News

— News: 2017-03-15

Paper by Prof. O. Schmitz on comparative studies on Helium exhaust with RMP fields at TEXTOR (tokamak) and LHD (heliotron/stellarator) was selected as highlight for 2016 in the IoP journal Nuclear Fusion.

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The paper on “Enhancement of helium exhaust by resonant magnetic perturbation fields at LHD and TEXTOR” was selected as a 2016 highlight in the top-journal Nuclear Fusion. The paper demonstrates for the first time that small amplitude, resonant magnetic perturbation (RMP) fields are a versatile and efficient fine-tuning actuator to control the helium exhaust from a magnetically confined plasma. Helium will be produced in future fusion reactors as ash of the fusion process and needs to be exhausted efficiently to maintain a burning plasma. In the paper it is shown that for the two leading configurations, i.e. a tokamak and stellarator plasma, helium exhaust can be controlled and substantially enhanced by these fine scale external magnetic fields. The study has motivated recent follow up experiments at the U.S. National Fusion facility DIII-D, in which such small scale magnetic fields are used for control of the plasma edge stability. The findings discussed in the paper suggest that enhanced helium exhaust is another beneficial aspect of these additional magnetic fields – a very important finding also for ITER, the next step fusion experiment presently under construction in southern France.

This work was funded by the U.S. Department of Energy under Early Career Grant DE-SC00013911.

— News: 2017-03-12

Paper on NSTX-U modeling with EMC3-EIRENE by Dr. H. Frerichs is among most read paper for 2016  in the top journal Physics of Plasmas 

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The paper on “Exploration of magnetic perturbation effects on advanced divertor configurations in NSTX-U” by Dr. H. Frerichs was added to the selection list of Physics of Plasma for 2016. The paper presents a first time systematic exploration of divertor conditions in the various advanced divertor configurations accessible at NSTX-U including the effects of resonant magnetic perturbation fields. This work was funded by the Department of Energy under funding DE-SC0012315.

— News: 2017-02-08

A review paper on detachment modeling with EMC3-EIRENE was published – IoP journal Plasma physics and Controlled Fusion. 

ppcfaa4da9f19_lrDr. Heinke Frerichs wrote chapter 3 about application towards detached regimes in tokamaks with Resonant Magnetic Perturbations. This work was funded by the

Department of Energy under grants DE-SC0012315 and DE-SC001391 (ECA).

Also, we congratulate Heinke to his promotion to an Associate Scientist.

— News: 2017-01-20

Systematic numerical study of helical SOL transport and limiter fluxes for Wendelstein 7-X using the EMC3-EIRENE code was published by PhD student Florian Effenberg in IoP journal Nuclear Fusion.

bildschirmfoto-2017-01-20-um-16-40-05This paper describes a systematic numerical survey of basic scrape-off layer physics features in the startup plasmas of Wendelstein 7-X. The magnetic structure is analyzed and connected to the transport and limiter heat and particle flux features. Radiative edge cooling is explored in this simplified geometry as a preparation for studies with the island diverter in the next experimental campaign.

— News: 2016-10-31

Strong presence of group members and affiliated group members on this years APS-DPP meeting in San Jose, California.

Please find all talks and poster linked below:

 

— News: 2016-09-09

Paper by Heinke Frerichs on 3-D edge modeling for Advanced Divertors at NSTX-Upgrade selected as Editor’s Pick in Physics of Plasmas.

Bildschirmfoto 2016-09-06 um 09.45.21The paper recently published in Physics of Plasmas by Dr. H. Frerichs discussing a survey of results on the effect of RMP fields on advanced divertor configurations at NSTX-Upgrade was selected as Editor’s Pick. Congratulations, Heinke!

In this paper, the EMC3-EIRENE code was used to explore basic divertor characteristics for the major advanced divertor configurations achievable at NSTX-U. The results highlighted the general geometrical benefits of the various divertor configurations. Moreover, the impact of RMP fields on the divertor conditions and the target fluxes was analyzed. This work was funded by the Department of Energy under grant DE-SC00012315.

— News: 2016-08-10

Paper on Enhancement of Helium Exhaust using Resonant Magnetic Perturbations was published.

A paper was published in Nuclear Fusion  today by Prof. O. Schmitz demonstrating on two devices that resonant magnetic perturbation (RMP) fields can be used to enhance the exhaust of helium from fusion plasmas. Screen Shot 2016-08-10 at 2.23.19 PMSufficient helium exhaust is a mandate for fusion reactors as the helium produced by the fusion reaction of deuterium and tritium needs to be exhausted from the plasma to avoid that fuel (D and T) is replaced by helium which does not fuse under the condition of a man build fusion reactor. A small level of helium in the plasma mix can be tolerated but the effective confinement time of helium must not exceed the energy confinement time by more then some factors.

Experiments proposed and conducted by Prof. O. Schmitz in collaboration with the local experimental teams at the limiter tokamak TEXTOR in Juelich, Germany and at the Large Helical Device LHD in Toki, Japan featuring the closed helical divertor have shown in a concerted approach that RMP fields substantially reduce this effective helium confinement time in the system. It was seen that the application of RMP fields yields increased retention of the helium which is recycled at the material interface. As the pumping efficiency for helium is small, this is an important mechanism to avoid the helium penetrating the plasma core domain again where the fusion processes happen. The plasma core at LHD was decontaminated substantially by the application of RMP fields with a drop of the helium content from 70% to 20% in the ion root confinement regime which is prone to impurity accumulation. This demonstrates that RMP fields can be used effectively to aid impurity exhaust even in unfavorable impurity transport regimes in heliotron type stellarator devices.

The figure below shows the effective helium confinement time measured at TEXTOR (left side) and at LHD ( right side). In both plots the effective confinement time is shown compared to the reference result without RMP field applied. Screen Shot 2016-08-10 at 2.25.14 PMA reduction of the global helium confinement of up to 50% at TEXTOR and up to 30% at LHD was shown. This work was supported by JSPS KAKENHI Grant Numbers 25420893, by start up funds of the Department of Engineering Physics and of the College of Engineering at the University of Wisconsin—Madison, USA and under grant DE-SC00013911 and DE-SC0006103 of the U.S. Department of Energy.

— News: 2016-06-29

Paper on 3-D edge modeling for Advanced Divertors at NSTX-Upgrade was published.

A paper was published in Physics of Plasmas today by Dr. H. Frerichs discussing a survey of results on the effect of RMP fields on advanced divertor configurations at NSTX-Upgrade. The EMC3-EIRENE code was used to explore basic divertor characteristics for the major advanced divertor configurations achievable at NSTX-U. The inherent flexibility of the modeling grid of EMC3-EIRENE enables such targeted studies on feasible time scales. The results highlighted the general geometrical benefits of the various divertor configurations. Moreover, the impact of RMP fields on the divertor conditions and the target fluxes was analyzed.

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This work was funded by the Department of Energy under grant DE-SC00012315. The systematic survey study is the basis for detailed analysis of neutral fueling and exhaust and in how far the divertor topology and the application of RMP fields impacts on these critical root mechanisms for density control at NSTX-U. This is the goal of the PhD project of Ian Waters and Kurt Flesh which will address this question in  a concerted approach with EMC3-EIRENE as feasible, state of the art tool and dedicated diagnostic activities.

— News: 2016-05-11

Paper on 3-D edge modeling for ELM control at ITER published in IoP Journal Nuclear Fusion.

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A paper was published presenting a thorough assessment of the impact resonant magnetic perturbation fields have on plasma edge transport and the divertor fluxes. This assessment utilizing the EMC3-EIRENE code is a result of a multi-year study within an international team and is presently being used as a baseline study in discussions of the advising bodies at ITER. Comparisons to experimental results from various RMP tokamaks is ongoing within the recently founded ITPA Divertor and Scrape-off layer activity on “Effect of 3-D fields on divertor conditions and plasma wall interaction as compatibility issue of RMP ELM control” (ITPA DSOL task 37). The paper appeared today in Nuclear Fusion.

This work was funded in part by the DoE Early Career Award and by Startup funds of the Department of Engineering Physics at the university of Wisconsin – Madison..

— News: 2016-04-07

Florian Effenberg wins one of the Student Poster Awards on the 2016 Sherwood Theory Conference!

Florian received this award for his poster on “3-D Modeling of Edge Transport and Plasma Surface Interactions for Wendelstein 7-X Startup Plasmas”. Congratulations to Florian!

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This work was funded by the Department of Energy under Grant DE-SC0014210.

— News: 2016-04-03

Stable plasma conditions in the MARIA helicon device!

Here are some exciting news about our helicon device MARIA which is used to explore stable access to laboratory scale high density plasmas. As always, “high” is relative, but we target on densities which are representative for possible next generation wake-field accelerators (high 10^20 per cubic meter) and also for divertor plasma conditions in fusion devices. A critical question for helicons is how this particular RF wave localized just below the lower-hybrid cut-off frequency is so effective ionizing a neutral gas and that above an empirical limit further fueling the dense plasma column seems very difficult as a depletion of the neutral population occurs.

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Our endeavor to shed light into this question is funded by the National Science Foundation (NSF) under the CAREER award. The device is used also as a facility in the research on 3-D Plasma Wall Interactions funded by the Department of Energy under the Early Career Award program.

In the past year, the two graduate students Jonathan Green and Victoria Winters managed to establish a reliably working facility in which a stable helicon plasma is obtained regularly. This plasma was now characterized for the first time in detail  and it was shown that with just 750 W of RF power, a plasma of 2.3 eV electron temperature, 0.1 eV Ion Temperature and 1.2 x 10^18 per cubic meter plasma density was obtained for time scales of 20 minutes. This is an excellent basis for further developing the plasma to the density regime in which neutral depletion occurs by enhancing the RF power. Power supplies to go up to 15kW are available and are being prepared for implementation together with a second antenna. Also, the setup of a sophisticated LIF dye laser system is ongoing to characterize the ionization process by active laser spectroscopy. This system will be used in addition for direct validation of collisional radiative models developed for application in the island divertor at Wendelstein 7-X. in collaboration with Prof. Stuart Loch, Auburn University and Dr. Jorge Munoz-Burgos from the Johns-Hopkins University.

Bildschirmfoto 2016-04-04 um 10.10.51The existing LIF setup based on a  diode laser has been used to explore a new method to measure the ion velocity. The symmetry of the anomalous Zeemen effect is being used to avoid the detailed de-convulution of the measured LIF spectrum. The demonstration of this technique is being presented as a poster by Jonathan Green this week on the 19th International Conference on Atomics Processes in Plasmas, Paris, France.

This research activity is carried out in a close collaboration with Prof. Noah Hershkowitz, Emeritus Professor in our department,  Prof. Greg Severn, Chair of the Department of Physics at the University of San Diego and with Dr. Umair Siddiqui, Post-Doctoral researcher at the West Virginia University. Links to the MPEX team at the Oak Ridge National Laboratory (ORNL) and the group of T. Klinger/O. Grulke at IPP Greifswald operating larger scale, high power density facilities are being established.

News: 2015-12-10

First plasma in Wendelstein 7-X and first measurements for us!

The first official plasma has been obtained in Wendelstein 7-X today at 2015-12-10T12:28:15.182965421Z in the official W7-X time base. We participated remotely in the inauguration ceremony and could feel the excitement of all people involved on this truly historic step in fusion sciences. Congratulations to the entire Wendelstein 7-X team on this monumental step.

We participate on the device with several diagnostic projects and a numerical study on plasma edge transport. The diagnostics which the graduate students L. Stephey and T. Kremeyer prepared in the past year and intensively during long term research visits this summer took data during the first plasma. Below a plot of the neutral pressure in the plasma periphery measured with the UW Madison Penning gauge at W7-X is shown. This 1stPlasmaPGis a collaborative project with IPP Greifswald and Dr. Uwe Wenzel was visiting this week for detailed discussionson the next steps in the project and also for a visit to our vacuum laboratory in which we prepare this diagnostic component for W7-X. RA T. Kremeyer is responsible for this project and he will conduct his PhD research on neutral gas dynamics and plasma fueling at W7-X. This work is funded by the Department of Energy under grant DE-SC0014210.

RA L. Stephey from the HSX Laboratory in the Department for Electrical and Computer Engineering works under this grant to measure limiter heat and particle fluxes at W7-X and establish a single reservoir particle balance. A first image from the first plasma at W7-X taken with a CCD camera with a filter which L. Stephey initialized and activated for measurements  is shown below. It shows the plasma column in front of the limiter at the inner side of the vacuum vessel. This activity is a close collaboration with Dr. G. Wurden from the Los Alamos National Laboratory. L. Stephey is also responsible for on-site maintenance and operation of an Oak Ridge Filter Scope system. Both systems and supplemental general diagnostics will be the basis to assess the W7-X particle balance and make direct comparisons to HSX.

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We are excited to be part of the U.S. team working on W7-X and look forward to fruitful and exciting physics studies on this unique device.

 

News: 2015-11-05

Two papers published in the present volume of Physics of Plasmas!


Bildschirmfoto 2015-11-06 um 09.23.06One paper deals with the helical modulation of the electrostatic potential around edge magnetic islands in tokamaks and the similarity to ion and electron root transport in stellarators. This paper is the result of a collaborative study with Drs. G. Spizzo and G. Ciaccio from the Reversed Field Pinch experiment RFX in Padua, Italy and uses a Hamiltonian drift orbit code ORBIT developed by R. White from Princeton Plasma Physics Laboratory. This work was funded in part under the Early Career Award from the Department of Energy grant DE-SC0013911.

A second paper authored by Dr. H. Frerichs presents results of
Bildschirmfoto 2015-11-06 um 09.26.18a detailed study of the interaction with fractal stochastic field structures due to perturbed fixed points in tokamak plasmas and the occurrence of counter streaming 3-D flow pattern. This paper is based on plasma configurations as obtained at the DIII-D U.S. National Fusion facility in San Diego, CA. This work was funded in part under the Early Career Award from the Department of Energy grant DE-SC0013911.

News: 2015-07-16

Wendelstein 7-X stellarator is ready for operation!

The Wendelstein 7-X stellarator designed, constructed and soon to be operated by the Max-Plank-Institute for Plasma Physics in Greifswald Germany is ready for operation. In the past couple of weeks the superconducting magnetic coils system of this first of its kind quasi-isodynamic optimized stellarator have been commissioned. Last week, mapping of the magnetic field structure with electron path of flight emission has shown that good magnetic flux surfaces are generated. Characteristic resonant surfaces in the magnetic structure have been identified and initial comparison to field line modeling has shown a good agreement with the predicted location of the flux surfaces. See recent press release for more information (http://www.ipp.mpg.de/3897638/07_15).

The device is now ready for operation and awaiting the operation license from the state government in Meckelnburg-Vorpommern. Congratulations to the entire W7-X team for this success. We are looking forward to work on this world-class facility.

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We are involved within the IPP-U.S. collaboration and contribute with experimental and numerical analysis of plasma edge transport and neutral/impurity household in the edge plasma to the program. Below is a figure from EMC3-EIRENE modeling (courtesy of Florian Effenberg, 3rd year grad student) showing the radiation distribution of double ionized carbon in the helical scrape-off layer during the limiter startup phase. This work is funded by the Department of Energy under grant DE-SC0013911.

 News: 2015-05-06

We received two more grants from the Department of Energy (DoE)!

(1) DoE Early Career Award funds work on “Plasma Materials Interaction with Three-Dimensional Plasma Boundaries”

(2) DoE Grant for International Stellarator Collaboration together with the Auburn University for work on “Three-dimensional equilibrium stability and its impact on island divertor performance at Wendelstein 7-X”

News: 2015-05-06

NSF funds our work on“Understanding of neutral particle physics to generate a helicon wave driven high density laboratory plasma”  as NSF-CAREER award.

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2015-02-18 – 3D Striation pattern paper under 2014 Highlights in Nuclear Fusion

The paper

Formation of a three-dimensional plasma boundary after decay of the plasma response to resonant magnetic perturbation fields
O. Schmitz, T.E. Evans, M.E. Fenstermacher, M.J. Lanctot, C.L. Lasnier, S. Mordijck, R.A. Moyer, and H. Reimerdes Nucl. Fusion 54, 012001 (2014)

is  among the 2014 Highlights in the IoP journal Nuclear Fusion.

 

2015-01-10Paper by Heinke Frerichs under 2014 Editor’s pick of Physics of Plasmas.

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The paper “Striation pattern of target and heat fluxes in three-dimensional simulations for DIII-D” is among the papers presented as Editor’s pick for 2014 in the AIP journal Physics of Plasmas. Congratulations Heinke!

2014-08-22 — Good News:  First plasma was launched at MARIA.

firstPlasma_2014

On September 16, 2014 the first plasma was launched in the renovated Magnetized AnisotRopic Ion-distribution Apparatus (MARIA). Victoria Winters, the graduate student working on the device accomplished this important step together with Umiar Siddiqui, a former PhD student of Prof. Hershkowitz who has setup the device.

The device will be a multi-purpose high density, low temperature plasma test facility. We will address atomic physics as well as plasma material interaction issues on the setup. It is planned to enhance the device for high density operation at detached divertor temperature conditions which requires enhancing the helicon wave power, coupling ion cyclotron heating and also improving the neutral fueling capacity.

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2014-08-22 — Good news: The first grant was awarded by the Department of Energy to our research group for work at NSTX-Upgrade!

Title: Control of Neutral Fueling and Helium Exhaust in NSTX-Upgrade Plasmas by Three-Dimensional Magnetic Control Fields. DoE Grant number DE-SC0012315.

Short description (public abstract):

This research targets the understanding and optimization of the physical processes that define fueling and exhaust of high temperature plasmas, which are being explored as a means to accomplish energy production by nuclear fusion. Very much like in a combustion engine, a well-controlled amount of fueling and efficient exhaust has to be realized to keep the burn media clean and at desired pressures for sustained energy production. In fusion plasma, hydrogen isotopes represent the fuel while helium is the ash (the “fusion product”) from the reaction cycle. Hydrogen is supplied from the outside into the outer boundary of the plasma. In contrast, the helium is born predominantly inside of the plasma. Hence, an efficient control mechanism for fueling and exhaust also deals with desired inward transport of fuel and outward transport of helium and impurities.

Three-dimensional magnetic fields have been used as an innovative control tool for plasma edge transport and for dedicated interaction with the neutral particle source at the surrounding wall elements. They will be employed in this research to address neutral fueling, as a particularly important topic in the spherical tokamak (ST) NSTX-Upgrade. The ST magnetic confinement concept offers more stable, high performance plasma operation at reduced system size. It therefore is an attractive candidate for compact fusion energy development facilities. However, the concept so far suffers from weak plasma density control, which limits the plasma regimes accomplished as well as the duration of an experiment pulse. This research aims on exploring if dedicated density control including reduction of impurity contamination of the plasma and sufficient helium exhaust can be accomplished by use of three-dimensional magnetic control fields. The work encompasses development and validation of suitable numerical tools to gain predictive capability for future devices and reactor scale experiments.