Method for measurement of beam emittance in a charged particle transport system

A method for determining beam emittance of a beam of charged particles at a plane in a charged particle transport system, comprising:

• obtaining a beam current profile for beam current passing a moving mechanism of the charged particle transport system and reaching a sampling Faraday cup located downstream of the moving mechanism, as a function of the position of the moving mechanism;
• numerically determining a derivative of the current profile with respect to the position of the mechanism;
• determining whether, within an overall range of mechanism positions over which the beam current measured at the sample cup varies as a function of position, there is some range of mechanism positions for which the range of divergences in the beam that would otherwise reach the sample cup will fall within an angle subtended by edges of the mechanism at the sample cup;
• determining based on the derivative, a beam current density ρ corresponding to the beam emittance, when there is some range of mechanism positions for which the range of divergences in the beam that would otherwise reach the sample cup will fall within the angle subtended by the edges of the mechanism at the sample cup;
• and
• determining, when there is no range of mechanism positions for which the range of divergences in the beam that would otherwise reach the sample cup will fall within the angle subtended by the edges of the mechanism at the sample cup, the beam current density by performing curve fitting techniques on the derivative of the beam current profile over a range of positions for which the mechanism intercepts beam current that would otherwise reach the sample cup.

A computer program tangibly stored on a computer-readable medium and operable to cause a computer to enable a user to determine beam emittance of a beam of charged particles at a plane in a charged particle transport system, the computer program comprising instructions to:

• obtain a beam current profile for beam current passing a moving, straight-edged mechanism of the charged particle transport system;
• determine a derivative of the current profile;
• determine a beam current density ρ based on of the derivative, the beam current density corresponding to the beam emittance;
• and
• determine if there is some range of mechanism positions for which a range of divergences in the beam that would otherwise reach the current sensor will fall within an angle subtended by edges of the mechanism at the current sensor.

A system to determine beam emittance of a beam of charged particles at a plane in a charged particle transport system, comprising:

• a straight-edged mechanism capable of being moved from a starting position at which neither edge of the mechanism intercepts current in the beam, through a range of intermediate position at one or more of which one or more edges of the mechanism intercept current in the beam, to a final position at which neither edge of the mechanism intercepts current in the beam;
• at least one sampling Faraday cup to measure beam current passing the mechanism and reaching the position of the sampling Faraday cup on a plane downstream of the mechanism;
• a derivative module to determine a derivative of measured sampling Faraday cup current with respect to mechanism position, as a function of mechanism position;
• and
• an analysis module to determine a beam current density ρ as a function of position and direction based on of the derivative, the beam current density corresponding to the beam emittance;
• wherein the analysis module includes a curve fitting module to determine beam current density, when there is no mechanism position for which the range of divergences in the beam that would otherwise reach the Faraday cup will fall within the angle subtended by the two edges of the mechanism at the Faraday cup, by performing curve fitting techniques on the derivative of the beam current profile over a range of positions for which the mechanism intercepts beam current that would otherwise teach the Faraday cup.