News and Events


U.S. Burning Plasma Organization eNews
Mar 31, 2016 (Issue 106)

 

USBPO Mission Statement: Advance the scientific understanding of burning plasmas and ensure the greatest benefit from a burning plasma experiment by coordinating relevant U.S. fusion research with broad community participation.

 

CONTENTS

Director’s Corner
C.M. Greenfield
Research Highlight
F. Bedoya et al.
Schedule of Burning Plasma Events  
Contact and Contribution Information

Director’s Corner

C.M. Greenfield

Upcoming decision points on ITER

The ITER Organization has been transformed in several ways since the beginning of 2015. Director General Bernard Bigot has now been in place for about a year, with the project management being restructured and simplified. A new project schedule and resource plan was developed, and is currently being reviewed by an external panel at the request of the ITER Council. The ITER Council will hear the results of this review at its June meeting, after which it will hopefully be made the official baseline.

Concern over delays in the project reached the US Congress, with funding for US contributions to ITER being limited in the last few years. The FY2016 budget language included a request for the Department of Energy to make a recommendation in May on whether the US should remain a partner in the ITER project.

ITER Tokamak Complex receives first component

Until now, work on the tokamak complex has focused solely on buildings. A new phase of ITER construction began recently with installation of the first tokamak component, a tritiated water holding tank installed in the Tritium Building. This is part of a larger system intended to remove and recover tritium from various parts of the tokamak.

The first tritiated water holding tank is set in place in the ITER Tritium building, marking the first installation of a component in the Tokamak Complex (Photo © ITER Organization).

Research Highlight

Fusion Engineering Science Topical Group, Leaders: David Rasmussen and Jean Paul Allaib

This is a summary of the design, testing and commissioning of the Materials Analysis Particle Probe (MAPP) plasma-material interactions (PMI) diagnostic being commissioned in the NSTX-U. The integration of MAPP is a multi-institution collaboration primarily between the University of Illinois at Urbana-Champaign led by Prof. J.P. Allain and PPPL scientists Robert Kaita and Charles Skinner. The diagnostic system is the first to provide in-vacuo and in-situ correlations of surface chemistry evolution during active wall conditioning and tokamak plasmas.

The Materials Analysis Particle Probe (MAPP) in NSTX-U: Deciphering surface chemistry effects on plasma performance

F. Bedoya 1, J.P. Allain 1, M. Lucia 2, R. Kaita 2, C. Skinner 2, D. Curreli 1
1 Department of Nuclear Plasma and Radiological Engineering, University of Illinois at Urbana Champaign, Urbana, IL 61801, USA.
2 Princeton Plasma Physics Laboratory, PO Box 451, Princeton, NJ 08543-0451, USA.

Managing the plasma wall interaction (PWI) remains a critical issue for the feasibility of thermonuclear magnetic fusion energy solutions. Key PWI issues in fusion tokamak reactors include the evolution of surface chemistry and its role on hydrogen retention and impurity pumping. In particular, how low- Z coatings such as lithium or boron can impact the behavior of plasma at the edge and in the core. PMI (plasma-material interactions) are particularly relevant for strategies that involve, for example, lowrecycling regimes and the use of lithium PFS (plasma-facing surfaces) to attain them. A critical knowledge gap in PMI research has been the inability to access the evolving plasma-facing surface during and in-between tokamak plasma discharges. Changes in surface chemistry and morphology due to ion bombardment and the difficulty of diagnosing plasma-facing surfaces, especially reactive surfaces, impede the development of a predictive understanding of the wall and its interaction with the plasma. Consequently, this impairs the ability to design advanced PFC materials for future plasma-burning fusion reactors.

In addressing this challenge a limited number of PMI probes have been implemented in tokamak divertor research in the past such as the DiMES and MiMES systems in DIII-D [1]. However, these systems only characterize the sample surfaces ex-situ thus compromising any time-sensitive chemistry-dependent surface information. To address this shortcoming and to provide a compact, versatile PMI probe system compatible with the highly chemically reactive system of lithium wall conditioning adopted by the NSTX research program, a new PMI probe was designed, constructed and tested known as the Materials Analysis Particle Probe (MAPP). MAPP is the first PMI diagnostic to capture the surface physics and chemistry in-vacuo and in-situ in a fusion tokamak system and correlate this data to controlled plasma shots [2-4]. MAPP is helping elucidate the complex physics and chemistry of multi-material PSI behavior at spatial scales of 10 to 100’s nm (penetration depth of incident energetic D atoms) to the macroscopic length scales of plasma behavior (e.g. ELMs, confinement, etc ...) in NSTX-U. Due to the harsh conditions in the tokamak edge, surface sensitive measurements in the order of 10 to 100-nm are nearly impossible. However, ion-induced modification mechanisms at fluxes above 1015 cm2s1 typically have time scales between a few seconds to 10’s of minutes (nearly 50-60 minutes). Therefore, correlations between surface chemistry and plasma behavior via surface conditioning are plausible by characterizing these plasma-facing surfaces in-situ (i.e. in the time scale of surface variation with plasma exposure) within the order of a few minutes to 10’s of minutes and correlated to ex-vessel controlled in-situ surface science experiments [5-6]. MAPP’s analysis capabilities include X-ray photoelectron spectroscopy (XPS), ion scattering spectroscopy (ISS), direct recoil spectroscopy (DRS), and thermal desorption spectroscopy (TDS). Surface chemistry is interrogated at the near surface by XPS ( 8 nm probing depth), and in addition the top 1-2 monolayers are probed using ISS. Direct recoil spectroscopy is a variation of ion scattering spectroscopy and is uniquely capable of directly detecting surface hydrogen. Heating the sample for TDS yields information on chemical binding mechanisms of deuterium retention. With incident particle energy distributions (e.g., from D ions) ranging from 5 eV up to 100’s of eV, the penetration range averages between 10-100 nm (ignoring any further bulk diffusion). Therefore, this suite of diagnostics is able to capture the chemical interactions that occur at the plasma-surface interface region.

fig1a.png
fig1b.png

Figure 1: (a) As AE activity increases with beam power, fast-ion transport inferred from the (b) NPA and (c) neutron emission suddenly increases are used to measure the time evolution of the above a phase-space dependent threshold.

Currently MAPP captures this information at a fixed radial location at the NSTX outboard divertor region. Near-term plans are focused on enhancing MAPP capabilities along three primary goals: i) upgrading the MAPP sample head with smart diagnostics, ii) high-fidelity OES (optical emission spectroscopy) along the MAPP probe surface, and iii) establish a proof-of-concept study for a PMI multi-probe satellite system that would complement MAPP measurements. Future plans also include the study of other advanced materials and their controlled exposure to designed plasma shots to guide materials and component options. Testing with MAPP will include: nanostructured low Z/high Z hybrids, nanocomposites, liquid metals and alloys, and mixed-materials testing.

MAPP is a multi-investigator and multi-institution collaborative effort given its complexity. These activities include integrating MAPP with sophisticated edge spectroscopic diagnostics led by Vlad Soukhanovskii (LLNL) and supported by Filipo Scotti (LLNL). Computational modeling validation and development in collaboration with Brian Wirth (U. Tenn) and Predrag Krstic (Stony Brook) is also an integral part of deciphering PMI in NSTX-U with MAPP serving as a key diagnostic platform. Ex-vessel surface science support is provided in collaboration with Bruce Koel’s group at Princeton University.

Engineering design challenges integrating MAPP with NSTX-U have been addressed by an extremely talented and dedicated engineering staff at PPPL. The MAPP head design and manipulation system was led by Lane Roquemore and Robert Ellis along with many other engineering staff to realize this enormous and complex effort. During the upgrade process in NSTX, MAPP was fully commissioned and tested in the Lithium Tokamak Experiment (LTX) led by Richard Majeski. Matthew Lucia conducted his PhD thesis on MAPP linking PFC surface characterization with LTX plasma performance [7-8]. This effort helped prepare the integration of MAPP into NSTX-U led by Robert Kaita with initial measurements made by Charles Skinner.

Integration with NSTX-U

Along with the fit-up procedure and testing of the various components to translate MAPP from its “analysis” position in Bay J to its “exposure” location, an update was made on the design for MAPP operation in NSTX-U. Fig. 2 shows a schematic of the updated procedure that describes a typical run for the MAPP diagnostic in the configuration of a “piggy-back” run for non-dedicated NSTX-U plasma shots.

fig2.png

Fig. 2. MAPP sequence of operation depicted in the schematic above for a typical NSTX-U plasma shot. The minimum time window of approximately 12 minutes is selected based on the con guration that would allow MAPP to be used as a piggy-back diagnostic in non-dedicated plasma shots in NSTX-U. Dedicated runs in NSTX-U speci cally designed for MAPP will be coordinated with the plasma-materials team at PPPL and would have a time sequence longer than a piggy-back experiment.

The sequence places demands on the time lapse of data acquisition for each surface characterization technique in MAPP. MAPP’s remote control system is based in a suite of interlinked LabVIEW R Virtual Instruments (VIs), one for each piece of equipment. The interaction among the VIs is managed by two central VIs. One controls a soft interlock system based on the pressure gauge installed in the chamber. It generates a safety signal that is distributed to other drivers, acting to ensure a safe operational pressure for the other experimental components the x-ray source, micro-channel plate detector and energy dispersive analyzer, ion pump, ion gun, and in-situ heating system. The other controls a hard interlock system, critical for MAPP’s operation in NSTX-U. Various MAPP components must be de-energized during NSTX-U plasma discharges due to the Tesla-scale magnetic fields present. Between discharges, these components may be safely energized for surface analysis. A minimum of 12 min must elapse between discharges, providing a window for MAPP operation and analysis. In this environment, analysis system VIs are running to acquire XPS, TDS, and ISS data. These VIs control the relevant voltages for each system, performing the required parameter scans, and then aggregate the data to generate spectra. MAPP was installed in NSTX-U in the summer of 2015. The mechanical installation included the vacuum chamber and the transfer system of the probe head (see Fig 3).

Current State

MAPP started collecting XPS data in December 2015. Currently the facility is being used to characterize the role of boron coatings on plasma stability and impurity control in NSTX-U. Although the tokamak is currently in a commissioning phase recent results obtained with MAPP are very exciting as these are beginning to distinguish key chemical changes on the PFCs that most likely are correlated with the plasma performance of NSTX-U. These correlations are the focus of this year’s experimental campaign for MAPP in NSTX-U.

In the course of the current campaign MAPP will be the key PMI diagnostic to investigate the chemical state of the plasma facing surfaces during the remaining stages of boronization, the transition from boronization to lithiumization as surface conditioning and ultimately during the rest of the experimental run, when NSTX-U will rely on Li as PFC.

fig3.png

Fig. 3. MAPP chamber and samples probe drive installed in NSTX-U during the construction period in the summer of 2015. MAPP is located in bay K under the lower divertor of the machine.

References

[1] C. P. C. Wong et al. J. Nucl. Mater. 196 871875, 1992.
[2] B. Heim et al. IEEE Trans. Plasma Sci. 40 735 739 Mar. 2012.
[3] C. N. Taylor et al. Rev. Sci. Instrum. 83 10D703 2012.
[4] F. Bedoya, “Study Of Temperature Dependence Of Hydrogen Retention In Lithium Coatings On Stainless Steel With The Materials Analysis Particle Probe (Mapp)” MSc, University of Illinois at Urbana-Champaign, Urbana, IL, 2015.
[5] C. N. Taylor, “Fundamental Mechanisms Of Deuterium Retention In Lithiated Graphite Plasma Facing Surfaces” Doctoral, Purdue University, West Lafayette, IN, USA, 2012.
[6] C. N. Taylor et al. Phys. Plasmas 21 057101, May 2014.
[7] M. Lucia et al. Rev. Sci. Instrum. 85 11D835, Nov. 2014. [8] Lucia, M., “Material Surface Characteristics and Plasma Performance in the Lithium Tokamak Experiment” Doctoral, Princeton University, Princeton, NJ, 2015.


Schedule of Burning Plasma Events

USBPO Public Calendar: View Online or Subscribe

2015         NSTX-U First Plasma — December 10 W7-X First Plasma —

2016         — 10th Anniversary of USBPO Formation —

March 29 - April 1US Transport Task Force WorkshopDenver, Colorado, USA
April 26-2916th IOS ITPA meetingGarching, Germany
May 30-June 3PSI ConferenceRome, Italy
June 5 - 9High Temperature Plasma Diagnostic ConferenceMadison, Wisconsin, USA
June 19-23International Conference on Plasma Sciences, ICOPSBanff, Alberta, Canada
June 27-3016th EP ITPA meetingSt. Paul-lez-Durance, France
June 27-July 118th International Conference on Plasma Physics (ICPP2018)Kaohsiung, Taiwan
July 4-8European Physical Society Conference on Plasma Physics (EPS)Leuven, Belgium
September 4-8Joint EU-US Transport Task Force MeetingLeysin, Switzerland
October 13-15ITER STAC MeetingKizu, Japan
October 17-2226th IAEA Fusion Energy ConferenceKyoto, Japan
October 24-26T&C ITPA meeting JAEANaka, Japan
October 31-November 458th APS Division of Plasma PhysicsSan Jose, California, USA
December 13-1437th Fusion Power Associates Annual Meeting and Symposium, Fusion Power Development: An International Venture

2019          JET DT-campaign — JT60-SA First Plasma —

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Contact and Contribution Information

This newsletter provides a monthly update on U.S. Burning Plasma Organization activities. The USBPO operates under the auspices of the U.S. Department of Energy, Fusion Energy Sciences (FES) division. All comments, including suggestions for content, may be sent to the Editor. Correspondence may also be submitted through the USBPO Website Feedback Form.

Become a member of the U.S. Burning Plasma Organization by signing up for a topical group.

Editor: Saskia Mordijck (mordijck@fusion.gat.com)

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