3-axis Mirnov probes
Design
The Re-Entrant Poloidal Array (REPA) consists of 84 Mirnov coils inserted into re-entrant tubes to simplify assembly and access, and avoid the need for vacuum-compatible materials which increase fabrication costs and difficulty. These coils are organized into groups of three, such that one coil is oriented co-axially with the tube, and the other two are orthogonal to the tube and one another. These 3-axis probes or "triplets" are arranged into 1. a poloidal array of 20 triplets, and 2. an "off-radial" array of 8 triplets.
Coil Parameters:
- Radius (R): 0.2" (0.51cm)
- Height (H): 0.2" (0.51cm)
- Flux Area (A=πD2/4): 0.126 sq. in. (0.811cm2)
- Number of windings (N): 400
- Sensitivity:
- Predicted (spred): 13.4 mVs/T
- Measured (smeas): 14.73 mVs/T
- Coil-to-coil Variation (σarray): 0.186 mVs/T (1.26%)
- Mean measurement error (σavg): 0.623 mVs/T (4.23%)
- Relative to prediction: 90.8%
Re-Entrant (RE) Probe Upgrade
The addition of new poloidal sensors and off-radial sensors has expanded the array from 18 triplets (54 coils) to 28 triplets (84 coils). As of Mar. 9th 2017, the planned layout includes includes 9 probes each inserted from the top and bottom rectangular ports (5 centered in 4 tubes, plus 4 to either side of center), and 10 (centered) probes inserted from the LFS rectangular port, between sections P and A.
The nominal probe positions and tube lengths are indicated here. Drawings for the tubes are here.
HFS Midplane RE Probe Positioning
Since the midplane HFS RE probe (both top and bottom) passes near to the two HFS-most shell-mounted poloidal flux loops, it was necessary to test the geometry (i.e. angle and machine-radial origin) for the re-entrant tube before finalizing the design. This was tested using a test mock-up.
Heat Loading
On 8/28/2018 a thermocouple was inserted into Top Center #2 (2nd-most inward) Tube to gauge the heating of re-entrant probe components when the shells are heated.
Calibration
REPA Mirnov calibrations were carried out in September 2018, using the Mirnov calibration Helmholtz coil. Individual coil calibration results and LEMO breakout polarities can be found in this Google spreadsheet.
Acquisition
With 5 poloidal array and 4 off-radial re-entrant probes on the top and bottom, plus 10 LFS-inserted probes, the full array uses (9+9+10)x3=84 channels. No feedthroughs are needed, since the probes are re-entrant. Old probes using Winchester connectors are inserted in all LFS re-entrant tubes, and in the LFS-most top and bottom re-entrant tubes (probes 4, 5, 16, and 17). New probes using D-sub connectors are inserted in PA tubes 1-3 and 18-20, and in all 8 off-radial tubes.
Due to the large number of sensors (84 total less 6 damaged coils) and the constraints of front panel access and the distribution of integrator gains, the mapping of sensors to integrator and digitizer channels is complicated. In general, poloidal array sensors go to integrator chassis 2 (PA 1-10) and 3 (PA 11-20); off-radial sensors go to chassis 1 (top) and 5 (bottom). In order to make sensors available for use by the PCS, all poloidal (i.e. "A/axial" and "P/perpendicular") PA sensors go to Neos channels 1-40, and all top and bottom off-radial sensors go to Neos channels 41-64. Expected to be less useful for the PCS, the toroidal PA sensors go to Helios channels 70-79 (bottom) and 86-95 (top).
Comprehensive and detailed mapping documents are available at the following links for integrators and digitizers.
Old Probes
PA probes 4-16 are old probes.
For ease of maintenance/repair, old re-entrant probes have machine-side connector assemblies. Each probe runs 3 twisted pairs of magnet wire out of its tube, requiring 6 connector pins. Each pair of probes (e.g. 1 and 2, 3 and 4, 5 and 6) share a Winchester connector to a multipair cable which runs to the [Digitizers#magneticsrack|magnetics rack].
Each cable terminates in a Winchester/LEMO breakout adapter. Each channel propagates an individual shield from the integrator LEMO shield ground, through a channel-dedicated pin on the Winchester connector, and into the re-entrant tube (Fig. 2).
New Probes
PA probes 1-3 and 18-20, and all off-radial re-entrant probes are new probes.
As with the old probes, for ease of maintenance/repair, new re-entrant probes will have machine-side connector assemblies. Each probe runs 3 twisted pairs of magnet wire out of its tube, requiring 6 connector pins. Probes 1 and 2, and 19 and 20 share a tube; all other tubes house only one probe. To minimize new cabling, Probes 1 and 2 (and on top, 19 and 20) run to a 15-pin D-sub, while probe 3 (and on top, 18) runs to a 9-pin D-sub. These connectors then share a single branched-off multi-pair shielded cable (Fig. 3). The left-hand (from LFS) pair of each off-radial set shares a 15-pin D-sub, as does the right-hand pair, and the two D-subs mate to a branched-off multi-pair shielded cable.
Each of the multi-pair cables (four cables in total) terminates at the magnetics rack in a 25-pin female D-sub, which mates to a D-sub/differential-LEMO breakout adapter. Each LEMO connector is individually labelled with its channel, either PA#x, T#x, or B#x where "x" is the orientation (A/P/T). The breakout adapter shell of each cable is tied to the magnetics rack ground bus and to the cable's common shield, which is propagated by shield braid up to the mouth of each re-entrant tube. The shield braids are insulated to prevent intermittent local ground loops.
Related Pages
Diagnostics
Magnetics (Local): Reentrant array | Toroidal array | Saddle coils | Shell eddy sensors
Magnetics (Areal): Poloidal flux loops | Loop voltage | Diamagnetic loop | IP Rogowski
Spectroscopy: Thomson scattering | ChERS | X-ray spectroscopy | Spectrometry | Vacuum UV spectroscopy
Microwaves: Reflectometry | Interferometry
Physical Probes: HFS edge probes | LFS SOL probes | RFEA
Operational Diagnostics: Ion gauges | Coil current monitors | Thermocouples | RTDs
