300
13.
THE ACCELERATION OF IONS
mutual repulsion, spread to the surface of the sphere, raising it to
a high potential.
Referring to the left half of gure 13—7, there is a supply of
.
comparatively low voltage, say 10 to 20 kilovolts from a transf0rmer-rectier—lter circuit.
This voltage is applied to two
electrodes located on opposite sides of the belt, at Â. The arrow
represents, either a row of needle points or a wire stretched parallel
-
to the belt and normal to its motion.
The dot represents a metal
surface with rounded, smooth edges and is called the
“
inductor
”
plate.” The system at  is called
“
the spray,” since thebrush
-
+
—
‘
+
+.
—
—
…
‘
_
+
0
+
-
-
_
C<—o
D
+
«.b
+
—
«:.:
-
_
+
__
_
+
.
+
—,
'
"—
+
O
‘.
'0-20 KVO
FIG. 13—7.
The Van de Graa‘ electro-static generator.
or
corona discharge sprays charges of one sign onto the belt
_The
is made of paper, rubber, Silk, etc., is often several
feet ln Wldth and travels at the rate of, say 5000feet per \m1nute
Thelimit of
which may be applied to the belt is of the order
centimeter on each surface and, lsset
.
the air. .. At C
gure 13—7,,the pes1twe
î
*=9‘her_ge
the hole by»means of a collector eoneetmg
ofehafppomteoroweThus the collector becomes charged
POSIÜVÊIV anddraWsam€gatlve
from “the sprayat,