GENERAL OPERATION 5-1
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Copyright © 2010 by Kaufman & Robinson, Inc., 1306 Blue Spruce Drive, Unit A, Fort Collins, CO 80524
Tel: 970-495-0187, Fax: 970-484-9350, Internet: www.ionsources.com
5. GENERAL OPERATION
The quickest way to start operation of the KRI Ion Source and its Controller is to
follow the sequence described in Section 4, Initial Operation. This section gives a
general overview of the ion source power supplies and their interconnection with
the ion source.
5.1 Description of Ion-Source/Controller Components
The operation of the End Hall Ion Source with its power supplies can be gener-
ally understood by reference to the schematic block diagram of Fig. 5-1.
The commonly used symbols for the currents and voltages are also shown in
Fig. 5-1. The voltage and current of the Keeper Power Supply are V
k
, and I
k
; the
voltage and current of the Emission Power Supply are V
b
, and I
b
; while the volt-
age and current of the Discharge Power Supply are V
d
, and I
d
. The discharge
voltage and current has sometimes been referred to as the anode voltage and
current and given as I
a
and V
a
, but only the symbols Id and Vd will be used
herein.
A mass
fl
ow controller (MFC) establishes a gas
fl
ow through the hollow cath-
ode of 100 sccm to establish a high enough pressure that a Paschen discharge
can be established when the keeper voltage, V
k
, of 800 volts is applied. The
Paschen discharge heats the hollow cathode until surfaces inside the cathode
tube are hot enough for thermionic emission. Once the thermionic emission is
established, only about 10 – 40 volts are required to keep the hollow cathode
ignited using 1.5 amps of keeper current, I
k
. After ignition, the gas
fl
ow to the
hollow cathode is reduced to the operating
fl
ow, typically 10 sccm.
After the hollow cathode is ignited, a negative bias voltage, V
b
, is applied to
the cathode to establish the electron emission. The Emission current, I
b
, is the
amount of electron current in amps that is available to operate the ion source.
With the Emission current initialized, the other MFC supplies gas to the ion
source. The neutral gas molecules
fl
ow into the anode. The Discharge Power
Supply applies a positive potential, V
d
, to the anode. Some of the electrons from
the hollow cathode are attracted to the positive anode, but they are impeded
by a magnetic
fi
eld (not shown in the
fi
gure). This magnetic
fi
eld con
fi
nes the
electrons until they bump into neutral gas atoms and knock off electrons, creat-
ing positive ions in the process. The ions are repelled from the positive anode
and
fl
ow outward. Some of the electrons from the hollow cathode mix with the
outward
fl
owing ions to equalize the charge. This mixture of ions and electrons
is the neutralized ion beam, although it is usually referred to as the ion beam
