News and Events

U.S. Burning Plasma Organization eNews

Mar 31, 2018 (Issue 128)


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  
Director’s Corner
C.M. Greenfield
Research Highlight
Saskia Mordijck
Schedule of Burning Plasma Events  
Contact and Contribution Information  

Announcements

NAS Burning Plasma committee

The NAS committee on “A Strategic Plan for U.S. Burning Plasma Research” held a public meeting on April 11-13 at Princeton Plasma Physics Laboratory. Presentations to the committee and additional public input submitted directly to the committee can be found here:

http://sites.nationalacademies.org/BPA/BPA_184701

 

New plasma book

Magnetic Helicity, Spheromaks, Solar Corona Loops, and Astrophysical Jets” by professor Paul M. Bellan of Caltech has recently been published.

 

ITER internships

An announcement for ITER internship opportunities for undergraduate and graduate students was recently posted. Please see the following link for a description: https://www.iter.org/jobs/internships

The proposed topics can be found here:

https://www.iter.org/doc/www/content/com/Lists/WebText_2014/Attachments/321/Call_for_topics-Internship_2018_V3.pdf

 

Director’s Corner

By C.M. Greenfield

New USBPO Task Group

The US Fusion Energy Science community has a history of doing excellent science and has made great strides (albeit sometimes at a slower pace than we’d like) toward a burning plasma. But a quick trip to Google will show you that most people don’t know about that. Our community has done a pretty good job reaching K-12 audiences through efforts by individuals, institutions, APS- DPP, and other groups. Much less effort has gone toward informing other scientific communities and the public, even though it would be to our great benefit for those groups to know about our work.

With that in mind, we are creating a new USBPO Task Group, to organize such outreach efforts.

One of the early efforts of the group will be to assemble a “library” of presentation material that members can use to prepare their own presentations. Work is going on now to prepare infrastructure for sharing this material. As we ramp this up, we will need both contributions of material and presenters. Our dream is to assemble a large enough “standing army” of present- ers that little or no travel will be needed to provide a speaker for a given audience.

We are aware that there are already some small efforts along the same lines. One example is the small (six speakers at any given time) Distinguished Lecturer in Plasma Physics program, organized by APS-DPP. But resources just aren’t there for parallel, competing efforts. Our inten- tion is to cooperate and share with such programs

Cami Collins (GA) has agreed to lead this Task Group as it ramps up its efforts. You can expect to hear more about this very soon.

Some good news from Washington

The House Subcommittee on Energy held a hearing entitled “The Future of U.S. Fusion Re- search” on March 6, with testimony given by Bernard Bigot (ITER Director General), Jim Van Dam (Acting Associate Director of DOE’s Fusion Energy Sciences office), Mickey Wade (General Atomics), and Mark Herrmann (Director of NIF at LLNL). The tone of the hearing was extraordi- narily positive toward fusion. Many of the panel members made very supportive statements both toward the domestic fusion program and U.S. support of ITER.

Transcripts and video of the hearing are posted at https://science.house.gov/legislation/hearings/subcommittee-energy-hearing-future-us-fusion- energy-research-1. It’s definitely must-see-TV for anybody with an interest in fusion.

This positive tone was still in evidence on March 21, when I and many of you descended on Washington for “Fusion Day,” an annual event filled with visits to Congressional and Senate offices to talk about fusion research. Despite the fact that government offices were technically closed due to the “snow emergency” (living in San Diego I always thought “snow emergency” meant three FEET of snow, not three INCHES!), almost all of our planned visits took place. I can’t speak for all of the participants, but the reception I found in the offices I visited was prob- ably the most positive toward both domestic fusion research and ITER that I had ever seen.

The next day, on March 22, the omnibus budget for FY2018 (which is half over already) was re- leased, and it was very generous to science in general, but unusually so to Fusion. Fusion Ener- gy Sciences received a 40% increase from FY2017 – $410M for the domestic fusion program and $122M in funding for ITER construction. I wish I could take credit for this for our discussions on Fusion Day, but I can’t – the decisions had already been made by then. I do believe the hearing had some impact, though. It’s difficult to predict what all this means for the future, but it’s certainly good news for the present.

 

Research Highlight

Diagnostics Topical Group (Leaders: Max Austin and Luis Delgado-Aparicio)

This month’s research highlight by Dr. Max Austin of the University of Texas describes the current state of the design of the ECE diagnostic for ITER. It points out some of the challenges for this system brought about by the high temperature and nuclear environment. Some of the chief issues and their solution, for each part of the system from the port plug to the instrument hall, are described. This topic is the subject of an invited talk at the upcoming High Temperature Plasma Diagnostic conference in San Diego.

The electron cyclotron emission diagnostic system on ITER

M.  E. Austin1, A. Basile2, J. H. Beno3, S. Danani4, R. Feder2, S. Houshmandyar1, A. E. Hubbard5, D. W. Johnson2, A. Khodak2, R. Kumar4, S. Kumar4, Vinay Kumar4, A. Ouroua3, S. B. Padasalagi4, H. K. B. Pandya4, P. E. Phillips1, W. L. Rowan1, J. Stillerman5, G. Taylor2, S. Thomas4, V. S. Udintsev6, G. Vayakis6, M. Walsh6, and D. Weeks3

1Institute for Fusion Studies, University of Texas at Austin, TX 78712, USA

2Princeton Plasma Physics Laboratory, Princeton, NJ 08543, USA

4Center for Electromechanics, University of Texas at Austin, TX 78758, USA

5ITER-India/Institute for Plasma Research, Bhat 382428, Gandhinagar, India

5Plasma Science and Fusion Center, MIT, Cambridge, MA 02139, USA

6ITER Organization, Route de Vinon sur Verdon, 13115, St Paul Lez Durance, France

7austin@fusion.gat.com

The plasma electron temperature, Te, is commonly measured by detecting electron cyclotron emission (ECE) from magnetic confinement devices such as ITER[1]. The radiation is typically in the millimeter wave range of frequencies, in the neighborhood of 100 GHz. And due to the strong absorbing nature of the plasmas near the cyclotron frequency, the radiation is emitted at the blackbody level for thermal distributions. This means that a simple measurement of power with an antenna properly coupled to the plasma yields Te. This is the basis for the ECE diagnos- tic for Te measurements on tokamaks. The conditions on ITER will be such that the absorption of EC waves will be even stronger, but due to the very high temperatures expected, plus the high radiation environment, the diagnostic system will face several challenges to providing useful data.

Because in a tokamak the dominant toroidal magnetic field B falls off as 1/R, the ECE at a given frequency is localized to a specific major radial location, since the electron cyclotron frequency fce = eB/gmec, where e is the electron charge, g is the relativistic gamma, me is the electron mass and c is the velocity of light. This is shown for an ITER case in Fig. 1 where several ECE har- monic are plotted versus major radius. The ECE frequency can be subject to a number of broad- ening mechanisms; the strongest is relativistic broadening for emission along a major radius, perpendicular to the magnetic field, which is the standard viewing direction. For electron tem- peratures 4 keV or lower the broadening is small, a few 10ths of a GHz corresponding to broad- ened widths of a few mm –this is smaller than the typical channel ~2 cm width set by the instru- mental bandwidth filters. So for current machines with maximum Te’s typically 4-6 keV, relativistic broadening can be ignored.

However, for ITER, the central Te is expected to reach 25 keV and higher. For this case the rela- tivistic broadening results in spatial widths of 5-10 cm for the measurement. Fortunately ITER is a much larger device so the poorer spatial resolution does not have as large an impact. But it will be harder to detect small Te oscillations, such as those caused by magnetohydrodynamic (MHD) modes [2], since the broadening results in spatial averaging that reduces the detected oscillation amplitude. Highly optimized fourier or similar techniques will be needed to find these modes in the ECE signals. Another consequence of the relativistic effects, also shown in Fig. 1, is that the broadening of higher harmonics causes absorption at the next lower harmonic, to the extent that the emission only escapes from the low-field-side of the magnetic axis and access to the high- field side is blocked. For this reason techniques like forward modeling will be required to get the most information from the measurements.

 


Figure 1. ECE harmonics vs major radius for ITER. The dashed magen- ta curves represent the zero tempera- ture resonant locations. The colored regions are contours of emissivity for a Te=25 keV plasma showing emis- sion only from the low-field side.


Figure 2. Diagram of the ITER Diagnostic Shield Mod- ule for the port containing the ECE front-end optics.

The calibration source is similar in design to units that have been historically employed for ECE instruments with a heated or cooled emissive surface. This type of source was typically inserted in the vessel during vents or coupled to the optics front end via a rotated mirror and hence could operate in air and/or be outside the tokamak. For ITER the source needs to operate in vacuum and be robust enough to handle the radiation, heat, and electromagnetic forces existing in the port plug. A design has been conceived and tested that employs a SiC emissive plate enclosed in a stainless steel casing with an internal radiating heat source. Several technical challenges have been overcome and a good design is in hand, as shown in Fig. 3 and described in Ref. [4].


Figure 3. Cutaway view of ITER hot calibration source showing SiC emitter surface (black object with pyramidal surface) just above the radiative heaters.

Transmitting the EC radiation from the port plug to the instruments in the diagnostic hall presents a significant challenge because minimizing the power loss will be crucial for good meas- urements. The transmission line (TL) will have to be about 40 m long with several bends. Corrugated waveguide has been the TL of choice for low-loss, but ITERs requirement for a wide frequency range, 70-1000 GHz, precludes its use since it transmits poorly above ~500 GHz. In- stead, some type of smooth walled waveguide, either circular metal or dielectric will have to be used. Testing of these two types is currently being done by the IN-DA[5].

Transmitting the EC radiation from the port plug to the instruments in the diagnostic hall pre- sents a significant challenge because minimizing the power loss will be crucial for good meas- urements. The transmission line (TL) will have to be about 40 m long with several bends. Cor- rugated waveguide has been the TL of choice for low-loss, but ITERs requirement for a wide frequency range, 70-1000 GHz, precludes its use since it transmits poorly above ~500 GHz. In- stead, some type of smooth walled waveguide, either circular metal or dielectric will have to be used. Testing of these two types is currently being done by the IN-DA[5].

Two types of instruments will be used to measure the ECE on ITER: 1) heterodyne radiometers will be used to detect the first and second harmonic ranges of frequencies and 2) Michelson in- terferometers will be employed to measure the broad multi-harmonic spectrum. The radiometers, each with ~60 channels, will provide detailed electron temperature profile measurements including the detection of small scale MHD modes that will be deleterious to discharge performance. The measurement of the second harmonic is somewhat of a challenge due to the high frequency range needed for 5 T operation. But a compact and robust receiver covering the necessary range of 200-300 GHz has been developed by a commercial supplier [6] and tested on DIII-D. The broad coverage of the Michelson interferometers will be useful for assessing the electron distribution function, to see if non-thermals are present, and to detect the EC power loss. These are tried-and-true systems that have been successfully employed in past and present machines.

The development of the ITER ECE diagnostic system is an ongoing collaborative project between the ITER Organization and the US and India Domestic Agencies. Resolution of the unique problems associated with the extremes of plasma temperature and radiation in the fusion environment have come from years of work involving laboratory experiments and modeling efforts. The resulting design has promise to provide a well-functioning system for ITER.

References

1.      Costley, A.E., Diagnostics for Experimental Thermonuclear Fusion Reactors, Plenum Press, New York (1998) 41.

2.      La Haye, R.J et al., Nucl. Fusion, 46, 451 (2006).

3.      Hartfuss, H-J and T. Geist, Fusion Plasma Diagnostics with mm-Waves, Wiley-VCH, Weinheim, Germany (2013) 151.

4.      A. Ouroua, et al., “Prototype design of a 700 0C in-vacuum blackbody source for in-situ calibration of the ITER ECE diagnostic,” IEEE Trans. on Plasma Science, Issue 99, 2017.

5.      Kumar, Ravinder et al., “Fabrication and Characterization of Transmission Line for ITER ECE Diagnostics,” 32nd National Symposium on Plasma Science & Technology, Gandhinagar, India, 07-10 November 2017.

6.      E.W. Bryerton et al., in 39th International Conference on Infrared, Millimeter, and THz Waves, W4_C-27.3, Tucson, Arizona, 12–19 September 2014.

Calendar of Burning Plasma Events

USBPO Public Calendar: View online or subscribe

2018                                               

May 7-10

5th IAEA DEMO Programme Workshop

Daejon, South Korea

May 8-11

US Transport Task Force (US-TTF) meeting

San Diego, CA

May 23-25

ITPA Energetic Particles Topical Group meeting

ITER HQ, France

June 17-22

International Conference on Plasma Surface Interactions (PSI)

Princeton, NJ

June 24-28

2018 IEEE International Conference on Plasma Science (ICOPS)

Denver, CO

July 2-6

EPS Conference on Plasma Physics

Prague, Czech Rep.

Sept 11-14

EU Transport Task Force (EU-TTF) meeting

Seville, Spain

Sept 17-20

ITPA Transport & Confinement Topical Group meeting

ITER HQ, Franc

October 1-3

ITPA MHD Disruptions & Control Topical Group meeting

Napoli, Italy

October 22-27

IAEA Fusion Energy Conference

Gandhinagar, Gujarat, India

October 29-31

ITPA Integrated Operation Scenarios Topical Group meeting

ITER HQ, France

October 29-31

ITPA Pedestal & Edge Physics Topical Group meeting

ITER HQ, France

November 5-9

60th Annual Meeting of the APS Division of Plasma Physics

Portland, OR

November 11-15

ANS 23rd Topical Meeting on the Technology of Fusion Energy (TOFE)

Orlando, FL

November 12-18

2nd Asia-Pacific Conference on Plasma Physics

Kanazawa, Japan

December 4-5

Fusion Power Associates 39th Annual Meeting & Symposium, Fusion Energy: Strategies & Expectations through the 2020s

Washington, DC

December 4-6

ITPA Coordinating Committee & CTP ExComm

ITER HQ, France

2019

JET DT-campaign (https://www.euro-fusion.org/newsletter/jet-full-throttle/)

October 21-25

61st Annual Meeting of the APS Division of Plasma Physics

Fort Lauderdale, Florida, USA

2020

JT60-SA First Plasma (http://jt60sa.org/)

 

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: Walter Guttenfelder (wgutten@pppl.gov)

 

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