PC-based control of a high-voltage injector

The stability of high voltage injectors is one of the major problems in any accelerator system. Most of the troubles encountered in the normal operation of an accelerator are connected with the ion source and associated high voltage platforms, regardless of the source or high voltage generator type. The quality of the ion beam injected in the accelerator strongly depends on the power supplies used in the injector and on the ability to control the non-electrical parameters (gas-flow, temperature, etc.). A wide used method in controlling is based on optical links between high-voltage platform and computer, the adjustments being more or less automated. Although the method mentioned above can be still useful in injector control, a different approach is presented in this work, i.e., the computer itself is placed inside the high-voltage terminal. Only one optical link is still necessary to connect this computer with an user-friendly host at ground potential. Requirements: - varying and monitoring the filament current; - gas flow control in the ion source; - reading the vacuum values; - current and voltage control for the anodic, magnet, extraction, suppression and lens' sources. Even in the high voltage terminal there are compartments with different voltages regardless the floating ground. In our injector the extraction voltage is applied on the top of the ion source including the filament and the anodic voltage. The extraction voltage is of maximum 30 kV. In this situation a second optical link is required to transfer the control for the anodic and magnet source power supply assuming the dedicated computer on the floating ground. One PC is placed inside the high voltage terminal and one PC outside the injector. The optical link (more precisely two optical wires) connects the serial ports. The inside computer is equipped with two multipurpose ADC/DAC and digital I/O card. They permit to read or output DC levels ranging between 0 to 10 volts or TTL signals. The filament current control was realized by a stepping motor that rotates a variable resistor through an insulating stick. Two hundred motor steps per complete rotation assumes a very good resolution in driving the filament current between 0 Amps and maximum 40 Amps. The gas flow control is realized by a stepping motor that drives a needle valve. The flow gas can be varied in very small steps. The vacuum read-out is performed by two gauges, Penning and Pirani, providing a 0 to 10 V analog signal. The DC voltages are input to two ADC channels. The current and voltage source control is performed by ADC and DAC channels that drive/read the source output. The outside computer presents an user friendly interface by a Visual Basic program. It permits to vary all the mentioned quantities and reports periodically (at every two seconds) the output values. The user drives the program only with the mouse, having complete control all over the electric hardware inside the injector. A fast reset function is also provided in case of severe malfunction. (author)