Device and method for measurement of proton beam source position and beamline center point

Abstract

A device and a method for measuring proton beam source position and beamline center are disclosed. The device includes N quadrupole magnets, a laser, a target and a scintillation screen; the target and the scintillation screen are arranged in front of and behind the N-quadrupole lens, respectively; the N-quadrupole lens can be converted to a M-quadrupole lens; the position of proton beam after being focused by the N- or M-quadrupole lens on the scintillation screen is measured; according to the amplification factor and the proton beam position, the offset of the proton beam source from the beamline center, as well as the position of the beamline center on the scintillation screen are calculated; the disclosure can accurately determine the position of the beamline center and the proton beam source by the use of N quadrupole magnets, combined with a scintillation screen.

Claims

1. A device for measuring a position of a proton beam source and a beamline center point, including: N quadrupole magnets, a laser, a target, and a scintillation screen, wherein: the N quadrupole magnets are coaxially arranged in a straight line along a central axis of a beamline to form an N-quadrupole lens; there is a distance between adjacent quadrupole magnets of the N quadrupole magnets; N is a natural number>3; the target interacts with a high-intensity laser pulse generated by the laser to generate a proton beam; the target is arranged in front of the N-quadrupole lens along the central axis of the beamline; the scintillation screen is arranged behind the N-quadrupole lens; a detection plane of the scintillation screen is perpendicular to the central axis of the beamline; the laser is configured to generate the high-intensity laser pulse, which interacts with the target to generate a proton beam; the proton beam is transmitted along a direction of the central axis of the beamline; after being focused by the N-quadrupole lens, a position of the proton beam measured on the scintillation screen is a.sub.1 in a horizontal direction, and a.sub.2 in a vertical direction, and an amplification factor of the proton beam after being focused by the N-quadrupole lens onto the scintillation screen is F.sub.1 in the horizontal direction, and F.sub.3 in the vertical direction.

2. The device for measuring the position of the proton beam source and the beamline center point according to claim 1, wherein the distance between adjacent quadrupole magnets is between 6 cm and 10 cm.

3. A method for measuring a position of a proton beam source and a beamline center point by using the device according to claim 1, including the following steps: 1) arranging N quadrupole magnets coaxially in a straight line along a central axis of a beamline to form an N-quadrupole lens, wherein there is a distance between adjacent magnets of the N quadrupole magnets, and N is a natural number≥3; 2) arranging a target and a scintillation screen respectively at two ends of the N-quadrupole lens, and making a detection plane of the scintillation screen to be perpendicular to the central axis of the beamline; 3) generating a high-intensity laser pulse by a laser, and the high-intensity laser pulse interacting with the target to generate a proton beam, which is transmitted along a direction of the central axis of the beamline; 4) after being focused by the N-quadrupole lens, a position of a beam spot of the proton beam measured on the scintillation screen is a.sub.1 in a horizontal direction, and a.sub.2 in a vertical direction, and an amplification factor of the proton beam after being focused by the N-quadrupole lens onto the scintillation screen is F.sub.1 in the horizontal direction, and F.sub.3 in the vertical direction; 5) converting the N-quadrupole lens to an M-quadrupole lens, wherein M<N and M is a natural number≥2; 6) generating a high-intensity laser pulse by the laser, and the high-intensity laser pulse interacting with the target to generate a proton beam, which is transmitted along the direction of the central axis of the beamline; 7) after being focused by the M-quadrupole lens, a position of a beam spot of the proton beam measured on the scintillation screen is b.sub.1 in the horizontal direction, and b.sub.2 in the vertical direction, and an amplification factor of the proton beam after being focused by the M-quadrupole lens onto the scintillation screen is F.sub.2 in the horizontal direction, and F.sub.4 in the vertical direction; and 8) calculating offsets L.sub.1 and L.sub.2 of a proton beam source from the beamline center point in the horizontal direction and the vertical direction respectively, as well as positions C.sub.1 and C.sub.2 of the beamline center point in the horizontal direction and the vertical direction respectively on the scintillation screen according to the amplification factor of the proton beam after being focused by the N-quadrupole lens onto the scintillation screen and the amplification factor of the proton beam after being focused by the M-quadrupole lens onto the scintillation screen and the position of the beam spot of the proton beam after being focused by the N-quadrupole lens and the position of the beam spot of the proton beam after being focused by the M-quadrupole lens: $L_1=\frac{a_1-c_1}{F_1}=\frac{b_1-c_1}{F_2}$ $L_2=\frac{a_2-c_2}{F_3}=\frac{b_2-c_2}{F_4}.$

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic diagram of an example device for measuring the proton beam source position and beamline center point in the horizontal direction of the present disclosure.

DETAILED DESCRIPTION

(2) The present disclosure will be further explained below through specific embodiments with reference to the drawings.

(3) Theoretically, it is required that the proton beam source generated by the interaction of the laser pulse and the target, the N-quadrupole lens and the scintillation screen are all located on the central axis of the beamline. In experiment, this is usually performed by simulating light. While there are deviations and difficulties in practical operation to achieve the centering accuracy of the order of microns. In experiment, the target needs to be disassembled and replaced frequently, and the laser needs to be adjusted frequently. Therefore, when the target is replaced and the experiment is restarted each time, the proton beam source position generated by the laser pulse and the target will vary. In the experiment, due to the limitations of the target position control system and possible errors, such as system crash, the proton beam source position will change. The method according to the disclosure can be used to determine and correct the offset of proton beam source position in time. It is difficult to accurately determine the beamline center point on the scintillation screen; in addition, the scintillation screen needs to be moved when the proton beam is not detected, thus it needs to be moved frequently. The method according to the present disclosure can accurately and conveniently determine the position of the beamline center point on the scintillation screen.

(4) The device for measuring a position of a proton beam source and a beamline center point C is seen in FIG. 1. Element L in FIG. 1, which extends from element C in FIG. 1 to element c.sub.1 in FIG. 1 comprises a central axis of the beamline. Element C in FIG. 1 comprises the beamline center point C. The device for measuring a position of a proton beam source and a beamline center point C includes: a quadrupole triplet lens Q, a laser, a target T and a scintillation screen S, wherein three quadrupole magnets are coaxially arranged in a straight line along the the central axis of the beamline L to form the quadrupole triplet lens Q and there is a distance between adjacent quadrupole magnets. Target T is arranged in front of the quadrupole triplet lens Q and the scintillation screen S is arranged at 165 cm behind the quadrupole triplet lens Q. A detection plane of the scintillation screen S is arranged perpendicularly to the central axis to the beamline L. A high-intensity laser pulse is generated by the laser, with the high intensity laser pulse: (a) interacting with the target T to generate a proton beam and (b) transmitted along the central axis of the beamline L. After the high intensity laser pulse is focused by the quadrupole triplet lens Q, the position of the proton beam on the scintillation screen S is a.sub.1 in the horizontal direction and the amplification factor of the proton beam on the scintillation screen S is F.sub.1 in the horizontal direction. The magnetic field strengths of the quadrupole magnets are 0.133, −0.111 and 0.134 T/cm respectively. The quadrupole triplet lens Q is converted to a quadrupole doublet lens by turning off the third quadrupole magnet. When the high-intensity laser pulse is generated by the laser after converting the quadrupole triplet lens Q to the quadrupole doublet lens and the high-intensity laser pulse interacts with the target T to generate a proton beam, the proton beam from the quadrupole doublet lens is also transmitted along the central axis of the beamline L. After being focused by the quadrupole doublet lens, the position of the proton beam from the quadrupole doublet lens on the scintillation screen S is b.sub.1 in the horizontal direction and the amplification factor of the proton beam on the scintillation screen S is F.sub.2 in the horizontal direction. The magnetic field strengths of the quadrupole magnets are 0.251 and −0.076 T/cm respectively.

(5) In the embodiment, the amplification factor F.sub.1 of the proton beam on the scintillation screen S after being focused by the quadrupole triplet lens is −2.488 in the horizontal direction, and the amplification factor F.sub.2 of the proton beam on the scintillation screen S after being focused by the quadrupole doublet lens is −17.332 in the horizontal direction. The pixel value in the image measured in the experiment is: a.sub.1=866, b.sub.1=906. According to the amplification factor and the position of the proton beam, the offset of the proton beam source from the central axis of the beamline is calculated as follows:

(6) $L_1=\frac{a_1-c_1}{F_1}=\frac{b_1-c_1}{F_2},$

(7) wherein c.sub.1 is the position of the beamline center point on the scintillation screen in the horizontal direction, and c.sub.1 is calculated as 859.3. According to the distance relationship between the pixel and the actual size, the offset L.sub.1 of the proton beam source from the beamline center point is calculated as 0.128 mm in horizontal direction.

(8) After moving the target by 0.13 mm, it is measured that a.sub.1=861 and b.sub.1=863, and it is calculated that c.sub.1=860.7. According to the distance relationship between the pixel and the actual size, it can be obtained that L.sub.1=0.006 mm. After adjustment, the deviation of the proton beam source from the central axis of the beamline in the horizontal direction is only 6 μm.

(9) Using the same method, the offset of the proton beam source from the central axis of the beamline in the vertical direction can be measured and corrected.

(10) Finally, it should be noted that the disclosure of the embodiments is to help further understand the present disclosure, and those skilled in the art can understand that various substitutions and modifications are possible without departing from the spirit and scope of the present disclosure and the appended claims. Therefore, the present disclosure should not be limited to the content disclosed in the embodiments, and the scope of protection of the present disclosure is defined by the claims.