Physics Research Projects 2016

Emmeline Douglas-Mann
Advisor: David Schaffner
Department: Physics

Construction of a Pulse-Forming Network

A plasma gun source requires the construction of a pulse-forming network (PFN) of capacitors. This circuit, consisting of 8 0.5mF capacitors and 8 inductors of optimised inductance, would give an ideal pulse with just sufficient current for plasma ejection over an extended period of time. This would make it possible to generate sustained plasma injection for studying turbulence. The first stage of construction is to design the PFN using LTSpice, and use simulations of current over time to determine the optimal magnitudes and combination of inductances that result in a long pulse of constant current. After simulating the network, it will be possible to construct it in the laboratory. A typical appropriate combination of inductances is expected to result in a flat current pulse that lasts for almost 300 microseconds. 

Codie Fiedler Kawaguchi
Mentor: David Schaffner 
Department: Physics

Stainless Steel Proximity Experiment

Current pulsed through a copper coil will generate a magnetic field. When this occurs inside a stainless steel vacuum chamber, the resultant magnetic field will be modified due to Faraday’s law of induction. Using hall probes, as well as Bdot probes these effects can be measured.The goal of this research is to explore these effects, to help determine how to minimize the impact it has on the overall experiment. Furthermore, this information will help advance fusion research being conducted by Bryn Mawr in collaboration with Swarthmore's SSX lab. It is expected that as the distance between the copper coil and stainless steel chamber is increased, the effects on the magnetic field will decrease.

Researchers have yet to achieve a self-sustaining fusion reaction in which the amount of energy put in is less than that being produced. Bryn Mawr and Swarthmore  aim to develop new modules in which to accelerate and compress plasma plumes with relatively low energy input and high stability. Hall probes and Bdot probes are used to calculate the time of flight in order to know how fast the plasma is being accelerated. The use of the stainless steel is both a practical, and cost efficient design that will be more accessible for future research.  

Clare Allsopp-Shiner, Leyla Fahim, Carrie Filion
Dr. Michael Schulz
Physics

Black Hole Greybody Factors in Schwarzchild Spacetime

The goal of our project is to calculate the greybody factor of black holes in Schwarzchild spacetime. Black holes radiate the full thermal spectrum near the event horizon, and the amount that the observed radiation differs from this perfect spectrum is referred to as the greybody factor. The radiation created at the event horizon is referred to as Hawking radiation and is a result of quantum effects. Only a small portion of the Hawking radiation that is created will travel past the event horizon, largely due to the extremal geometry surrounding the black hole. Our research will focus on determining how much of the Hawking radiation created at the event horizon will travel outwards to infinity, i.e. how much will be able to tunnel out of the event horizon into the space beyond. In order to determine this, we will calculate the effective potential utilizing the Klein-Gordon Equation in Schwarzchild spacetime and then we will calculate transmission coefficient and the potential of tunneling through this potential. Calculating the tunneling potential and how the radiation at infinity differs from the perfect thermal spectrum emitted helps us further our understanding about black holes and their radiation. This is also applicable to the holography principle. 

Hayley Johnson
Professor David Schaffner
Physics

Stainless Steel Proximity Experiment

Generating and accelerating plasma in a conductive stainless steel chamber affects the magnetic fields inside, due to Faraday’s Law of Induction. These effects will interfere with measurements of the magnetic field due to a pulsed coil (which will later be used to accelerate plasma) inside the chamber. This work is being done in conjunction with work at the Swarthmore Spheromak Experiment, which uses a glass chamber instead of stainless steel. Both facilities are attempting to efficiently accelerate and compress plasma for the long-term goal of fusion technology as part of the project for Accelerating Low-Cost Plasma Heating and Assembly (ALPHA). Initial determinations of the effect of the stainless steel chamber will be made by using a B-dot probe to measure the magnetic field of a pulsed coil placed at incremental distances from a stainless steel plate. As the coil is moved farther from the plate, the plate’s interference with the magnetic field is expected to lessen. Preliminary data-taking suggests that at close proximity, the plate’s effects may be drastic enough to reverse the coil’s magnetic field entirely.

Zhimin (Cheryl) Liu and Jiayi (Rose) Lin
Mentor: Michael Noel
Department of Physics

Investigating the Interactions among Ultracold Rubidium Atoms in Rydberg States

Rubidium atoms cooled to a velocity near zero and trapped at a certain location in space can be excited to high lying Rydberg States with a system of tunable diode lasers. These atoms have strong dipole moments, and can exchange energy through the dipole-dipole interaction.

The laser beams from the diode lasers are tuned to the appropriate wavelength and locked with circuits. Lasers operating at 780nm are used to cool and trap atoms in a magneto-optical trap (MOT). Two other diode lasers (766nm, 1265nm), are tuned to excite the Ultracold Rubidium atoms from the 5p3/2 state to the 5d5/2 state, and finally to the np3/2d state (the Rydberg State).

Our laboratory was recently moved so we will focus on rebuilding the previous laser system and MOT in the new laboratory. By the time the entire system is working effectively, we will start to observe the trapped Ultracold Rubidium atoms and to investigate their interactions.