Y. Miura

ITER L mode confinement database

This special topic describes the contents of an L mode database that has been compiled with data from Alcator C-Mod, ASDEX, DIII, DIII-D, FTU, JET, JFT-2M, JT-60, PBX-M, PDX, T-10, TEXTOR, TFTR and Tore Supra. The database consists of a total of 2938 entries, 1881 of which are in the L phase while 922 are ohmically heated only (ohmic). Each entry contains up to 95 descriptive parameters, including global and kinetic information, machine conditioning and configuration. The special topic presents a description of the database and the variables contained therein, and it also presents global and thermal scalings along with predictions for ITER. The L mode thermal confinement time scaling, determined from a subset of 1312 entries for which the τE,th are provided, is τE,th = 0.023Ip0.96BT0.03R1.83(R/a)0.06 κ0.64ne0.40Meff0.20P-0.73 in units of seconds, megamps, teslas, metres, -, -, 10-9 m-1

Global energy confinement H-mode database for ITER

Describes the content of an H-mode confinement database that has been assembled for the ITER project. Data were collected from six machines of different sizes and shapes: ASDEX, DIII-D, JET, JFT-2M, PBX-M and PDX. A detailed description of the criteria used in the selection of the data and the definition of each of the variables is given. The authors also present an analysis of the conditions of the database, the scalings (power law and offset linear) of the data with both dimensional and dimensionless variables, and predictions of the expected confinement time for ITER

ITER H mode confinement database update

This paper describes an update of the H mode confinement database that has been assembled for the ITER project. Data were collected from six machines of different sizes and shapes: ASDEX, DIII-D, JET, JFT-2M, PBX-M and PDX. The updated database contains better estimates of fast ion energy content and thermal energy confinement times, discharges with RF heating, data using boronization, beryllium and pellets, more systematic parameter scans, and other features. The list of variables in the database has been expanded, and the selection criteria for the standard dataset have been modified. We also present simple scalings of the total and thermal energy confinement time to the new dataset

H mode power threshold database for ITER

The ITER Threshold Database, which at present comprises data from nine divertor tokamaks, is described. The main results are presented and discussed. The properties and dependences of the power threshold in individual devices are reviewed. In particular, the analysis shows a rather general linear dependence on magnetic field, but a non-monotonic density dependence that varies from device to device. Investigation of the combined database suggests that the threshold dependence Pthres approximately=0.3neBT2.5 shows reasonable agreement with the data. This expression yields Pthres approximately=150 MW at a density of 0.5*1020 m-3 for ITER. Other expressions with weaker size dependence, and therefore lower threshold power for ITER, are also discussed. Their agreement with the present data is poorer than that of the above expression. In addition, the database is investigated by statistical discriminant analysis. The edge data included at present are described and discussed. Finally, there is a discussion of the implications of the results for ITER

Results from the ITER H-mode threshold database

The ITER H-mode threshold database, which currently includes data from nine divertor tokamaks is presented. The results obtained for single devices and for the combined data set are given. The similarities and differences between the different devices are shown. Possible expressions for the H-mode threshold in agreement with the data are given and the extrapolation to ITER is discussed.

Investigation of edge localized mode in the JFT-2M Tokamak

The edge localized mode (ELM) was investigated in detail on the JFT-2M tokamak. Spatially, a pivot point was observed inside the separatrix flux surface. Temporally, an ELM event starts from the precursor oscillation, of which the growth rate was about 40 mu s. Another high frequency oscillation with about 300 kHz was found during the magnetic fluctuation burst. Just after the burst, a poloidal electric current (ELM current) was induced in the scrape-off layer. During the ELM, the particle flux to the divertor plates was transiently enhanced by a factor of about 4. The profile of the induced flux was 2-3 times broader than that in the ELM-free period. The total particle flux induced by one ELM was evaluated to be about 5% of the total plasma particles. The ELM current is characterized by its direction and its large fluctuation level. Furthermore, it was found that a large opposite current exists near the strike points on both divertor plates

Thickness of ExB velocity shear at the plasma edge in the JFT-2M H-mode

The poloidal rotation velocity profiles both in L- and H-mode measured in JAERI Fusion Torus 2 Modified (JFT-2M) (Phys. Rev. Lett. 65, 1364 (1990)) are compared with H-mode models based on ion orbit loss. The profiles of poloidal rotation velocity measured in L- and H-mode are consistent with the calculation which consists of ion orbit loss model. The observed dependence of the thickness of the layer of high shear Er on poloidal gyro-radius is explained by the radial transport of poloidal rotation velocity.

Rapid change of ion energy distribution and floating potential at L/H transition in the JFT-2M tokamak

Rapid changes of the main ion energy distribution at transitions from L-to-H, H-to-L and during ELMs are studied by time of flight neutral measurements in the JFT-2M tokamak. At the L to H transition, 200-400 mu s prior to the start of Halpha drop, an increase of the high energy neutral flux above an energy of 200 eV is observed. An energy of higher than 200 eV for hydrogen corresponds to the collisionless condition v*i<l just inside the separatrix. The change of the main ion energy distribution after sawtooth crash during an L-mode phase is also studied. The change of the ion energy distribution just after sawtooth crash is the same as that at L/H-transition. The floating potential measured in the SOL also shows the rapid jump to more positive just after the sawtooth crash (at the same time as the change of an ion energy distribution). This shows the increase of ion outflux in the SOL and might correspond to the change in the ion energy distribution. This may be the reason why most H-modes are triggered by a sawtooth. These observations support theories predicting an important role for ion loss for the L/H-transition.

Geometric dependence of the energy confinement time scaling for H-mode discharges

The dependence of the H-mode energy confinement time τE on the plasma elongation and the divertor configuration is studied. A regression analysis of the H-mode database is presented in which the dependence on the closed/open divertor configuration, estimated from the ASDEX experiments, is included. The dependence of τE on the elongation factor k is found to be positive (approximately k0.6) for ELM-free H-mode discharges, in accordance with experimental results for ELM-free limiter H-mode plasmas in JFT-2M. In addition, the influence of the X-point configuration (single null or double null) on the confinement time is briefly addressed