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College of Saint Benedict and Saint John's University DigitalCommons@CSB/SJU

Celebrating Scholarship and Creativity Day Undergraduate Research

4-26-2018

Farnsworth-Hirsch

Michael Nelson College of Saint Benedict/Saint John's University, [email protected]

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Part of the Physics Commons

Recommended Citation Nelson, Michael, "Farnsworth-Hirsch Fusor" (2018). Celebrating Scholarship and Creativity Day. 36. https://digitalcommons.csbsju.edu/ur_cscday/36

This Presentation is brought to you for free and open access by DigitalCommons@CSB/SJU. It has been accepted for inclusion in Celebrating Scholarship and Creativity Day by an authorized administrator of DigitalCommons@CSB/SJU. For more information, please contact [email protected]. Farnsworth-Hirsch Fusor By: Michael Nelson Advisor: Dr. Dean Langley Outline

§ Introduction § Purpose § Materials § Picture § Theory § System Theory § Electrical Theory § Theory § Experiment § Results § Conclusions § Citations § Questions § Nuclear Fusion heralded as energy of future § Limitless fuel supply § Little waste § Fusors work by colliding hydrogen isotopes § -deuterium and deuterium- collisions Introduction § Deuterium-deuterium collisions are much safer § Majority of byproducts will not exit chamber § Exception is § emission flux most reliable gauge of fusor success § Farnsworth-Hirsch fusor operates using electrostatic confinement § Deuterium fuel contained in an electrostatic potential well § Inner grid run at high at negative polarity, outer Introduction chamber shell grounded (cont.) § Deuterium particles ionize, flow towards ground § Positively charged deuterium flow towards chamber center § Collisions of ions at high speeds § Study neutron emission from nuclear fusion § Observe efficiency of the Farnsworth-Hirsch Purpose fusor § Compare power input versus power output § Vacuum System § Mechanical roughing pump § Diffusion pump § Various pressure sensors rated to high vacuum § gauge § Viewport § feedthrough § Tungsten wire probe Materials

Photo courtesy of Kurt J. Lester Company § Power Supply § Variable autotransformer (Variac) § 15kV transformer Materials § Four 40kV rated diodes (cont.) § 155nF capacitor rated for 65kV § Voltage divider § One 1MΩ resistor and one 300MΩ resistor § Neutron Detector § Bubble dosimeter

Materials (cont.)

Photo courtesy of Bubble Technology Industries Inc. Picture Picture (cont.) Picture (cont.) § Attaining high vacuum is critical to running a stable fusion reaction § 10^-6 Torr before § 10^-3 Torr during § Low pressure environments allow ions to travel at faster speeds § Raises chance of successful collisions Vacuum System § Real gasses behave like ideal gasses at high temperatures and low pressures Theory § Ideal gas model applicable to this experiment § Need direct current power supply, negative polarity § Clear neutron emission at around 30kV at 10mA § 15kV at 30mA transformer with alternating current Electrical § Full bridge rectifier § Smoothing capacitor Theory § Voltage divider § Measure output § Discharge capacitor Smoothing Capacitor Full Bridge A Rectifier 1MΩ V

300MΩ

Voltage Electrical Divider 15kV Fusor Theory (cont.) ~ Transformer Chamber § Capacitor § 65kV and 155nF C = (Q / V) Q = C * V Q = (155 * 10-9 F) * (6.5 *104 V) Q = 0.01 C Electrical § Voltage Divider Theory (cont.) § 1MΩ and a 300MΩ resistor Vout = Vin * (R2 / (R1 + R2) )

Vout = Vin * (1MΩ / (1MΩ + 300MΩ) )

Vout = Vin * (1 / 301)

Vout = 15,000V * (1 / 301)

Vout = 49.83 § High Voltage Arcing § Max voltage = 15kV § 3MV/m for arcing through air d = max distance of an arc through air (3,000,000V / 1m) = (15,000V / d) (3,000,000V) * d = (15,000V) * (1m) Electrical d = 15,000V*m / 3,000,000 V Theory (cont.) d = .005m = 5mm § Power Supply

§ Vmax = 15kV and Imax = 30mA P = V * I P = (15 * 103 V) * (30 * 10-3 A) P = 450W § To determine fusor success, must calculate § Bubble Dosimeter § Must convert number of bubbles into neutron flux (n/s):

Nuclear Fusion Neutron dosage (mrem/run time) = Number of counted bubbles / Bubble Sensitivity Theory Neutron dosage (n/cm^2/s) = 8 * Neutron dosage (mrem/hr) Total Neutron Flux (n/s) = (4 * pi * r^2) * Neutron dosage

§ Error range of +/- 20% on the dosimeters § Setting up Vacuum § End of August – early March § Vacuum Chamber § Detached from previous experiment § Plastic tubing rated for 10^-2 Torr § Mechanical Roughing Pump Experiment § Cleaned filter § Fixed hose connecting pump to chamber § Diffusion Pump § Professor Gearhart § No cleaning necessary § Got it working § 2.8 * 10^-7 Torr § Setting up Vacuum § End of August – early March § New lid § Mishandling of order at Ickler Experiment § Leak troubles (cont.) § Troubleshooting § Snoop – liquid leak detector § Took lid back two times § Fixed § 1.9 * 10^-7 Torr § Preparing Power Source § March – Present § Supplies § Found transformer, big capacitor § Purchased diodes, resistors Experiment § Built and tested full bridge rectifier (cont.) § Small , small diodes, small capacitor § Troubles – bad diodes § High Voltage § Built full circuit with all supplies § Used Variac to test § Troubles – Arcing at ~10kV Smoothing Capacitor Full Bridge A Rectifier 1MΩ V

300MΩ

Voltage Experiment Divider 15kV Fusor (cont.) ~ Transformer Chamber

Where arcing occurred Experiment (cont.) Diffusion Pump

1.E–04

Refilled cold trap 1.E–05 Pressure (Torr)

Results 1.E–06

0 10 20 30 40 50 Time (min)

Diffusion pump, Ion gauge degas Refilled cold trap ion gauge degas turned off turned on 15kV Power Supply 10000

8000

6000

4000 Voltage Output (V)

2000 Results (cont.) 0 0 20 40 60 80 100 Voltage Input (V)

§ Linear-- y=A+Bx § Reduced chi-squared of 0.25 § A = 4.784 +/- 6.9 § B = 93.56 +/- 0.43 § Ran out of time § Future § Insulation on circuit § Bubble dosimeter Conclusion § Deuterium § Left behind § Quality vacuum chamber § Large power supply § 450W § Dunbar, R. (2017). Experimental Physics: Paschen’s Law & Langmuir Probe (Unpublished undergraduate thesis). Saint John's University. § Hull, R. (1997). The Farnsworth/Hirsch Fusor. The Bell Jar, 6(3), 1-8. § Klopfer, B. (2012). The Fusor (Rep.). Stanford, CA: Citations Stanford University. § Pogrebnyak, I. (2010, January). The Energy Source of Tomorrow: Benefits of Nuclear . Retrieved February, 2018, from http://pitjournal.unc.edu/article/energy-source- tomorrow-benefits-nuclear-fusion-power Questions?