Stable X=ray tungsten filament - uses pre-tensioned helical heater under shielded well in cathode

摘要

One problem with stability of emmission in the operation of X Ray tubes lies in the distortion or displacement under thermal stresses in the directly heated cathode-filament. This is overcome by using a tungsten filament (46) wound as a helical spring and held in tension between two pillar-electrodes (44,45) mounted in an insulated base (43) and carrying the filament current. Under typical operating conditions it is sufficient to set the strain in the spring to not less than 10% above its length when cold. Electrons are drawn off by the anode only from the coiled section, the ends and the electrodes are shielded by overhanging plates (48,49) set in the cathode-well (51) above the filament. ADVANTAGE - Heating and ageing effects on cathode geometry are minimised.