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Investigating Angelfish Instability: Parameter Scaling and Diagnostic Insights

This study explores the parameter scaling of 'Angelfish' instability, primarily focusing on low field conditions (≈3kG) and early discharge phases. The research examines factors such as low density, low current, and weak drive, utilizing diagnostics like MSE, reflectometry, FLIP, NPA, and the Mirnov array. Key objectives include developing scalings for frequency chirp rates, mode amplitudes, and secondary modes, while comparing data from various shots and sources. The findings, emphasizing the need for comprehensive data acquisition, aim to extend Angelfish stability and enhance understanding of resonance conditions and suppression mechanisms.

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Investigating Angelfish Instability: Parameter Scaling and Diagnostic Insights

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  1. Parameter scaling of ‘Angelfish’ instability • Best examples, most of data, is at low field (≈3kG) and early in discharge. • Low density? • Low current? • Weak drive (low fast ion beta)? • Study mode with MSE, reflectometer, FLIP, NPA and Mirnov polarization array. • Develop scaling for frequency chirp rate, mode amplitude, burst frequency and secondary modes.

  2. Most good data at low field, lowish density • There are a few higher field points; needs more study. • Angelfish seen with either source A or B, or with multiple sources • Chirping faster with multiple sources?

  3. Considerable analysis can be done if available data is acquired Dispersion relation: Resonance condition:

  4. Some evidence of Angel-suppression with HHFW • However, there is a single burst towards end of RF pulse; incomplete suppression. • Also, shots 113982-113985 are 'similar' shots, two with HHFW, two without, suggesting suppression. • Hope for more data…

  5. Experiment Outline: • Reproduce good Angelfish shot (113263 or 114147): • Acquire full diagnostic data set (MSE, reflectometer, polarization data). • Try to extend period of good Angelfish: • Flattop current earlier. • Try HHFW stabilization: • High power first, then power scan? • Change phasing? • Parameter scans (perhaps optimistic): • TF - easiest • Density? • Beam parameters (most difficult)

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