Publications by Boris Stepanov

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The European DEMO, i.e. the demonstration fusion power plant designed in the framework of the Roadmap to Fusion Electricity by the EUROfusion Consortium, is approaching the end of the pre-conceptual design phase, to be accomplished with a Gate Review in 20 ...

Five medium size NbTi cable-in-conduit conductors with parametric variations in the cable layout were fabricated of three different strands to investigate their DC performance, AC loss behaviour and transient stability by means of the SULTAN facility. A co ...

After completing the qualification tests of the ITER cable-in-conduit conductors (CICC), the tests of samples from the series manufacture are running in the SULTAN test facility in Villigen, Switzerland. The key test for the conductor samples is the current sharing temperature, Tcs, at the nominal operating field and current, i.e. the maximum temperature at which the conductors operate before developing an electric field of 10 μV/m. All the TF samples fulfilled the ITER requirement of Tcs ≥ 5.8 K after 1000

The Swiss Plasma Center (SPC) has developed a layout of Toroidal Field (TF) coil for EUROfusion DEMO tokamak, based on the reference tokamak baseline of 2015. Each TF coil winding pack is wound with graded Nb3Sn conductors and consists of 12 single layers, ...

The coupling currents loss for fusion conductors is frequently assessed applying a sinusoidal field sweep of fixed, small amplitude and variable frequency. From the initial slope of the loss curve, the coupling loss time constant is derived and applied in ...

High Temperature Superconductors (HTS) are promising materials for future fusion magnets. One of HTS conductors' main issues is the quench protection: the quench develops much slower than in LTS, delaying the quench detection by voltage monitoring and caus ...

The German SUpraLeiterTest ANlage (SULTAN) test facility at the Centre de Recherches en Physique des Plasma (CRPP), Villigen, is a worldwide unique tool to test high current superconductors over a broad range of operating conditions. The key component of the facility is a set of forced flow superconducting coils to generate a background field up to I I T. A flux pump supplies the test sample with current up to 100 kA. A set of pulsed coils generates a transverse, time varying field, with amplitude up to 4 T

The EUROfusion DEMO is being designed as the fusion machine to be built after ITER. During the preconceptual phase, several design options are investigated by theoretical analyses as well as tests on newly developed conductor prototypes. One design option ...

Five subsize NbTi cable-in-conduit conductors with parametric variations were fabricated and their DC performance was tested in the SULTAN facility. A comparison of the measured strand data and the cable performances clearly indicates that the current carrying capacity of the conductors is considerably reduced due to the self-field effect. This result reflects that because of the high transverse resistance the interstrand current sharing is not very efficient. Furthermore, the take-off electric field was fo

During the test of ITER conductors at nominal conditions, a degradation of the current sharing temperature has been observed after electromagnetic cyclic loading. Rather than focusing on the microscopic phenomena at the origin of the degradation, the degra ...

The series production of Nb3Sn and NbTi cable-inconduit conductors (CICC) for the winding of various coils in the International Thermonuclear Experimental Reactor (ITER) magnet system is being completed in 2015. The tests of the ITER conductor samples are ...

The ITER CICC will undergo a number of cool-down and warm-up cycles over the lifetime of the plant. The standard SULTAN based ITER conductor qualification test normally includes one thermal cycle in the test sequence. In many samples a performance degradation was observed following this thermal loading. In order to investigate the effect of multiple thermal cycles on the TF conductor short sample, additional repeated thermal cycles to liquid nitrogen temperature were carried out on the left leg of the CNTF3

Direct current tests performed in the past on the conductor samples of the toroidal field (TF) ITER coils revealed degradation of current sharing temperature, T-cs. The degradation progresses with repetitive electromagnetic loading, and also with thermal c ...

Prototype conductors for the ITER magnets have been tested extensively in the SULTAN facility at CRPP in the last decade. The in-depth characterization of the high current carrying conductors provided a valuable feedback in the design, with performance optimization and cost reduction. From the transient stability results on full size, short length conductor samples, the temperature margin required to withstand the plasma disruption has been found to be much smaller than originally assumed. A comparison betw

The experiments of Cable-in conduit conductor (CICC) short samples with high proportion of segregated copper strands have been carried out in SULTAN facility last September. These experiments aimed to investigate transient stability and AC losses of CICC conductor coated with different resistive barriers (Pb-30Sn-2Sb or Ni plating on strands) and to check the design of PF and TF CICC for HT-7U magnets. The resistive barriers' influences on the stability and AC losses of CICC are evaluated. These experimenta

A short sample of the NbTi cable-in-conduit conductor (CICC) manufactured for the ITER PF insert coil has been tested in the SULTAN facility at CRPP. The short sample consists of two paired conductor sections, identical except for the sub-cable and outer w ...

Two full-size conductor samples using advanced Nb3Sn strands were tested in the SULTAN facility in 2005-2006 within (I,B,T) ranges close to the ITER operating conditions (B-MAX similar to 12 T, T similar to 5 K). Each sample includes two conductor legs, co ...

Various tests, either on full-size joint samples or on model coils confirmed that current distribution may play a crucial role in the electrical behaviour of CICC in operating conditions. In order to evaluate its influence, CEA developed a code (ENSIC) the main feature of which is a CICC electrical model including a discrete resistive network associated with superconducting lengths. Longitudinal and transverse resistances are also modeled, representing either joint or conductor. In our paper we will present

The contact resistance distribution among the current-carrying elements of three ITER conductor terminations is measured in the JORDI (JOint Resistance DIstribution) test facility at CRPP. One sample is based on Nb3Sn strands, the other two are NbTi cable- ...

In summer 2015, a new reference baseline is issued for the DEMO EUROfusion tokamak. Thereafter, the toroidal field (TF) coils have been updated with the new layout of the react-and-wind conductor proposed by the Swiss Plasma Center (SPC). Each TF coil cons ...

Boris Stepanov

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Advance in the conceptual design of the European DEMO magnet system

DC performance, AC loss and transient field stability of five medium size NbTi cable-in-conduit conductors with parametric variations

Summary of the Test Results of ITER Conductors in SULTAN

Inter-Layer Joint of Nb3Sn React&Wind Cables for Fusion Magnets

A new test method of AC loss assessment for fusion conductors

Upgrade and Commissioning of the SULTAN Facility to Host Quench Experiments on HTS High Current Conductors

Upgrade of operating range for SULTAN test facility

AC Loss Measurement of the DEMO TF React&Wind Conductor Prototype No. 2

DC performance of subsize NbTi cable-in-conduit conductors

Statistical analysis of the current-sharing temperature evolution in Nb3Sn cable-in-conduit-conductors for ITER

Statistics of Test Results for the ITER Nb3Sn and NbTi Conductors in the SULTAN Facility

Effect of Thermal Loading on Nb3Sn CICC Performance

T-cs degradation of ITER TF samples due to fast current discharges

Recent results from R&D on superconductors at CRPP

Test results and analyses of conductor short samples for HT-7U

Test results of the ITER PF insert conductor short sample in SULTAN

Analysis of DC properties and current distribution in TFAS ITER conductor samples using high J(C) Nb3Sn advanced strands

Effect of current distribution on the voltage-temperature characteristics: study of the NbTiPF-FSJS sample for ITER

Results of contact resistance distribution in NbTi and Nb3SnITER conductor termination

Inter-Layer Joint for the TF Coils of DEMO-Design and Test Results