Richard Reksoatmodjo - Academia.edu (original) (raw)

Papers by Richard Reksoatmodjo

In order to successfully design, build, and launch a solid rocket capable of surpassing the inter... more In order to successfully design, build, and launch a solid rocket capable of surpassing the internationally-recognized boundary of space, 100 kilometers, the Propulsion Team will have to manufacture one of the largest amateur rocket motors ever made. To accomplish this goal, the team will design and test a series of scaled motors, including a six-inch diameter motor, an eight-inch diameter motor, and the final spaceflight motor, estimated to be roughly ten inches in diameter. To complete tests of all three motors, the team must design, construct, and test the motor case and its respective components, the nozzle, and the actual motor itself. In the case of the spaceflight vehicle, the motor will be roughly 300 pounds of ammonium perchlorate composite propellant that will power the rocket to speeds over Mach 5 in under fifteen seconds. The team hopes that with successful motor testing and acquisition of data, trends in the behavior and performance of solid rocket motors as they increa...

Bulletin of the American Physical Society, Nov 11, 2021

Bulletin of the American Physical Society, Nov 9, 2021

Bulletin of the American Physical Society, Nov 8, 2021

APS Division of Plasma Physics Meeting Abstracts, 2019

Nuclear Materials and Energy, 2021

Abstract SOLPS-ITER modeling of EDA H-mode experiments on Alcator C-Mod find that the electron de... more Abstract SOLPS-ITER modeling of EDA H-mode experiments on Alcator C-Mod find that the electron density pedestal structure is unaffected by increased gas fueling when approaching ITER-like opaqueness conditions. SOLPS-ITER simulations show a decrease in the neutral penetration depth with increasing pedestal density, similar to prior experiments (Hughes et al., 2006). Neutral density and penetration depth vary poloidally, and we show that the highest neutral densities at the separatrix are found closest to the gas puff locations both on the high field side and the low field side. The decrease in the neutral penetration depth with increasing pedestal density, as well as the decrease in the neutral density at the separatrix, are not just limited to the midplane, but persist at every poloidal location. We find, however, that when gas puffs of similar magnitude as those employed in experiments are added, a much larger increase in the electron density is observed over the whole modeled plasma radius. This does suggest that changes in transport will need to be included self-consistently.

The formation of the electron density pedestal is found to be unaffected by high scrape-off layer... more The formation of the electron density pedestal is found to be unaffected by high scrape-off layer neutral opacity in experiments performed on Alcator C-Mod, in H-mode regimes approaching ITER-like edge neutral opacities. In order to assess the relative role of fueling versus transport at the plasma edge, we use the SOLPS-ITER code suite to initially calculate the radial and poloidal neutral density profiles for a discharge at high opacity as well as one at lower opacity. Probing gas puffs of varying magnitude were applied to these high-density (ne,SEP ~ 1*1020 m-3) EDA H-modes at high plasma current (1.3MA) as well as to discharges at reduced current (1.0MA) and density, and thus opacity. Simulated electron density and temperature profiles are matched to upstream experimental data by varying the radial transport coefficients in SOLPS-ITER, revealing midplane neutral densities an order of magnitude lower in the high current discharge (~1014 m-3) vs the lower current discharge...

The Eagle Space Flight Team was created with the goal of becoming the first undergraduate team to... more The Eagle Space Flight Team was created with the goal of becoming the first undergraduate team to design, build, and launch a rocket capable of suborbital spaceflight. To accomplish this task, the team is broken down into multiple sub teams, each focused on a specific aspect of research. The Propulsion group’s concentration is on the development, manufacturing, and testing of the solid-propellant rocket motors to be used in the team’s flight vehicles. In order to do this, the team must create a new propellant formulation, perform a ballistic characterization of that propellant, and then use it to design motors tailored to the flight profiles for which each flight vehicle is intended. The end goal of the research conducted during the 2014-2015 academic year is a 4-inch-diameter motor capable of launching a flight vehicle to 40,000-50,000-feet. Ignite Grant Awar

Electric propulsion systems are critical to extending the lifetimes of satellites and other space... more Electric propulsion systems are critical to extending the lifetimes of satellites and other spacecraft. They are an increasingly important area of research for space industry companies looking to offer the longest lifetimes for commercial satellites. Electrothermal thrusters are Electric Propulsion (EP) devices that use electric power (electro) to generate heat (thermal) which is applied to a propellant, driving up pressure and enthalpy, which (in short) increases thrust output. Electric propulsion systems, compared with conventional chemical propulsion methods, have higher impulse ratings, higher thrust efficiency, better controllability, and longer operational lifetimes. The team has presented an electric propulsion project focused on designing, constructing, testing, and ultimately optimizing a simple electrothermal propulsion system. Through optimization of design parameters such as propellant mass flow rate, nozzle shape/length, cathode placement, and tangentially injected propellant, the hope is to optimize the thrust and specific impulse (Isp) performance levels of the propulsion system. The team has proposed that a simple arcjet can be constructed and operated to demonstrate feasibility of low-power electric propulsion systems, and allowing the investigation of the relevant properties such as thrust, specific impulse, and efficiency. The findings will contribute to the small body of knowledge regarding ultra-low-power arcjets of less than 1 kW in power, and their performance. Ignite Grant Award, Invited Oral Presentatio

Bulletin of the American Physical Society, 2017

was designed, constructed and calibrated for use on a fast infrared camera employed to measure te... more was designed, constructed and calibrated for use on a fast infrared camera employed to measure temperatures on the lower divertor tiles of the NSTX-U tokamak. This adaptor efficiently and evenly filters and distributes long-wavelength infrared photons between 8.0 and 12.0 microns across the 128x128 pixel detector of the fast IR camera. By determining the width of these separated wavelength bands across the camera detector, and then determining the corresponding average photon count for each photon wavelength, a very accurate measurement of the temperature, and thus heat flux, of the divertor tiles can be calculated using Plank's law. This approach of designing an exterior dispersive adaptor for the fast IR camera allows accurate temperature measurements to be made of materials with unknown emissivity. Further, the relative simplicity and affordability of this adaptor design provides an attractive option over more expensive, slower, dispersive IR camera systems.

Bulletin of the American Physical Society, 2018

Nuclear Fusion, 2021

We present experimental inferences of cross-field impurity transport coefficients for AlcatorC-Mo... more We present experimental inferences of cross-field impurity transport coefficients for AlcatorC-Mod plasmas without edge-localized modes, leveraging a novel forward model for the entire Ca K α spectrum, including satellite lines within the spectral range, to compare to high-resolution x-ray imaging crystal spectroscopy (XICS). These measurements are complemented by extreme ultra-violet (EUV) spectroscopy that constrains transport closer to the edge. Using new atomic data sets for both XICS and EUV analysis has enabled consideration of line ratios across both spectral ranges and has increased the accuracy of inferred transport coefficients. Inclusion of charge exchange between edge thermal neutrals and impurities is shown to be extremely important in C-Mod pedestals. Atomic D neutral densities from experimental D Ly α measurements at the midplane are compared to SOLPS-ITER simulations, finding good agreement. Bayesian inferences of impurity transport coefficients are presented for L-,...

Journal of Physics B: Atomic, Molecular and Optical Physics, 2021

X-ray transitions of the very high-n Rydberg series in Ar16+ have been observed from Alcator C-Mo... more X-ray transitions of the very high-n Rydberg series in Ar16+ have been observed from Alcator C-Mod tokamak plasmas. Individual emission lines up to 1s16p-1s2 have been resolved and the central chord line brightnesses with principal quantum number n between 7 and 16 are generally found to decay as 1/n α , with α slightly larger than 3. In the plasma periphery, emission from 1s9p-1s2 and 1s10p-1s2 are found to be significantly enhanced relative to this decrease, indicative of selected population of these levels through charge exchange between background neutral deuterium in the ground state and Ar17+. An unresolved feature between the wavelengths of 1s27p-1s2 and 1s30p-1s2 is also present, which arises through charge exchange with neutral deuterium in the n* = 3 excited state. The brightnesses of transitions populated by charge exchange are spatially up/down asymmetric, with an excess on the side of the magnetic surface X-point. The relative brightness of the unresolved very high-n feature compared to 1s7p-1s2 is found to increase with electron temperature and decrease with electron density. Simulations of line emission just on the long wavelength side of the Ar16+ ionization limit indicate that the principal quantum number decay exponent is closer to α = 4 at very high n. The brightness dependence on n below 16 is in excellent agreement with calculations from the flexible atomic code package.

Nuclear Fusion, 2020

, la découverte d'ostraca mentionnant le toponyme des Agoras précisément au nord du dromos, près ... more , la découverte d'ostraca mentionnant le toponyme des Agoras précisément au nord du dromos, près des bains ptolémaïques, permet de valider définitivement cette hypothèse.

Plasma Physics and Controlled Fusion, 2021

We present Aurora, an open-source package for particle transport, neutrals and radiation modeling... more We present Aurora, an open-source package for particle transport, neutrals and radiation modeling in magnetic confinement fusion plasmas. Aurora's modern multi-language interface enables simulations of 1.5D impurity transport within high-performance computing frameworks, particularly for the inference of particle transport coefficients. A user-friendly Python library allows simple interaction with atomic rates from the Atomic Data and Atomic Structure database as well as other sources. This enables a range of radiation predictions, both for power balance and spectroscopic analysis. We discuss here the superstaging approximation for complex ions, as a way to group charge states and reduce computational cost, demonstrating its wide applicability within the Aurora forward model and beyond. Aurora also facilitates neutral particle analysis, both from experimental spectroscopic data and other simulation codes. Leveraging Aurora's capabilities to interface SOLPS-ITER results, we demonstrate that charge exchange is unlikely to affect the total radiated power from the ITER core during high performance operation. Finally, we describe the ImpRad module in the OMFIT framework, developed to enable experimental analysis and transport inferences on multiple devices using Aurora.