RF kicker cavity to increase control in common transport lines

Abstract

A method of controlling e-beam transport where electron bunches with different characteristics travel through the same beam pipe. An RF kicker cavity is added at the beginning of the common transport pipe or at various locations along the common transport path to achieve independent control of different bunch types. RF energy is applied by the kicker cavity kicks some portion of the electron bunches, separating the bunches in phase space to allow independent control via optics, or separating bunches into different beam pipes. The RF kicker cavity is operated at a specific frequency to enable kicking of different types of bunches in different directions. The phase of the cavity is set such that the selected type of bunch passes through the cavity when the RF field is at a node, leaving that type of bunch unaffected. Beam optics may be added downstream of the kicker cavity to cause a further separation in phase space.

Claims

1. A method of controlling electron bunch types having various specific energies in an energy recovered linac (ERL) having a common transport pipe with an upstream end and a downstream end, comprising: providing a radio frequency (RF) kicker cavity at the upstream end of the common transport pipe; providing RF energy to the kicker cavity; selecting electron bunches at a first specific energy to be kicked in energy by the kicker cavity; setting an operational RF frequency of the kicker cavity at a multiple of the frequency at which the selected electron bunches pass through the common transport pipe; and applying RF energy to the kicker cavity to provide a kick in the energy of the selected electron bunches to separate the selected bunches in phase space from any bunches not at the specific energy of the selected electron bunches.

2. The method of claim 1 wherein the operational RF frequency of the kicker cavity is a steering frequency that is determined by the equation
f.sub.steering=(k/n)f.sub.RF wherein n is the number of passes and k is any integer, and f.sub.RF is the linac RF frequency.

3. The method of claim 1 wherein the kick is in a transverse direction.

4. The method of claim 1 wherein the kick is in a longitudinal direction.

5. The method of claim 1 wherein the operational RF frequency of the kicker cavity is not a multiple of the linac RF frequency.

6. The method of claim 1 further comprising beam optics downstream of the kicker cavity to affect one region of phase space and not the others.

7. The method of claim 1 further comprising beam optics downstream of the kicker cavity to form a steering cavity for separating two bunch types in a x-direction.

8. The method of claim 7 wherein the steering cavity includes a quadrupole and a sextupole closely packed in series to generate a magnetic field that affects bunch types of a specific energy.

9. The method of claim 1 wherein a phase of the kicker cavity is set to enable the selected electron bunches pass through the cavity when a RF field is at a node, leaving the specific energy of the selected electron bunches unaffected.

Description

DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a block diagram of a 3-pass ERL with bunch frequency equal to the linac frequency.

(2) FIG. 2 is a series of plots depicting the focusing of slightly space-separated bunches using a quadrupole and a sextupole closely packed in series to generate a magnetic field that does not affect one bunch type, but does focus the other type.

DETAILED DESCRIPTION

(3) The present invention is a method for controlling bunches with different characteristics that are travelling through a common beam pipe and seeing the same optics in a particle accelerator. Controlling bunches of different types with the same magnets is a challenge. Optimizing the lattice for one type of bunch typically worsens control for the other types of bunches.

(4) The method includes affecting different bunch types in different ways to enable independent control over different bunch types in common ERL transport lines. The method includes providing an RF kicker cavity at the beginning of the common transport pipe, and/or at various locations along the common transport path to achieve independent control of different bunch types. For a common transport line the method includes applying RF energy to electron bunches with a kicker cavity by a) kicking some portion of the bunches; b) separating bunches in phase space to allow independent control via optics; or c) separating bunches into different beam pipes.

(5) The kicker cavity is operated at a specific frequency that will enable kicking of different types of bunches in different directions.

(6) As an example, with reference to FIG. 1 below, the operational RF frequency of the kicker cavity is set at a multiple of the frequency with which one selected type of bunch passes the common transport pipe, while avoiding any frequency that is a multiple of the linac RF frequency. The operational RF frequency of the kicker cavity is a steering frequency that is determined by the equation
f.sub.steering=(k/n)f.sub.RF
wherein n is the number of passes and k is any integer, and f.sub.RF is the linac frequency.

(7) The phase of the cavity is set such that the selected type of bunch passes through the cavity when the RF field is at a node, leaving that type of bunch unaffected. The other types of bunches, arriving at a different RF field phase in the kicker cavity, do get kicked by the kicker cavity. The kick can be in the transverse directions, but could also be in the longitudinal direction.

(8) By operating the kicker cavity in the aforementioned manner, the bunch types can be separated in phase space. As an example, when there are two bunch types, one bunch type could go straight while the other bunch type is kicked in the positive x-direction. Other configurations are also possible through appropriate selection of frequency and relative phasing, for example, when all bunches are kicked but in different directions. If the kicks are done on crest, the distortions of the electron bunches are minimized.

(9) Beam optics that only affect one region of phase space and not the others can then be added downstream of the kicker cavity to cause a separation in phase space. As an example, with reference to FIG. 2 below, beam optics in the form of a steering cavity is used to separate two bunch types in the x-direction. A quadrupole and a sextupole can then be closely packed in series to generate a magnetic field that does not affect one bunch type, but does focus the other type. Alternately, the separated bunches could be directed to independent transport channels.

(10) Although the description above contains many specific descriptions, materials, and dimensions, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention. Thus the scope of the invention should be determined by the appended claims and their legal equivalents, rather than by the examples given.