Interaction Region

https://docs.astro.columbia.edu/attachment/wiki/SavinGroup/MergedBeams/EndSection/interaction%20end%20section%201.png?format=raw
Starting at the Chopper the interaction region begins. We measure the H2 molecules formed here from Associative Detachment interactions between laser induced H atoms and H- ions. In this section the overlap between the Ion and Neutral beams are measured using two NEC Beam Profile Monitors (model 80). The distance between the monitors is 45.7 cm. The region ends at the quadrupole.

Beam Profile Monitors

To measure our beam position and profiles using a National Electrostatics Corporation (NEC) Beam Profile Monitor Model 80 (BPM). The BPM operates by rotating a helical wire through the beam. The axis of rotation is 45o to the horizontal plane of the beam. The wire rotates at 19 cycles per second. During one complete rotation the wire passes through the beam once horizontally and once vertically due to the shape of the wire. When the wire passes through the beam, secondary electrons are released and collected. This electron current is measured as a function of time. By matching the corresponding signal within the timing of one rotation you can measure the electron current induced when the wire scans vertically and horizontally. The magnitude of the electron current is prortional to the magnitude of the beam current, hence giving us our vertical and horizonal profiles.

The BPMs are used to monitor the position of the beams and also to measure the overlap of the ion beam with the neutral beam. This is done by blocking the ion beam upstream at the chopper electrostatic lens. With the laser on, the laser induced neutral beam passes through the chopper field and the beam profile can be measured. Then the laser is turned off and the chopper is grounded. This allows the ion beam with out laser induced neutrals to pass through. The ion beam profile is then measured and the overlap can be determined.

Quadrupole Lens

After the particle stream passes through the photo-detachment region, it passes to a quadrupole lens (Quad). The Quad leads the ions into a Faraday Cup where the ion currnet is measured. Afterwards the neutral particles consisting of H2 and H atoms pass through.