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The Australian National University

The MHD Documentation Database (MDDB)

An overview of the MDDB project is given in a CWGM7 presentation, available here.

Background

Aim: provide a reference documentation database of MHD modes observed in all major stellarators.

Useful for: finding parameterisation of modes (e.g. Alfvén scaling) across many shots, also for cross-machine comparisons

How: The MHD documentation database (MDDB) will be generated using automated techniques scanning 10,000s of shots.

Data: choose Mirnov channels -- arrays on all devices, an "always-on" diagnostics, likely to have consistent configuration (sampling, gain, etc) across many shots.

Since 2007, data mining results have been obtained from H- 1, Heliotron J, TJ-II, W7AS and LHD. (also JT-60). In this time our methods have improved, however this means that results from each device are somewhat ad hoc. Different code versions, different pre-processing filters, different clustering algorithms. Code had limitations: both in how easily it could be extended, and code complexity became barrier to new users In order to make pyfusion code usable for collaborators, and to allow a systematic treatment across all devices, significant refactoring was required

Roadmap

MDDB 1.0

will document only those modes which we can treat rigorously with our current methods

  • strong, coherent modes
  • no standing waves
  • defined solely by Mirnov phase structure (not amplitude)
  • time-independent treatment (~0.5 ms samples)
  • probabilistic phase structure representation (von Mises distribution)
  • single set of Mirnov coils (skip shots with missing coils)
  • SVD-based mode detection, correlation threshold SV grouping

MDDB 1.1

  • include missing coils, and newer coils (e.g. 16 3-axis helical array in H-1)

MDDB 2.0+

  • lower energy threshold for modes
  • broadband fluctuations
  • time dependence

MDDB 1.0 structure

The MDDB 1.0 schema consists of five tables:

The mode table

Mode ID Channel A Channel B Delta phase: mu Delta phase: gamma

The documentation table

Mode ID Documentation

The instance table

Instance ID Shot Time (0.5ms interval) Frequency Signal strength

The mapping table

Instance ID Mode ID Likelihood

The supplementary instance table (possibly sparse)

Instance ID ne B iota heating etc... etc...

Target dataset for MDDB 1.0

H-1 Heliotron J LHD TJ-II W7AS
Shots 58000-64050 20000-last 75000-last 14570-last 51000-55000
Mirnov coils 20 coil poloidal array 14 coil poloidal array 6 coil toroidal array, 15 coil helical array 15 coil poloidal array 16 coil poloidal array
Sample rate 1 MHz 1 MHz 1 MHz 312.5 kHz 333 kHz

Related pages: Pyfusion code used in generating the MDDB

Updated:  25 January 2011/Responsible Officer:  H-1 Facility Manager /Page Contact:  H-1 Website Administrator