University of Arizona Physics Department

Physics 445/545 I
The 2 MV Van de Graaff Accelerator
A Three Week Advanced and Graduate Laboratory Project
using the UA Physics Department 2-MV Van de Graaff Facility
Prepared by William S. Bickel


Office: PAS 273
E-mail: bickel@physics.arizona.edu
(520)621-2524/2534


The Van de Graaff accelerator is opened, the ion sourceis inserted and tuned, the tank is closed, pumped down and filled with N2 and CO2.

Week one:

1. Short lecture on the Van de Graaff accelerator, tour of facility, Van de Graaff accelerator, Magnet, Beam Pipes, Vacuum Pumps, Slit Controls, Target Chamber Optics, Electronics

2. Van de Graaff is turned on, ion source lit, and a mass scan made of ion source output. Calibrate magnet field B via BvQ = mv2/R to get magnetic field B as a function of Energy E and mass m calibration curve.

2. Van de Graaff is turned on, ion source lit, and a mass scan made of ion source output. Calibrate magnet field B via BvQ = mv2/R to get magnetic field B as a function of Energy E and mass m calibration curve.

3. Beam pipe and target chambers: valves, fore- and diffusion pumps, pump-down rates, cold traps, pressure, density, vacuum, mean free path, collision frequency, monolayer build-up.

4. Target chamber assembly: beam-foil, beam-gas, and other beam-particle excitations. Optical and electronic setup to measure beam currents, photon intensities and get spectra.

Week two:

5. Data taking. Wavelength and intensity measurements as a function of energy, mass i(beam), target, projectiles, geometry, position. Spectra from vacuum UV through the visible (l300-8000Å). Beam current and intensity (PMT) normalization.

6. Data collection. Meter, stripchart, counter-timer, MCA, computer (PC). Determine time constants. PMT current, counts, counts/sec, dwell times of; MCA, counting times, response time of strip chart. Measure spectra. Put data into computer through AD-DA counting board. Compare all data taking techniques.

7. Measure spectra as a function of all parameters and measure intensities I as a function of x, p, E, ---- Get decay curves.

Week three:

8. Get data into a computer and onto disk. Analyze it with LAB CALC or other standard analysis programs. Discuss error, uncertainties, calibrations to NBS-NIST (machine energy, intensities, wavelengths), counting statistics, DE, stability, resolution, JND.

9. Final Result: a relative or absolute cross section, spectrum or intensity curve for a projectile on a target. The data (results) can be new or reproducible results to compare to theory or a previous experiment.

    Students will do all adjustments, calibrations and data taking. They will operate the entire facility. They will assemble a beam-pipe pumping system: fore- and diffusion pump, cold trap, valves, target chamber and gauge circuits to measure pressure. They will be expected to build a mechanical device using the machine shop and an electrical device using electronic skills and techniques. They will learn how to apply standard spectral analysis techniques to their data: curve fit, extract line centers and wavelengths, measure widths, intensities and shapes. Their data will be compared to fundamental constants or accepted standards. Error analysis will be applied to all data.



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