CRC Press eBooks

Designing an Atomic Beam

Cyril Bernard Lucas

Published Nov 27, 2013• 0 citations

Abstract

Generally lower temperatures of evaporation make most aspects of oven design easier than those discussed in Chapter 5 and included in this group are ovens for the production of beams of alkali metals and their salts. Some special techniques are, however, necessary to handle the alkali metals because of their reactivity with moist air, which increases with atomic number Z. One solution is to produce the beam by a reaction of stable substances in the oven and we begin the discussion of the alkali metals with those cases in Section 4.2. We then consider in Section 4.3 more conventional ovens where the material to be evaporated is loaded directly into the oven. In Section 4.4 we turn to the alkali halides, which have problems due to their corrosiveness in the liquid and vapour state. Ovens where an ampoule of material has to be broken are discussed in Section 4.5. Finally in this chapter we discuss recycling ovens, where material that is not formed into a useful beam is returned to the oven.

DOI: 10.1201/b16345-10

Related papers

Theory of Collimated Atomic Beam Formation

Cyril Bernard Lucas

If a beam is to be produced from a material that is solid or liquid at laboratory temperature, then it must be converted to a vapour in an oven before it passes through the beam-forming impedance. In the reviews mentioned in Section 1.2, the approach has usually been to give details of numerous designs. In this chapter, we discuss the general design principles, and then the next two chapters become more of a reference source for the evaporation of different substances. We thus include the experience of a large number of experimenters who have needed to heat a liquid or solid substance to form it into an atomic or molecular beam. If the material can be evaporated and raised to a temperature to give the required input pressure at the input to the impedance at a temperature less than about 1500 K, it is usual to describe the heating device as an oven. At higher temperatures, the device is usually called a furnace, but the distinction is not really necessary. Hence we will avoid the term except for thermal dissociation of a molecular species, discussed in Chapter 6, when very high temperatures are usually needed, so a furnace is a more appropriate term. For convenience we will also term a completely different approach, namely, the evaporation of the material by direct electron beam heating of the surface (Section 3.2.5) as an oven. ‘Crucible’ is used by many authors interchangeably with ‘oven,’ but it often implies a container for the material to be evaporated that is placed within a heated envelope.

CRC Press eBooksNov 27, 20130 citations

Simple oven design for highly reactive metal beam applications

Luis Bañares, Ángel González Ureña

An oven design suitable for producing stable beams of highly reactive metals is reported. Its attraction is in its simplicity, low cost and versatility in molecular beam and atomic/molecular physics experiments involving highly reactive metals such as rubidium, caesium, etc. An application is described for the case of atomic caesium, where the metal is produced by the chemical reaction Ba(s)+CsCl(s) to BaCl(s)+Cs(v). One of the main advantages of the present design is the use of a thin-walled, stainless steel pipe, as crucible and heater simultaneously, which considerably simplifies its design. With respect to the experimental method, the simplicity in the loading, working and cleaning procedures compared with the use of pure metal should be noted.

Journal of Physics E Scientific InstrumentsDec 1, 19896 citations

Other Indications

Cyril Bernard Lucas

Two topics that logically follow a chapter on gases are included here, namely, the recirculation of gases used to form beams and the levitation of solids. This was originally undertaken with gas beams, but we take liberties with the chapter title by including other methods that may prove useful for atomic beam production. Details of the vacuum systems in which the beam is produced, such as pumping and differential pumping, have not, in general, been included when discussing experiments, since these tend to be closely associated with the experiment for which the beam is required. Neither have general vacuum techniques been discussed, since these are covered in the many textbooks devoted to them. We nevertheless include details of methods that have been or could be used to recycle gases used in atomic beam experiments, since these tend not to be included elsewhere. It is also not our practice to discuss atomic beam applications such as those that are covered by the review articles referred to in Section 1.2, but we make an exception for levitation by atomic beams, since we are not aware of any review that includes these. We then add other levitation techniques that might prove useful for producing beams of refractory metals.

CRC Press eBooksNov 27, 20130 citations

A compact and efficient strontium oven for laser-cooling experiments

M. Schioppo, N. Poli, M. Prevedelli +4 more

Here we describe a compact and efficient strontium oven well suited for laser-cooling experiments. Novel design solutions allowed us to produce a collimated strontium atomic beam with a flux of 1.0 × 10(13) s(-1) cm(-2) at the oven temperature of 450 °C, reached with an electrical power consumption of 36 W. The oven is based on a stainless-steel reservoir, filled with 6 g of metallic strontium, electrically heated in a vacuum environment by a tantalum wire threaded through an alumina multi-bore tube. The oven can be hosted in a standard DN40CF cube and has an estimated continuous operation lifetime of 10 years. This oven can be used for other alkali and alkaline earth metals with essentially no modifications.

arXiv:1209.5639Review of Scientific InstrumentsOct 1, 201260 citations

Recirculating atomic beam oven

Gary M. Carter, David E. Pritchard

We describe an atomic beam oven that reuses alkali metal in the unused portion of the beam. This is accomplished by condensing the desired vapor on a cooled jacket from which it may be drained back into the oven.

Review of Scientific InstrumentsJan 1, 19788 citations

Concluding Observations

Cyril Bernard Lucas

In Section 1.1 we introduced the subject of atomic and molecular beam formation by stating that a beam with a cosine distribution is obtained when the beam-forming impedance is a circular orice and that a narrow slit has also been employed to produce an improved beam. Most relevant theoretical papers use the convention of referring to ‘molecules’ for both atoms and molecules, but we continue to retain the consistent use of ‘atoms’ to mean both atoms and molecules unless a distinction is necessary. Following the introduction of the basic equations of the kinetic theory of gases in Section 2.2, the relatively simple expressions for the beam formed by an orice were introduced in Section 2.3. It was also mentioned in Section 1.1 that when the impedance is a single tube a much narrower collimated beam is obtained and that by employing an array of tubes a greatly improved beam intensity is obtained. In this chapter we present the theory of beam formation to include the more difcult case of ow through a tube. We only briey mention calculations that only apply when Γ ≤ 10 where Γ is the ratio of length l to diameter d (Section 2.5). These are of little interest for atomic beam formation, but are needed for calculations of Knudsen cell operation, which are outside the scope of this work. Following the discussion of the basic theory, we present in the next chapter simplications that make the design of an atomic beam and the predictions of its performance easier. However, we warn that an extensive comparison of theoretical results with experiment in Chapter 11 points to an unsatisfactory disagreement between theory and experiment for the beam halfwidth, especially in the case of gaseous rather than vapour beams and also particularly when the beam-forming impedance is a focussing capillary array.

CRC Press eBooksNov 27, 20130 citations