A radio-controlled trencher for accurate installation of shallow ditches and pipelines

An inexpensive, radio-controlled, rotary trencher was developed for installing partially-buried surface pipes on an accurate grade. The method was developed for use with the Cablegation automated surface irrigation system and other gated pipe systems. The trencher is mounted on a farm tractor and offset to cut the trench behind the rear tractor wheel. The grade is remotely controlled by an operator sighting through an ordinary surveying instrument and adjusting the cutting depth via a radio control. Tests have shown that the trench grade can be controlled to an accuracy of ±10 mm (0.03 ft). The trencher and control system costs about $1500, not including the surveying instrument

Scintillator-based diagnostic for fast ion loss measurements on DIII-D

A new scintillator-based fast ion loss detector has been installed on DIII-D with the time response 100 kHz needed to study energetic ion losses induced by Alfvén eigenmodes and other MHD instabilities. Based on the design used on ASDEX Upgrade, the diagnostic measures the pitch angle and gyroradius of ion losses based on the position of the ions striking the two-dimensional scintillator. For fast time response measurements, a beam splitter and fiberoptics couple a portion of the scintillator light to a photomultiplier. Reverse orbit following techniques trace the lost ions to their possible origin within the plasma. Initial DIII-D results showing prompt losses and energetic ion loss due to MHD instabilities are discussed. © 2010 American Institute of Physics.U.S. Department of Energy DE-FC02-04ER54698, SC-G903402, DE-FG03-94ER5427

Convective beam ion losses due to Alfven eigenmodes in DIII-D reversed-shear plasmas

Coherent losses of neutral beam ions are observed at frequencies corresponding to toroidal and reversed-shear Alfven eigenmodes (RSAEs) in DIII-D. ´ Reversed-shear profiles are created by injecting beam power during the plasma current ramp. Beam ion losses stemming from Alfven eigenmode activity ´ contribute to flattening of the energetic ion density profile in such discharges. This is the first observation of convective beam ion losses due to RSAEs. The energies and pitch angles of lost ions are measured and found to exist within a well-defined region of phase space. Loss flux signals decrease in time as current penetrates and Alfven eigenmode activity becomes more core ´ localized. Preliminary Monte Carlo simulations of energetic ion interactions with measured mode structures show the dominant loss mechanism is a transition from a counter-passing orbit to a trapped orbit that is lost to the wall.US Department of Energy DE-AC05-06ER23100, SC-G903402, DE-FC02-04ER5469

Quantum Phase Transitions and Conserved Charges

The constraints on the scaling properties of conserved charge densities in the vicinity of a zero temperature ($T$), second-order quantum phase transition are studied. We introduce a generalized Wilson ratio, characterizing the non-linear response to an external field, $H$, coupling to any conserved charge, and argue that it is a completely universal function of $H/T$: this is illustrated by computations on model systems. We also note implications for transitions where the order parameter is a conserved charge (as in a $T=0$ ferromagnet-paramagnet transition).Comment: 19 pages, REVTEX 3.0, 8 uuencoded Postscript figues appended, YCTP-xxx

Numerical Study of the Spin-Flop Transition in Anisotropic Spin-1/2 Antiferromagnets

Magnetization processes of the spin-1/2 antiferromagnetic $XXZ$ model in two and three spatial dimensions are studied using quantum Monte Carlo method based on stochastic series expansions. Recently developed operator-loop algorithm enables us to show a clear evidence of the first-order phase transition in the presence of an external magnetic field. Phase diagrams of closely related systems, hard core bosons with nearest-neighbor repulsions, are also discussed focusing on possibilities of phase-separated and supersolid phases.Comment: 4 pages, Revtex version 4, with 4 figures embedded, To appear in Phys. Rev.

Scrape-off layer ion acceleration during fast wave injection in the DIII-D tokamak

Fast wave injection is employed on the DIII-D tokamak as a current drive and electron heating method. Bursts of energetic ions with energy Eo > 20 keV are observed immediately following fast wave injection in experiments featuring the 8th ion cyclotron harmonic near the antenna. Using the energy and pitch angle of the energetic ion burst as measured by a fast-ion loss detector, it is possible to trace the origin of these ions to a particular antenna. The ion trajectories exist entirely within the scrape-off layer. These observations are consistent with the presence of parametric decay instabilities near the antenna strap. It is suggested that the phase space capabilities of the loss detector diagnostic can improve studies of wave injection coupling and efficiency in tokamaks by directly measuring the effects of parametric decay thresholds.US Department of Energy SC-G903402, DE-FG03-97ER4415, DE-FG02-89ER53296, DE-FG02-08ER549

Preliminary Studies of Magnetic NDE Techniques for Identifying Neutron Embrittlement of Pressure Vessel Steel

In operating nuclear reactors, the steel pressure vessel is exposed to neutron irradiation. The high energy part (\u3e1 MeV) of this irradiation, over a long period, makes the steel brittle and susceptible to rupture

Beam ion losses due to energetic particle geodesic acoustic modes

We report the first experimental observations of fast-ion loss in a tokamak due to energetic particle driven geodesic acoustic modes (EGAMs). A fast-ion loss detector installed on the DIII-D tokamak observes bursts of beam ion losses coherent with the EGAM frequency. The EGAM activity results in a significant loss of beam ions, comparable to the first orbit losses. The pitch angles and energies of the measured fast-ion losses agree with predictions from a full orbit simulation code SPIRAL, which includes scattering and slowing-down.U.S. Department of Energy DE-FC02-04ER 54698, SC-G903402, DE-AC02-09CH1146

Condensation of Hard Spheres Under Gravity: Exact Results in One Dimension

We present exact results for the density profile of the one dimensional array of N hard spheres of diameter D and mass m under gravity g. For a strictly one dimensional system, the liquid-solid transition occurs at zero temperature, because the close-pakced density, $\phi_c$, is one. However, if we relax this condition slightly such that $phi_c=1-\delta$, we find a series of critical temperatures T_c^i=mgD(N+1-i)/\mu_o with \mu_o=const, at which the i-th particle undergoes the liquid-solid transition. The functional form of the onset temperature, T_c^1=mgDN/\mu_o, is consistent with the previous result [Physica A 271, 192 (1999)] obtained by the Enskog equation. We also show that the increase in the center of mass is linear in T before the transition, but it becomes quadratic in T after the transition because of the formation of solid near the bottom