13—7.
THE ACCELERATOR TUBE
303
well known.
It is also possible to generate undamped, high
voltages at high frequencies by means of Vacuum tube oscillators
and resonance transformers.14
An x—ray machine of this type is
shown
in
gure 13—11.
OSCILLATOR
The oscillator is of the
tuned
plate-tuned
grid
'
,
'
'
type,
has
considerable
OH
OH
power (1OQ kw.) and
is
®*䣔
supplied With unrect1ed
:
.
nsooov
a.c.
A s1ngle turn of cop—
A.C.
a
per tubing is used to couple
'
to the quarter wave reso“ii"1
nance
coil (C).
The coil
\
is grounded at its upper
FILAMENT
E C
end and is water cooled.
\
:
A
grid (G) is provided 3…93__
__".—"
With a.c. so that electrons
L
\ANODE
LEAD
can
leave
the
lament
:
4/
only when the lower end
GRID G
VOLTAGE
ï£
A
electrons have been pro—
_
duced.
The machine may also be used for ion acceleration
by the substitution of a horizontal tube for the anode and of a
source of ions for the lament.
ACCELERATOR TUBES
13—7.
The Accelerator Tube.—The acceleration of ions by
means of a high voltage generator
involves the use of a spec1al
vacuum
tube.
First of all, the tube itself must be suic1ently
long that sparkover does not occur from one end to the other in
the air outside.
The source of ions and the target may be mounted
on long supports very near to each other in the center of the highly
evacuated tube, since exceedingly high voltages are needed t_°
break down even a few millimeters of good vacuum (10—5 mïuf‘
meter pressure or lower).
High
tubes and rect1—
ers (see figure 13—6) are often built in this manner.
The salient features of the tubes used at very h1gh voltages