Ambient office =  68 nanosieverts per hour

Ambient outside = 102 nanosieverts per hour

Soil exposed to rain water = 103 nanosieverts per hour

Evercrisp apple from Central Market = 108 nanosieverts per hour

Tap water = 78 nanosieverts per hour

Filter water = 60 nanosieverts per hour

Part 2 of 2 Parts (Please read Part 1 first)
     Biswas’s advisor Paul Bonoli has a great deal of experience with traditional “ray-tracing” models. These models evaluate a wave trajectory by dividing it into a series of rays. Bonoli has used this model for decades in his own research to understanding plasma behavior. Unfortunately, these models have serious limitations. Bonoli says that he is pleased that “the research results in Bodhi’s doctoral thesis have refocused attention on the profound effect that edge turbulence can have on the propagation and absorption of radio-frequency power.”
     Ray-tracing modeling of plasma scattering do not fully capture all the wave physics. A “full-wave” model of the old type would be prohibitively expensive. In order to solve the problem of tracking scattering economically, Biswas splits his analysis into two parts. The first part utilizes ray tracing to model the trajectory of the wave in the tokamak assuming that there is no turbulence present. The second part modifies this ray-trajectory with the new scattering model that takes turbulent plasma filaments into account.
     Biswas says that “This scattering model is a full-wave model, but computed over a small region and in a simplified geometry so that it is very quick to do. The result is a ray-tracing model that, for the first time, accounts for full-wave scattering physics.” Biswas points out that this model bridges the gap between simple scattering models that fail to match experimental data and full-wave models that are much too expensive. The result is that reasonable accuracy is achieved at a low cost. Biswas adds that “Our results suggest scattering is an important effect, and that it must be taken into account when designing future RF antennas. The low cost of our scattering model makes this very doable.”
      Syun’ichi Shiraiwa is a staff research physicist at the Princeton Plasma Physics Laboratory. He said that “This is exciting progress. I believe that Bodhi’s work provides a clear path to the end of a long tunnel we have been in. His work not only demonstrates that the wave scattering, once accurately accounted for, can explain the experimental results, but also answers a puzzling question: why previous scattering models were incomplete, and their results unsatisfying.”
     Work is now progressing to apply this new modeling method to more plasmas from the Alcator C-Mod and other tokamaks. Biswas believes that this new model will be especially applicable to high-density plasmas. The standard ray-tracing model has been noticeably inaccurate when attempting to deal with this type of tokamak. He is also excited that the model could be validated by the DIII-D National Fusion Facility. They are carrying out experiments in collaboration with PSFC. He said, “The DIII-D tokamak will soon be capable of launching lower hybrid waves and measuring its electric field in the scrape-off layer. These measurements could provide direct evidence of the asymmetric scattering effect predicted by our model.”
     Tokamaks are used in many laboratories for fusion research. Any improvement in understanding how they operate will have a big impact on global fusion research.

Ambient office = 80 nanosieverts per hour

Ambient outside = 73 nanosieverts per hour

Soil exposed to rain water = 73 nanosieverts per hour

Red lettuce from Central Market = 87 nanosieverts per hour

Tap water = 62 nanosieverts per hour

Filter water = 57 nanosieverts per hour

Part 1 of 2 Parts
     In nuclear fusion research it is critical to understand how radio frequency electromagnetic waves travel or propagate inside the turbulent interior or a nuclear fusion reactor in order to maintain an efficient and continuously operating fusion reactor. RF waves are transmitted by an antenna in the donut-shaped vacuum chamber that is a common component of a magnetic confinement device known as a tokamak. The waves heat the plasma fuel in the reactor and drive its current around the toroidal interior of the tokamak. The efficiency of this process can be influenced by how the wave’s trajectory is altered or scattered by the conditions inside the reactor.
     Researcher have attempted to investigate these RF wave processes utilizing sophisticated computer simulations to match the experimental conditions recorded in the fusion reactors. A good match between these two would tend to validate the computer model. This would raise confidence in using the computer simulations to explore new physics. It would also help design future RF antennas that would perform more efficiently. Current simulations can accurately calculate how much total current is driven by the RF waves. However, they do a poor job in predicting exactly where in the plasma this current is produced.
     MIT researchers have just published a new paper in the Journal of Plasma Physics. In the paper, the researchers have suggested that existing computer models of RF simulations have not properly taken into account the manner in which these waves are scattered as they encounter dense turbulent filaments present in the edge of the plasma. This edge is known as the “scrape-off layer (SOL).
     Bodhi Biswas is a graduate student at the Plasma Science and Fusion Center (PSFC) under the direction of Senior Research Scientist Paul Bonoli with the School of Engineering, Distinguished Professor of Engineering Anne White and Principal Research Scientist Abhay Ram who is the lead author of the journal article. Ram compares the scattering of the plasma that takes place in this situation to a water wave hitting a lily pad. He said, “The wave crashing with the lily pad will excite a secondary, scattered wave that makes circular ripples traveling outward from the plant. The incoming wave has transferred energy to the scattered wave. Some of this energy is reflected backwards (in relation to the incoming wave), some travels forwards, and some is deflected to the side. The specifics all depend on the particular attributes of the wave, the water, and the lily pad. In our case, the lily pad is the plasma filament.”
     Up to the present, fusion researchers have not taken these filaments and their patterns of scattering into consideration when modeling the turbulence inside a tokamak. This has led to a serious underestimation of wave scattering. Biswas used data from PSFC tokamak Alcator C-Mod to show that employing the new method they developed for modeling RF-wave scattering from SOL turbulence provides results that are considerably different from the older models. They provide a much better match with the data derived from the operation of the tokamak. The “lower-hybrid” wave spectrum is crucial to driving plasma current in a steady state tokamak. It appears to scatter asymmetrically which is an important effect that is not accounted for in previous models.
Please read Part 2

Ambient office = 88 nanosieverts per hour

Ambient outside = 74 nanosieverts per hour

Soil exposed to rain water = 3 nanosieverts per hour

Asparagus from Central Market = 122 nanosieverts per hour

Tap water = 132 nanosieverts per hour

Filter water = 122 nanosieverts per hour

Ambient office = 80 nanosieverts per hour

Ambient outside = 85 nanosieverts per hour

Soil exposed to rain water =95 nanosieverts per hour

Blueberry from Central Market = 158 nanosieverts per hour

Tap water = 93 nanosieverts per hour

Filter water = 109 nanosieverts per hour