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118157-001 Rev C
X-Ray Tube Overview:
There are numerous X-ray tubes available depending on the user application. The tube requirement is
normally the first component selected for a specific application before any of the other subsystem
requirements. There are two basic types of x-ray tubes. One type is called a single ended or “Unipolar”
while the other is a double ended or “Bipolar”. The single ended tube only requires one high voltage
source and a filament supply in order to emit X-rays. The source voltage is usually negative with respect
to earth ground.
External cooling may be required during operation of the tube depending on the level of power output.
Single ended tubes are cooled by water circulation systems specially designed to remove heat from the
anode during operation. The circulation system consists of a water reservoir tank, pump, hoses and a
fan circulating over a radiator that is very similar to an automobile cooling system. The hoses from the
cooling system connect to the grounded side of the tube. The tube may have special fittings and will
identify the water input and output side. The flow rate and capacity of the cooling system will generally
rely on the recommendations of the tube manufacturer and operating power level. On higher power
tubes, a chiller subsystem may be required. The chiller utilizes a compressor and pump to maintain
lower water temperatures for higher wattage tubes. Both systems measure the input temperature with
respect to output temperature of the water and employ an interlock system to remove high voltage on
the X-ray tube preventing damage. Various Coolers and Chillers are available with the XRV Sub-System
and are described later in this manual.
Standard single ended tube operating voltages range from 75kV to a maximum of 225kV and may be
purchased through Spellman as part of the XRV Sub-System.
Higher voltage tubes are double-ended or “Bipolar” meaning a negative and a positive high voltage
source is required for operation. The tube operates in a similar fashion as the single ended tube with the
exception that the anode is at high voltage potential in addition to the cathode instead of being at
ground potential. Ground potential is located in the center of the tube rather than at one end. Bipolar
tubes require two X-ray generators as opposed to one.
Bipolar X-ray tubes require oil cooling as opposed to water -cooled systems. The oil serves as an
electrical insulation medium internal to the tube in addition to cooling the anode. Oil cooled systems
use a heat exchanger (oil to water) that is isolated from the oil circulation flowing through the tube. As
with water-cooled systems, the manufacturer will specify the heat removal capacity and flow rates.
These can be compared with the recommendations for X-ray tube thermal management set by the tube
manufacturer. Like the water-cooled system, these systems employ the use of thermal interlocks
terminating high voltage if the tube begins to overheat.
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