Changes From Source

Changes level 2 makes to the data in the MAST archive: how it is resampled in time, and changes to values, grouped by level 2 dataset. The data files do not flag these changes. See also Release History.

Policy

Action	When
Correct	The cause is established, the true value is known independently, and the result can be checked against unaffected channels
Withhold (publish NaN)	The value is inconsistent with related channels and the correct value is unknown
Keep	The value records what a calculation was given, such as EFIT’s inputs

Summary

Dataset	Variable	UDA source	Correction	Shots
magnetics	flux_loop_flux, CC04	AMB	Withheld	25366 onwards
magnetics	b_field_tor_probe_saddle_field, M02, M08, M012	ASM	Sign reversed	24782–30473
magnetics	b_field_tor_probe_saddle_voltage, M02, M08, M012	XMB	Sign reversed	11708–24781
magnetics	b_field_tor_probe_saddle_voltage	XMB	Offset subtracted	11708–30473
magnetics	b_field_tor_probe_cc_field, b_field_pol_probe_cc_field	XMC	Scaled to tesla	All
equilibrium	flux_loop_measured, index 3	EFM	Kept	25470–25793
equilibrium	All variables	EFM	Missing values are NaN, not −999	All
pf_active	coil_current	AMC	Scaled to coil current	All

Scale factors

Variable	Channels	Factor	Shots	Reason
pf_active.coil_current	SOL	×0.5	All	Parallel feed reads twice the coil current
pf_active.coil_current	P2IL FEED, P2IU FEED	×12	All	Current stored per turn
pf_active.coil_current	P2OL FEED, P2OU FEED, P3L FEED, P3U FEED	×8	All	Current stored per turn
pf_active.coil_current	P4L FEED, P4U FEED, P5L FEED, P5U FEED	×23	All	Current stored per turn
pf_active.coil_current	P6L, P6U	×4	All	Current stored per turn
magnetics.b_field_tor_probe_cc_field, magnetics.b_field_pol_probe_cc_field	Every channel	×2×10⁻⁶	All	Voltage to tesla
magnetics.b_field_tor_probe_saddle_field	M02, M08, M012	×−1	24782–30473	Wiring polarity
magnetics.b_field_tor_probe_saddle_voltage	M02, M08, M012	×−1	11708–24781	Wiring polarity

Unit conversions declared in the archive (such as kA to A) are not listed.

Time grids

All datasets except thomson_scattering and wall are resampled onto uniform grids with a zero-order hold: each grid point takes the most recent sample at or before it. Grids start at −0.1 s (−0.01 s for spectrometer_visible).

Dataset	Time axes
equilibrium, charge_exchange	time: 5 ms
summary	time: 1 ms
bolometer	time: 0.5 ms
magnetics	time: 0.2 ms; time_saddle: 20 µs; time_mirnov: 2 µs; time_omaha: 0.5 µs
pf_passive, tf	time: 0.2 ms
pulse_schedule, controllers, gas_injection, pf_active	time: 50 µs
interferometer	time: 20 µs
spectrometer_visible	time: 20 µs; time_bes: 0.5 µs
soft_x_rays	time: 2 µs

Not every shot has time_omaha or time_bes.

• Grid times are exact; a change can appear up to one step late.

• Data before the grid start is not published. About 95% of shots have plasma onset between −0.13 s and −0.04 s; the earliest is −0.92 s.

• thomson_scattering keeps the laser pulse times; wall has no time axis.

magnetics

Flux loop CC04 withheld (AMB)

Field	Value
Variable	flux_loop_flux, channel CC04
UDA signal	AMB_FL/CC04
Shots	25366 onwards
Correction	Withheld (NaN)
Introduced	#155

Background. On shots 25470–25793, CC04 reads with its sign reversed relative to the other centre column loops (CC03, CC05, CC07, CC09): slope −1.000, correlation −0.9997 over 183 shots. From 25794 it is flat at about 6×10⁻⁵ Wb. EFIT’s inputs hold the same values (see equilibrium).

Assumptions.

• The cause is unknown, so we withhold rather than flip.

• The last shot that agrees with the other loops is 25365 and the first reversed is 25470; nothing in between has plasma. We withhold from 25366.

• 141 of the 324 shots in 25470–25793 have no plasma or no CC04 data, so the whole window is withheld.

Change. CC04 is NaN from 25366. It keeps its place on flux_loop_channel, so the array shape does not change.

Impact. Use NaN-aware reductions. The original values are unchanged in UDA (AMB_FL/CC04). For earlier shots, see Known limitations.

Saddle coil field: M02, M08 and M012 sign-corrected (ASM)

Field	Value
Variable	b_field_tor_probe_saddle_field, channels M02, M08, M012
UDA signal	ASM_SAD/M02, ASM_SAD/M08, ASM_SAD/M012
Shots	24782–30473
Correction	×−1
Introduced	#157

Background. These coils were wired with reversed polarity, and ASM_SAD applies a fixed sign flip to compensate. The wiring was changed between shots 24742 and 24783, after which the flip reverses these coils relative to the others. The raw signal (XMB_SAD) flips at the same point:

shot    | raw   M02   M08   M12 | analysed M02   M08   M12
24736   | -1.04 -1.00 -1.09     | +1.03 +0.99 +1.00
24741   | -1.03 -1.01 -1.07     | +1.03 +0.99 +1.00
        |   ---- wiring changed between 24742 and 24783 ----
24785   | +1.02 +0.98 +1.01     | -1.19 -1.07 -0.97

Each coil regressed on the median of the others: +1 agrees, −1 reversed.

Across the 12,778 shots with ASM_SAD, only these three coils stand out:

Channel	Shots reversed	Shots agreeing
M02	814	4409
M08	825	4330
M012	815	4427
Every other coil	40 or fewer (noise)	about 5250

Assumptions. The analysed data agrees with the other coils before 24782 and is reversed from 24785, with no usable data in between. The sign is the only difference: once corrected, the three coils agree with the eight unaffected ones.

Change. ×−1 for shots 24782–30473; earlier shots unchanged.

Impact. Differs from ASM_SAD by a sign over 24782–30473.

Derived signals. UDA signals computed from these coils (ASM_SAD/D02 2-8, ASM_SAD/D05 6-12 and the locked mode detector ASM_OUT) are not published. Recompute them from the corrected coils if needed.

Saddle coil voltage: M02, M08 and M012 sign-corrected (XMB)

Field	Value
Variable	b_field_tor_probe_saddle_voltage, channels M02, M08, M012
UDA signal	XMB_SAD/OUT
Shots	11708–24781
Correction	×−1
Introduced	#157

The raw voltages follow the wiring, so these channels are reversed before the wiring change: the opposite range to the saddle coil field. This variable is already processed (offset subtracted, below), so it is corrected to the field’s sign convention. Differs from XMB_SAD by a sign over 11708–24781.

Saddle coil voltage: offset subtracted (XMB)

Field	Value
Variable	b_field_tor_probe_saddle_voltage, every channel
UDA signal	XMB_SAD/OUT
Shots	11708–30473
Correction	Mean of the first ten samples subtracted
Introduced	#55

The raw voltages sit on an offset. Level 2 subtracts the mean of each channel’s first ten samples, assuming they precede the plasma and the offset is constant; any drift remains. Differs from XMB_SAD by a constant per channel.

Centre column Mirnov coils scaled to tesla (XMC)

Field	Value
Variable	b_field_tor_probe_cc_field, b_field_pol_probe_cc_field
UDA signal	XMC/CC/MT, XMC/CC/MV
Shots	All
Correction	×2×10⁻⁶

The archive stores these as raw voltages; level 2 multiplies by 2×10⁻⁶ to give tesla. The factor’s origin is undocumented and unverified, so treat absolute magnitudes with caution. Shape and timing are unaffected.

equilibrium

CC04 kept in EFIT’s inputs (EFM)

Field	Value
Variable	flux_loop_measured, index 3 of n_flux_loop
UDA signal	EFM_SILOP_(X)
Shots	25470–25793
Correction	None

Index 3 holds the reversed CC04 values EFIT was given (see magnetics). They are kept as a record of the fit’s inputs; use n_flux_loop_order to exclude them. flux_loop_reconstructed is unaffected. EFIT’s flux loop weights and χ² (EFM_FWTSI, EFM_SILOP_CHISQ) are zero on these shots, so whether EFIT used CC04 is unknown.

Missing values are NaN, not −999 (EFM)

Field	Value
Variable	All variables
UDA signal	EFIT data (EFM)
Shots	All
Correction	Missing values are NaN

Some archive EFIT data marks missing values as −999, which looks like a real value. Level 2 uses NaN; a check of ten shots (15000–30421) found no −999. Treat −999 as missing if you read EFIT data from UDA.

pf_active

Coil currents scaled to the coil current (AMC)

Field	Value
Variable	coil_current
UDA signal	AMC_SOL CURRENT, AMC_P2IL FEED CURRENT and the other PF coil currents
Shots	All
Correction	Fixed factor per channel (see Scale factors)
Introduced	#110, #129, #153

Background. The archive stores feed currents per turn. The solenoid’s parallel feed reads twice its coil current.

Change. Each coil is multiplied by its number of turns (12 for P2 inner, 8 for P2 outer and P3, 23 for P4 and P5, 4 for P6) and the solenoid is halved. Checked against EFIT’s PF current inputs, and by re-running FreeGSNKE on a case that failed unscaled.

Impact. The factors came in over three changes, so older files may be scaled differently. See Release History.

gas_injection

Valve channels change across MAST (XDC)

valve_voltage is the voltage on each valve; valve_target_voltage is the target waveform for each valve group, G1–G12. Both come from UDA’s XDC gas signals. The archive’s valve set changes over MAST, so valve_voltage has different channels by shot range:

Shots	valve_voltage channels
1–25911	12, by target group: G1–G12
25912–26755	19 valves, including HM12, HEOA, HEOB
26756–28355	18: HM12 split into HM12A, HM12B; no HEOA, HEOB
28356–30471	20: as above plus HEOA, HEOB, always empty

From 28356, labels in both variables are lower case (tc5a, g1). No data for shots 25912–25936 or 28356–28451.

Targets and valves. From 25912, valve_voltage has fuelling_groups and impurity_groups attributes mapping each target to its valves. The mapping comes from MAST operations records, not the data.

Target	Valves	Kind
G1	TC5A, TC5B, TC11	Fuelling
G2	BC5	Fuelling
G3	HL1, HU6, HU8	Fuelling
G4	HU11	Fuelling
G5	HL11	Impurity
G6	BC11	Impurity
G7	HECC	Impurity
G8	HEOA, HEOB (obsolete)	Impurity
G9	HM12, or HM12A and HM12B	Impurity
G10	IBIL	Impurity
G11	IBFUA, IBFUB	Fuelling
G12	IBFLA, IBFLB	Fuelling

The attributes are JSON with full UDA names; channel labels are the last part of each name:

import json
import xarray as xr

gas = xr.open_zarr("https://s3.echo.stfc.ac.uk/mast/level2/shots/30421.zarr", group="gas_injection")
groups = json.loads(gas.valve_voltage.attrs["fuelling_groups"])
label = lambda name: name.replace("/", "_").split("_")[-1]

valves = groups["/xdc/gas/t/g1"]   # ["/xdc/gas/f/tc5a", "/xdc/gas/f/tc5b", "/xdc/gas/f/tc11"]
gas.valve_voltage.sel(valve_channel=[label(v) for v in valves])

Empty targets.

• Fuelling targets (G1–G4, G11, G12) on many shots, consistent with fuelling mode, where the valves share one flow request.

• G8 from about shot 27300 (obsolete HEO valves).

• All targets from about shot 25800 to 27200; cause unknown.

The ECEL and HFS valves are intermittent and not published.

Known limitations

Not fixed at the time of writing.

Data	Limitation
magnetics.b_field_tor_probe_saddle_field, M09	Empty: there is no ASM_SAD/M09. An all-NaN channel means the signal is missing, not that the diagnostic was off.
magnetics.b_field_tor_probe_saddle_voltage	The last three channels are M010–M012 up to shot 27619 and M10–M12 from 27620, following the archive
magnetics.flux_loop_flux, CC04	Intermittently flat on 792 shots in 22372–25365, published as near-zero noise rather than NaN
magnetics.flux_loop_flux	15 of the 19 loops in AMB_FL; P2L/1, P3L/1, P5U/4 and P6U/1 are missing, though EFIT uses them
Flux loop P5L/3	Position (R = 1.7463 m, Z = −0.5322 m) does not mirror P5U/3 (about 1.55 m, −0.564 m)
equilibrium.beta_pol	EFIT’s definition (boundary poloidal field), but the description gives the IMAS one, 4∫p dV / (R₀ μ₀ Ip²), which is about 20% lower (shot 30039, 0.3 s: 0.61 against 0.49). #158
thomson_scattering radius	AYC_R drifts up to 1.8 cm within a shot but is taken from the first time step
bolometer.power	Declared in W/m², but IMAS types it in W; unresolved
Not published	Halo currents (AMH); most Mirnov channels (3 in b_field_pol_probe_omv_voltage, 3 in b_field_tor_probe_cc_field, 5 in b_field_pol_probe_cc_field)

Reporting a problem

Open an issue on fair-mast with the signal, shot range and what you expected.