Download or read book Motional Stark Effect Diagnostic Expansion for the DIII D Tokamak written by and published by . This book was released on 2005 with total page 29 pages. Available in PDF, EPUB and Kindle. Book excerpt: A repositioning of a heating neutral beam on the DIII-D tokamak provides an opportunity to expand and improve the Motional Stark Effect diagnostic (MSE) used to constrain the current profile. D[alpha] emission from the neutral beam is split into components parallel ([pi]) and perpendicular ([sigma]) to the total electric field ETotal = vxB + Eplasma. The MSE diagnostic measures the polarization of the [sigma] component to determine the local magnetic field pitch angle Bz/B[phi] and the local radial plasma electric field ER. This is typically done using the EFIT current profile reconstruction code. Two independent measurements of the pitch angle [gamma] at each radius are required to differentiate the contributions from the Stark and plasma electric fields. Presently, three MSE diagnostics provide multiple views of a single neutral beam. Our ability to accurately differentiate Bz and ER is limited because these views do not overlap with sufficient radial resolution in some locations, and this limits the accuracy of the current profile reconstructions. The beam rearrangement allows us to build a fourth MSE view of a second beam injected counter to the plasma current. The combination of the new view with the old will improve radial resolution about a factor of 3, reduce ER uncertainty by a factor of 2 in the core and 5-6 in the edge, and reduce Bz uncertainty by 20-30%. The design of the new system is presented in this paper, focusing on the mechanical and optical details at the tokamak port on which it will be installed.

Download or read book An Overview Of The Motional Stark Effect Diagnostic On DIII D And Design Work For An ITER MSE written by and published by . This book was released on 2007 with total page 6 pages. Available in PDF, EPUB and Kindle. Book excerpt: The advanced tokamak research program at DIII-D relies critically on the measurement of the current density profile. This was made possible by the development of a Motional Stark Effect (MSE) polarimeter that was first installed in 1992. Three major upgrades have since occurred, and improvements in our understanding of critical performance issues and calibration techniques are ongoing. In parallel with these improvements, we have drawn on our DIII-D experience to begin studies and design work for MSE on burning plasmas and ITER. This paper first reviews how Motional Stark Effect polarimetry (MSE) is used to determine the tokamak current profile. It uses the DIII-D MSE system as an example, and shows results from the latest upgrade that incorporates an array of channels from a new counter-Ip injected neutral beam. The various calibration techniques presently used are reviewed. High-leverage or unresolved issues affecting MSE performance and reliability in ITER are discussed. Next, we show a four-mirror collection optics design for the two ITER MSE views. Finally, we discuss measurements of the polarization properties of a few candidate mirrors for the ITER MSE.

Download or read book Development of the B Stark Motional Stark Effect Diagnostic for Measurements of the Internal Magnetic Field in the DIII D Tokamak written by Novimir Antoniuk Pablant and published by . This book was released on 2010 with total page 414 pages. Available in PDF, EPUB and Kindle. Book excerpt: A new diagnostic, B-Stark, has been developed at the DIII-D tokamak for measurements of the magnitude and direction of the internal magnetic field. The B-Stark system is a version of a motional Stark effect (MSE) diagnostic based on the Stark split D/[alpha] emission from injected neutral beams. This diagnostic uses the spacing of the Stark lines to measure the magnitude of the magnetic field, and the intensities of the [pi]3 and [sigma]1 lines to measure the magnetic pitch angle. These lines originate from the same upper level, and are therefore not dependent on the n=3 level populations. The measurement of the magnetic pitch angle requires a specific viewing geometry with respect to the neutral beams, which is provided by the B-Stark diagnostic installation. The B-Stark technique may have advantages over MSE polarimetry diagnostics in future devices with high densities and temperatures, such as ITER. Under these conditions coatings on the plasma facing mirrors are expected, which can cause changes in the polarization state of the reflected light. The B-Stark technique is insensitive to the polarization direction, and can calibrate for polarization dependent transmission by using an in-situ beam-into-gas calibration. This dissertation describes the development and characterization of the B-Stark diagnostic. The hardware design and spectral fitting techniques are discussed in detail. Calibration procedures are described including the in-situ determination of the beam emission line profiles, viewing geometry and properties of the collection optics. The performance of the system is evaluated over the range of plasma conditions accessible at DIII-D. Measurements of the magnetic field have been made with toroidal fields in the range 1.2 - 2.1Tesla, plasma currents in the range 0.5 - 2.0MA, densities between 1.7 - 9.0 x 1019m−3, and neutral beam voltages between 50 - 81keV. These results are compared to values found from plasma equilibrium reconstructions (EFIT) and the MSE polarimetry system on DIII-D. The B-Stark system has been shown to provide measurements with a random errors as low as 0.2-0.3° in the magnetic pitch angle and 0.001-0.002T in [B]. Finally, proposed future improvements for the B-Stark diagnostic are presented.

Download or read book Fast Motional Stark Effect Diagnostic Measurements of Hybrid like Magnetic Flux pumping and Neoclassical Tearing Modes in the DIII D Tokamak written by Joshua Daniel King and published by . This book was released on 2011 with total page 105 pages. Available in PDF, EPUB and Kindle. Book excerpt: MSE measurements reveal hybrid-like flux-pumping associated with 2/1 NTM-ELM coupling. Analysis of MSE signals using digital lock-in amplifiers shows the strength of the flux-pumping is more than twice that of typical hybrid discharges. This flux-pumping maintains the minimum safety factor above unity, thereby avoiding sawteeth. The strength of the flux-pumping and ELM-NTM coupling have a clear upward dependence on normalized beta and NTM-pedestal proximity. The size of the island does not appear to effect flux-pumping, except that the mode must be present, suggesting the island chain serves as a radial pivot surface around which poloidal flux is pumped from the core to the edge. This result implies that higher normalized fusion performance (lower q95 and higher beta) may be achieved in hybrid discharges that contain a partially suppressed 2/1 NTM. ELM-NTM coupling consists of an Alfvénic timescale drop in the island width followed by a resistive recovery. The recovery phase is successfully modeled using the modified Rutherford equation. The depth of the drop in island width increases as the size of the ELM increases. To aid in the design of a highly resolved MSE pedestal measurement, full spectral analysis was preformed on existing edge channels. This analysis has revealed that coherent core MHD oscillations cause interference with present dual PEM polarimeters. Avoiding this interference requires a dedicated pedestal polarimeter with second harmonic frequencies greater than those of MHD fluctuations.

Download or read book Motional Stark Effect Upgrades on DIII D written by and published by . This book was released on 1994 with total page 9 pages. Available in PDF, EPUB and Kindle. Book excerpt: The measurement and control of the plasma current density profile (or q profile) is critical to the advanced tokamak program on DIII-D.A complete understanding of the stability and transport properties of advanced operating regimes requires detail poloidal field measurements over the entire plasma radius from the core to the edge. In support of this effort, the authors have recently completed an upgrade of the existing MSE diagnostic, increasing the number of channels from 8 to 16. A new viewing geometry has been added to the outer edge of the plasma which improves the radial resolution in this region from 10 cm to

Download or read book A Digital Lock in Upgrade of the Motional Stark Effect Diagnostic on DIII D written by and published by . This book was released on 2010 with total page 6 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book The multichannel Motional Stark Effect diagnostic in the JFT 2M tokamak written by Kensaku Kamiya and published by . This book was released on 2001 with total page 17 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book DIII D Disruption Experiment Results written by and published by . This book was released on 1995 with total page 4 pages. Available in PDF, EPUB and Kindle. Book excerpt: Tokamak discharges are frequently ended by disruptions, an instability leading to a very sudden termination of the plasma. Although numerous studies of disruptions have been made, critical data is still needed to develop theoretical models for fundamental aspects of the disruption. This paper describes simultaneous profile measurements of the current, temperature, and density during the disruptive phase of a beam heated single-null divertor discharge in the DIII-D tokamak. The stored energy is lost early in the first phase of the disruption (thermal quench) after which the central temperature is a few hundred eV, and following the start of the current decay (current quench) the temperature has fallen to 100 eV. The current profile measured using the Motional Stark Effect (MSE) diagnostic is observed to flatten rapidly (

Download or read book Recent Results from the DIII D Tokamak written by and published by . This book was released on 1998 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt: The DIII-D national fusion research program focuses on establishing the scientific basis for optimization of the tokamak approach to fusion energy production. The symbiotic development of research, theory, and hardware continues to fuel the success of the DIII-D program. During the last year, a radiative divertor and a second cryopump were installed in the DIII-D vacuum vessel, an array of central and boundary diagnostics were added, and more sophisticated computer models were developed. These new tools have led to substantial progress in the understanding of the plasma. The authors now have a better understanding of the divertor as a means to manage the heat, particle, and impurity transport pumping of the plasma edge using the in situ divertor cryopumps effectively controls the plasma density. The evolution of diagnostics that probe the interior of the plasma, particularly the motional Stark effect diagnostic, has led to a better understanding of the core of the plasma. This understanding, together with tools to control the profiles, including electron cyclotron waves, pellet injection, and neutral beam injection, has allowed them to progress in making plasma configurations that give rise to both low energy transport and improved stability. Most significant here is the use of transport barriers to improve ion confinement to neoclassical values. Commissioning of the first high power (890 kW) 110 GHz gyrotron validates an important tool for managing the plasma current profile, key to maintaining the transport barriers. An upgraded plasma control system, ''isoflux control, '' which exploits real time MHD equilibrium calculations to determine magnetic flux at specified locations within the tokamak vessel and provides the means for precisely controlling the plasma shape and, in conjunction with other heating and fueling systems, internal profiles.

Download or read book An Upgrade of the Magnetic Diagnostic System of the DIII D Tokamak for Non axisymmetric Measurements written by and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Here, the DIII-D tokamak magnetic diagnostic system has been upgraded to significantly expand the measurement of the plasma response to intrinsic and applied non-axisymmetric "3D" fields. The placement and design of 101 additional sensors allow resolution of toroidal mode numbers 1 ≤ n ≤ 3, and poloidal wavelengths smaller than MARS-F, IPEC, and VMEC magnetohydrodynamic (MHD) model predictions. Small 3D perturbations, relative to the equilibrium field (10-5

Download or read book Measurement of the Current Profile in Fusion Tokamaks Using the Motional Stark Effect Diagnostic written by Sam Gibson and published by . This book was released on 2021 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1991 with total page 1102 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book MOTIONAL STARK EFFECTS POLARIMETRY FOR THE CURRENT PROFILE DIAGNOSTIC IN DIII D written by D. WROBLEWSKI and published by . This book was released on 1990 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Q profile Measurements with Motional Stark Effect in DIII D written by and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Motional Stark Effect (MSE) has emerged as the most reliable technique for the measurement of q profiles in tokamaks equipped with neutral beams. On DIII-D, two separate 8-channel MSE instruments are utilized, giving 16 radial measurements. The viewing geometry for each instrument is designed to optimize radial resolution (1.5 cm

Download or read book The Multichannel Motional Stark Effect Diagnostic on TFTR written by and published by . This book was released on 1992 with total page 17 pages. Available in PDF, EPUB and Kindle. Book excerpt: Although the q profile plays a key role in theories of instabilities and plasma equilibrium, it has been quite difficult to measure until the recent development of the motional Stark effect (MSE) diagnostic. A multichannel motional Stark effect polarimeter system has recently been installed on the Tokamak Fusion Test Reactor (TFTR). The diagnostic can measure the magnetic field pitch angle (?{sub p} = tan−1 (B{sub T})/(B{sup p})) at ten radial locations. The doppler shifted D{sub alpha} radiation from a TFTR heating beam is viewed near tangential to the toroidal magnetic field via a re-entrant front surface reflecting mirror. The field of view covers from inboard of the magnetic axis to near the outboard edge of the plasma with a radial spatial resolution of 3--5 cm. A high throughput f/2 optics system results in an uncertainty for?{sub p} of -0.1°--0.2° with a time resolution of -5--10 ms. Initial pinch angle profiles from TFTR have been obtained. The MSE data is consistent with the estimated magnetic axis position from external magnetic measurements and the q=1 radius is in good agreement with the inversion radius from the electron cyclotron emission temperature measurements.

Download or read book The Multichannel Motional Stark Effect Diagnostic on TFTR written by F. M. Levinton and published by . This book was released on 1992 with total page 14 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Current Profile Modeling to Extend the Duration of High Performance Advanced Tokamak Modes in DIII D written by and published by . This book was released on 1998 with total page 5 pages. Available in PDF, EPUB and Kindle. Book excerpt: In DIII-D, as in a number of tokamaks, high performance is obtained with various optimized magnetic shear configurations that exhibit internal transport barriers. Negative central shear (NCS) discharges are created transiently during the current ramp-up by auxiliary heating and current drive from neutral beam injection. Both q{sub min} and the radius at which it occurs, [rho]{sub qmin}, decrease with time as the Ohmic current diffuses inward. The q-profiles calculated using EFIT with external magnetic and Motional Stark Effect (MSE) measurements as constraints are comparable to those calculated with the Corsica code, a time-dependent, 2D equilibrium and 1D transport modeling code. Corsica is used to predict the temporal evolution of the current density from a combination of measured profiles, transport models and neoclassical resistivity. Using these predictive capabilities, the authors are exploring methods for increasing the duration and [rho]{sub qmin} of the NCS configuration by local control of the current density profile with simulations of the possible control available from the electron cyclotron heating and current drive system currently being upgraded on DIII-D. Their intention is not to do a detailed investigation of transport models but rather to provide a reasonable model of heat conductivity to be able to simulate effects of electron cyclotron heating (ECH) and current drive (ECCD) on confinement in NCS configurations. The authors adjust free parameters (c, c1 and c2) in the model to obtain a reasonable representation of the temporal evolution of electron and ion temperature profiles consistent with those measured in selected DIII-D shots. In all cases, they use the measured density profiles rather than self-consistently solve for particle sources and particle transport at this time.