The 2009 spring semester's cyclotron project was to design, construct, install, and operate an electrostatic deflector. The deflector 'peels' the ions out of their circular orbit to an orbit with a larger bend radius. Such a deflection channel is typically used to extract the cyclotron's beam from the chamber and send it down a transport beamline to an experiment station. It was not the intention of this project to extract the beam. Rather, we're using the electrostatic deflection channel as an EXB (wein) filter. Only ons of specific velocity will propagate through the channel, thus providing a method of measuring the beam's energy. Figure 1 shows the electrostatic deflector assembly. We have designed it to be modular, thus removable.
Our design intercepted the circulating beam at a radius of 4.0 inches, and deflected it to a radius of 4.5 inches in a 46 degree arc. The nominal radius of curvature of the deflector is 7.0 inches, thus the electrostatic field 'undoes' 3.0 inches of B-field curvature.

Fig.7 The electrostatic deflector assembly shown edge on. The thin Stainless Steel (SS) vertical sheet is grounded and separates the deflection channel from the primary acceleration region.

Fig.10 Relative placement of the electrostatic deflector assembly placement when placed in the chamber.

Fig.12 The beam is finally 'caught' on a phosphor screen that is located down stream of the deflection channel. Thus only ions with the correct velocity will hit and light up the screen.

Fig.13 The electrostatic deflector assembly finally installed in the chamber. The back of the phosphor screen is the smaller plate mounted on the left of the deflector assembly.
The following photos display the construction, installation, and operation of the electrostatic deflector. A superb job by both cyclotron student Tim P. and the Rutgers Physics and Chemistry Machine shop.! (Spring 2009)

Fig.20 500 keV protons hitting the screen. The HV power supply could only give us 28 kV on the electrode, we calculated that we needed 33 kV to center the spot on the screen. A 50 kV supply is on order.
At a reduced B-field (0.5 Tesla) but at the same frequency we should be able to detector molecular hydrogen (H2+). Indeed we saw that, and something else! This figure is a series of photos of the screen, starting at a deflector voltage of 1.5 kV and ending at 8.0 kV in 0.5 kV increments. The second peak, at 6.5 kV is molecular hydrogen. Any guesses as to the 3.5 kV peak ? We have a couple ideas, but we'd like to hear you thoughts.


Fig.24 The HV lead from the resistor (top of magnet) to the chamber, and the HV voltage monitoring probe. The phosphor screen view port is immediately to the right of the HV feedthrough.
Click here for Cyclotron Student Tim P.'s final class presentation on the deflector project. Many thanks go the folks in the Physics and Chemistry Machine shop, not just for the beautiful machining but for their patients in guiding the student in mechanical drawing as we as offering many suggestions that made the project functional. The cyclotron team is also very apreciative of Prof. Mohan Kalelkar for providing the needed support to make this project a reality.