This application claims priority from Japanese Patent Application No. 2001-64,712 under 35 U.S.C. xc2xa7119.
The present invention relates to a septum electromagnet for deflecting and splitting a particle beam, an electromagnet for deflecting and splitting a particle beam, and a method of deflecting a particle beam. The present invention is useful for introducing particle beams into and extracting particle beams from a charged particle accelerator.
BACKGROUND OF THE INVENTION
Conventionally, a septum electromagnet is used to introduce particle beams into and extract particle beams from a charged particle accelerator. FIGS. 1 and 2 are, respectively, transverse and longitudinal cross sectional views of a conventional septum electromagnet. With reference to FIGS. 1 and 2, an electric current flowing through a storehouse-shaped coil that includes an inner conductor 1 and a septum conductor 3 generates inside a yoke 5 a magnetic field B in a direction perpendicular to the plane of FIG. 1. Since it is shielded by septum conductor 3, the magnetic field B cannot leak beyond yoke 5.
A conventional septum magnet of a type shown in FIGS. 1 and 2 can be used to deflect the path of a particle beam that passes through the magnetic field B. The magnetic field B deflects by an angle xcex8, and thereby varies, a given orbit (lead-orbit) of a particle beam as it passes through the accelerator. Because septum conductor 3 shields magnetic field B, a beam having an orbit (round-orbit) that passes beyond the septum electromagnet cannot be deflected by the magnetic field B. A given particle beam can, therefore, be removed from the charged particle accelerator by passing the given particle beam through the septum electromagnet.
A drawback of the septum electromagnet as shown in FIGS. 1 and 2 is that septum conductor 3 requires a strong support structure to withstand the very large electromagnetic force exerted by magnetic field B. However, because there is only a small amount of space in the septum electromagnet, it is difficult to provide an adequate support member for septum conductor 3 in the septum electromagnet.
Moreover, if the strength of the magnetic field B is increased, yoke 5 may be saturated in permeability and thereby cause partial leakage of the magnetic field B beyond yoke 5 and a consequent deflection of particle beams on the round-orbit. To reduce leakage of magnetic field B, a magnetically shielding plate (not shown) may be positioned adjacent septum conductor 3, but this configuration may deteriorate the performance of the septum electromagnet because of the substantial increase of the thickness of septum conductor 3.
It is an object of the present invention to provide a new septum electromagnet for deflecting and splitting a particle beam, a new electromagnet for deflecting and splitting a particle beam, and a method of deflecting a particle beam using the septum electromagnet or the electromagnet.
The present invention relates to a septum electromagnet for deflecting and splitting a particle beam. A preferred embodiment of the septum electromagnet comprises a septum conductor that divides the septum electromagnet to define first and second beam deflecting magnetic pole spaces. First and second magnetic fields are generated in, respectively, the first and second beam deflecting magnetic pole spaces by electric currents flowing through the coil of the septum conductor. The direction of the first magnetic field is opposite to the direction of the second magnetic field, such that a particle beam passing through the first beam deflecting magnetic pole space is angularly deflected by an amount and a particle beam passing through the second beam deflecting magnetic pole space is angularly deflected by an opposite amount.
The septum electromagnet of the present invention may be disposed on a particle beam orbit of a charged particle accelerator. A beam on a lead-orbit and a beam on a round-orbit in the charged particle accelerator pass through, respectively, the first and second beam deflecting magnetic pole spaces of the septum electromagnet.
A first magnetic field is generated at the first beam deflecting magnetic pole space, and a second magnetic field is generated at the second beam deflecting magnetic pole space. Since the direction of the first magnetic field is preferably opposite to that of the second magnetic field, electromagnetic forces having opposite directions act on the particle beams on the lead-orbit and the round-orbit. This results in deflection of a particle beam on the lead-orbit in a direction opposite that of the deflection of a particle beam on the round-orbit. The lead-orbit and the round-orbit of the particle beams are sufficiently variable that the two particle beams can be split. This enables extraction of a particle beam from the charged particle accelerator.
Conversely, reversing the direction of the first and second beam deflecting magnetic pole spaces enables introduction of a particle beam into the charged particle accelerator.
The septum magnet of the present invention is divided by the septum conductor to define the first beam deflecting magnetic pole space and the second beam deflecting magnetic pole space. Therefore, the first and the second magnetic fields exert forces on the septum conductor. Because the first and second magnetic fields exert forces in opposite directions, they cancel each other out near the septum conductor. The septum conductor can, as a consequence, be supported in the septum electromagnet more easily than in conventional septum electromagnets.
For example, if the first magnetic field leaks beyond the first deflecting magnetic pole space of the septum electromagnet, any leaked component of the first magnetic field will be cancelled by a leaked component of the second magnetic field. Because the net magnetic leakage for the septum electromagnet is inhibited by the presence of magnetic fields in opposite directions, a magnetic shielding plate is not needed.
An aspect of the invention relates to an electromagnet for deflecting and splitting a particle beam. The electromagnet comprises a septum electromagnet that is divided into a first beam deflecting magnetic pole space and a second beam deflecting magnetic pole space by a combination of a septum conductor and an auxiliary electromagnet. First and second magnetic fields of preferably opposite directions are generated in, respectively, the first and second beam deflecting magnetic pole spaces by electric currents flowing on the coils of a septum conductor. Thus, a first particle beam passing through the first beam deflecting magnetic pole space is angularly deflected in a direction that is opposite to the direction of angular deflection of a particle beam passing through the second beam deflecting pole space. The deflection of a beam that passed through the second beam deflecting magnetic pole space is further offset, or cancelled out, by a deflection imparted by the auxiliary electromagnet.
An auxiliary electrode is provided in addition to the septum electromagnet as mentioned above. The auxiliary electrode can offset and thereby cancel out the deflection imparted to a particle beam passing through the second beam deflecting magnetic pole space. A particle beam on a round-orbit is not deflected, therefore, and continues to move on the same round-orbit.
As a result, the electromagnet of the present invention deflects and splits only a beam on a lead-orbit, which is taken out of a charged particle accelerator without disturbing the acceleration of a beam on a round-orbit.
Additional aspects and advantages of this invention will be apparent from the following detailed description of preferred embodiments thereof, which proceeds with reference to the accompanying drawings.