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Establish a transparent, signal-processing-based baseline for detecting internal reconnection event (IRE) timing in VEST using routinely available diagnostics, before relying on higher-level unsupervised classification or morphology discovery.
The immediate goal is not to define one universal physical reconnection_onset. Instead, detect independently observable event markers and compose them into an IRE candidate with explicit provenance.
Primary routine signals supported by the published VEST IRE observations are:
plasma current -> positive current spike
magnetic fluctuation -> abrupt magnetic burst
loop voltage -> rapid excursion / spike
H-alpha -> emission burst
O I -> impurity-emission burst
Ion Doppler spectroscopy (IDS) measurements of ion heating and rotation response are scientifically important but are excluded from the production detector because they are not routinely available at sufficient temporal/spatial coverage.
Conceptually:
Ip -> current_spike_onset
Mirnov / dBdt -> magnetic_burst_onset
Vloop -> loop_voltage_excursion
H-alpha -> halpha_burst_onset
O I -> oi_burst_onset
|
v
multi-diagnostic coincidence
|
v
IRE candidate
The detector should remain interpretable enough that every IRE candidate can be traced back to the original waveform, preprocessing, threshold/persistence rule, and timing uncertainty.
Scientific basis
The primary reference is:
S. Kim, J. Y. Jang, Y. Kim, and Y. S. Hwang (2021), Acceleration of ion rotation during internal reconnection events in the versatile experiment spherical torus (VEST), Nuclear Fusion 61, 126011. https://doi.org/10.1088/1741-4326/ac2b78
The paper reports the following recurring IRE signatures in the representative VEST discharges:
a positive plasma-current spike;
an abrupt magnetic fluctuation/burst;
a rapid loop-voltage spike/excursion;
bursts in H-alpha and O I emission;
ion heating and rotation changes observed with IDS.
The paper also shows two important constraints for detector design:
A strong MHD precursor is not required. One discharge has substantial pre-IRE magnetic activity, while another remains comparatively quiet until an abrupt magnetic burst at the IRE.
Loop-voltage sign is not universal. Ramp-up and ramp-down IREs show loop-voltage spikes in opposite directions, while the current spike, magnetic burst, and ion-heating response remain qualitatively similar.
Therefore, precursor activity should be optional metadata rather than a required IRE criterion, and loop voltage should be treated as a signed-independent excursion rather than a fixed-sign threshold.
1. Detect diagnostic-level events independently
Do not begin with a single monolithic detect_ire() rule.
First expose independently testable diagnostic events.
A suitable scalar may be derived from one or more validated Mirnov / magnetic-fluctuation channels, for example an RMS/envelope or derivative-excursion metric.
Do not require a long precursor mode to exist before the burst.
Treat these as optical/radiative response events, not direct definitions of reconnection onset.
Reuse signal-independent burst/onset/change-point primitives rather than introducing line-specific threshold code where possible.
2. Compose diagnostic events into an IRE candidate
After the individual events are validated, compose them using temporal coincidence.
Initial hypothesis:
primary evidence:
current spike
+ magnetic burst
supporting evidence:
loop-voltage excursion
H-alpha burst
O I burst
A first conservative candidate rule may require the current-spike and magnetic-burst events to occur within a configurable coincidence window:
[
|t_{I_p} - t_B| < \Delta t_{\rm coincidence}.
]
Supporting optical/loop-voltage events should strengthen the interpretation but should not initially be mandatory if the corresponding diagnostic is unavailable or unusable.
Do not hide missing data behind a lower threshold. Distinguish explicitly between:
no supporting event detected
supporting diagnostic unavailable
supporting diagnostic ambiguous/unusable
The coincidence tolerance must be derived from diagnostic bandwidth/timebase and corpus validation, not chosen as an undocumented constant.
3. Preserve observable timing rather than claiming exact reconnection onset
If later multi-diagnostic and physics analysis justifies a higher-level IRE transition time, it should be derived from the observable event set with explicit assumptions and uncertainty.
4. Relative timing as a first physics product
Once the observable events exist, provide event-to-event timing quantities such as:
and analogous quantities for loop voltage and O I.
These should use the common temporal-relation infrastructure from #667 rather than creating IRE-specific timing utilities where possible.
Population distributions of these delays can then answer whether the routine signatures form a reproducible event sequence or only a broad coincidence class.
5. Compare against existing unsupervised IRE detection
Where labels/results from the existing VAFT-based unsupervised IRE study are available, use them as an independent comparison target rather than as ground truth.
For each method, report at least:
signal-processing only
unsupervised only
agreement
and inspect disagreements manually.
The main questions are:
Are most IREs recoverable from explicit current-spike + magnetic-burst logic?
Which weak, overlapping, or morphologically unusual events require the unsupervised approach?
Does unsupervised detection improve event discovery, while explicit signal processing gives more reproducible onset timing?
Are false positives dominated by disruptions, capacitor transients, ordinary MHD bursts, or optical spikes?
Do not automatically replace the existing unsupervised method. The purpose is to establish a physically transparent baseline and quantify where more complex methods add value.
6. Corpus and negative controls
Validation must include more than hand-picked strong IREs.
At minimum inspect:
Positive cases
strong IRE with quiet pre-event MHD;
IRE with strong precursor / tearing activity;
ramp-up IRE;
ramp-down IRE;
weak / incomplete IRE where available;
recovery after IRE;
disruption-associated IRE-like events where available.
Negative / confounding cases
ordinary current evolution without IRE;
smooth ramp-down;
isolated magnetic burst without current spike;
current transient without magnetic burst;
capacitor/power-supply transient;
H-alpha / O I burst unrelated to IRE;
failed or marginal plasma;
terminal disruption without a clear recoverable IRE morphology.
Power-system transients must be handled explicitly, especially because the 2021 paper notes a second OH-capacitor discharge near the current peak in the analyzed shots.
7. Architecture
Keep generic signal processing separate from IRE semantics.
Conceptually:
vaft.process.onset / generic signal primitives
sustained excursion
derivative transient
burst envelope
change point
|
v
IRE diagnostic event adapters
current spike
magnetic burst
Vloop excursion
H-alpha burst
O I burst
|
v
IRE composition
|
v
#667 plasma-evolution timeline
The generic processing layer must not contain VEST/IRE-specific event names or thresholds.
equilibrium/stability interpretation of why the IRE occurred;
replacing the existing unsupervised IRE method before corpus-level comparison;
ML forecasting or causal inference.
The first target is a transparent, reproducible signal-processing baseline for observable IRE timing, with higher-level IRE interpretation and physics association layered on top.
Summary
Establish a transparent, signal-processing-based baseline for detecting internal reconnection event (IRE) timing in VEST using routinely available diagnostics, before relying on higher-level unsupervised classification or morphology discovery.
The immediate goal is not to define one universal physical
reconnection_onset. Instead, detect independently observable event markers and compose them into an IRE candidate with explicit provenance.Primary routine signals supported by the published VEST IRE observations are:
Ion Doppler spectroscopy (IDS) measurements of ion heating and rotation response are scientifically important but are excluded from the production detector because they are not routinely available at sufficient temporal/spatial coverage.
Conceptually:
The detector should remain interpretable enough that every IRE candidate can be traced back to the original waveform, preprocessing, threshold/persistence rule, and timing uncertainty.
Scientific basis
The primary reference is:
S. Kim, J. Y. Jang, Y. Kim, and Y. S. Hwang (2021),
Acceleration of ion rotation during internal reconnection events in the versatile experiment spherical torus (VEST),
Nuclear Fusion 61, 126011.
https://doi.org/10.1088/1741-4326/ac2b78
The paper reports the following recurring IRE signatures in the representative VEST discharges:
The paper also shows two important constraints for detector design:
Therefore, precursor activity should be optional metadata rather than a required IRE criterion, and loop voltage should be treated as a signed-independent excursion rather than a fixed-sign threshold.
1. Detect diagnostic-level events independently
Do not begin with a single monolithic
detect_ire()rule.First expose independently testable diagnostic events.
Plasma current
Candidate outputs:
Use robust baseline-relative signal processing on
Ipand/ordIp/dt.The production criterion should distinguish an abrupt positive IRE-associated spike from normal current evolution, ramp-down, and isolated noise.
Reuse generic onset / sustained-excursion primitives from #409 where appropriate.
Magnetic fluctuation
Candidate outputs:
A suitable scalar may be derived from one or more validated Mirnov / magnetic-fluctuation channels, for example an RMS/envelope or derivative-excursion metric.
Do not require a long precursor mode to exist before the burst.
Optional precursor products may remain separate:
These are useful characterization quantities but not mandatory evidence for the IRE itself.
Loop voltage
Candidate output:
Detect an abrupt deviation relative to the local baseline or slope.
Do not encode a fixed sign such as:
because the 2021 VEST paper reports opposite spike directions for ramp-up and ramp-down IREs.
H-alpha and O I
Candidate outputs:
Treat these as optical/radiative response events, not direct definitions of reconnection onset.
Reuse signal-independent burst/onset/change-point primitives rather than introducing line-specific threshold code where possible.
2. Compose diagnostic events into an IRE candidate
After the individual events are validated, compose them using temporal coincidence.
Initial hypothesis:
A first conservative candidate rule may require the current-spike and magnetic-burst events to occur within a configurable coincidence window:
[
|t_{I_p} - t_B| < \Delta t_{\rm coincidence}.
]
Supporting optical/loop-voltage events should strengthen the interpretation but should not initially be mandatory if the corresponding diagnostic is unavailable or unusable.
Do not hide missing data behind a lower threshold. Distinguish explicitly between:
The coincidence tolerance must be derived from diagnostic bandwidth/timebase and corpus validation, not chosen as an undocumented constant.
3. Preserve observable timing rather than claiming exact reconnection onset
Use names tied to what is actually measured:
Do not immediately expose:
as though it were directly measured.
If later multi-diagnostic and physics analysis justifies a higher-level IRE transition time, it should be derived from the observable event set with explicit assumptions and uncertainty.
4. Relative timing as a first physics product
Once the observable events exist, provide event-to-event timing quantities such as:
[
\Delta t_{B-I}
= t_{\rm magnetic\ burst} - t_{\rm current\ spike},
]
[
\Delta t_{H-I}
= t_{\rm H\alpha\ burst} - t_{\rm current\ spike},
]
and analogous quantities for loop voltage and O I.
These should use the common temporal-relation infrastructure from #667 rather than creating IRE-specific timing utilities where possible.
Population distributions of these delays can then answer whether the routine signatures form a reproducible event sequence or only a broad coincidence class.
5. Compare against existing unsupervised IRE detection
Where labels/results from the existing VAFT-based unsupervised IRE study are available, use them as an independent comparison target rather than as ground truth.
For each method, report at least:
and inspect disagreements manually.
The main questions are:
Do not automatically replace the existing unsupervised method. The purpose is to establish a physically transparent baseline and quantify where more complex methods add value.
6. Corpus and negative controls
Validation must include more than hand-picked strong IREs.
At minimum inspect:
Positive cases
Negative / confounding cases
Power-system transients must be handled explicitly, especially because the 2021 paper notes a second OH-capacitor discharge near the current peak in the analyzed shots.
7. Architecture
Keep generic signal processing separate from IRE semantics.
Conceptually:
The generic processing layer must not contain VEST/IRE-specific event names or thresholds.
The IRE-specific layer should preserve:
8. Relationship to existing work
Acceptance criteria
Non-goals
reconnection_onsettimestamp;The first target is a transparent, reproducible signal-processing baseline for observable IRE timing, with higher-level IRE interpretation and physics association layered on top.