Conceptual Design of the Argonne 6-GeV Synchrotron Light Source
The Argonne National Laboratory Synchrotron Light Source Storage Ring is designed to have a natural emittance of 6.5 × 10-9 m for circulating 6-GeV positrons. Thirty of the 32 long straight sections, each 6.5-m long, will be available for synchrotron light insertion devices. A circulating positron current of 300 mA can be injected in about 8 min. from a booster synchrotron operating with a repetition time of 1.2 sec. The booster synchrotron will contain two different rf systems. The lower frequency system (38.97 MHz) will accept positrons from a 360-MeV linac and will accelerate them to 2.25 GeV. The higher frequency system (350.76 MHz) will accelerate the positrons to 6 GeV. The positrons will be produced from a 300-MeV electron beam on a tungsten target. A conceptual layout is shown in Fig. 1. Related papers on the Argonne Synchrotron Light Source may be found in references 1-3.
An Inexpensive Positron Converter of High Reliability and High Yield
A new positron converter of the simplest construction is described, consisting of a multiple fixed tungsten target and a very small helical positron lens, both inside a small vacuum chamber. By utilizing the good vacuum insulating properties the lens may be pulsed with 6000 A at an operating voltage of 10 kV without insulating material, except for the vacuum feed throughs, for which the extremely radiation-resistant aluminiumoxide ceramic is used. The lens construction out of a copper pipe allows direct water cooling and gives sufficient mechanical strength without further reinforcement. The system has been in operation for 3 years and gives a positron conversion ratio I+/I- of 0.8 % as a routine value for an e--energy of 300 MeV, where the positron energy spread is within ± 1.5 MeV. Compared to a dc-lens saving factors of about 500 in weight, 50 in power consumption and 100 in cost have been achieved.
Measurement and Demonstration of Thermal Expansion Coefficient
There are many classroom demonstrations, such as the ball-and-ring experiment, for showing the existence of thermal expansion of solids. The coefficient of linear expansion α (= increase in length divided by the original length times the change in temperature) may be measured in high school laboratories using a number of methods.1–4 In this paper we describe an especially simple experiment for determining α for a metal rod. It is based on the well-known optical lever method and is suitable for either a laboratory experiment or a classroom exercise.