HT Power Supply – This means it will provide a high volta in (KV), DC voltage, which is useful for plasma glow cleaning, and to a small extent DC sputtering, if the KV is provided up to 4 to5 Kilo volts. Basically, it is a step-up transformer, which builds the high KV, and then a rectifier, which converts the stepped up ac voltage into DC voltage.
       LT Power Supply– This is providing low voltage but high current. Because for evaporation of any metal you need a high current (20 to 70 Amps), to melt the evaporation material kept on the boat.  So you need an LT power supply. It basically consists for a step-down transformer, which produces a low voltage and a high current at the secondary, and you evaporation electrodes where you connect the tungsten filament are connected to this output.

A high tension describes the main power supply to the circuit, which produces the current between anode and cathode.

A low-tension line is a low voltage line and a high-tension line is a high voltage line.