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Section 4.4: Mode Indicator and Adjustments
The power supply can be operated in one of 3 possible modes. These are MANUAL, LOCAL, and
REMOTE. Adjustment of the parameters for the 5 individual power supplies will depend upon
which mode is selected. The mode can be selected by pressing the MODE button on the key pad.
Below is a table that has the power supply parameters and which of those can be adjusted in the
various modes.
SOURCE PARAMETER, ABBREVIATION
LOCAL
REMOTE
MANUAL
Beam Current, BI (mA)
Adjustable
Adjustable
-
Beam Voltage, BV (V)
Adjustable
Adjustable
Adjustable
Accelerator Current (mA)
†
-
-
-
Accelerator Voltage, ACCEL (V)
Adjustable
Adjustable
Adjustable
Discharge Current (A)
†
-
-
-
Discharge Voltage, DISC V(V)
Adjustable
Adjustable
Adjustable
Cathode Filament Current, CI (A)
-
-
Adjustable
Neutralizer Emission Current, E/B RATIO (mA)
Adjustable
Adjustable
-
Neutralizer Filament Current, NI (A)
-
-
Adjustable
† These parameters cannot be adjusted using the IBEAM power supply. The accelerator
current is induced by charge-exchange ions created in the vicinity of the accelerator grid [see
reference 11]. The production of these charge-exchange ions is proportional to the source
gas flow rate and chamber pressure. The charge-exchange ions are attracted to the
accelerator grid, impinge, and are detected as accelerator current. The impingement process
will result in sputtering of the accel grid and excessive accelerator current will reduce the life
of the grid. For properly aligned grids and reasonable operating conditions, the accelerator
current is typically less than 10% of the beam current. Similarly, the discharge current is
dependent upon the source gas and magnetic field strength inside the source body. The
discharge current is increased or decreased by changes to the cathode filament current.
In LOCAL mode, the IBEAM allows the user to set a specified beam current (or ion dose). When
the source and beam switches are ON, the IBEAM will attempt to run the source at the specified
beam current. More specifically, the IBEAM will adjust the cathode filament current to control the
beam current. Increasing the cathode filament current will increase the emission of electrons into
the discharge chamber. As this is done, the plasma density increases in the discharge chamber,
thereby more ions can be extracted and an increased beam current is observed.