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Book Overview of Results from the National Spherical Torus Experiment NSTX

Download or read book Overview of Results from the National Spherical Torus Experiment NSTX written by and published by . This book was released on 2009 with total page 45 pages. Available in PDF, EPUB and Kindle. Book excerpt: The mission of NSTX is the demonstration of the physics basis required to extrapolate to the next steps for the spherical torus (ST), such as a plasma facing component test facility (NHTX) or an ST based component test facility (ST-CTF), and to support ITER. Key issues for the ST are transport, and steady state high [beta] operation. To better understand electron transport, a new high-k scattering diagnostic was used extensively to investigate electron gyro-scale fluctuations with varying electron temperature gradient scale-length. Results from n = 3 braking studies confirm the flow shear dependence of ion transport. New results from electron Bernstein wave emission measurements from plasmas with lithium wall coating applied indicate transmission efficiencies near 70% in H-mode as a result of reduced collisionality. Improved coupling of High Harmonic Fast-Waves has been achieved by reducing the edge density relative to the critical density for surface wave coupling. In order to achieve high bootstrap fraction, future ST designs envision running at very high elongation. Plasmas have been maintained on NSTX at very low internal inductance l{sub i} H"0.4 with strong shaping ([kappa] H"2.7, [delta] H"0.8) with [beta]{sub N} approaching the with-wall beta limit for several energy confinement times. By operating at lower collisionality in this regime, NSTX has achieved record non-inductive current drive fraction f{sub NI} H"71%. Instabilities driven by super-Alfvenic ions are an important issue for all burning plasmas, including ITER. Fast ions from NBI on NSTX are super-Alfvenic. Linear TAE thresholds and appreciable fast-ion loss during multi-mode bursts are measured and these results are compared to theory. RWM/RFA feedback combined with n = 3 error field control was used on NSTX to maintain plasma rotation with [beta] above the no-wall limit. The impact of n> 1 error fields on stability is a important result for ITER. Other highlights are: results of lithium coating experiments, momentum confinement studies, scrape-off layer width scaling, demonstration of divertor heat load mitigation in strongly shaped plasmas, and coupling of CHI plasmas to OH ramp-up. These results advance the ST towards next step fusion energy devices such as NHTX and ST-CTF.

Book Overview of the Initial NSTX Experimental Results

Download or read book Overview of the Initial NSTX Experimental Results written by Masayuki Ono and published by . This book was released on 2000 with total page 12 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book National Spherical Torus Experiment NSTX

Download or read book National Spherical Torus Experiment NSTX written by Masayuki Ono and published by . This book was released on 2000 with total page 12 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book Initial Results from the National Spherical Torus Experiment NSTX

Download or read book Initial Results from the National Spherical Torus Experiment NSTX written by and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: With a small, high-power density, and compact fusion core, Spherical Tori (ST) can provide an attractive path to a reactor or a volumetric neutron source. The National Spherical Torus Experiment (NSTX) is a proof-of-principle experiment that will explore the physics of low aspect ratio in scientifically interesting and aggressive regimes. To accomplish this mission, NSTX is designed to produce plasmas with R/a= 0.85 m/0.68 m[approximately] 1.25, I[sub p]= 1 MA, B[sub T][le] 0.6 T, [kappa][le] 2.2, [delta][le] 0.5, heating powers of up to 11 MW (6 MW High Harmonic Fast Waves, 5 MW, 80 keV, D[sup 0] Neutral Beam Injection), and operation over a wide range of shapes and configurations. The OH solenoid and PF coils on NSTX are capable of producing approximately 1 V-sec of inductive flux, which, alone, is sufficient for plasma breakdown and for increasing the plasma current to the MA level. Breakdown, however, will be assisted by EC preionization. Co-axial Helicity Injection (CHI)[sup 4] provides the opportunity for V-sec savings during breakdown as well as for completely non-inductive startup to about 500 kA.

Book Recent Progress on the National Spherical Torus Experiment NSTX

Download or read book Recent Progress on the National Spherical Torus Experiment NSTX written by and published by . This book was released on 2003 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book New Capabilities and Results for the National Spherical Torus Experiment

Download or read book New Capabilities and Results for the National Spherical Torus Experiment written by and published by . This book was released on 2008 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The National Spherical Torus Experiment (NSTX) produces plasmas with toroidal aspect ratio as low as 1.25, which can be heated by up to 6 MW High-Harmonic Fast Waves and up to 7 MW of deuterium Neutral Beam Injection. Using new poloidal fields coils, plasmas with cross-section elongation up to 2.7, triangularity 0.8, plasma currents Ip up to 1.5 MA and normalized currents Ip/a·BT up to 7.5 MA/m·T have been achieved. A significant extension of the plasma pulse length, to 1.5 s at a plasma current of 0.7 MA, has been achieved by exploiting the bootstrap and NBI-driven currents to reduce the dissipation of poloidal flux. Inductive plasma startup has been supplemented by Coaxial Helicity Injection (CHI) and the production of persistent current on closed flux surfaces by CHI has now been demonstrated in NSTX. The plasma response to magnetic field perturbations with toroidal mode numbers n = 1 or 3 and the effects on the plasma rotation have been investigated using three pairs of coils outside the vacuum vessel. Recent studies of both MHD stability and of transport benefitted from improved diagnostics, including measurements of the internal poloidal field using the motional Stark effect (MSE). In plasmas with a region of reversed magnetic shear in the core, now confirmed by the MSE data, improved electron confinement has been observed.

Book Results of NSTX Heating Experiments

Download or read book Results of NSTX Heating Experiments written by D. Mueller and published by . This book was released on 2002 with total page 8 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book An Overview of Recent Physics Results from NSTX

Download or read book An Overview of Recent Physics Results from NSTX written by and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Currently, the National Spherical Torus Experiment (NSTX) is being upgraded to operate at twice the toroidal field and plasma current (up to 1 T and 2 MA), with a second, more tangentially aimed neutral beam (NB) for current and rotation control, allowing for pulse lengths up to 5 s. Recent NSTX physics analyses have addressed topics that will allow NSTX-Upgrade to achieve the research goals critical to a Fusion Nuclear Science Facility. These include producing stable, 100% non-inductive operation in high-performance plasmas, assessing plasma-material interface (PMI) solutions to handle the high heat loads expected in the next-step devices and exploring the unique spherical torus (ST) parameter regimes to advance predictive capability. Non-inductive operation and current profile control in NSTX-U will be facilitated by co-axial helicity injection (CHI) as well as radio frequency (RF) and NB heating. CHI studies using NIMROD indicate that the reconnection process is consistent with the 2D Sweet-Parker theory. Full-wave AORSA simulations show that RF power losses in the scrape-off layer (SOL) increase significantly for both NSTX and NSTX-U when the launched waves propagate in the SOL. Moreover, Toroidal Alfven eigenmode avalanches and higher frequency Alfven eigenmodes can affect NB-driven current through energy loss and redistribution of fast ions. The inclusion of rotation and kinetic resonances, which depend on collisionality, is necessary for predicting experimental stability thresholds of fast growing ideal wall and resistive wall modes. Neutral beams and neoclassical toroidal viscosity generated from applied 3D fields can be used as actuators to produce rotation profiles optimized for global stability. DEGAS-2 has been used to study the dependence of gas penetration on SOL temperatures and densities for the MGI system being implemented on the Upgrade for disruption mitigation. PMI studies have focused on the effect of ELMs and 3D fields on plasma detachment and heat flux handling. Simulations indicate that snowflake and impurity seeded radiative divertors are candidates for heat flux mitigation in NSTX-U. Studies of lithium evaporation on graphite surfaces indicate that lithium increases oxygen surface concentrations on graphite, and deuterium-oxygen affinity, which increases deuterium pumping and reduces recycling. In situ and test-stand experiments of lithiated graphite and molybdenum indicate temperature-enhanced sputtering, although that test-stand studies also show the potential for heat flux reduction through lithium vapour shielding. Non-linear gyro kinetic simulations have indicated that ion transport can be enhanced by a shear-flow instability, and that non-local effects are necessary to explain the observed rapid changes in plasma turbulence. Predictive simulations have shown agreement between a microtearing-based reduced transport model and the measured electron temperatures in a microtearing unstable regime. Finally, two Alfven eigenmode-driven fast ion transport models have been developed and successfully benchmarked against NSTX data. Upgrade construction is moving on schedule with initial physics research operation of NSTX-U planned for mid-2015.

Book Recent Physics Results from NSTX

Download or read book Recent Physics Results from NSTX written by R. E. Bell and published by . This book was released on 2006 with total page 14 pages. Available in PDF, EPUB and Kindle. Book excerpt: The National Spherical Torus Experiment (NSTX) has made considerable progress in advancing the scientific understanding of high performance long-pulse plasmas needed for ITER and future low-aspect-ratio Spherical Torus (ST) devices. Plasma durations up to 1.6s (5 current redistribution times) have been achieved at plasma currents of 0.7 MA with non-inductive current fractions above 65% while achieving {beta}{sub T} and {beta}{sub N} values of 16% and 5.7 (%mT/MA), respectively. Newly available Motional Stark Effect data has allowed systematic study and validation of current drive sources and improved the understanding of ''hybrid''-like scenarios. In MHD research, six mid-plane ex-vessel radial field coils have been utilized to infer and correct intrinsic error fields, provide rotation control, and actively stabilize the n=1 resistive wall mode at ITER-relevant low plasma rotation values. In transport and turbulence, the low aspect ratio and wide range of achievable {beta} in NSTX provide unique data for confinement scaling studies. A new high-k scattering diagnostic is investigating turbulent density fluctuations with wavenumbers extending from ion to electron gyro-scales. In the area of energetic particle research, cyclic neutron rate drops have been associated with the destabilization of multiple large Toroidal Alfven Eigenmodes (TAEs) similar to the ''sea-of-TAE'' modes predicted for ITER. Three wave coupling processes between energetic particle modes and TAEs have also been observed for the first time. In boundary physics, advanced shape control has been utilized to study the role of magnetic balance in H-mode access and ELM stability. Peak divertor heat flux has been reduced by a factor of 5 using an H-mode compatible radiative divertor, and Lithium conditioning has demonstrated particle pumping and improved thermal confinement. Finally, non-solenoidal plasma start-up research is particularly important for the ST, and Coaxial Helicity Injection has now produced 160kA plasma currents on closed magnetic flux surfaces.

Book Interferometry and Vibration Compensation on the National Spherical Torus Experiment Upgrade

Download or read book Interferometry and Vibration Compensation on the National Spherical Torus Experiment Upgrade written by Evan Richard Scott and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The National Spherical Torus Experiment (NSTX) located at the Princeton Plasma Physics Laboratory (PPPL) has recently undergone an extensive upgrade to NSTX-U. The Far-infrared Tangential Interferometer/Polarimeter (FIReTIP) system, previously installed on NSTX before the upgrade, is an important laser-based plasma diagnostic for line-integrated plasma density measurements with high temporal resolution. Due to extensive changes to NSTX during the upgrade process, the FIReTIP system has been dramatically altered from its previous configuration, including an extensive waveguide installation both outside and within the NSTX-U test cell; only the lasers and previous electronics are reused. The modification and reinstallation of the system are presented.One of the primary goals of FIReTIP on NSTX-U is to provide real-time density measurements for density feedback control of the tokamak plasma. By nature, FIReTIP is susceptible to noise from mechanical vibrations. For the plasma core, this problem is generally avoided through use of mechanical vibration isolation units to dampen vibrations on sensitive components, such as retroreflectors for the laser beams. In FIReTIP’s new configuration, however, mechanical vibration isolation cannot be used because the retroreflector is mounted to the inside wall of the NSTX-U vacuum vessel. To compensate for the effects of vibrations, two methods have been investigated.A visible light interferometer will be employed on FIReTIP to measure mechanical vibrations independently of the plasma, thereby allowing the effects of vibrations to be subtracted from the measured plasma density. The previous FIReTIP system employed a visible light interferometer with promising results, but this system was not capable of unambiguous determination of the direction of vibrations and was therefore unsuited for real-time correction of the FIReTIP system. The visible light interferometer has been upgraded to a heterodyne interferometer system capable of such unambiguous measurements and real-time density corrections. Additionally, the use of active noise cancellation via Kalman filtering has been explored for use with FIReTIP alongside the visible light interferometer. Active noise cancellation offers many advantages for vibration compensation if it can be implemented in a reliable and robust manner, including lower costs and vibration compensation applied to multiple locations of interest on the system. Both the accuracy and feasibility of active noise cancellation on the FIReTIP system are presented as a proof of principle of this novel technique.