Page:Design and Calibration of a New Apparatus to Measure the Specific Electronic Charge.pdf/19

 -15- II. The Design of the Apparatus.

2.0 Introduction.

The equipment necessary to carry out a measurement of e/m0 based on the theory given in I above involves many problems of vacuum, Radio Frequency, Electron Ballistics, electronics, etc. An attempt was made to obtain an integrated plan in which these factors combined to determine the final design. The apparatus consists of four main, and essentially independent, parts. We shall, accordingly, first treat general considerations and then each of these parts separately.

2.1 General Design Considerations.

It was clear from the outset that the heart of the apparatus would consist of a long evacuated tube with an electron source at one end, a collector at the other end, and the cavity somewhere in between. In figure 6,a cross sectional view of the final design arrived at is shown. The vacuum envelope and header are made of aluminum for reasons both of lightness and because aluminum is a good vacuum metal from the standpoint of occluded gas. All of the vacuum joints in the envelope use "O-ring" seals. ("O-rings" are a seamless molded rubber ring available from The Los Angeles Plastic and Rubber Products Co. ) Metal to metal aluminum joints are arc welded. Type 51ST Alcoa aluminum was used as it is the most readily weldable of the aluminum alloys. We were perhaps fortunate that no vacuum leaks occurred in the welds. Immediately inside of these aluminum tubes are a series of six concentric tubes made alternately