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Chapter 3: Operating Principles
This chapter explains the functions necessary for successful operation. It
is intended to help the user understand how the source and controller
function together. Information and recommendations are offered to
avoid unexpected operating circumstances which may cause equipment
damage. It is suggested that this material be read before using the unit for
the first time and used as a reference if questions arise during routine
operation.
Source Considerations
The Mark II Controller has been designed to power the Mark/Mark
series end-Hall Effect type gridless ion source and neutralizer. This source
type creates a beam of ions through the interaction of electric and mag-
netic fields in the source’s discharge region. Ions accelerate away from the
anode with an energy that depends on where they were created. The
mean ion beam energy is typically 60% of the discharge voltage. The
actual ion beam current is typically 20% of the discharge current. The dis-
charge current is a function of the anode voltage, the source gas flow, and
the emission current. The controller automatically adjusts these indepen-
dent system variables to maintain the target operating condition. Refer to
the ion source’s technical manual for additional information.
Controller/Power Supply Function
The automatic start sequence is enabled when the BEAM button is
pressed and the controller is in AUTO mode. This sequence initiates
ramping the source gas flow to the start gas flow setting. Next, the Anode
Voltage , VA, is increased until it reaches the user selected starting value.
Then, the cathode is heated to thermionic emission temperature by the
cathode supply. The filament current rises until there is a source discharge
or until it reaches its target value.
The discharge is initiated by electrons that are accelerated toward the
anode and strike neutral atoms or molecules, thereby generating ions.
This gaseous mixture of electrons and ions constitutes a discharge plasma.
The interaction of the electrons in this plasma with the magnetic field
also establishes the electric field that accelerates the ions. This accelera-
tion has significant components in both the radial and axial directions.
The accelerating potential varies over the discharge region; ions are pro-
duced with a substantial spread in energy, depending on their position at
ionization.
