THE CYCLOTRON 91 



Dees D\ and D 2 are connected through an inductance in the manner 

 shown, so that they form a capacitance in an oscillatory circuit. If a 

 high-frequency potential is applied to the dees so that an alternating 

 voltage (± 50,000 volts) is operative between them while the electrical 

 center of the dee circuit is always at zero potential, an accelerating force 

 is developed by the electric field across the diametral gap between the 

 dees. Within the hollow dees, however, there exists a nearly field-free 

 region. 



An insulator is inserted through the port at S to carry the connections 

 to the hot tungsten spiral filament situated at the center of the vacuum 

 chamber. This filament is kept at about 1000 volts negative with 

 respect to the earth potential. 



The vacuum chamber may be filled with hydrogen, deuterium, or 

 helium at low pressure. Positive ions are produced at the center of 

 the vacuum chamber by collisions of the thermoelectrons with the gas 

 molecules. 



A positive ion in the gap between the two dees will be accelerated 

 by the intense electric field across this gap. In Fig. 11-15 is shown 

 such an ion accelerated across the gap from A to B, after which it will 

 pass into the field-free interior of D\. Under the influence of the per- 

 pendicular magnetic field the ion will trace out a semicircular path BC 

 within the dee and arrive at C. If the time which the ion has spent 

 within Di is equal to half of the periodic time of oscillation of the high- 

 frequency driving circuit, then, when the ion emerges into the gap be- 

 tween the dees at C, the electric high-frequency field will be reversed 

 and the ion will be given a second acceleration from C to E. It then 

 enters the field-free region inside of D 2 with a greater velocity than it 

 had when it passed through D x . Having a greater entrance velocity 

 at E, it will describe a half-circle of greater radius and arrive at F to 

 receive a further acceleration. As the speed increases, the ion describes 

 larger and larger semicircles until it reaches the periphery of the chamber 

 at(?. 



The magnetic intensity H will deflect the ion to describe a semicircle 

 of radius R such that mv 2 /R = Hev, where v is the velocity of the ion 

 of net charge e and mass m. After a large number of accelerations the 

 energy of the ion is \mv 2 = eV, so that 



H 2 R 2 e 



2m 



If e is expressed in electrostatic units and V in volts 



V = H 2 R 2 - (16.7 X 10- 20 ) volt 

 m 



