Showing 1–13 of 13 results for author: Chrystal, C

Spacecraft heat shield study in the DIII-D tokamak

Authors: Dmitri M. Orlov, Evdokiya G. Kostadinova, Igor Bykov, Dmitri L. Rudakov, Roman Smirnov, Jayson Barr, Gabrielle Bladon, Alessandro Bortolon, Justin Burzachiello, Lane Carlsson, Colin Chrystal, Jason Escalera, Jessica Eskew, Graeson Griffin, Michael O. Hanson, Georg Herdrich, Jeffrey Herfindal, Al Hyatt, Truell Hyde, Charles Lasnier, Claudio Marini, Lorin Matthews, Adam McLean, Christopher A. Mehta, Renato Perillo , et al. (11 additional authors not shown)

Abstract: We report a new experimental platform developed at the DIII-D National Fusion Facility to investigate carbon ablation and spallation under extreme heat fluxes relevant to fusion plasma-facing components and high-enthalpy atmospheric entry. Carbon samples were exposed to parallel heat fluxes of $30$--$40~\mathrm{MW\,m^{-2}}$ in the scrape-off layer using two complementary approaches: stationary car… ▽ More We report a new experimental platform developed at the DIII-D National Fusion Facility to investigate carbon ablation and spallation under extreme heat fluxes relevant to fusion plasma-facing components and high-enthalpy atmospheric entry. Carbon samples were exposed to parallel heat fluxes of $30$--$40~\mathrm{MW\,m^{-2}}$ in the scrape-off layer using two complementary approaches: stationary carbon rods inserted near the divertor strike point and slow-launch carbon pellets injected vertically into the edge and core plasma. Pellets penetrating the core experienced heat fluxes approximately an order of magnitude higher. The conditions reproduce key aspects of the shock-layer environment encountered by the Galileo probe during entry into Jupiter's atmosphere. Fast visible imaging, divertor spectroscopy, infrared thermography, CO$_2$ interferometry, and post-exposure profilometry provided measurements of ablation rates, surface recession, and temperature evolution. Measured mass-loss rates of $(1$--$3)\times10^{-2}~\mathrm{g\,cm^{-2}\,s^{-1}}$ agree with semi-empirical aerospace ablation models, while wedge-shaped rods exhibited greater ablation than cylindrical and concave samples. UEDGE-DUSTT simulations incorporating parallel plasma flows, ${\bf j}\times{\bf B}$ forces, and ablation-cloud shielding reproduce the measured pellet trajectories and ablation timescales. These results establish tokamak plasma as a high-heat-flux environment for validating carbon ablation models and studying material response and impurity dynamics in reactor-relevant divertor plasmas. △ Less

Submitted 28 July, 2026; v1 submitted 26 July, 2026; originally announced July 2026.

Dependence of Momentum Transport on the Dominant Turbulence Regime in the DIII-D Tokamak

Authors: C. F. B. Zimmermann, C. Chrystal, E. Perez, T. Tala, C. Angioni, S. Haskey, F. Khabanov, R. M. McDermott, G. McKee, A. Salmi, L. Schmitz

Abstract: Accurate prediction of toroidal plasma rotation is essential for optimizing confinement and stability in future fusion devices. This work investigates turbulent core momentum transport in the DIII-D tokamak across a transition from ion-temperature-gradient (ITG)- to trapped-electron-mode (TEM)-dominated turbulence. A momentum transport framework previously developed for ASDEX Upgrade is applied to… ▽ More Accurate prediction of toroidal plasma rotation is essential for optimizing confinement and stability in future fusion devices. This work investigates turbulent core momentum transport in the DIII-D tokamak across a transition from ion-temperature-gradient (ITG)- to trapped-electron-mode (TEM)-dominated turbulence. A momentum transport framework previously developed for ASDEX Upgrade is applied to modulated neutral beam injection experiments, separating diffusive, convective, and residual-stress contributions via Fourier analysis of the rotation response. The dataset spans low-rotation conditions, dominant electron heating, and background ExB shearing rates below turbulence growth rates, accessing more reactor-relevant conditions. Gyrokinetic CGYRO and gyrofluid TGLF calculations confirm the scan covers an ITG-to-TEM transition. The analysis yields Prandtl numbers near unity. The pinch number shows no explicit dependence on the transition, instead ordering roughly with the logarithmic density gradient. The normalized residual stress, in contrast, exhibits a non-monotonic, V-shaped dependence across the transition: co-current in deep ITG and deep TEM regimes, near-zero or counter-current in the intermediate mixed-mode regime. This trend collapses onto an approximately linear dependence against electron kinetic profile gradients, suggesting residual stress generation by profile-shearing effects. Weaker background ExB shearing further shifts residual stress toward counter-current values. Linear CGYRO simulations for representative ITG and TEM discharges yield Prandtl and pinch numbers in good agreement with experiment, supporting gyrokinetic momentum-transport predictions in TEM-dominated regimes. These results indicate residual stress plays an important role in core rotation prediction for low-torque plasmas and should be included in predictive models of future reactor scenarios. △ Less

Submitted 16 July, 2026; originally announced July 2026.

First divertor exposure experiments of a renewable boron pebble aggregate in DIII-D

Authors: Erick Martinez-Loran, Angelica Ottaviano, Santhosh T. A. Kumar, Gabriel Brewster, Renato Perillo, Dmitry Rudakov, Jun Ren, Jonathan D. Coburn, Robert Kolasinski, Ryan Thomas Hood, Cedric K. W. Tsui, Charles Lasnier, Filippo Scotti, Dihn D. Truong, Gilson Ronchi, Igor Bykov, Colin Chrystal, Žana Popović, Shawn Zamperini, Florian Effenberg, Mathias Groth, Dmitri M. Orlov, Jose Boedo, Eric M Hollmann

Abstract: Boron pebble aggregate was tested for the first time as a high-heat-flux granular plasma-facing material in a tokamak divertor. Exposures of up to $q_{\parallel} = \SI{80}{\MW\per\m\squared}$ incident heat flux were conducted in the DIII-D tokamak. Single protruding rods of pebble aggregate composed of sintered amorphous boron pebbles bound with carbon binder were mounted in the Divertor Material… ▽ More Boron pebble aggregate was tested for the first time as a high-heat-flux granular plasma-facing material in a tokamak divertor. Exposures of up to $q_{\parallel} = \SI{80}{\MW\per\m\squared}$ incident heat flux were conducted in the DIII-D tokamak. Single protruding rods of pebble aggregate composed of sintered amorphous boron pebbles bound with carbon binder were mounted in the Divertor Material Evaluation System (DiMES) sample holders and exposed to L-mode lower single null (LSN) plasmas. Under these heat loads, significant boron dust emission from the boron spheres was observed, and this dust dominates the divertor boron ionization source. Only about half of the released boron was recovered locally as mm-sized particles; with the rest presumably lost mainly as dust into the plasma and vacuum chamber. Preliminary estimates suggest that the rate of surface recession of $\sim$1 cm/s in the pebble conglomerate within the plasma divertor is consistent with the recession rates observed in laser bench tests subjected to normal-incidence heat loads. Although core performance was not adversely affected by the high boron dust emission, future work will need to improve the boron pebble aggregate design to reduce boron dust emission at high heat loads. △ Less

Submitted 15 June, 2026; originally announced June 2026.

Impurity-driven turbulence opens a pathway to ELM-free operation and enhanced pedestal stability in tokamaks

Authors: Santanu Banerjee, T. Macwan, A. Bortolon, R. Groebner, K. Barada, R. Maingi, T. Osborne, T. L. Rhodes, C. Chrystal, Z. Yan

Abstract: Edge-localized modes (ELMs) impose severe transient heat, and particle loads on plasma-facing components, posing a critical challenge for steady-state operation of tokamak fusion reactors. Existing ELM control techniques either rely on externally applied perturbations or operate within narrow parameter windows, raising concerns for reactor scalability. Here we demonstrate that controlled injection… ▽ More Edge-localized modes (ELMs) impose severe transient heat, and particle loads on plasma-facing components, posing a critical challenge for steady-state operation of tokamak fusion reactors. Existing ELM control techniques either rely on externally applied perturbations or operate within narrow parameter windows, raising concerns for reactor scalability. Here we demonstrate that controlled injection of a low-Z impurity can fundamentally modify pedestal transport and stability, enabling access to long ELM-free periods through impurity-driven turbulence. Using boron (B) powder injection in the DIII-D tokamak, we observe a progressive reduction of ELM frequency, culminating in long ELM-free phases. Pedestal stability analysis reveals a pronounced decoupling of peeling and ballooning stability boundaries at moderate B injection levels, opening a stability channel toward super-high confinement operation. At higher injection rates, long (~300 ms) ELM-free periods are achieved. Fluctuation measurements show that B injection selectively enhances low-frequency pedestal turbulence, increasing inter-ELM particle transport and regulating pedestal gradients. The establishment of a feedback loop between turbulence, particle transport, and the resulting modification of pedestal conditions, indicated by the observed hysteresis loop in the evolution of density fluctuations in response to the B injection rate, is presented. △ Less

Submitted 1 June, 2026; originally announced June 2026.

Comments: 22 pages, 10 figures

Non-dimensional confinement scaling in similar negative triangularity plasmas on the DIII-D and TCV tokamaks

Authors: A. Marinoni, C. Chrystal, S. Coda, R. Coosemans, C. Marini, M. Podesta, O. Sauter, M. Agostini, M. E. Austin, E. Belli, J. Candy, M. Gorelenkova, D. Hamm, A. W. Hyatt, M. Knolker, M. La Matina, P. Lunia, S. Mordijck, A. O. Nelson, T. H. Osborne, C. Paz-Soldan, L. Porte, U. Sheikh, F. Scotti, K. E. Thome , et al. (3 additional authors not shown)

Abstract: Similarity experiments were performed on the DIII-D and TCV tokamaks to explore the scaling of energy confinement in negative triangularity plasmas using non-dimensional variables. Near up-down symmetric plasmas with large top-bottom averaged negative triangularity were created in a lower single null configuration, with the shape of the separatrix being closely matched between the two devices. The… ▽ More Similarity experiments were performed on the DIII-D and TCV tokamaks to explore the scaling of energy confinement in negative triangularity plasmas using non-dimensional variables. Near up-down symmetric plasmas with large top-bottom averaged negative triangularity were created in a lower single null configuration, with the shape of the separatrix being closely matched between the two devices. The normalized energy confinement is found to weakly improve at increasing collisionality and, between the two devices, shows a machine size scaling behavior between Bohm and gyro-Bohm. Engineering scaling on a large DIII-D dataset is in agreement with the non-dimensional experiment. △ Less

Submitted 12 March, 2026; originally announced March 2026.

Broadening of the Divertor Heat Flux Profile in High Confinement Tokamak Fusion Plasmas with Edge Pedestals Limited by Turbulence in DIII-D

Authors: D. R. Ernst, A. Bortolon, C. S. Chang, S. Ku, F. Scotti, H. Q. Wang, Z. Yan, Jie Chen, C. Chrystal, F. Glass, S. Haskey, R. Hood, F. Khabanov, F. Laggner, C. Lasnier, G. R. McKee, T. L. Rhodes, D. Truong, J. Watkins

Abstract: Multi-machine empirical scaling predicts an extremely narrow heat exhaust layer in future high magnetic field tokamaks, producing high power densities that require mitigation. In the experiments presented, the width of this exhaust layer is nearly doubled using actuators to increase turbulent transport in the plasma edge. This is achieved in low collisionality, high confinement edge pedestals with… ▽ More Multi-machine empirical scaling predicts an extremely narrow heat exhaust layer in future high magnetic field tokamaks, producing high power densities that require mitigation. In the experiments presented, the width of this exhaust layer is nearly doubled using actuators to increase turbulent transport in the plasma edge. This is achieved in low collisionality, high confinement edge pedestals with their gradients limited by turbulent transport instead of large-scale, coherent instabilities. The exhaust heat flux profile width and divertor leg diffusive spreading both double as a high frequency band of turbulent fluctuations propagating in the electron diamagnetic direction doubles in amplitude. The results are quantitatively reproduced in electromagnetic XGC particle-in-cell simulations which show the heat flux carried by electrons emerges to broaden the heat flux profile, directly supported by Langmuir probe measurements. △ Less

Submitted 5 August, 2024; v1 submitted 29 February, 2024; originally announced March 2024.

Comments: 8 pages, 11 figures

Journal ref: Phys. Rev. Lett. 132, 235102 (2024)

ELM-free Enhanced Dα H-mode with Near Zero NBI Torque Injection in DIII-D Tokamak

Authors: T. Macwan, K. Barada, J. F. Parisi, R. Groebner, T. L. Rhodes, S. Banerjee, C. Chrystal, Q. Pratt, Z. Yan, H. Wang, L. Zeng, M. E. Austin, N. A. Crocker, W. A. Peebles

Abstract: Enhanced $D_α$ H-mode (EDA H-mode), an ELM-free H-mode regime, is explored in neutral beam heated, lower single null plasmas with near zero torque injection. This regime exhibits a good energy confinement ($\mathrm{H}_{\mathrm{98y2}}$ $\sim 1$) with $β_N \sim 2$, high density, regime access at low input power, and no ELMs. This paper further presents the time-resolved measurements of electron and… ▽ More Enhanced $D_α$ H-mode (EDA H-mode), an ELM-free H-mode regime, is explored in neutral beam heated, lower single null plasmas with near zero torque injection. This regime exhibits a good energy confinement ($\mathrm{H}_{\mathrm{98y2}}$ $\sim 1$) with $β_N \sim 2$, high density, regime access at low input power, and no ELMs. This paper further presents the time-resolved measurements of electron and ion density, temperature, plasma rotation, and radial electric field during the EDA H-mode phase and examines the dynamics of the edge quasi-coherent mode (QCM). Measurements using multiple fluctuation diagnostics reveal the QCM to be a separatrix spanning mode, peaking just inside the separatrix, existing in a wide range of $k_{\perp}ρ_s \sim 0.1-1.2$ with multiple harmonics, and propagating with a very small phase velocity in the plasma frame, where $k_{\perp}$ is the binormal wavenumber and $ρ_s$ is the ion sound radius. Linear gyrokinetic simulations of an EDA H-mode discharge with CGYRO indicates that the trapped electron mode (TEM) and electron temperature gradient (ETG) are dominant instabilities in the region where QCM is unstable. Qualitative analysis indicates that the properties of TEM are consistent with the experimental observed characteristics of the QCM. These similarities suggest that the QCM might be a TEM instability existing in the edge region of the EDA H-mode plasmas. △ Less

Submitted 9 February, 2024; originally announced February 2024.

Comments: 28 pages, 15 figures, 1 table

Saturation of fishbone instability through zonal flows driven by energetic particle transport in tokamak plasmas

Authors: G. Brochard, C. Liu, X. Wei, W. Heidbrink, Z. Lin, M. V. Falessi, F. Zonca, Z. Qiu, N. Gorelenkov, C. Chrystal, X. Du, J. Bao, A. R. Polevoi, M. Schneider, S. H. Kim, S. D. Pinches, P. Liu, J. H. Nicolau, H. Lütjens, the ISEP group

Abstract: Gyrokinetic and kinetic-MHD simulations are performed for the fishbone instability in the DIII-D discharge #178631, chosen for validation of first-principles simulations to predict the energetic particle (EP) transport in an ITER prefusion baseline scenario. Fishbone modes are found to generate zonal flows, which dominate the fishbone saturation. The underlying mechanisms of the two-way fishbone-z… ▽ More Gyrokinetic and kinetic-MHD simulations are performed for the fishbone instability in the DIII-D discharge #178631, chosen for validation of first-principles simulations to predict the energetic particle (EP) transport in an ITER prefusion baseline scenario. Fishbone modes are found to generate zonal flows, which dominate the fishbone saturation. The underlying mechanisms of the two-way fishbone-zonal flows nonlinear interplay are discussed in details. Numerical and analytical analyses identify the fishbone-induced EP redistribution as the dominant generation mechanism for zonal flows. The zonal flows modify the nonlinear dynamics of phase space zonal structures, which reduces the amount of EPs able to resonate with the mode, leading to an early fishbone saturation. Simulation results including zonal flows agree quantitatively with DIII-D experimental measurements of the fishbone saturation amplitude and EP transport, supporting this novel saturation mechanism by self-generated zonal flows. Moreover, the wave-particle mode-locking mechanism is shown to determine quantitatively the fishbone frequency down-chirping, as evident in GTC simulation results in agreement with predictions from analytical theory. Finally, the fishbone-induced zonal flows are possibly responsible for the formation of an ion-ITB in the DIII-D discharge. Based on the low EP transport and the large zonal flow shearing rates associated with the fishbone instability in gyrokinetic simulations of the ITER scenario, it is conjectured that high performance scenarios could be designed in ITER burning plasmas through fishbone-induced ITBs. △ Less

Submitted 6 February, 2024; originally announced February 2024.

Speeding up charge exchange recombination spectroscopy analysis in support of NERSC/DIII-D realtime workflow

Authors: Aarushi Jain, Laurie Stephey, Erik Linsenmayer, Colin Chrystal, Jonathan Dursi, Hannah Ross

Abstract: We report optimization work made in support of the development of a realtime Superfacility workflow between DIII-D and NERSC. At DIII-D, the ion properties measured by charge exchange recombination (CER) spectroscopy are required inputs for a Superfacility realtime workflow that computes the full plasma kinetic equilibrium. In this workflow, minutes matter since the results must be ready during th… ▽ More We report optimization work made in support of the development of a realtime Superfacility workflow between DIII-D and NERSC. At DIII-D, the ion properties measured by charge exchange recombination (CER) spectroscopy are required inputs for a Superfacility realtime workflow that computes the full plasma kinetic equilibrium. In this workflow, minutes matter since the results must be ready during the brief 10-15 minute pause between plasma discharges. Prior to this work, a sample CERFIT analysis took approximately 15 minutes. Because the problem consists of many calculations that can be done independently, we were able to restructure the CERFIT code to leverage this parallelism with Slurm job arrays. We reduced the runtime to approximately 51 seconds -- a speedup of roughly 20x, saving valuable time for both the scientists interested in the CER results and also for the larger equilibrium reconstruction workflow. △ Less

Submitted 18 September, 2023; v1 submitted 15 September, 2023; originally announced September 2023.

Comments: 8 pages, 5 figures. Not a preprint- this work was rejected from a conference proceedings, so arXiv will hopefully be the final home Updated to add arXiv link/DOI to header of paper

Simultaneous access to high normalized current, pressure, density, and confinement in strongly-shaped diverted negative triangularity plasmas

Authors: C. Paz-Soldan, C. Chrystal, P. Lunia, A. O. Nelson, K. E. Thome, M. E. Austin, T. B. Cote, A. W. Hyatt, A. Marinoni, T. H. Osborne, M. Pharr, O. Sauter, F. Scotti, T. M. Wilks, H. S. Wilson

Abstract: Strongly-shaped diverted negative triangularity (NT) plasmas in the DIII-D tokamak demonstrate simultaneous access to high normalized current, pressure, density, and confinement. NT plasmas are shown to exist across an expansive parameter space compatible with high fusion power production, revealing surprisingly good core stability properties that compare favorably to conventional positive triangu… ▽ More Strongly-shaped diverted negative triangularity (NT) plasmas in the DIII-D tokamak demonstrate simultaneous access to high normalized current, pressure, density, and confinement. NT plasmas are shown to exist across an expansive parameter space compatible with high fusion power production, revealing surprisingly good core stability properties that compare favorably to conventional positive triangularity plasmas in DIII-D. Non-dimensionalizing the operating space, edge safety factors below 3, normalized betas above 3, Greenwald density fractions above 1, and high-confinement mode (H-mode) confinement qualities above 1 are simultaneously observed, all with a robustly stable edge free from deleterious edge-localized mode instabilities. Scaling of the confinement time with engineering parameters reveals at least a linear dependence on plasma current although with significant power degradation, both in excess of expected H-mode scalings. These results increase confidence that NT plasmas are a viable approach to realize fusion power and open directions for future detailed study. △ Less

Submitted 7 September, 2023; originally announced September 2023.

Saturation of fishbone instability by self-generated zonal flows in tokamak plasmas

Authors: G. Brochard, C. Liu, X. Wei, W. Heidbrink, Z. Lin, N. Gorelenkov, C. Chrystal, X. Du, J. Bao, A. R. Polevoi, M. Schneider, S. H. Kim, S. D. Pinches, P. Liu, J. H. Nicolau, H. Lütjens

Abstract: Gyrokinetic simulations of the fishbone instability in DIII-D tokamak plasmas find that self-generated zonal flows can dominate the nonlinear saturation by preventing coherent structures from persisting or drifting in the energetic particle phase space when the mode frequency down-chirps. Results from the simulation with zonal flows agree quantitatively, for the first time, with experimental measu… ▽ More Gyrokinetic simulations of the fishbone instability in DIII-D tokamak plasmas find that self-generated zonal flows can dominate the nonlinear saturation by preventing coherent structures from persisting or drifting in the energetic particle phase space when the mode frequency down-chirps. Results from the simulation with zonal flows agree quantitatively, for the first time, with experimental measurements of the fishbone saturation amplitude and energetic particle transport. Moreover, the fishbone-induced zonal flows are likely responsible for the formation of an internal transport barrier that was observed after fishbone bursts in this DIII-D experiment. Finally, gyrokinetic simulations of a related ITER baseline scenario show that the fishbone induces insignificant energetic particle redistribution and may enable high performance scenarios in ITER burning plasma experiments. △ Less

Submitted 22 January, 2024; v1 submitted 4 January, 2023; originally announced January 2023.

Comments: Accepted in Physical Review Letters : https://journals.aps.org/prl/accepted/b0073Yf2Q4c1a78cb8611348c9fa5932b12922776

Journal ref: Physical Review Letters 2024

The Dependence of the Impurity Transport on the Dominant Turbulent Regime in ELM-y H-mode Discharges

Authors: Tomas Odstrcil, Nathan Howard, Francesco Sciortino, Colin Chrystal, Chris Holland, Eric Hollmann, George McKee, Kathreen Thome, Teresa Wilks

Abstract: Laser blow-off injections of aluminum and tungsten have been performed on the DIII-D tokamak to investigate the variation of impurity transport in a set of dedicated ion and electron heating scans with a fixed value of the external torque. The particle transport is quantified via the Bayesian inference method, which, constrained by a combination of a charge exchange recombination spectroscopy, sof… ▽ More Laser blow-off injections of aluminum and tungsten have been performed on the DIII-D tokamak to investigate the variation of impurity transport in a set of dedicated ion and electron heating scans with a fixed value of the external torque. The particle transport is quantified via the Bayesian inference method, which, constrained by a combination of a charge exchange recombination spectroscopy, soft X-ray measurements, and VUV spectroscopy provides a detailed uncertainty quantification of the transport coefficients. Contrasting discharge phases with a dominant electron and ion heating reveal a factor of 30 increase in midradius impurity diffusion and a 3-fold drop in the impurity confinement time when additional electron heating is applied. Further, the calculated stationary aluminum density profiles reverse from peaked in electron heated to hollow in the ion heated case, following a similar trend as electron and carbon density profiles. Comparable values of a core diffusion have been observed for W and Al ions, while differences in the propagation dynamics of these impurities are attributed to pedestal and edge transport. Modeling of the core transport with non-linear gyrokinetics code CGYRO [J. Candy and E. Belly J. Comput. Phys. 324,73 (2016)], significantly underpredicts the magnitude of the variation in Al transport. The experiment demonstrates a 3-times steeper increase of impurity diffusion with additional electron heat flux and 10-times lower diffusion in ion heated case than predicted by the modeling. However, the CGYRO model correctly predicts that the Al diffusion dramatically increases below the linear threshold for the transition from the ion temperature gradient (ITG) to trapped electron mode (TEM). △ Less

Submitted 22 April, 2020; originally announced April 2020.

Comments: submitted to Physics of Plasmas

An optical fiber-taper probe for wafer-scale microphotonic device characterization

Authors: C. P. Michael, M. Borselli, T. J. Johnson, C. Chrystal, O. Painter

Abstract: A small depression is created in a straight optical fiber taper to form a local probe suitable for studying closely spaced, planar microphotonic devices. The tension of the "dimpled" taper controls the probe-sample interaction length and the level of noise present during coupling measurements. Practical demonstrations with high-Q silicon microcavities include testing a dense array of undercut mi… ▽ More A small depression is created in a straight optical fiber taper to form a local probe suitable for studying closely spaced, planar microphotonic devices. The tension of the "dimpled" taper controls the probe-sample interaction length and the level of noise present during coupling measurements. Practical demonstrations with high-Q silicon microcavities include testing a dense array of undercut microdisks (maximum Q = 3.3x10^6) and a planar microring (Q = 4.8x10^6). △ Less

Submitted 9 February, 2007; originally announced February 2007.

Comments: 8 pages, 5 figures, for high-res version see http://copilot.caltech.edu/publications/index.htm