Dear Burning Plasma Aficionados:

This newsletter provides a short update on U.S. Burning Plasma Organization activities. Comments on articles in the newsletter may be sent to the editor (Tom Rognlien trognlien at llnl.gov) or assistant editor (Rita Wilkinson ritaw at mail.utexas.edu).

Thank you for your interest in Burning Plasma research in the U.S.!

Director's Corner by J. W. Van Dam

Second Notice: Scholarships for 2011 ITER Summer School

The 5^th ITER International Summer School will be held in Aix en Provence, France, during June 20-24, 2011. The theme of this year’s Summer School will be “MHD and Energetic Particles.” These Schools are primarily designed for graduate students, postdocs, and young researchers. If you are interested in attending, please go to the School’s web site and register. The registration deadline has been extended to April 1.

The USBPO will make available eight scholarships for US participants to this year’s ITER Summer School. “US participants” must be US citizens working at US institutions. The scholarships will cover round-trip airfare, registration fee, and six nights of student housing, which are the three items that constitute the bulk of the expenses. Participants’ home institutions are encouraged to supplement the scholarships to cover other travel-related expenses. Please send applications to Prof. Michael Mauel, chair of the USBPO Council. In each application, please include (1) a vita, (2) a list of publications, (3) a statement about the reasons why your participation at this School would be beneficial, and (4) a letter of reference from a senior scientist who is knowledgeable about you. Please submit applications for scholarships by March 23.

New Appointments

Sibylle Guenter (photo courtesy of Max Planck Institute)

Since the USBPO is integrated with the ITPA on the national level, let me report that the international leader of the ITPA Topical Group on Energetic Particles, Prof. Dr. Sibylle Guenter, became the new Scientific Director of the Max Planck Institute of Plasma Physics on February 1 of this year. She stepped down as the ITPA topical group leader and was replaced by the then-deputy leader, Dr. Kouji Shinohara (JAEA). Congratulations to Sibylle. The detailed news release from the Max Planck Institute about her new appointment can be found at the Institute’s website.

Rich Hawruluk (photo courtesy of PPPL)

The ITER Organization has announced that Dr. Richard Hawryluk (Princeton Plasma Physics Laboratory) has been appointed as the new Deputy Director-General for Administration. Rich is well known in the US and international fusion science communities. He led the deuterium-tritium campaign on the TFTR tokamak, was deputy director of PPPL during the period 1997-2008, and more recently served as the head of the ITER and Tokamaks Department at PPPL. Rich also chaired the US Fusion Facilities Coordinating Committee and led the international working group to design in-vessel coils for vertical stability and ELM control on ITER. The ITER Organization will greatly benefit from his broad range of experience and capabilities.

ITER Progress

ITER Progress A new gallery of photographs can be viewed on the ITER Organization website. Recent photos in this collection show the significant progress in construction on the ITER worksite at Cadarache.

Video clips are posted in another website; go here if you wish to view movies of construction, of presentations, and related material.

In addition, as reported in the ITER Newsline (issue #165), the ITER Webmaster has installed the first of several live webcams on the construction site (click on the link provided on the web page. You can now watch the construction progress on your computer screen in real time (but only during daylight hours).

Excavation for the future Tokamak Complex Seismic Isolation Pit (photo courtesy of PPPL)

Spring ITPA Meetings

One of the ITPA topical groups, namely, that for MHD Stability, already held its spring 2011 meeting (March 1-4, Ahmedabad, India). The next topical group meeting will be for the Pedestal and Edge Physics Topical Group, March 30-April 1, Cambridge, MA. You can see the complete schedule of ITPA spring meetings on the USBPO ITPA listing page.

Postings for Senior ITER Positions

We just received word that the following senior positions at the ITER Organization have been posted.

• Director of Directorate for General Administration, ADM-001
• Director of Directorate for Plasma Operation, FST-001
• Director of Directorate for Tokamak, TKM-001
• Director of Directorate for Central Engineering & Plant, CEP-001
• Director of Directorate for CODAC, Heating & Diagnostics, CHD-001
• Head of Finance and Budget Division ADM-003
  

Detailed job descriptions can be accessed on the ITER website. Applications from qualified and interested persons should be submitted by the deadline of April 3. Be sure to include the Personal History Form as well.

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USBPO Topical Group Highlights

(Editors note: The BPO Diagnostics Topical Group works to facilitate U.S. efforts in developing advanced measurement techniques for existing and future magnetic fusion devices [leaders are Jim Terry and David Brower]. This month's Research Highlight by Novimir Pablant et al. summarizes development of an x-ray imaging crystal spectrometer system that measures ion temperature and toroidal rotation in existing devices and is now being designed for use in ITER.)

Measurements of the ion temperature (T_i) and plasma toroidal rotation velocity (V_φ) across the minor radius are crucial for understanding burning plasmas and ITER as well as current tokamak devices. The rotation velocity profile is important in understanding and controlling the plasma stability, while measurements of the ion-temperature profile are important for plasma heating, the study of confinement modes, and heat transport. For ITER, profiles of both T_i and V_φ need to be measured with a spatial resolution of 1/30 the minor radius, and with a time resolution of 10 ms for V_φ and 100 ms for T_i. In current devices these parameters have typically been measured using charge-exchange recombination (CER), which relies on neutral-beam injection. In future devices, such as ITER, CER-based diagnostics are expected to have difficulties in making temperature and rotation measurements deep in the core due to poor neutral-beam penetration.

New developments in x-ray spectroscopy have made these types of measurements possible using an x-ray imaging crystal spectrometer (XICS) system, which has been selected for ITER to be a primary diagnostic for profile measurements of T_i and V_φ, and to be a secondary diagnostic for the electron temperature (T_e) and poloidal velocity (V_θ) [1,2]. The development of this diagnostic for ITER has been allocated to the US, and detailed design work is currently underway as a joint project between PPPL, LLNL and MIT. The planned ITER XICS system (shown in Fig. 1) will use emission from intrinsic impurities, providing a non-perturbative measurement. The conceptual design review for this diagnostic is scheduled for November 2011.

Fig. 1. Proposed layout geometer for the ITER x-ray imaging crystal spectrometer system. Here both the core system (shown in green), which is a US undertaking, and the edge system, which is an Indian contribution, are shown. For the core system both a radial view and a view with a tangential component are used to distinguish Vθ and Vφ. In addition, to obtain coverage across the minor radius two arrays are needed, leading to a total of four XICS arrays for the core system.

X-ray emission from highly charged impurity ions has been an important diagnostic tool for magnetically confined fusion plasmas for the last three decades [3]. Recent developments in diagnostic design and detector technology have allowed tremendous advances in x-ray measurements, and in particular for the XICS diagnostic. This type of diagnostic in now installed at many of the major fusion facilities including Alcator C-Mod, NSTX, KSTAR and EAST, and an installation is underway at LHD. At C-Mod this diagnostic is now considered an essential diagnostic for profile measurements of the ion-temperature and toroidal rotation velocity.

The XICS diagnostic utilizes a spherically bent quartz crystal to provide a 1D image of line-integrated spectra from highly charged impurity species in the plasma. A conceptual diagnostic layout is shown in Fig. 2. At the temperatures routinely seen in current devices, T_i = 1-3 keV, the typical impurity used is helium-like Ar¹⁶⁺. At the higher temperatures expected in ITER, helium-like Fe and neon-like W have been identified as favorable impurities. Measurements of the iontemperature (T_i) are made from the Doppler broadening of the spectral lines, while the electron-temperature (T_e) is found from the relative intensities of dielectronic satellite lines to resonant emission lines. The Doppler shift of the lines is used to measure the plasma rotation velocities (V_θ and V_φ). Local temperature and rotation values can be inferred from these line-integrated spectra through tomographic inversion, which relies on a plasma equilibrium reconstruction. The XICS system can also play an important role in the monitoring of intrinsic impurities.

The XICS diagnostic technique has benefited greatly from the development of x-ray detectors based on modern CMOS hybrid-pixel technology, in particular the Pilatus II detector developed by the Paul Scherrer Institute and commercially produced by Dectris [4,5]. Each of these detectors comprises ~100,000 pixels, and has a pixel pitch of 172 × 172 μm². Each pixel has a high single-photon count rate capability of 2 MHz and low neutron response. These detector modules are radiation hardened and have been tested to a fluence of 10¹⁴ cm^-2 using 1 MeV neutrons.

Fig. 2. Conceptual diagram of the XICS diagnostic geometry. Shown is a representation of the light cone corresponding to a single pixel on the detector (point P), which is placed on the Rowland circle. Because of the astigmatism of the spherically bent reflector, one obtains two mutually perpendicular (meridional and sagittal) line foci of the point P at Bm and Bs, respectively. Imaging is done in the vertical direction, allowing a full profile of the plasma to be recorded. Spectra are recorded in the horizontal direction on the camera based on the requirement that the Bragg condition is satisfied for the incoming x-rays. Each wavelength corresponds to a range of toroidal angles due to the astigmatism (exaggerated in this diagram); this is the preferred experimental arrangement on tokamaks where the x-ray emissivity is uniform along the field lines. The arrangement shown has rotational symmetry about the line normal to the crystal center (which passes through the point O).

The non-perturbative nature of the XICS diagnostic has allowed it to play an integral role in studying RF heating and intrinsic rotation in recent experiments at C-Mod. A variety of experiments have been carried out to study the intrinsic (spontaneous) plasma rotation in Lmode, H-mode and internal transport barrier (ITB) plasmas [6]. These experiments are an important step towards the understanding of the physics behind intrinsic rotation and the extrapolation to ITER plasmas. In a different set of experiments using lower-hybrid current drive (LHCD), the XICS diagnostic was critical for the observation of localized self-generated flows caused by the driven current [7]. Similarly experiments have been done using ion-cyclotron radio frequency (ICRF) minority heating (MH) and mode conversion (MC), demonstrating that while MH ICRF has little effect on the flow velocities, MC ICRF can be used as an effective tool to drive toroidal and poloidal plasma rotation [8]. All three of these experiments have important implications for rotation and velocity shear control without the use of neutral beam injection. Before the installation of the XICS diagnostic these types of experiments were difficult, if not impossible, since the standard measurement technique, charge exchange recombination spectroscopy, requires beam injection, which adds both momentum and heating to the plasma. Data from the XICS system at C-Mod is illustrated in Fig. 3 showing both the raw spectra and the measured rotational velocity.

Implementation of XICS on ITER has unique challenges, many of which have already been addressed by the teams at PPPL and LLNL, while others are being addressed in current and planed experiments. One challenge for deployment on ITER is the handling of the large neutron background. This background poses two problems: reduced signal-to-noise ratios leading to a reduction in measurement accuracy, and diagnostic lifetime due to damage of the detectors. We are currently working with several groups to develop radiation-hardened detectors that will address these concerns. The signal-to-noise issue can be largely eliminated though the use of a detector with adjustable lower and upper energy discriminators [2]. Testing of such a detector, produced by the Medipix consortium, of which the ITER organization is a part, will be done on NSTX and C-Mod.

Fig. 3. Data from the XICS system on Alcator C-Mod (shot 1080306014). The figure on the left shows raw spatially resolved spectral data for a single time-frame. The apparent toroidal velocity, measured from the Doppler shifts of the emission lines, is shown in the right figure. In the initial Ohmic mode phase, the plasma is rotating counter to the plasma current direction. ICRF heating is added at t = 0.6 s causing the toroidal rotation to change direction and reach a value of 40 km/s. Between t=1.1 and 1.4 s, LHCD is added, reducing the rotation velocity, which recovers afterward until the end of the ICRF heating at 1.5 s.

Another challenge for the ITER system will be maintaining an accurate wavelength calibration. For the current diagnostic installations, this calibration has been done by utilizing locked-mode plasma discharges where plasma rotation and, therefore, the Doppler shift of the emission lines, is expected to be zero. For ITER however this technique will not be feasible, and instead an external calibration source is required. Experiments are underway to determine the feasibility of using foils with absorption edges or known line sources to provide an in-situ wavelength calibration technique. To maintain an accurate wavelength calibration, the temperature of the crystal must be monitored and kept constant. As the crystal temperature changes, thermal expansion causes the crystal lattice spacing to change slightly. Even changes in the crystal temperature of ~1º C can have a significant impact on the final measured rotation velocity. The various sources of crystal heating are being studied on C-Mod, along with the development of techniques to regulate the crystal temperature.

This is an exciting time for the use and development of the XICS diagnostic technique. There are many experiments planned that will rely on data from this technique, and the diagnostic is maturing into a fully characterized and reliable system. Some highlights of upcoming experiments in the next year are:

• Additional studies of intrinsic rotation and momentum transport on C-Mod, EAST and KSTAR.
• Continued studies of RF heating (LH, ICRF and ECCD) on NSTX and C-Mod.
• Fast (20 kHz) XICS measurement on C-Mod using the newly developed Eiger detector from the Paul Scherrer Institute.
• Impurity monitoring and transport measurements utilizing intrinsic (Fe, Mo in NSTX, W in C-Mod) and injected impurities (Ar, Kr, Ca). In particular, analysis is underway to understand the effect on transport and MHD stability of non-deliberate release of Mo from the walls in C-Mod. These experiments will also allow for improved characterization of the emission spectra from these various species.
• Investigation of non-Maxwellian electron energy distribution functions though line intensity ratios in C-Mod. Particular emphasis will be on the effect of RF heating on the highenergy electron tail.
• Extension of the XICS diagnostic technique to stellarator geometries on LHD in Japan. This project will provide the highest spectral resolution of any of the currently installed systems. The lack of toroidal symmetry will provide a challenge in the development of accurate inversion techniques.

In addition to the continued development of XICS diagnostics, we are also developing other x-ray diagnostic techniques that utilize this new x-ray detection technology. An example is the energy resolving pinhole camera diagnostic, which is currently being developed for installation on Alcator C-Mod.

References

1. P. Beiersdorfer, G.V. Brown, J. Clementson, J. Dunn, K. Morris, E. Wang, R. L. Kelley, C.A. Kilbourne, F.S. Porter, M. Bitter, R. Feder, K.W. Hill, D. Johnson, and R. Barnsley, Rev. Sci. Instruments 81 , 10E323 (2010).
2. K.W. Hill, M. Bitter, L. Delgado-Aparicio, D. Johnson, R. Feder, P. Beiersdorfer, J. Dunn, K. Morris, E. Wang, M. Reinke, Y. Podpaly, J. E. Rice, R. Barnsley, M. O’Mullane, and S.G. Lee, Rev. Sci. Instruments 81, 10E322 (2010).
3. M. Bitter, H. Hsuan, K. W. Hill, and M. Zarnstorff, Physica Scripta 1993, 87 (1993).
4. C. Broennimann, E. Eikenberry, B. Henrich, R. Horisberger, G. Huelsen, E. Pohl, B. Schmitt, C. Schulze-Briese, M. Suzuki, T. Tomizaki et al., J. Synchrotron Rad. 13, 120 (2006), ISSN 0909-0495.
5. http://www.dectris.com/sites/pilatus100k.html (2010).
6. J.E. Rice, A.C. Ince-Cushman, M.L. Reinke, Y. Podpaly, M.J. Greenwald, B. LaBombard, and E.S. Marmar, Plasma Phys. Controlled Fusion 50, 124042 (2008).
7. A. Ince-Cushman, J.E. Rice, M. Reinke, M. Greenwald, G. Wallace, R. Parker, C. Fiore, J.W. Hughes, P. Bonoli, S. Shiraiwa, A. Hubbard, S. Wolfe, I. H. Hutchinson, E. Marmar, M. Bitter, J. Wilson, and K. Hill, Phys. Rev. Lett. 102, 035002 (2009).
8. Y. Lin, J.E. Rice, S.J. Wukitch, M.J. Greenwald, A.E. Hubbard, A. Ince-Cushman, L. Lin, E.S. Marmar, M. Porkolab, M.L. Reinke, N. Tsujii, J.C. Wright, and A. C.-M. Team, Phys. Plasmas 16, 056102 (2009).

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Announcements

Submit BPO-related announcements for next month’s eNews to Tom Rognlien at trognlien at llnl.gov.

Upcoming Burning Plasma Events

Click here to visit a list of previously concluded events.

2011 Events

March 30 - April 1, 2011 20th ITPA Pedestal and Edge Topical Group Meeting Cambridge, Massachusetts, USA

April 4-5, 2011 ITPA Transport & Confinement Topical Group Meeting San Diego, California USA

April 5, 2011 abstract deadline closed Edge Coordinating Committee Workshop on RMP San Diego, California USA

April 6-9, 2011 abstract deadline closed Joint US-EU Transport Task Force (TTF) Workshop San Diego, California USA

April 11-13, 2011 ITPA Energetic Particles Topical Group Meeting Frascti, ITALY

April 11-14, 2011 ITPA Integrated Operation Scenarios Topical Group Meeting JET, Culham, UNITED KINGDOM

April 11-14, 2011 abstract deadline closed Workshop on Stochasticity in Fusion Plasmas (SFP 20110) Jülich, GERMANY

April 20-22, 2011  abstracts deadline closed 2011 IEA Fusion Modeling Workshop on Materials Lawrence Livermore National Laboratory, Livermore, California USA

May 2-4, 2011 2011 International Sherwood Fusion Theory Conference Austin, Texas USA

May 9-13, 2011 13th International Workshop on Plasma-Facing Materials and Components for Fusion Applications (PFMC-13) and 1st International Conference on Fusion Energy Materials Science (FEMaS-1) Rosenheim, GERMANY

May 15-19, 2011 15th International Conference on Emerging Nuclear Energy Systems (ICENES) San Francisco, California USA

May 16-19, 2011 ITPA SOL and Divertor Topical Group Meeting Helsinki, FINLAND

May 23-26, 2011 ITPA Diagnostics Topical Group Meeting FOM, NETHERLANDS

June 1-3, 2011 19th Topical Conference on Radio Frequency Power in Plasmas (C.K. Phillips and J.R. Wilson, PPPL) Newport, Rhode Island USA

June 20-24, 2011 registration deadline April 1 ITER International Summer School on MHD and Energetic Particles Aix en Provence, FRANCE

June 26-30, 2011 abstract deadline closed 38th IEEE International Conference on Plasma Science (ICOPS) and the 24th Symposium on Fusion Engineering (SOFE) Chicago, Illinois USA

Jun 27-Jul 1, 2011 38th European Physical Society Conference on Plasma Physics Strasbourg, FR EPS

Fall 2011 ITPA Diagnostics Topical Group Meeting CHINA

Sept 5-7, 2011 IAEA Technical Meeting on Theory of Plasma Instabilities Austin, Texas  USA

Sept 8-10, 2011 IAEA Technical Meeting on Energetic Particles in Magnetic Confinement Systems Ausitn, Texas USA

TBA ITPA Energetic Particles Topical Group Meeting Austin, Texas  USA

TBA---tentatively scheduled ITPA MHD Topical Group Meeting Padova, ITALY

Sep 11-16, 2011 10th International Symposium on Fusion Nuclear Technology Portland, Oregon USA

Sep 19-21, 2011 13th International Workshop on Plasma Edge Theory in Fusion Devices South Lake Tahoe, California USA

October 5-7, 2011 ITPA Transport & Confinement Topical Group Meeting Cadarache, FRANCE

October 5-7, 2011 ITPA Pedestal and Edge Topical Group Meeting York, UNITED KINGDOM

Oct 16-21, 2011 15th International Conference on Fusion Reactor Materials (ICFRM-15) Charleston, South Carolina USA

October 18-21, 2011 ITPA Integrated Operational Scenarios Topical Group Kyoto University, JAPAN

Nov 14-18, 2011 53rd APS Division of Plasma Physics Annual Meeting Salt Lake City, Utah USA

December 12-15, 2011 ITPA CC & CTP-ITPA Joint Experiments Meeting Cadarache, FRANCE

December 2011 or January 2012 ITPA Divertor and SOL (PSI Selection Committee) Topical Group Meeting Jüelich, GERMANY

Click here to visit a Directory of Other Plasma Events

Please contact the administrator with additions and corrections.

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