296
13.
THE ACCELERATION OF IONS
There is a focussing action on the ion beam each time it crosses
the gap
between the dees, due to the electro—static eld.
(See
_
Electron Optics in chapter 6.) As a result, the emergent beam
contains a large percentage of the ions which left the source.
The cyclotron chamber (gures 13—2 and 13—3) is evacuated
at rst to 10”5 to 10“6 millimeter after which a gas, such as hydrogen, deuterium or helium, is admitted to a pressure of 10‘4 to
10_3 millimeter of mercury (just below the glow point). Elec—
trons from the lament F, focussed into a vertical column by the
‘
magnetic eld, bombard the gas and create positive ions. The
ions are then accelerated by the negative dee. Their number
depends on the number of bombarding electrons, the gas pressure
and the effective length of the electron beam (somewhat less than
the distance between the top and bottom plates of the dees).
Output currents up
to 50 microamperes have been obtained.
The deecting plates have a radius of curvature from fteen
to thirtÿ per
cent greater than that of the ions to be deected.
Since the ions are of high energy, large electro—static forces are
,
needed, say
20 to 100 kilovolts per centimeter.
‘
The strength of the emergent ion beam may be measured by
means Of a shallow faraday chamber or a collecting wire of tungsten
(to avoid excessive production of neutrons) connected to a micro—
ammeter or electrometer.
The energy may be reduced by introducing absorbing foils in the path of the beam.
Materials to be
bombarded by the ions may be located either inside the chamber
or in the open air beyond a thin platinum window (say 0.000,1 inch
thick) supported on a water cooled grid.
Several microamperes of
5.8_ Mev deuterons will produce a lavender colored glow for 25
_
centimeters in theair.
A vacuum tube for the beam may be
fastened to the side of the cyclotron and experiments carried out
_
many feet away from the strong magnetic eld. However, iron
:
pieces or focussing coils are needed to concentrate the beam upon a
'
small area, since it is divergent as it leaves the
_
-.
THE PRODUCTION or HIGH VOLTAGES
,
,
_
The familiar static machine, the induction coil, the transformer
_
_
and the Tesla coil, as sources of direct, uni-direbtional, altérnating ‘
_
and high frequency voltages of high value need not be discussed
'
»
here.
'
.
_
'.
13.
THE ACCELERATION OF IONS
There is a focussing action on the ion beam each time it crosses
the gap
between the dees, due to the electro—static eld.
(See
_
Electron Optics in chapter 6.) As a result, the emergent beam
contains a large percentage of the ions which left the source.
The cyclotron chamber (gures 13—2 and 13—3) is evacuated
at rst to 10”5 to 10“6 millimeter after which a gas, such as hydrogen, deuterium or helium, is admitted to a pressure of 10‘4 to
10_3 millimeter of mercury (just below the glow point). Elec—
trons from the lament F, focussed into a vertical column by the
‘
magnetic eld, bombard the gas and create positive ions. The
ions are then accelerated by the negative dee. Their number
depends on the number of bombarding electrons, the gas pressure
and the effective length of the electron beam (somewhat less than
the distance between the top and bottom plates of the dees).
Output currents up
to 50 microamperes have been obtained.
The deecting plates have a radius of curvature from fteen
to thirtÿ per
cent greater than that of the ions to be deected.
Since the ions are of high energy, large electro—static forces are
,
needed, say
20 to 100 kilovolts per centimeter.
‘
The strength of the emergent ion beam may be measured by
means Of a shallow faraday chamber or a collecting wire of tungsten
(to avoid excessive production of neutrons) connected to a micro—
ammeter or electrometer.
The energy may be reduced by introducing absorbing foils in the path of the beam.
Materials to be
bombarded by the ions may be located either inside the chamber
or in the open air beyond a thin platinum window (say 0.000,1 inch
thick) supported on a water cooled grid.
Several microamperes of
5.8_ Mev deuterons will produce a lavender colored glow for 25
_
centimeters in theair.
A vacuum tube for the beam may be
fastened to the side of the cyclotron and experiments carried out
_
many feet away from the strong magnetic eld. However, iron
:
pieces or focussing coils are needed to concentrate the beam upon a
'
small area, since it is divergent as it leaves the
_
-.
THE PRODUCTION or HIGH VOLTAGES
,
,
_
The familiar static machine, the induction coil, the transformer
_
_
and the Tesla coil, as sources of direct, uni-direbtional, altérnating ‘
_
and high frequency voltages of high value need not be discussed
'
»
here.
'
.
_
'.