Ring-coupled cavity resonator

Abstract

Spin polarized beams are an essential tool in the study of nuclear physics using particle accelerators. Particle accelerators can produce spin polarized beams, but a technology is needed to continuously monitor, in real time and non-invasively, the beam's polarization direction and quality. Without this capability, there is no way to automate polarization quality optimization. The ring-coupled cavity resonator provides a mechanism to enhance the interaction between a cavity resonator and the spin of passing particles, and provides a method to determine and monitor, in real time and non-invasively, beam magnetization and longitudinal spin polarization direction and quality.

Claims

1. An apparatus for measuring the spin orientation and magnetization of charged particle beams, comprised of a cavity resonator with a bore for the passage of the beam to be measured; and a conductive ring positioned coaxially within the bore of said cavity resonator for the passage of the beam to be measured, whereby the interaction of the beam passing through the conductive ring couples to a resonance in the cavity resonator; and an antenna coupled to the cavity's resonance for measurement of its amplitude and phase.

Description

DRAWINGS FIGURE

(1) FIG. 1 is a conceptual illustration of the interaction between the ring coupled cavity resonator and the magnetic field of a particle bunch with longitudinal spin polarization or bulk magnetization.

(2) FIG. 2 is an exploded view of an embodiment of the invention.

REFERENCE NUMERALS IN DRAWING

(3) 1. Vacuum flange adapters 2. Vacuum enclosure nipple 3. Coaxial vacuum feed through 4. Antenna 5. Antenna mounting hardware 6. Ring coupler/drive antenna 7. Ring coupler/drive antenna support 8. Cavity wall segments 9. Spacers 10. Cavity end walls 11. Support rods 12. Rod fasteners

DESCRIPTION OF THE INVENTION

(4) The ring-coupled cavity resonator assembly is enclosed within a vacuum vessel that is comprised of two vacuum flange adapters (1) and a vacuum enclosure nipple (2). The two vacuum flange adapters (1), adapt the nipple's flange size to the to the beam pipe's flange size and back again, providing, with the nipple, a vacuum enclosure for the ring coupled cavity resonator. A coaxial vacuum feedthrough (3) penetrates the vacuum enclosure and provides a radio frequency/microwave connection to the cavities antenna (4). Antenna mounting hardware (5) provides the antenna support from within the cavity, and can be metallic or non-metallic depending on the antenna design. The ring coupler/drive antenna (6) is metallic and is supported to allow passage of the beam through it by the ring coupler/drive antenna support (7). The ring coupler/drive antenna support can be metallic or non-metallic depending on its geometry. FIG. 2 shows support spokes that are orthogonal to the electric field of transverse electric modes and can be metallic or non-metallic without detrimentally effecting the operation of TE.sub.011 mode. Because the wall currents that support the TE.sub.011 mode are purely azimuthal, the resonant cavity in this embodiment is defined by the inside surface of a stack of flat cavity wall segments (8) that are insulated from one another by spacers (9), and the cavity end walls (10). Electrically insulating spacers disrupt TM modes by preventing the wall current that support them, and microwave absorbing spacers can prevent additional cavity modes from potential interaction with the beam.

(5) Support rods (11) are attached to a vacuum flange adapter, and the cavity assembly is captured with rod fasteners (12). Compression of the assembly with these fasteners can be used for fine tuning the frequency of resonance.

Operation of the Invention

(6) In operation, the ring coupled cavity resonator is integrated into a beam line so that a bunched beam passes through the ring coupler/drive antenna that is positioned within the resonant cavity. The operational frequency of the cavity is selectable by the size and shape of the cavity. The resonant frequency of the cavity can be selected to be any frequency component of the ring current that is induced by the passing bunches. In the case of a beam bunch magnetometer, the cavities resonance frequency could be a harmonic of the bunch frequency. Measurement of the amplitude of the cavities resonance is a measurement of the beams total magnetization. Measurements of the difference of the magnitude and phase of the resonance as the beams spin orientation is modulated can be used to determine the longitudinal polarization direction, polarization quality, and beam magnetization simultaneously. To increase the sensitivity of longitudinal polarization measurements, the cavities resonant frequency can be selected to detect a more subtle frequency component within the ring's current, including bunch polarization modulation, or a modulation sideband induced by polarization modulation.

(7) The coaxial vacuum feedthrough (3) and antenna (4) are used to exchange signals to and from the cavity resonator. A sensitive receiver could be used to measure low power signals. A phase sensitive quadrature demodulator or I/Q receiver could be used to measure changes in the relative phase and amplitude of the cavity resonance as compared to the accelerators clock as the beams spin orientation is modulated. Additionally, the feedthrough and antenna could be used to actively drive a mode to interact with the beam, or to increase the power of signals extracted by the beam by influencing the ring current.