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ABSTRACT: The main ECRH scenarios for the W7-X Stellarator are described. Both X2 (low and moderate densities) and O2 scenarios (high density) have been studied. Since O2 scenario cannot be realized without pre-heating, transition from X2 to O2 scenarios has been discussed. Due to a lack of Ohmic transformer, only ECCD is available for compensating the bootstrap current and for controlling the edge rotational transform value. The efficiency of ECCD for all main scenarios has been estimated. All simulations have been performed by a 1D transport code coupled self-consistently with ray-tracing code.
17th Joint Workshop on Electron Cyclotron Emission and Electron Cyclotron Resonance Heating, Deurne, The Netherland; 05/2012
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M. Thumm,
G. Gantenbein, V. Erckmann,
S. Illy,
S. Kern,
W. Kasparek,
C. Lechte,
W. Leonhardt,
C. Liévin,
A. Samartsev,
A. Schlaich,
M. Schmid
[show abstract]
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ABSTRACT: A 10 MW, 140 GHz ECRH system with a pulse duration of 30 minutes is currently under construction for the stellarator W7-X at Greifswald. The RF power will be provided by 10 gyrotrons. A European collaboration has been established to develop and build 9 (out of 10) tubes each with an output power of 1 MW for continuous wave (CW) operation. This contribution reports on recent results with the series gyrotrons.
Vacuum Electronics Conference (IVEC), 2011 IEEE International; 03/2011
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G. Gantenbein, V. Erckmann,
S. Illy,
S. Kern,
W. Kasparek,
C. Lechte,
W. Leonhardt,
C. Liévin,
A. Samartsev,
A. Schlaich,
M. Schmid,
M. Thumm
[show abstract]
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ABSTRACT: A 10 MW, 140 GHz ECH system is currently under construction for the stellarator W7-X. The RF power will be provided by 10 tubes. A European collaboration has been established to develop and build 9 (out of 10) gyrotrons each with an output power of 1 MW for continuous wave (CW) operation. This contribution reports on recent results with the series gyrotrons.
Infrared Millimeter and Terahertz Waves (IRMMW-THz), 2010 35th International Conference on; 10/2010
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ABSTRACT: New devices and concepts for fast switching and combination of millimeter-wave beams at high power are being developed. From the first prototype measurements up to high-power running tests, their properties and limitations are increasingly known. The development of new concepts for use in fusion experiments is continuous: the status of research, with focus on new achievements on the theoretical modeling of resonating diplexers with dielectric beam splitters is reported.
Infrared Millimeter and Terahertz Waves (IRMMW-THz), 2010 35th International Conference on; 10/2010
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W.A. Bongers,
W. Kasparek,
A.J.H. Donné,
A.P.H. Goede,
M.R. de Baar,
F.C. Schüller, V. Erckmann,
J. Stober,
E. Westerhof,
F.J. Amerongen,
B.A. Hennen,
P.W.J.M. Nuij,
J.W. Oosterbeek,
D.M.S. Ronden,
D.J. Thoen,
T. Tongerlo,
D. Wagner
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ABSTRACT: Experiments on TEXTOR have successfully demonstrated the proof of principle of using Electron Cyclotron Emission (ECE) measured along the Electron Cyclotron Resonance Heating (ECRH) line-of-sight for the control of magnetohydrodynamic (MHD) modes. This work, which was done with a quasi-optical system, motivates the further development and implementation of a similar, but in-waveguide system for detection and control of Neoclassical Tearing Mode (NTM) in larger fusion machines. Progress on the implementation of such a system on ASDEX-Upgrade, based on waveguides equipped with a Fast Directional Switch (FADIS), is presented. Since FADIS, will be installed at ASDEX, to switch the gyrotron power between different launchers, FADIS can also be employed as a frequency filter serving the purpose of separating a low-power ECE signal from the high power ECRH radiation as required in the co-aligned ECE-ECRH setup. Because additional absorptive filtering is required after the FADIS ECE output in and a non resonant two-beam Mach-Zehnder-type interferometer was chosen. This system has been built and partially tested.
Infrared Millimeter and Terahertz Waves (IRMMW-THz), 2010 35th International Conference on; 10/2010
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D Zhang,
R Burhenn,
R Koenig,
L Giannone,
P A Grodzki,
B Klein,
K Grosser,
J Baldzuhn,
K Ewert, V Erckmann,
M Hirsch,
H P Laqua,
J W Oosterbeek
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ABSTRACT: A bolometric diagnostic system with features necessary for steady-state operation in the superconducting stellarator W7-X was designed. During a pulse length of 1800 s with an ECRH (electron cyclotron resonance heating) power of 10 MW, the components suffer not only from a large thermal load but also from stray radiation of the nonabsorbed isotropic microwaves. This paper gives an overview of the technical problems encountered during the design work and the solutions to individual problems to meet the special requirements in W7-X, e.g., component thermal protection, detector offset thermal drift suppression, as well as a microwave shielding technique.
The Review of scientific instruments 10/2010; 81(10):10E134. · 1.52 Impact Factor
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A. Bruschi, V. Erckmann,
W. Kasparek,
M.I. Petelin,
M. Thumm,
W. Bin,
S. Cirant,
O. D'Arcangelo,
F. Hollmann,
L. Lubyako,
F. Noke,
B. Plaum,
F. Purps,
H. Zohm
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ABSTRACT: Electron Cyclotron Resonance Heating (ECRH) systems for next step large fusion-devices operate at a Continuous Wave (CW) power well beyond 10 MW generated by a large number of gyrotrons with typically 1 MW power per unit. The combination of the power of two (or more) gyrotrons and switching of the power between different launchers for different physics applications is an attractive feature for such systems. The combination of beams from different gyrotrons would reduce the number of transmission lines and the requirements on port space. Fast switching between two antennas synchronously with the Magneto-Hydro Dynamic (MHD) modes frequency would increase the efficiency of mode stabilization. Both combination and switching as well as power sharing between different ports can be performed with high-power four-port diplexers using small frequency differences or small frequency-shift keying of the gyrotrons, respectively. Fast directional switches (FADIS) and beam combiners (BC) can be designed on the basis of different physical mechanisms: some selected design variants were investigated and the results are presented. Considerations on the integration of FADIS/BC's into large ECRH systems and their use in test arrangements are presented.
IEEE Transactions on Plasma Science 07/2010; · 1.17 Impact Factor
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ABSTRACT: The next step in the Wendelstein stellarator line is the large superconducting device Wendelstein 7-X (W7-X), which is currently under construction in Greifswald. Steady-state operation is an intrinsic feature of stellarators, and one key element of the W7-X mission is to demonstrate steady-state operation at reactor-relevant plasma conditions, as required for an economic fusion reactor. Such steady-state operation requires development of special technologies to be discussed in this paper.
IEEE Transactions on Plasma Science 04/2010; · 1.17 Impact Factor
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ABSTRACT: High power cw gyrotrons operate with an RF-power of up to 1 MW and efficiencies of 35-60 %. The waste power remains in the spent electron-beam and must be dissipated in the gyrotron-collector. Such collectors have strong sophisticated water-cooling systems for continuous operation. The electron-beam strike area on the collector surface is moved between an upper and a lower turning point by sweeping magnet fields in order to achieve a smooth power deposition.
Infrared, Millimeter, and Terahertz Waves, 2009. IRMMW-THz 2009. 34th International Conference on; 10/2009
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ABSTRACT: The next step in the Wendelstein stellarator line is the large superconducting device Wendelstein 7-X, presently under construction in Greifswald. Steady-state operation is an intrinsic feature of stellarators, and one key element of the Wendelstein 7- X mission is to demonstrate steady-state operation at reactor relevant plasma conditions, as required for an economic fusion reactor. Such steady-state operation requires development of special technogies to be discussed in this paper.
Fusion Engineering, 2009. SOFE 2009. 23rd IEEE/NPSS Symposium on; 07/2009
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ABSTRACT: This paper discusses the use of some relatively new quasi-optical structures for configuring high-power gyrotron-based millimeter-wave systems for plasma fusion, microwave technologies, electron accelerators, radar, and communication. Techniques for wave combining and switching, and for wave matching to transmitters, receivers, and antennas are analyzed.
IEEE Transactions on Electron Devices 06/2009; · 2.32 Impact Factor
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R König,
J Cantarini,
H Dreier, V Erckmann,
D Hildebrandt,
M Hirsch,
G Kocsis,
P Kornejew,
M Laux,
H Laqua,
E Pasch,
S Recsei,
V Szabó,
H Thomsen,
A Weller,
A Werner,
R Wolf,
M Y Ye,
S Zoletnik
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ABSTRACT: The stellarator Wendelstein 7-X will allow for quasicontinuous operation with the duration only being limited to two 30 min discharges per day, at a continuous heating power of 10 MW electron cyclotron resonance heating (ECRH) at 140 GHz, by the capacity of the cooling water reservoir. This will result in high thermal loads on all plasma facing components of 50-100 kW/m(2) from radiation alone and of up to about 500 kW/m(2) on components additionally exposed to convective loads. In high density scenarios toroidally varying ECRH stray radiation levels of 50-200 kW/m(2) need to be coped with, requiring careful material selection and different shielding and hardening techniques. Furthermore, a gradual buildup of coatings on plasma facing optical components, which without any measures being taken, would lead to high transmission losses already within a few days of long pulse operation (equivalent to about 1 year of operation in pulsed devices like JET or ASDEX-upgrade) and therefore needs to be prevented as much as possible. In addition in situ cleaning as well as absolute calibration techniques need to be developed for all plasma facing optical systems. Here we report about some of our efforts to find, for various types of diagnostics, ways to cope with these adverse effects. Moreover, we give a few examples for individual diagnostic specific issues with respect to quasicontinuous operation, such as the development of a special integrator for the magnetic diagnostics as well as special interferometer types which can cope with unavoidable vibrations and slow path length changes due to, e.g., thermal expansion of the plasma vessel.
The Review of scientific instruments 11/2008; 79(10):10F337. · 1.52 Impact Factor
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ABSTRACT: Amplitude modulation of the 50 Hz AC sweeping current of transversal sweeping systems reduces the maximum averaged power density on the collector wall as compared to an unmodulated system. This makes transversal sweeping a very attractive alternative to conventional longitudinal sweeping systems for high power CW Gyrotrons.
Infrared, Millimeter and Terahertz Waves, 2008. IRMMW-THz 2008. 33rd International Conference on; 10/2008
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ABSTRACT: The development of the ECRH-antennas and in-vessel components for cw operation in the Wendelstein7-X stellarator is presented together with first test results.
Infrared, Millimeter and Terahertz Waves, 2008. IRMMW-THz 2008. 33rd International Conference on; 10/2008
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G. Gantenbein,
H. Braune,
G. Dammertz, V. Erckmann,
S. Ely,
S. Kern,
W. Kasparek,
H.P. Laqua,
C. Lechte,
F. Legrand,
W. Leonhardt,
C. Lievin,
G. Michele,
B. Piosczyk,
O. Prinz,
M. Schmid,
M. Thumm
[show abstract]
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ABSTRACT: Summary form only given. A 10 MW ECRH system is currently under construction for the stellarator W7-X which will be built up and operated by IPP in Greifswald, Germany. The RF power will be provided by 10 gyrotrons. A European collaboration has been established to develop and build the 10 gyrotrons each with an output power of 1 MW for continuous wave (CW) operation. Nine gyrotrons are being manufactured by Thales Electron Devices (TED), Velizy, France, one gyrotron was produced by CPI, Palo Alto, CA and has passed the acceptance tests at IPP. The acceptance tests of the TED gyrotrons are performed at the test stand at FZK and on site at IPP. The first series tube yielded a total output power of 0.98 MW, with an efficiency of 31 % (with non-depressed collector) in short pulse operation and of 0.92 MW in pulses of 1800 s (efficiency of almost 45 % at a depression voltage of 29 kV). The Gaussian mode output power was 0.91 MW. The RF power, measured in a calorimetric load at the end of a 25 m long quasi-optical transmission line with seven mirrors, was 0.87 MW. In this contribution topical results of the series gyrotrons will be reported.
Plasma Science, 2008. ICOPS 2008. IEEE 35th International Conference on; 07/2008
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ABSTRACT: The paper describes some new oversized, quasi-optical, electrodynamic components applicable to high-power millimeter-wave systems.
Vacuum Electronics Conference, 2008. IVEC 2008. IEEE International; 05/2008
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M. Thumm,
P. Brand,
H. Braune,
G. Dammertz, V. Erckmann,
G. Gantenbein,
S. Illy,
W. Kasparek,
H.P. Laqua,
C. Lechte,
W. Leonhardt,
G. Michel,
G. Neffe,
B. Piosczyk,
M. Schmid,
M. Weissgerber
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ABSTRACT: During the last years, electron cyclotron heating (ECH) was proven to be one of the most attractive heating schemes for stellarators because it provides net-current-free plasma startup and heating. Both the stellarator Wendelstein 7-X (W7-X), which is under construction at the Max-Planck-Institut fu umlr Plasmaphysik, Greifswald, Germany, and the International Thermonuclear Experimental Reactor (ITER) tokamak, which will be built in Cadarache, France, will be equipped with a strong ECH and current-drive system. Both systems are comparable in frequency and have continuous-wave capability (140 GHz, 10 MW for W7-X and 170 GHz, 24 MW for ITER). The commissioning of the ECH plant for W7-X is well underway; the status of the project and the first integrated full-power test results from two modules are reported and may provide valuable input for the ITER plant. The ten gyrotrons at W7-X will be arranged in two subgroups symmetrically to a central beam duct in the ECH hall. The RF wave of each subgroup will be combined and transmitted by a purely optical multibeam-waveguide (MBWG) transmission line from the gyrotrons to the torus. The combination of five 1 MW gyrotron beams to one beam line with a power of 5 MW reduces the complexity of the system considerably. The single- and MBWG mirrors and the polarizers have been manufactured. Cold tests of a full-size uncooled prototype line delivered an efficiency exceeding 90%. The microwave power will be launched to the plasma through ten chemical-vapor-deposited-diamond barrier windows and in-vessel quasi-optical plug-in launchers, allowing each 1-MW RF beam to be steered independently. The polarization, as well as the poloidal and toroidal launch angles, will be adjusted individually to provide optimum conditions for different heating and current-drive scenarios.
IEEE Transactions on Plasma Science 05/2008; · 1.17 Impact Factor
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ABSTRACT: A fast directional switch (FADIS) is described, which allows controlled switching of high-power microwaves between two outputs. A possible application could be synchronous stabilization of neoclassical tearing modes (NTMs). Generally, the device can be used to share the installed EC power between different types of launchers or different applications (e.g. in ITER, midplane/upper launcher). The switching is performed electronically without moving parts by a small frequency-shift keying of the gyrotron (some tens of megahertz), and a narrow-band diplexer. The device can be operated as a beam combiner also, which offers attractive transmission perspectives in multi-megawatt ECRH systems. In addition, these diplexers are useful for plasma diagnostic systems employing high-power sources due to their filter characteristics.The principle and the design of a four-port quasi-optical resonator diplexer is presented. Low-power measurements of switching contrast, mode purity and efficiency show good agreement with theory. Preliminary frequency modulation characteristics of gyrotrons are shown, and first results from high-power switching experiments using the ECRH system for W7-X are presented.
Nuclear Fusion 04/2008; 48(5):054010. · 4.09 Impact Factor
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M Hirsch,
J Baldzuhn,
C Beidler,
R Brakel,
R Burhenn,
A Dinklage,
H Ehmler,
M Endler, V Erckmann,
Y Feng, [......],
K McCormick,
F Sardei,
E Speth,
U Stroth,
F Wagner,
A Weller,
A Werner,
H Wobig,
S Zoletnik,
for the Team
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ABSTRACT: Wendelstein 7-AS was the first modular stellarator device to test some basic elements of stellarator optimization: a reduced Shafranov shift and improved stability properties resulted in β-values up to 3.4% (at 0.9 T). This operational limit was determined by power balance and impurity radiation without noticeable degradation of stability or a violent collapse. The partial reduction of neoclassical transport could be verified in agreement with calculations indicating the feasibility of the concept of drift optimization. A full neoclassical optimization, in particular a minimization of the bootstrap current was beyond the scope of this project. A variety of non-ohmic heating and current drive scenarios by ICRH, NBI and in particular, ECRH were tested and compared successfully with their theoretical predictions. Besides, new heating schemes of overdense plasmas were developed such as RF mode conversion heating—Ordinary mode, Extraordinary mode, Bernstein-wave (OXB) heating—or 2nd harmonic O-mode (O2) heating. The energy confinement was about a factor of 2 above ISS95 without degradation near operational boundaries. A number of improved confinement regimes such as core electron-root confinement with central Te ≤ 7 keV and regimes with strongly sheared radial electric field at the plasma edge resulting in Ti ≤ 1.7 keV were obtained. As the first non-tokamak device, W7-AS achieved the H-mode and moreover developed a high density H-mode regime (HDH) with strongly reduced impurity confinement that allowed quasi-steady-state operation (τ ≈ 65 τE) at densities (at 2.5 T). The first island divertor was tested successfully and operated with stable partial detachment in agreement with numerical simulations. With these results W7-AS laid the physics background for operation of an optimized low-shear steady-state stellarator.
Plasma Physics and Controlled Fusion 03/2008; 50(5):053001. · 2.42 Impact Factor
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ABSTRACT: In order to avoid significant change of the edge value of the rotational transform in the W7-X stellarator, electron cyclotron current drive (ECCD) will be used for compensating the bootstrap current (an ohmic transformer is absent). Since ECCD efficiency is quite sensitive not only to the plasma parameters, but also to the magnetic configuration, it is an important task to estimate properly the range of ECCD values taking into account all features of the magnetic configuration, and to assess its ability to counteract the residual bootstrap current. In this work we analyze the requisite ECCD for scenarios with the different magnetic configurations with help of the ray-tracing code TRAVIS, coupled self-consistently with the 1D transport code. The neoclassical transport modeling is based on the DKES database of mono-energetic transport coefficients.
11/2007;
