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U.S. Burning Plasma Organization eNews
January 31, 2015 (Issue 92)

 

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

Announcements  
Research Highlight
G.L. Jackson, et al.
Lithium-induced Enhanced Pedestal High Performance Plasmas in DIII–D
ITPA Update
Schedule of Burning Plasma Events
Contact and Contribution Information

Announcements

Graduate Student Research Opportunity through the DOE Office of Science

The Department of Energy’s (DOE) Office of Science is pleased to announce that the Office of Science Graduate Student Research (SCGSR) program is now accepting applications for the 2015 solicitation.

The application deadline is 5:00 pm ET on Tuesday, April 14, 2015.

The SCGSR program supports supplemental awards to outstanding U.S. graduate students to conduct part of their Ph.D. research at a DOE national laboratory in collaboration with a DOE laboratory scientist for a period of 3 to 12 consecutive months—with the goal of preparing graduate students for scientific and technical careers critically important to the DOE Office of Science mission. The research opportunity is expected to advance the graduate students’ overall doctoral thesis while providing access to the expertise, resources, and capabilities available at the DOE laboratories. The supplemental award provides for additional, incremental costs for living and travel expenses directly associated with conducting the SCGSR research project at the DOE host laboratory during the award period. The project periods may begin anytime between October 2015 and September 2016.

The SCGSR program provides access to the entire Office of Science research portfolio, including Fusion Energy Science. Graduate students who are interested in using the SCGSR opportunity to engage in fusion research are encouraged to contact Dr. Ping Ge (Ping.Ge@science.doe.gov) for more information.

Detailed information about the program, including eligibility requirements and access to the online application system, can be found at: http://science.energy.gov/wdts/scgsr/.

New Documents Available on the Burning Plasma Organization Website

The BPO Web Seminar of January 23, 2015 was given by Brad Nelson, Chief Engineer with the US ITER Project Office, who shared details concerning US contributions to the ITER project. The presentation slides are now available on the BPO website, Report on Activities of US ITER Project. This was a successful web seminar with 42 remote connections bringing in approximately 75 attendees. The BPO extends its gratitude to the US ITER Project Office for its effort in preparing and communicating this information.

The final FESAC Report on “Strategic Planning: Priorities Assessment and Budget Scenarios” is available for download. A collection of many separate materials related to the production of this report is available on the special BPO webpage concerning this particular FESAC charge, 2014 FESAC Strategic Planning Panel.


Research Highlight

Pedestal and Divertor/SOL Topical Group, Leaders: R. Maingi and P. Stangeby

The spatial width of the edge transport barrier, the “pedestal width”, is typically restricted to a few percent of the normalized poloidal flux. Here, a new instability was identified that broadens the pedestal width by ~100%. In conjunction with Lithium injection, a synergistic effect is observed, transiently increasing the edge stability limit and allowed pedestal pressure by 60–100%. Understanding the physics behind the enhanced pedestal stability should help in optimization of pedestal height in present and future devices.

Lithium-induced Enhanced Pedestal High Performance Plasmas in DIII–D

G.L. Jackson1, T.H. Osborne1, R. Maingi2, and Z. Yan3
1 General Atomics, PO Box 85608, San Diego, CA 92186-5608, USA
2 Princeton Plasma Physics Laboratory, PO Box 451, Princeton, NJ 08543, USA
3 University of Wisconsin-Madison, 1500 Engineering Dr., Madison, WI 53706, USA

Lithium (Li) injection was recently used in DIII–D experiments to produce discharges featuring long phases without perturbative edge instabilities (edge localized modes, or ELMs). These plasmas demonstrate good confinement at high pedestal pressure and large pedestal width compared to discharges that exhibit ELMs without lithium injection [1,2]. Both high and low Z intrinsic impurities that can be released from the plasma facing surfaces were reduced in the core of these discharges. The higher pedestal pressure can, in principle, lead to better confinement and higher plasma pressure in the plasma core with less auxiliary heating power. If this enhanced pedestal can be extended to near steady-state conditions, it may prove a viable operating regime for burning plasma devices.

In these experiments Li was injected as an aerosol (44 µm diameter spherical particles) using a lithium dropper [3] supplied by the Princeton Plasma Physics Laboratory.

Shown in Fig. 1 is a typical Li-injected pulse with two long ELM-free phases and two shorter phases after Li injection commenced at 2.0 s. The increase in pedestal width occurs on a short timescale of the order of 10 ms, Fig. 1(a), while the electron pedestal pressure increases monotonically throughout the ELM-free phase, Fig. 1(b).

Figure 1

Figure 1: (a) Pedestal width (black) increases after lithium injection (green). (b) Pedestal pressure (black) rises monotonically during the ELM free phases, independent of the amplitude of the core lithium (green). (c) H-factor (red) is also higher during the long ELM free phases.

The H-factor, a figure of merit measuring energy confinement of the plasma, Fig. 1(c) is ≈ 1 during the non-Li ELMing phase but increases to ≈ 1.8 at the end of the long ELM-free phases with lithium, typical of other high confinement regimes observed in tokamaks. Although only modest amounts of Li are introduced (0.014 g during the time shown in Fig. 1) lithium is detected in the core plasma, Fig. 1(b). As shown in this figure, the onset of the enhanced pedestal phases is independent of the amount of Li in the plasma, hence the trigger for this mode might not be a core Li effect.

During the enhanced pedestal phase, bursts of density fluctuations in the frequency range 40–110 kHz are observed in the plasma edge using beam emission spectroscopy (BES) with a burst period on the order of 1 ms, as shown in Fig. 2. Within these bursts, the frequency chirps rapidly both up and down and individual bursts are associated with increases in deuterium (Dα) and carbon (CIII) emission from the divertor. After the CIII and Dα decrease, implying that with the density fluctuations, particle transport in the edge region is increased, a desirable feature to limit unwanted impurity buildup in the plasma core. BES measurements indicate that the density fluctuations are located in the pedestal near the separatix and are associated with a local flattening of the pressure profile in this region. The maximum fluctuation amplitude is rather large, ñ/n up to 8%.

The local flattening of the pressure profile near the separatrix contributes to wider and higher pedestals obtained in discharges with Li injection. The pedestal pressure and width agree well with the EPED1.0 edge stability model predictions in phases without the bursts, however the model under-predicts the pressure and width in phases where the bursts are present.

Figure 2

Figure 2: (a) Density fluctuations inferred from the BES diagnostic appear in bursts, chirping in frequency (inset). (b) D and CIII are higher during the bursty chirping phase. Vertical green lines show the increase in D during typical density bursts.

Although the wider pedestal has been observed transiently without lithium injection, here it is sustained with an increase in pedestal pressure and confinement. If the enhanced pedestal phase can be achieved in steady state conditions, it improves the prospects for applicability in future burning plasma devices with elevated wall temperatures, which may restrict or eliminate access to low recycling regimes. Furthermore, other materials such as beryllium or tungsten aerosols, more compatible with fusion reactors, might also lead to an enhanced pedestal and these should be investigated.

This work was supported in part by the US Department of Energy under DE-FC02-04ER54698.

References

[1] G.L. Jackson, et al, “Enhanced Pedestal Performance in DIII-D Elm-free H-modes with Lithium Injection”, Proc. 25th IAEA Fusion Energy Conference, St. Petersburg, Russia (2014)

[2] T.H. Osborne, et al., Nucl. Fusion, (submitted 2015)

[3] D.K. Mansfield, et al., Fusion Eng. Design 85, 890 (2010)


ITPA Update

More information concerning the ITPA may be found at the Official ITPA Website.


Schedule of Burning Plasma Events

USBPO Public Calendar: View Online or Subscribe

Diagnostics Topical Group
  The following report is a reduced version of the detailed summary prepared by R. Boivin and posted to the BPO Diagnostics Forum. The next meeting of the ITPA Diagnostics group will be held at NIFS-Japan on May 19–23, 2015.
  The 27th meeting of the ITPA group on diagnostics, was held at the IO Headquarters in Cadarache, France over November 3–7, 2014. The meeting was preceded by Progress Reports from the IO and Euro-Fusion in the areas of diagnostic developments for Burning Plasma Experiments (including ITER).
  A series of talks and discussions focused on the 4 current High-Priority Items. They are:
  • Determination of the life time of plasma facing mirrors used in optical systems
Issues associated with first mirror lifetime continue to be at the forefront of discussions and testing, at numerous labs around the lab, especially in Europe and Russia. Single crystal mirrors (e.g. molybdenum) have shown more resiliency to erosion, and more robust against frequent in-situ cleaning.
  • Assessment of impacts of in-vessel wall reflections on diagnostics
Since ITER’s first wall will be all metallic, it is expected that reflections will be common place for all IR and visible diagnostic systems. One extreme case will be the Hα imaging or survey system, where the signal collected has been found to be dominated by reflections.
  Development of methods of measuring the energy and density distribution of escaping alphas
The measurement of lost alpha flux remains a difficult challenge in ITER, and presently these measurements are only covered by the set of IR cameras. Other approaches such as gamma ray imaging, alpha-CHERS types (near the edge) or tile modification are still being explored with various degree of success.
  • Development of Plasma Control System measurement Requirements
In conjunction with the development of the Plasma Control System (PCS) for ITER, requirements associated with the sensors (e.g. diagnostics) are being finalized. These requirements may be different than the ones that were developed originally for the diagnostics for physics analysis.
  Additional volunteers are being sought for the various working groups within the topical group. These specialist working groups (SWGs) include the following:
 
Fusion Products First Mirrors Active Spectroscopy
Passive Spectroscopy Microwave Diagnostics Laser Aided Diagnostics
First Wall Diagnostics Radiation Effects Real Time Diagnostics
  If you wish to join these groups, please send a note to R. Boivin. These groups work almost exclusively through email, with workloads varying greatly between these groups and the task at hand.
 
2015
NSTX-U First Plasma —
W7-X First Plasma —
 
February 14, DEADLINE for abstract submission to the 12th International Symposium on Fusion Nuclear Technology
 
March 4–6, 7th IAEA Technical Meeting on Theory of Plasma Instabilities, Frascati, Italy
 
March 10–12, ITPA: Joint meeting of the Transport & Confinement and Pedestal & Edge Physics Topical Groups, Ahmedabad, India
 
March 16–18, Sherwood Fusion Theory Conference, New York, NY, United States
 
March 16–27, Joint ICTP–IAEA Advanced School and Workshop on Modern Methods in Plasma Spectroscopy, ICTP — Miramare, Trieste, Italy
 
March 23 – April 3, Winter School on Turbulence, Magnetic Fields and Self Organization in Laboratory and Astrophysical Plasmas, Les Houches, France
 
March 25–27, ITPA: Energetic Particles Topical Group Meeting, ITER Headquarters, France
 
April 14, DEADLINE to apply for the DOE Office of Science Graduate Student Research (SCGSR) Program
 
April 14–17, 1st European Conference on Plasma Diagnostics, Frascati, Italy
 
April 14–17, ITPA: MHD Topical Group Meeting, ITER Headquarters, France
 
April 20–23, ITPA: Integrated Operating Scenarios Topical Group Meeting, Barcelona, Spain
 
April 27–29, 21st Topical Conference on Radiofrequency Power in Plasmas, Lake Arrowhead, CA, United States
 
April 28 – May 1, US/EU Transport Task Force Workshop, Salem, MA, United States
 
May 18–22, 15th International Conference on Plasma-facing Materials and Components for Fusion Applications, Aix-en-Provence, France
 
May 19–23, ITPA Diagnostics Topical Group Meeting, NIFS, Japan
 
June 22–26, 42nd EPS Conference on Plasma Physics, Lisbon, Portugal
 
August 24 – September 4, 2th Carolus Magnus Summer School on Plasma and Fusion Energy Physics
 
September 14–18, 12th International Symposium on Fusion Nuclear Technology, Jeju Island, South Korea
 
November 16–20, 57th APS Division of Plasma Physics Meeting, Savannah, GA, United States

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