Spencer E. Olson

Gridless DSMC

This work concerns the development of a gridless method for modeling the inter-particle collisions of a gas. Conventional fixed-grid algorithms are susceptible to grid-mismatch to the physical system, resulting in erroneous solutions. On the contrary, a gridless algorithm can be used to simulate various physical systems without the need to perform grid-mesh optimization. An octree algorithm provides the gridless character to a direct simulation Monte Carlo (DSMC) code by automatically sorting nearest-neighbor gas particles into local clusters. Automatic clustering allows abstraction of the DSMC algorithm from the physical system of the problem in question. This abstraction provides flexibility for domains with complex geometries as well as a decreased code development time for a given physical problem. To evaluate the practicality of this code, the time required to perform the gridless overhead from the octree sort is investigated. This investigation shows that the gridless method can indeed be practical and compete with other DSMC codes. To validate gridless DSMC, results of several benchmark simulations are compared to results from a fixed-grid code. The benchmark simulations include several Couette flows of differing Knudsen number, low-velocity flow past a thin plate, and two hypersonic flows past embedded objects at a Mach number of 10. The results of this comparison to traditional DSMC are favorable. This work is intended to become part of a larger gridless simulation tool for collisional plasmas. Corresponding work includes a gridless field solver using an octree for the evaluation of long range electrostatic forces. We plan to merge the two methods creating a gridless framework for simulating collisional-plasmas.

Time averaging of multimode optical fiber output for a magneto-optical trap

We demonstrate a method for increasing the amount of power available for laser cooling applications by using a multimode optical fiber. Through randomization of phase shifts of modes within the fiber on time scales faster than the center-of-mass response time of the atoms, a smooth time-averaged trapping beam is generated. The principle has been demonstrated in a pyramidal magneto-optical trap. The method is particularly suitable for the harnessing of the high output power of broad-area diode lasers for laser cooling.

Tunable axial potentials for atom-chip waveguides

We present a method for generating precise magnetic potentials that can be described by a polynomial series along the axis of a cold atom waveguide near the surface of an atom chip. With a single chip design consisting of several wire pairs, various axial potentials can be created by varying the ratio of the currents in the wires, including double wells, triple wells, and pure harmonic traps with suppression of higher order terms. We use this method to design and fabricate a chip with modest experimental requirements. Finally, we use the chip to demonstrate a double well potential.

Two-dimensional grating magneto-optical trap

We demonstrate a two dimensional grating magneto-optical trap (2D GMOT) with a single input beam and a planar diffraction grating in

Ex vacuo atom chip Bose-Einstein condensate

^{87}

On the stability of atom chip interferometers

Rb. This configuration increases experimental access when compared with a traditional 2D MOT. As configured in the paper, the output flux is several hundred million rubidium atoms/s at a mean velocity of 19.0

Pressure-driven evaporative cooling in atom guides

\pm~0.2

Optimized High-Resolution Simulation of a THz Traveling Wave Tube Amplifier

m/s. The velocity distribution has a 3.3

PID feedback for load-balanced parallel gridless DSMC

\pm~1.7

Continuous propagation and energy filtering of a cold atomic beam in a long high-gradient magnetic atom guide

m/s standard deviation. We use the atomic beam from the 2D GMOT to demonstrate loading of a three dimensional grating MOT (3D GMOT) with