CN107481831A - A cooling method for a superconducting magnet of a superconducting cyclotron - Google Patents

Abstract

The invention belongs to the field of superconducting cyclotrons. In order to solve the problems of complicated cooling process and long cooling time of existing superconducting magnet cooling methods in my country, the present invention provides a cooling method for superconducting magnets in superconducting cyclotrons. The cooling method comprises the following steps: 1. evacuating the superconducting magnet; 2. performing liquid nitrogen refrigeration on the superconducting magnet, and simultaneously adjusting the radial rod length of the superconducting magnet; Vacuumize; 4. Refrigerate the superconducting magnet with liquid helium to complete the cooling. The method for cooling the superconducting magnet of the superconducting cyclotron of the present invention adopts a two-stage cooling method, including a liquid nitrogen cooling process and a liquid helium cooling process. The cooling steps are reasonably designed, the cooling time is short, and the operation is convenient. Under the premise of coil cooling requirements, the consumption of liquid nitrogen and liquid helium can be effectively saved.

Description

A cooling method for a superconducting magnet of a superconducting cyclotron

technical field

The invention belongs to the field of superconducting cyclotrons, in particular to a cooling method for a superconducting magnet of a superconducting cyclotron.

Background technique

A cyclotron is a particle accelerator, which uses the combined action of a magnetic field and an electric field to cause charged particles to perform cyclotron motion, and a device that repeatedly accelerates the cyclotron-moving charged particles with a high-frequency electric field. Among them, the superconducting cyclotron is the core equipment of the current medical proton therapy accelerator.

Medical proton therapy accelerator is the most cutting-edge radiation therapy equipment in the world today. It can treat tumors with microscopic proton and heavy ion radiation. It has remarkable curative effect, good development prospects and huge commercial value. At present, only a few developed countries have mastered and applied it. This technology; while our country is in the research and development stage, there is no mature technology for adoption. However, due to commercial interests and other considerations, many key technologies related to medical proton therapy accelerators have not been disclosed so far, which makes the research and development work in our country require breakthroughs in relevant key technologies one by one to be completed.

The magnetic field of the superconducting cyclotron is mainly provided by the superconducting coil, and the superconducting coil needs a certain low temperature condition to enter the superconducting state, so the superconducting magnet needs to be cooled. However, the cooling process of superconducting magnets in superconducting cyclotrons in my country is complicated, takes a long time, and is not yet mature. Therefore, in order to realize the development of medical proton therapy accelerators, it is necessary to develop an effective superconducting cyclotron. A cooling method for accelerator superconducting magnets.

Contents of the invention

In order to solve the problems of complicated cooling process and long cooling time of existing superconducting magnet cooling methods in my country, the present invention provides a cooling method for superconducting magnets in superconducting cyclotrons. This cooling method comprises the following steps:

(1) vacuumize the superconducting magnet, and carry out vacuum leak detection to the superconducting magnet after vacuumizing;

(2) Transport liquid nitrogen from a liquid nitrogen tank to the superconducting magnet through the liquid nitrogen delivery pipeline, turn on the first refrigerator to refrigerate the liquid nitrogen transported into the superconducting magnet, and gradually make the superconducting magnet The temperature in the body drops below 77K; at the same time, adjust the radial rod length of the superconducting magnet to match the cold shrinkage of the superconducting magnet;

(3) discharge the liquid nitrogen in the superconducting magnet, then vacuumize the superconducting magnet while feeding helium gas, and carry out vacuum leak detection to the superconducting magnet;

(4) Transport liquid helium into the superconducting magnet through the liquid helium tank through the liquid helium delivery pipeline, turn on the second refrigerator to refrigerate the liquid helium transported into the superconducting magnet, and gradually make the superconducting magnet The temperature in the body drops below 4.5K, and the cooling of the superconducting magnet is completed.

In step (1), the vacuuming equipment for vacuuming the superconducting magnet is preferably a molecular pump unit.

It is preferable to adopt a bellows connection between the molecular pump unit and the superconducting magnet.

In step (1), it is preferable to evacuate the superconducting magnet with a vacuum degree of 1×10 ^-2 Pa.

In step (1), it is preferred that the vacuum leak detection requires a leak rate lower than 1×10 ⁻¹⁰ PaL/s.

It is preferred that the first refrigerating machine adopts a single-stage refrigerating machine.

In step (2), the temperature inside the superconducting magnet is gradually reduced to below 77K, preferably 70K.

In step (3), it is preferred that the vacuum leak detection requires a leak rate lower than 1×10 ⁻¹⁰ PaL/s.

It is preferred that the second refrigerating machine adopts a secondary refrigerating machine.

In step (4), the temperature inside the superconducting magnet is gradually reduced to below 4.5K, preferably 4.2K.

In summary, the superconducting cyclotron superconducting magnet cooling method of the present invention adopts a two-stage cooling process, including a liquid nitrogen cooling process and a liquid helium cooling process. The cooling steps are reasonably designed, the cooling time is short, and the operation is convenient. It can effectively save the consumption of liquid nitrogen and liquid helium on the premise of meeting the cooling requirements of superconducting coils.

detailed description

The implementation of the present invention will be further described below in combination with specific examples.

Example

The cooling method of superconducting cyclotron superconducting magnet of the present invention, a kind of preferred embodiment thereof is as follows:

(1) Connect the vacuum pumping port of the superconducting magnet with the molecular pump unit with bellows. Two molecular pump units are used in total, and are connected to the two vacuum pumping ports of the superconducting magnet with two bellows. Turn on the molecular pump unit to evacuate the inside of the superconducting magnet and monitor the vacuum degree. When the vacuum degree is lower than 1×10 ^-2 Pa, the evacuation is completed. For vacuum leak detection of superconducting magnets, the leak rate is required to be lower than 1×10 ^-10 PaL/s.

(2) Connect the superconducting magnet and the liquid nitrogen tank with a liquid nitrogen infusion tube, fix one end of the liquid nitrogen infusion tube to the liquid nitrogen tank, and insert the other end of the liquid nitrogen infusion tube into the infusion port of the superconducting magnet. Open the valve of the liquid nitrogen tank, input liquid nitrogen into the superconducting magnet from the liquid nitrogen tank, and start the liquid nitrogen cooling. Turn on the single-stage refrigerators, a total of two single-stage refrigerators are turned on at the same time. Monitor the temperature of the superconducting magnet. When the temperature of the superconducting magnet drops to 70K, close the valve of the liquid nitrogen tank, stop inputting liquid nitrogen into the superconducting magnet, and stop the single-stage refrigerator. Adjust the length of the radial tie rods of the superconducting magnet to prevent the radial tie rods from being overstressed. A total of 4 radial tie rods are used.

(3) Pressurize the superconducting magnet, discharge the liquid nitrogen inside it, remove the liquid nitrogen infusion tube, and feed helium into the infusion port of the superconducting magnet while vacuuming. For vacuum leak detection of superconducting magnets, the leak rate is required to be lower than 1×10 ^-10 PaL/s.

(4) Connect the superconducting magnet and the liquid helium tank with a liquid helium infusion tube, fix one end of the liquid helium infusion tube to the liquid helium tank, and insert the other end of the liquid helium infusion tube into the infusion port of the superconducting magnet. Open the valve of the liquid helium tank to input liquid helium into the superconducting magnet, and start the cooling of the liquid helium. Turn on the secondary refrigerator to continuously liquefy the helium gas generated during the cooling of the liquid helium and return it to the superconducting magnet. A total of 4 secondary refrigerators are used, 3 of which are turned on, and the other one is used as a backup. Monitor the temperature of the superconducting magnet. When the temperature of the superconducting magnet drops to 4.2K, close the valve of the liquid helium tank, stop inputting liquid helium into the superconducting magnet, and complete the liquid helium cooling of the superconducting magnet.

Claims (10)

1. a kind of cool-down method of superconducting cyclotron superconducting magnet, it is characterised in that the cool-down method comprises the following steps：

(1) superconducting magnet is vacuumized, vacuum leak hunting is carried out to the superconducting magnet after vacuumizing；

(2) liquid nitrogen is conveyed into the superconducting magnet from liquid nitrogen container by liquid nitrogen transfer pipeline, opens the first refrigeration machine to conveying Liquid nitrogen in the superconducting magnet is freezed, and the superconducting magnetic body temperature is down to below 77K；At the same time, The radial direction pull bar length of the superconducting magnet is adjusted, is allowed to match with superconducting magnet shrinkage amount；

(3) liquid nitrogen in the superconducting magnet is discharged, then the superconducting magnet is vacuumized when being passed through helium, to superconduction Magnet carries out vacuum leak hunting；

(4) liquid helium is conveyed into the superconducting magnet from liquid helium tank by liquid helium transfer pipeline, opens the second refrigeration machine to conveying Freezed to the liquid helium in the superconducting magnet, the superconducting magnetic body temperature is down to below 4.5K, described in completion The cooling of superconducting magnet.

2. the cool-down method of superconducting cyclotron superconducting magnet as claimed in claim 1, it is characterised in that：Step (1) In, the vaccum-pumping equipment vacuumized to superconducting magnet is molecule pump assembly.

3. the cool-down method of superconducting cyclotron superconducting magnet as claimed in claim 2, it is characterised in that：The molecular pump Connected between unit and superconducting magnet using bellows.

4. the cool-down method of superconducting cyclotron superconducting magnet as claimed in claim 1, it is characterised in that：Step (1) In, it is described that superconducting magnet is vacuumized, it is desirable to which that vacuum reaches 1 × 10^-2Pa。

5. the cool-down method of superconducting cyclotron superconducting magnet as claimed in claim 1, it is characterised in that：Step (1) In, the vacuum leak hunting requires that leak rate is less than 1 × 10^-10PaL/s。

6. the cool-down method of superconducting cyclotron superconducting magnet as claimed in claim 1, it is characterised in that：First system Cold uses single stage.

7. the cool-down method of superconducting cyclotron superconducting magnet as claimed in claim 1, it is characterised in that：Step (2) In, described the superconducting magnetic body temperature is down to below 77K, its temperature is 70K.

8. the cool-down method of superconducting cyclotron superconducting magnet as claimed in claim 1, it is characterised in that：Step (3) In, the vacuum leak hunting requires that leak rate is less than 1 × 10^-10PaL/s。

9. the cool-down method of superconducting cyclotron superconducting magnet as claimed in claim 1, it is characterised in that：Second system Cold uses two stage cooler.

10. the cool-down method of superconducting cyclotron superconducting magnet as claimed in claim 1, it is characterised in that：Step (4) In, described the superconducting magnetic body temperature is down to below 4.5K, its temperature is 4.2K.