An X-ray tube has a cathode, an anode target to emit X-rays, and a vacuum envelope which houses the cathode and the anode target. The vacuum envelope has a first metal member connected to the anode target, a second metal member which is connected to the first metal member and has a coefficient of thermal expansion lower than that of the first metal member, and an electrically insulating annular ceramic member connected to the second metal member and the cathode. In addition, the X-ray tube has a cooling system which is connected to the first metal member and forms a cooling passage. Furthermore, the X-ray tube has an adapter which is in contact with the first metal member, surrounds the second metal member and has a thermal conductivity higher than that of the second metal member, and a heat-transfer medium placed between the ceramic member and the adapter.
1. An X-ray tube, comprising:
a cathode to emit electrons;
an anode target to emit X-rays by incident electrons emitted from the cathode;
a vacuum envelope housing the cathode and the anode target, the vacuum envelope including:
a first metal member connected to the anode target and extending in a direction along a tube axis of the x-ray tube, the first metal member having an X-ray radiation window;
a second metal member connected to the first metal member, extending in a direction along the tube axis, and having a coefficient of thermal expansion lower than that of the first metal member; and
an electrically insulating annular ceramic member connected to the second metal member and the cathode, and projecting from the cathode in a direction perpendicular to the tube axis; and
an adapter placed so as to be in contact with the first metal member, and surrounding the second metal member outside the vacuum envelope, and having a thermal conductivity higher than that of the second metal member;
a heat-transfer medium placed between the ceramic member and the adapter, outside the vacuum envelope; and
a cooling system connected to the first metal member and forming a cooling passage through which coolant flows, wherein heat released from the anode target is conducted to the cooling system directly or indirectly via the first metal member, and heat released from the cathode is conducted to the cooling system indirectly via the ceramic member, the heat-transfer medium, the adapter, and the first metal member.
2. The X-ray tube according to claim 1 , wherein the coolant is pure water.
3. The X-ray tube according to claim 1 , wherein the coolant is water solution whose main ingredient is water.
4. The X-ray tube according to claim 1 , wherein the anode target is in contact with the coolant.
5. The X-ray tube according to claim 1 , wherein the first metal member is in contact with the coolant.
6. The X-ray tube according to claim 1 , wherein the ceramic member and the heat-transfer medium face each other to sandwich the second metal member therebetween in a thickness direction of the second metal member.
7. The X-ray tube according to claim 1 , wherein the heat-transfer medium is in contact with the ceramic member.
8. The X-ray tube according to claim 1 , wherein a thickness of the adapter is larger than that of the second metal member.
9. The X-ray tube according to claim 1 , wherein the heat-transfer medium is a metal formed in mesh.
10. The X-ray tube according to claim 1 , wherein the heat-transfer medium is a metal formed in a shape which has characteristic of a spring.
11. The X-ray tube according to claim 1 , wherein a surface opposite to a vacuum side surface of the ceramic member is flat.
12. The X-ray tube according to claim 1 , wherein the anode is grounded.
13. The X-ray tube according to claim 12 , wherein the cathode has a filament, and a first cathode lead-in terminal and a second cathode lead-in terminal which are connected to the filament, the first cathode lead-in terminal and the second cathode lead-in terminal extend to the outside of the vacuum envelope, and a high voltage-plug which supplies the high voltage to the cathode is connected to the first cathode lead-in terminal and the second cathode lead-in terminal extending the outside of the vacuum envelopes.