2,329 research outputs found
Radial penetration of flux surface shaping in tokamaks
Using analytic calculations, the effects of the edge flux surface shape and
the toroidal current profile on the penetration of flux surface shaping are
investigated in a tokamak. It is shown that the penetration of shaping is
determined by the poloidal variation of the poloidal magnetic field on the
surface. This fact is used to investigate how different flux surface shapes
penetrate from the edge. Then, a technique to separate the effects of magnetic
pressure and tension in the Grad-Shafranov equation is presented and used to
calculate radial profiles of strong elongation for nearly constant current
profiles. Lastly, it is shown that more hollow toroidal current profiles are
significantly better at conveying shaping from the edge to the core.Comment: 11 pages, 13 figure
Optimized up-down asymmetry to drive fast intrinsic rotation in tokamaks
Breaking the up-down symmetry of the tokamak poloidal cross-section can
significantly increase the spontaneous rotation due to turbulent momentum
transport. In this work, we optimize the shape of flux surfaces with both
tilted elongation and tilted triangularity in order to maximize this drive of
intrinsic rotation. Nonlinear gyrokinetic simulations demonstrate that adding
optimally-tilted triangularity can double the momentum transport of a tilted
elliptical shape. This work indicates that tilting the elongation and
triangularity in an ITER-like device can reduce the energy transport and drive
intrinsic rotation with an Alfv\'{e}n Mach number on the order of . This
rotation is four times larger than the rotation expected in ITER and is
sufficient to stabilize MHD instabilities. It is shown that this optimal shape
can be created using the shaping coils of several experiments.Comment: 16 pages, 5 figure
Detection and Prevention of Android Malware Attempting to Root the Device
Every year, malefactors continue to target the Android operating system. Malware which root the device pose the greatest threat to users. The attacker could steal stored passwords and contact lists or gain remote control of the phone. Android users require a system to detect the operation of malware trying to root the phone. This research aims to detect the Exploid, RageAgainstTheCage, and Gingerbreak exploits on Android operating systems. Reverse-engineering 21 malware samples lead to the discovery of two critical paths in the Android Linux kernel, wherein attackers can use malware to root the system. By placing sensors inside the critical paths, the research detected all 379 malware samples trying the root the system. Moreover, the experiment tested 16,577 benign applications from the Official Android Market and third party Chinese markets which triggered zero false positive results. Unlike static signature detection at the application level, this research provides dynamic detection at the kernel level. The sensors reside in-line with the kernel\u27s source code, monitoring network sockets and process creation. Additionally, the research demonstrates the steps required to reverse engineer Android malware in order to discover future critical paths. Using the kernel resources, the two sensors demonstrate efficient asymptotic time and space real-world monitoring. Furthermore, the sensors are immune to obfuscation techniques such as repackaging
Conditions for up-down asymmetry in the core of tokamak equilibria
A local magnetic equilibrium solution is sought around the magnetic axis in
order to identify the key parameters defining the magnetic-surface's up-down
asymmetry in the core of tokamak plasmas. The asymmetry is found to be
determined essentially by the ratio of the toroidal current density flowing on
axis to the fraction of the external field's odd perturbation that manages to
propagate from the plasma boundary into the core. The predictions are tested
and illustrated first with an analytical Solovev equilibrium and then using
experimentally relevant numerical equilibria. Hollow current-density
distributions, and hence reverse magnetic shear, are seen to be crucial to
bring into the core asymmetry values that are usually found only near the
plasma edge.Comment: 6 pages, 2 figures, submitted for publicatio
On the Complexity of Decomposable Randomized Encodings, Or: How Friendly Can a Garbling-Friendly PRF Be?
Teaching TAs To Teach: Strategies for TA Training
"The only thing that scales with undergrads is undergrads". As Computer Science course enrollments have grown, there has been a necessary increase in the number of undergraduate and graduate teaching assistants (TAs, and UTAs). TA duties often extend far beyond grading, including designing and leading lab or recitation sections, holding office hours and creating assignments. Though advanced students, TAs need proper pedagogical training to be the most effective in their roles. Training strategies have widely varied from no training at all, to semester-long prep courses. We will explore the challenges of TA training across both large and small departments. While much of the effort has focused on teams of undergraduates, most presenters have used the same tools and strategies with their graduate students. Training for TAs should not just include the mechanics of managing a classroom, but culturally relevant pedagogy. The panel will focus on the challenges of providing "just in time", and how we manage both intra-course training and department or campus led courses
A new quasilinear model for turbulent momentum transport in tokamaks with flow shear and plasma shaping
In tokamak experiments, sufficiently strong flow shear reduces
turbulent transport, thereby improving the prospects for fusion power plants.
It is therefore of great importance to efficiently explore parameter space to
find where strong plasma flow can be achieved. To this end, we propose a new,
physically motivated quasi-linear model for estimating momentum transport from
turbulence in the presence of toroidal flow shear and plasma shaping. The
method gives good estimates of momentum transport for up-down asymmetric
geometries as well as low magnetic shear and tight aspect ratio. The results
are benchmarked with high-fidelity nonlinear GENE simulations, demonstrating
that it provides a fast and accurate estimate of momentum transport.Comment: 34 pages, 17 figure
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