Charged particle generating apparatus

Details Charged particle generating apparatus Charged particle generating apparatus

1999-12-16

2001-11-20

Vu, David (Department: 2821)

Electric lamp and discharge devices: systems

With cathode or cathode heater supply circuit

Pulsating or a.c. supply to the cathode or heater circuit

C315S107000

Reexamination Certificate

active

06320319

ABSTRACT:

This patent application claims priority based on Japanese patent application, H10-357755 filed on Dec. 16, 1998, the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a charged particle generating apparatus for generating charged particles, and more particularly to a charged particle generating apparatus capable of preventing damage, which may be caused by incomplete contact between the cable connecting the electrode and the generating apparatus, to an electrode discharging charged particles.
2. Description of the Related Art
FIG. 1
shows a block diagram of a conventional charged particle generating apparatus. The charged particle generating apparatus
10
includes a first electrode
12
, a second electrode
14
, a current source
16
, a first voltage source
18
, a third electrode
20
, a second voltage source
22
and a third voltage source
24
. The charged particle generating apparatus
10
further includes a connection cable J
1
and a connection cable J
2
. The connection cable J
1
shown in
FIG. 1
makes an electrical connection between the second electrode
14
and the voltage source
18
. The connection cable J
2
makes an electrical connection between the first electrode
12
and the current source
16
. The charged particle generating apparatus
10
is an electron gun generating an electron beam
30
.
The current source
16
supplies current to the first electrode
12
in order to heat the first electrode
12
to a predetermined temperature. The voltage source
18
then applies voltage to the second electrode
14
to generate an electric field between the first electrode
12
and the second electrode
14
. The electric field is generated in such a way that the charged particles are attracted toward the second electrode
14
. Thus, the electron beam
30
is discharged from the first electrode
12
to the second electrode
14
because of the attraction formed by the electric field generated by the second electrode
14
. The second voltage source
22
applies negative voltage to the third electrode
20
. The result of this is that the third electrode
20
electrically attracts the electron beam
30
toward the second electrode
14
. The third voltage source
24
maintains the particle generating apparatus
10
with a negative potential to earth so that the electron beam
30
is easily discharged.
FIG. 2
(
a
) shows a current/time chart showing the ideal controlled current to be applied to the first electrode
12
for heating the first electrode
12
by the current source
16
. If the maximum current Ih is applied to the first electrode
12
in one step, a large amount of current flows through the first electrode
12
instantaneously. This causes unequal heat distribution on the first electrode
12
and increases the tension in a part of the first electrode
12
. The maximum current Ih is generally 2 to 3 amperes. The tension increase in the part of the first electrode
12
is undesirable because it may damage the first electrode
12
. Therefore, the current is gradually applied to the first electrode
12
up to the maximum current Ih as shown in
FIG. 2
(
a
). The time “t1” is on average from approximately ten seconds to one hundred seconds.
FIG.
2
(
b
) shows a voltage/time chart showing the ideal controlled voltage to be applied to the second electrode
14
by the voltage source
18
. If the maximum voltage Vmax is applied to the second electrode
14
in one step, the first electrode
12
may be damaged. The maximum voltage Vmax is generally about 5 kV to 7 kV. When the maximum voltage Vmax is applied to the second electrode
14
, instantaneously a large amount of current may flow through the first electrode
12
. This increases the tension in a part of the first electrode
12
. Therefore, the voltage is gradually applied to the second electrode
14
up to the maximum voltage Vmax as shown in FIG.
2
(
b
). The period between t
1
and t
2
is on average from approximately ten seconds to one hundred seconds.
The current/time characteristics and the voltage/time characteristics respectively shown in FIGS.
2
(
a
) and
2
(
b
) are predetermined by software included in the charged particle generating apparatus
10
. Therefore, the conventional charged particle generating apparatus
10
cannot respond to an accident happening to any of the components included in the apparatus
10
, for example, the current/time characteristic and the voltage/time characteristic when the connection cables J
1
and J
2
do not work normally.
FIG.
3
(
a
) shows a current/time chart showing current applied at time t
3
to the first electrode
12
by the current source
16
when the electric connection between these (the connection cable J
2
) is accidentally disconnected. The electric connection is then reformed at time t
4
. When the electric connection between the first electrode
12
and the current source
16
is disconnected at time t
3
, the current does not flow through the first electrode
12
thereby cooling it. When the electric connection between the first electrode
12
and the current source
16
is reformed at time t
4
, the maximum current Ih as shown in FIG.
2
(
a
) is applied to the first electrode
12
instantaneously. As described above, if the maximum current is applied to the first electrode
12
in one step, the first electrode
12
may be damaged.
FIG.
3
(
b
) shows a voltage/time chart showing voltage to be applied to the second electrode
14
by the voltage source
18
when the electric connection between these (the connection cable ii) is accidentally disconnected at time t
5
. The electric connection is then reformed at time t
6
. When the electric connection between the second electrode
14
and the voltage source
18
is disconnected at time t
5
, voltage is not supplied to the second electrode
14
. When the electric connection between the second electrode
14
and the voltage source
18
is reformed at time t
6
, the maximum voltage Vmax as shown in FIG.
2
(
b
) is instantaneously applied to the second electrode
14
. As described above, if the maximum voltage is applied to the second electrode
14
in one step, a large amount of current may flow through the first electrode
12
and cause damage to the first electrode
12
.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide a charged particle generating apparatus that overcomes the above issues in the related art. This object is achieved by combinations described in the independent claims. The dependent claims define further advantageous and exemplary combinations of the present invention.
In order to solve the above-stated problem, the present invention provides a charged particle generating apparatus comprising: a first electrode for discharging charged particles; a second electrode for generating an electric field to attract the charged particles from the first electrode; a voltage source for generating an attraction voltage to generate the electric field between the first electrode and the second electrode; an electrode current measurement unit for measuring electrode current flowing through the second electrode in accordance with an amount of the charged particles discharged from the first electrode to the second electrode; and a power supply shut-down circuit for shutting down power supply to the voltage source to terminate the generation of the attraction voltage based on the electrode current measured by the electrode current measurement unit.
The power supply shut-down circuit may comprise a comparator for comparing the electrode current measured by the electrode current measurement unit with a predetermined value, the power supply shut-down circuit shutting down power supply to the voltage source to terminate the generation of the attraction voltage when the comparator detects the measured electrode current is less than the predetermined value.
In order to solve the above-stated problem, the present invention further provides a charged particle generating apparatu

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