the laser beam with the atomic beam. With the first method a free running single-mode cw dye laser beam and an atomic beam are aligned perpendicular with an accuracy of 0.25 mrad. This alignment takes typically 2 h. The second method needs a laser beam that is absolutely stabilized to the investigated atomic transition. With this method a 0.2-mrad accurate perpendicular alignment is obtained within only 5 min