Magnetic field compensation in a linear accelerator

1. A system comprising:

a linear accelerator having a central axis;

an ion pump including an ion pump magnet having an ion pump magnet position, an ion pump magnet shape, an ion pump magnet orientation, and an ion pump magnet magnetic field profile; and

a compensating magnet having a position, a shape, an orientation, and a magnetic field profile, wherein at least one of the position, shape, orientation, and magnetic field profile reduce at least one component of a magnetic field in the linear accelerator resulting from the ion pump magnet,

wherein an ion pump magnet polarity and a compensating magnet polarity are substantially perpendicular to the central axis.

2. The system of claim 1 , wherein at least one of the position, shape, orientation, and magnetic field profile of the compensating magnet is substantially similar to at least one of the ion pump magnet position, ion pump magnet shape, ion pump magnet orientation, and ion pump magnet magnetic field profile of the ion pump.

3. The system of claim 1 , wherein the ion pump magnet and the compensating magnet each have a C-shape, each of the C-shapes having an opening, and wherein the openings of the C-shapes face each other.

4. The system of claim 1 , wherein the linear accelerator has an electron beam path and the reduction of the at least one component of a magnetic field in the linear accelerator reduces the magnetic field along the electron beam path.

5. The system of claim 1 , wherein at least one of the position, shape, orientation, and magnetic field profile of the compensating magnet are configured to reduce a gradient of the magnetic field in the linear accelerator.

6. The system of claim 1 , wherein the compensating magnet is a current carrying coil.

7. The system of claim 1 , wherein the orientation of the compensating magnet is such that the magnetic field due to the ion pump magnet is substantially canceled in at least one location in the linear accelerator.

8. The system of claim 1 , wherein the linear accelerator has an electron beam path and the orientation of the compensating magnet is such that the magnetic field due to the ion pump magnet is substantially canceled along the electron beam path.

9. The system of claim 1 , wherein at least one of the position, shape, orientation, and magnetic field profile of the compensating magnet and at least one of the ion pump magnet position, ion pump magnet shape, ion pump magnet orientation, and ion pump magnet magnetic field profile are selected to cause the least reduction in a beam quality of the linear accelerator.

10. The system of claim 1 , wherein at least one of the ion pump magnet and the compensating magnet are located closer to a linear accelerator target than to a source of charged particles in the linear accelerator.

11. The system of claim 1 , wherein the ion pump magnet orientation and the orientation of the compensating magnet are such that the ion pump magnet polarity and the compensating magnet polarity are substantially opposite to one another.

12. The system of claim 1 , wherein the ion pump magnet and the compensating magnet are oriented at approximately 45 degrees relative to the central axis.

13. The system of claim 1 , wherein at least one of the ion pump magnet and the compensating magnet further comprising a yoke.

14. The system of claim 13 , wherein at least one of the ion pump magnet and the compensating magnet further comprising two permanent magnets, wherein the yoke connects the two permanent magnets.