The authors present the results of experimental studies on a discharge in the Tokamak-6 device with a specific instability whose appearance coincides with a sudden jump in the transverse energy of the plasma. It is shown that in these discharge regimes the current is carried by a relatively small group of runaway electrons with energies of 10 - 500 keV, while the main plasma with n̄e ≃ 3 × 1012 cm−3 has a low temperature (Te, Ti ∼ 10 eV) and carries practically no current. Preionization of the working gas or the introduction of a relatively small (∼ 2 – 3%) local inhomogeneity in the longitudinal magnetic field converts these runaway discharges into normal Tokamak discharges.
This paper describes the updates to and analysis of the International Tokamak Physics Activity (ITPA) Global H-Mode Confinement Database version 3 (DB3) over the period 1994-2004. Data have now been collected from 18 machines of different sizes and shapes: ASDEX, ASDEX
The condition of the latest version of the ELMy H-mode database has been re-examined. It is shown that there is bias in the ordinary least squares regression for some of the variables. To address these shortcomings three different techniques are employed: (a) principal component regression, (b) an error in variables technique and (c) the selection of a better conditioned dataset with fewer variables. Scalings in terms of the dimensionless physics variables, as well as the standard set of engineering variables, are also derived. The new scalings give a very similar performance for existing scalings for ITER at the standard βn of 1.6, but a much improved performance at higher βn.
The operational space (I p − n) for long-pulse scenarios ( t burn ∼ 1000 s, Q 5) of ITER has been assessed by 1.5D core transport modelling with pedestal parameters predicted by the EPED1 code by a set of transport codes under a joint activity carried out by the Integrated Operational Scenario ITPA group. The analyses include the majority of transport models (CDBM, GLF23, Bohm/gyroBohm (BgB), MMM7.1, MMM95, Weiland, scaling-based) presently used for interpretation of experiments and ITER predictions. The EPED1 code was modified to take into account boundary conditions predicted by SOLPS4 for ITER. In contrast to standard EPED1 assumptions, EPED1 with the SOLPS boundary conditions predicts no degradation of the pedestal pressure as density is reduced. Lowering the plasma density to n e ∼ (5-6) × 10 19 m −3 leads to an increased plasma temperature (similar pedestal pressure), which reduces the loop voltage and increases the duration of the burn phase to t burn ∼ 1000 s with Q 5 for I p 13 MA at moderate normalized pressure (β N ∼ 2). These ITER plasmas require the same level of additional heating power as the reference Q = 10 inductive scenario at 15 MA (33 MW NBI and 17-20 MW EC heating and current drive power). However, unlike the 'hybrid' scenarios considered previously, these H-mode plasmas do not require specially shaped q profiles nor improved confinement in the core for the transport models considered in this study. Thus, these medium density H-mode plasma scenarios with I p 13 MA present an attractive alternative to hybrid scenarios to achieve ITER's long-pulse Q 5 scenario and deserve further analysis and experimental demonstration in present tokamaks.
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