Bulletin of the American Physical Society
51st Annual Meeting of the APS Division of Plasma Physics
Volume 54, Number 15
Monday–Friday, November 2–6, 2009; Atlanta, Georgia
Session NO4: International Tokamak Research and ITER |
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Chair: Raffi Nazikian, Princeton Plasma Physics Laboratory Room: Regency VI |
Wednesday, November 4, 2009 9:30AM - 9:42AM |
NO4.00001: Summary of steady-state research during 23 years of JT-60 tokamak experiments Mitsuru Kikuchi This talk summarizes the achievement of steady state research during 23 years of JT-60 tokamak experiment. JT-60 was one of 3 large tokamaks, which started its operation in April 1985 and completed in August 2008. Before the modification to JT-60U, up to 80{\%} of plasma current was driven by the bootstrap current and the steady state tokamak reactor concept SSTR was proposed in 1990. Theory of generalized Ohm's law in tokamak was developed. Negative shear configuration was first proposed (1992) and becomes popular in advanced tokamak research now. Formation of internal transport barrier (ITB) in PS(1994) and NS(1997) leads to enhanced bootstrap current fraction in the core region. Physics of NBCD and ECCD was developed using N-NBI and ECCD systems. A current hole (CH) was observed as unique structure formation(2001). Stabilization of RWM with small toroidal rotation $\sim $0.4{\%}V$_{A}$ is important step to sustain high plasma pressure above no-wall limit(2007). Demonstration of full CD with 75{\%} bootstrap current fraction and rest by NBCD was made under relatively high q$_{95}\sim $8(2005) and access to low q$_{95}\sim $5 was reached by the stabilization of RWM(2008). All these results favors the concept of SSTR, but simultaneous sustainment of high bootstrap {\&} high beta operation is left for future study. [Preview Abstract] |
Wednesday, November 4, 2009 9:42AM - 9:54AM |
NO4.00002: Comparison of long pulse single and double null divertor plasma behaviors in EAST H.Y. Guo, X. Gao, J. Li, G.-N. Luo, S. Zhu, J.F. Chang, W. Gao, X.Z. Gong, Q.S. Hu, Q. Li, T.F. Ming, J. Ou, Y.J. Shi, B.N. Wan, D.S. Wang, J. Wang, Z.W. Wu, B.J. Xiao, Q. Xu, L. Zhang, W. Zhang Divertor performance has been assessed in the new EAST superconducting tokamak for both single null (SN) and double null (DN) configurations. Stable DN discharges over 60 seconds have been achieved for the first time in EAST with active wall conditioning and divertor pumping. Particle and heat fluxes to both inner and outer divertor targets are lower for DN, but with stronger asymmetry favoring outer divertors, as compared to SN. Plasmas exhibit a large amplitude broadband turbulence in the outer divertors for both SN and DN, as indicated by Langmuir probe measurements. The turbulence level is significantly reduced in the inner divertors, especially for DN. DN operation also leads to an up-down asymmetry with higher power and particle fluxes to the divertors with their $\nabla $B drift toward the X-point. Revering B$_{T}$ shows a strong influence on the observed divertor asymmetries. As an active means to control power and particle fluxes to the target plates, localized divertor puffing has been explored in EAST under long pulse operating conditions. This presentation will highlight these recent advances. [Preview Abstract] |
Wednesday, November 4, 2009 9:54AM - 10:06AM |
NO4.00003: Real time Suppression MHD with Active Feedback Modulating LHW\&IBW on HT-7 Superconducting Tokamak J.S. Mao, J.R. Juo, H. Wang, Y.W. Sun, B.J. Ding A active modulation LHW and IBW have used successfully for real-time measure and suppress MHD on the superconducting tokamak HT-7. DAQ2010 advanced data acquisition card was used. We also did the synergy modulation experiment of LHW \& IBW. A feedback system was used which activated modulation only when MHD activity reach a predetermined level so as to optimize the current drive through out the discharge. The LHCD modulation was varied in power and frequency, with the frequency always being less than the resistive skin time (100ms). Optimal MHD suppression was achieved when modulating LHW power $>$ 200kW, and frequency of 50Hz. Details of the MHD suppression will be discussed in this poster. The amplitude, interval and the period of LHW and IBW modulation pulse can be adjusted very conveniently. The modulation LHW \& IBW can be delivered very fast at the any time during the discharge. The modulation LHW \& IBW period was always much shorter than the plasma resistive time. So the profile of plasma current is changed much fast than the plasma resistive time. [Preview Abstract] |
Wednesday, November 4, 2009 10:06AM - 10:18AM |
NO4.00004: The Real Mission of ITER G.A. Wurden ITER will operate subject to multiple physics and engineering constraints, and to be successful it must satisfy many constraints simultaneously. One of the most serious issues it will face is learning how to handle 100-400 MJ of plasma energy that can be quickly released in the event of a disruption, and the conversion of an additional 500 MJ of stored poloidal magnetic field energy. The number of full energy disruptions that the armor system can survive is very small. The consequences of multi-megaampere beams of runaway electrons (created in a disruption) hitting water-cooled armor tiles will be catastrophic for ITER if not mitigated. A survey of disruption features in existing machines is discussed. A coordinated global effort to avoid, control, and mitigate tokamak disruptions must be developed with the highest priority. [Preview Abstract] |
Wednesday, November 4, 2009 10:18AM - 10:30AM |
NO4.00005: Spectrally resolved measurements of runaway electrons during plasma disruptions in the TEXTOR tokamak Timur Kudyakov, Oswald Willi, Karl Heinz Finken, Sadrilla Abdullaev, Michael Lehnen, Sergey Bozhenkov, Marcin Jakubowski, Yuhong Xu A new diagnostic, a probe, has been developed to provide the absolute number of runaways and their spectrum at the plasma edge. Additionally, measurements of the thermal load from incident runaway electrons in the material were performed by two thermocouples installed in the probe. The probe consists of 9 YSO (Y$_{2}$SiO$_{5}$ : Ce) crystals. Different thicknesses of stainless steel filters allow to measure the spectrum of runaways with energies between 4 and 30 MeV. Disruptions were provoked by massive gas injection (Ar, Kr, Xe) in to stable TEXTOR discharges. In the thermal quench the loss of runaways produced at the start up of the discharge was detected by the probe. During the current quench a current plateau of runaway electrons is formed. It was found that during the current quench runaway electrons are coming from the plasma as a set of bursts. Such parameters of runaways as their absolute number, the spectrum and the corresponding thermal load in the tungsten plate were measured during thermal and current quenches. [Preview Abstract] |
Wednesday, November 4, 2009 10:30AM - 10:42AM |
NO4.00006: Investigation of vapor cloud formation and dynamic behavior during plasma strikes similar to fusion disruptions Travis Gray, Vijay Surla, David Ruzic The Divertor Erosion and Vapor shielding eXperiment (DEVeX) at the University of Illinois at Urbana-Champaign is designed to produce plasmas with densities on the order of 10$^{21}$~m$^{-3}$ with a electron temperature greater than 100~eV. This is accomplished with the rapid discharge of a 64 kJ capacitor bank through a conical shaped $\theta$-pinch coil. This study utilizes a thin lithium film as the target. The expanding lithium vapor cloud is measured with an axial array of calibrated photodiodes. Vapor temperature is deduced from a collisional-radiative model of lithium interactions with energetic ions and electrons from the bombarding plasma and found to be 1-2~eV. The vapor cold is also found to cool adiabatically as it expands into the vacuum chamber after the plasma strike. Furthermore, the thin lithium film reduces the incident energy to the target (compared to a bare, non-lithium coated target) by up to 81\%. The result is a significantly cooler target temperature under similar plasma bombardment. [Preview Abstract] |
Wednesday, November 4, 2009 10:42AM - 10:54AM |
NO4.00007: The Negative Ion based Diagnostic Neutral Beam for ITER B. Schunke, H. Decamps, M. Dremel, R. Hemsworth, A. Tanga, M. Bandyophadhyay, B. Baruah, A. Chakraborty, C. Rotti, S. Shah, M. Singh, N. Singh The ITER dedicated Diagnostic Neutral Beam (DNB) is under construction. It is the basis for the Motional Stark Effect measurements at the ITER plasma edge and charge exchange spectroscopy. The DNB shares many features of the ITER Heating Neutral Beams (HNBs), but will operate only in hydrogen and inject $\sim $2~MW of 100~keV of H$^{0}$ into the ITER plasmas. The same Cs seeded RF negative ion source is used as for the HNBs. The strong influence of the residual fields on the H$^{-}$ and electrons in the accelerator has led to a new design of the magnetic filter in the ion source. Electron dumps consisting of parallel, vertical, cooled, plates between groups of beamlets immediately downstream of the accelerator prevent excessive electron power reaching the DNB cryopumps. The 4 channel gas neutralizer is made of cooled panels with special protection for the leading edges. Residual ions are deflected electrostatically onto cooled panels based on CuCrZr Heat Transfer Elements. A retractable calorimeter allows commissioning and beam profile measurements. It will be shown how imposed commonalities with the HNBs have influenced the design choices. The baseline DNB operating scenario and the engineering issues (lifetime, fatigue etc.), will be discussed. [Preview Abstract] |
Wednesday, November 4, 2009 10:54AM - 11:06AM |
NO4.00008: The Motional Stark Effect Diagnostic for ITER E.L. Foley, F.M. Levinton, H.Y. Yuh The United States has been tasked with the development and implementation of a Motional Stark Effect (MSE) system on ITER. In the harsh ITER environment, MSE is particularly susceptible to degradation, as it depends on polarimetry, and the polarization reflection properties of surfaces are highly sensitive to thin film effects due to plasma deposition and erosion of a first mirror. We propose a comprehensive approach to the challenges, one which incorporates a sophisticated calibration system for the polarization measurement and also a spectrometer-based system for measurement of the line spacing in the Stark spectrum. The high fields and high beam energy in ITER allow this spectral measurement to be made with good precision for determination of the magnetic field magnitude. Conceptual designs for the MSE system on ITER will be presented. [Preview Abstract] |
Wednesday, November 4, 2009 11:06AM - 11:18AM |
NO4.00009: ITER IC H{\&}CD system: physics requirements and performance predictions P. Lamalle, B. Beaumont, F. Kazarian, A. Loarte, R. Mitteau, C. Sch\"uller, A. Mukherjee, R. Goulding, F. Jaeger, D. Rasmussen, D. Swain, R. Sartori, M. Nightingale, E. Lerche, A. Lyssoivan, A. Messiaen, D. Van Eester, R. Weynants, R. Maggiora, D. Milanesio, L. Colas, R. Dumont The ITER Ion Cyclotron Heating and Current Drive (IC H{\&}CD) system will deliver 20MW of radio frequency power to the plasma in quasi continuous operation during the different phases of the experimental programme. It must have a high availability and reliably couple to ELMy H-Mode plasmas. It has the additional functionality of performing wall conditioning (ICWC) at powers up to $\sim $3MW. The paper will 1) discuss the physics and design requirements on the system, 2) review the main scenarios planned for H{\&}CD and ICWC, 3) describe the main features of the current design, 4) discuss performance predictions based on recent modelling, and 5) present the key measures under implementation to reduce risks on performance. [Preview Abstract] |
Wednesday, November 4, 2009 11:18AM - 11:30AM |
NO4.00010: SOL Width Studies for ITER Ramp-up D.L. Rudakov, J.A. Boedo, R.A. Moyer, R.A. Pitts, A.W. Leonard, G.L. Jackson, C.J. Lasnier, P.C. Stangeby, J.G. Watkins, L. Zeng The present ITER scenarios contain limiter phases in Ohmic or L-mode for ramp-up and ramp-down. Dependencies of scrape-off layer (SOL) density and temperature e-folding lengths on discharge parameters were studied in inner-wall limited (IWL) and lower single null (LSN) discharges on DIII-D in order to benchmark the currently used power flux scaling based on divertor measurements from a number of tokamaks. Scans of the plasma current $(q_{95})$, density, and heating power have been performed. The power flux e-folding lengths derived from the reciprocating probe measurements near the outboard midplane in the IWL configuration are on the average a factor of $\sim 2$ larger than those predicted by the scaling for an outer-wall limited configuration. Probe measurements in LSN configuration were also benchmarked against infrared camera data from the lower divertor. [Preview Abstract] |
Wednesday, November 4, 2009 11:30AM - 11:42AM |
NO4.00011: Confinement and Pedestal Characteristics in H-mode With ECH Heating R. Prater, J.S. deGrassie, P. Gohil, T.H. Osborne, C.C. Petty, E.J. Doyle, B. Hudson, M. Murakami Good global confinement in H-mode discharges when electron heating is dominant is critical to the success of ITER, since the proposed heating schemes predominantly heat electrons. Most of the world database is derived from discharges with high power positive-ion neutral beam injection (NBI), which primarily heats the ions. Issues for dominant electron heating include the H-mode power threshold and effect on rotation, density profile, global confinement, pedestal height, and ELM characteristics. In DIII-D the electron cyclotron heating power is 3.5 MW, so observations of these effects can be made at powers well above the threshold. A study of a few relevant discharges suggests that the H-mode pedestal is not much different from that in NBI, and the global confinement relative to balanced NBI-only may be around 10\% smaller. The H-mode pedestal and ELM characteristics are also not greatly different than for NBI H-modes, and this will be compared with EPED1 modeling. [Preview Abstract] |
Wednesday, November 4, 2009 11:42AM - 11:54AM |
NO4.00012: Dynamic Confinement of ITER Plasma by X-Mode Driver at Electron Cyclotron Frequency Range V. Alexander Stefan Nonlinear interaction of the electron cyclotron X-Mode driver\footnote{R. Prater et. al., \textit{Nucl. Fusion }48, No 3 (March 2008).} with the ITER plasma leads to the dynamic rf plasma confinement in addition to the rf turbulent heating. The dynamics of unstable dissipative trapped particle modes (DTPM)\footnote{V. Alexander Stefan, 2009 APS April Meeting; May 2-5, 2009, Denver, Colorado; Abstract: K1.00028} strongly coupled to Trivelpiece-Gould (T-G) modes is studied for the gyrotron frequency of 170GHz; X-mode power of 24 MW CW; and with on-axis B-field of 10T. In the case of dynamic control of DTPM turbulence and for the heavily damped T-G modes, the energy confinement time scalings are evaluated. The ITER plasma-ignition criterion is analyzed in terms of the X-Mode power. [Preview Abstract] |
Wednesday, November 4, 2009 11:54AM - 12:06PM |
NO4.00013: ITER Test Blanket Module (TBM) Error Field Experiments in DIII-D M.J. Schaffer, J.A. Snipes Proposed ITER tritium breeding TBMs would contain ferromagnetic steel near the plasma and would make a localized peak magnetic perturbation of about 1.6\%. While some effects can be computed, e.g.\ modified ion orbits, other important consequences cannot, such as global energy confinement and the L- to H-mode transition power. Therefore, an approximate scaled mockup of the error field from two TBMs in one port, as planned for ITER, will be installed temporarily in a DIII-D equatorial port to study its effects on plasmas. The mockup uses active electromagnet coils rather than passive steel for experimental flexibility. Numerical calculations show that the TBM error vacuum field has no strong resonant harmonics, but a natural resonant valley instead. However, the field has strong non-resonant harmonics, and non-resonant braking of plasma rotation is anticipated. The experiments will be performed in Autumn 2009, and we plan to report first results at this meeting. [Preview Abstract] |
Wednesday, November 4, 2009 12:06PM - 12:18PM |
NO4.00014: Turbulent impurity transport in ITER based on theory and CMOD data W. Horton, Sean Fu, W. Rowan, I.O. Bespamyatnov, S. Futatani, S. Benkadda A key ITER issue is the turbulent radial transport from drift waves of impurities, especially beryllium. Impurtiy transport has been important in earlier tokamak transport research TFTR, CMOD and is treated for ITG in Dong and Horton, 1995. A new formulation based on nonlinear interactions of the dim=4 vector field associated with the eigenvalues and eigenvectors is formulated and solved for ITER parameters and for CMOD with Boron impurity. In a low dimensional truncation of the turbulence we find the bifurcations between L , H and ITB confinement regimes. Three-component fluid equations are used to find the eigenmodes and eigenfrequencies of the nonuniform, magnetized plasma with a four dimensional fluctuation vector X(k,n) composed of fluctuations of the electron density, the working gas ion density, the impurity density and the electrostatic plasma potential. The nonlinear dynamics is evaluated in (i) the collisional drift waves appropriate for the scrape off layer (SOL) and the edge plasma in limiter discharges and in (ii) the trapped electron mode-ITG core plasma taken in the limit of a Terry-Horton model. The particle fluxes are a function of the power spectrum of the plasma potential fluctuations and the gradient parameters charactering the L, H and ITB confinment modes. Fluctuation levels are taken from simulation. [Preview Abstract] |
Wednesday, November 4, 2009 12:18PM - 12:30PM |
NO4.00015: High-Speed Pellet Injection for Ignition Experiments by Ignitor$^1$ F. Bombarda, A. Frattolillo, S. Migliori, L.R. Baylor, B. Coppi he path to ignition chosen by the Ignitor program$^2$ is based on the outstanding confinement and purity properties of high density plasma regimes. Typically, these correspond to peak densities $n_0\cong 0.7 - 1 \times 10^{21} \rm m^{-3}$ and were discovered and investigated originally by axisymmetric high magnetic field machines. Record high values of density and confinement time were obtained on the Alcator C machine following the injection of deuterium pellets that were intended to stabilize modes of the ITG kind. In order to control the density profile during the initial current rise phase of the discharge, which is critical for optimizing the Ohmic and fusion heating rates in Ignitor, a fast pellet injector has been developed in collaboration between ENEA and ORNL. The 4- barrel, two stage injector will deliver pellets of different size and speeds into the plasma from the low field side. The Ignitor Pellet Injector (IPI) has completed two experimental campaigns, reaching pellet speeds up to 2 km/s, and a third campaign is due soon. After reaching the target performances ($\leq$ 4 km/s), the injector will be ready for installation on existing experiments. Simulations carried out for JET and LHD indicate that on both devices the IPI could provide much needed deep fueling in high temperature plasmas.\\ $^1$Sponsored in part by ENEA of Italy and by the U.S. D.O.E.\\ $^2$B. Coppi, A. Airoldi, et al., \textit{Nucl. Fusion} \textbf {41(9)}, 1253 (2001) [Preview Abstract] |
Wednesday, November 4, 2009 12:30PM - 12:42PM |
NO4.00016: High Particle Density Path to Fusion$^*$ B. Coppi, F. Bombarda, P. Detragiache, A. Airoldi, G. Cenacchi, A. Sestero Experiments by the heliotron LHD machine have confirmed the outstanding confinement and purity properties of plasmas with peak densities $n_{0} \sim 10^{21}m^{-3}$ that had been originally discovered and investigated by the high-field line of machines (Alcator and FT). The finding of these regimes opened the way to aim at reaching ignition conditions on the basis of existing knowledge of plasma physics and available technologies. The high field and high particle density approach represented by Ignitor [1] ($R_{0}\cong1.32$ m, $a \times b\cong 0.47 \times 0.86$ $m^{2}$, $B_{T}\leq13$ T, $I_{p}\leq11$ MA) remains the only one that can be pursued realistically in the near term in order to reach ignition. The choice of machine parameters have been guided by the criterion of optimizing the Ohmic and $\alpha$-particle heating process, with the possible assistance of modest amount of RF power, and that of studying the physics and the control of meaningful burning plasmas in regimes sufficiently far from well known operational limits (e.g. density and $\beta$ limits). Achieving these conditions (including, $t_{pulse}\sim \tau_{crd}\gg \tau_{E}\gg \tau_{sd}$) will provide the proof of scientific feasibility of power producing reactors. Studies of reactors concepts (e.g. material testing reactors, neutron sources, tritium poor reactors, etc.) based on the Ignitor approach are being reconsidered. *Sponsored in part ENEA of Italy and by the U.S. D.O.E. [1] B. Coppi, A. Airoldi, F. Bombarda, \textit{et al., Nucl. Fusion} \textbf{41 (9)}, 1253 (2001). [Preview Abstract] |
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