Design Studies of a Microwave-driven Ion Source Ying-Xing Lin Minnesota State University, Mankato Advisor: Vladimir Derenchuk IUCF August 5, 2003

Pre-Injector Assembly Side View

Cross sectional view of the plasma chamber and the extraction system describe 4 electrodes Boron Nitride keeps the ions from recombining into H2+

Beam current measured at the beam stop VS. the ion gauge pressure This plot shows the beam current measured at the beam stop as the pressure of the ion gauge changes at different electron suppression voltages. The Pressure is changed by bleeding in nitrogen gas through a needle valve closed to the extraction regiony

Goals Minimize N2 gas usage in the vacuum chamber Improve the beam intensity Minimize the spread of the beam

PBGUNS Particle Beam GUN Simulation the computer code of PBGUNS is written in FORTRAN and is about 53,000 lines long used for the simulation of axisymmetric and 2-D electron and ion extraction problems: relativistic, thermionic, field emission, sputter ejection, positive and negative ion extraction… solves Poisson’s Equation using iterative relaxation techniques on a rectangular array of squares determines the plasma boundary for plasma sources and does not require a “curvature” or any other knowledge of the beam or plasma

Result of PBGUNS simulation define angle Define 4 electrodes, angle, red line, green line,

Result of PBGUNS simulation

multiplier 4 95% of the rays are included in the ellipse

dR/dz determinses how parallel the beam is smaller the value, more parallel the beam is Rmax value determines the size of the beam smaller the value, smaller the beam

Angle=66 degrees, Distance = 5.5mm define angle

6.5mm

7.5mm

8.5mm

9.5mm

10.5mm

11.5mm

12.5mm

13.5mm

14.5mm

15.5mm

5.5mm

6.5mm

7.5mm

8.5mm

9.5mm

10.5mm

11.5mm

12.5mm

13.5mm

14.5mm

15.5mm

Determine the effect of plasma current

with 2 different mass, see how many percentage of heavier mass should be added to have the smallest emittance and beam size

Angle = 80 degrees

Angle = 54 degrees

The Final Design

20 mm length

100 mm length

Conclusion Even though the scale was wrong for most of the simulations, the trend of each plot is still going to be the same with the right scale; The final design might still be optimal, more simulations need to be run to confirm it Use Maxwellian angular distribution for the plasma source type instead and check if the optimal design is still the same.