Coils of real wire, the slotted-cylinder tests and R_net of a driver

.gitignore

@@ -174,3 +174,4 @@ junit/
 # Quarto
 .quarto/
 README_files/
+.rnet_cache/

CHANGELOG.md

@@ -7,6 +7,19 @@ format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 
 ### Added
 
+- `Feed3D`: coils of real wire in the 3D field. The coil current flows along grid edges
+  across a gap between the terminals of an `ImpedanceConductor3D` (a delta-gap source) and
+  returns on its surface, so the impedance includes the coil's own loss and proximity
+  effect; terminals not joined through one piece of metal are refused. Tested on a coaxial
+  line against its closed form (reactance to 0.13 %, resistance to 4 % at a / h = 4) and on
+  a ring of wire.
+- The slotted-cylinder test of step R4 as unit tests (`test_cutcell.py`): the z-invariant
+  slotted tube against NGSolve to 0.1 % with cut cells (staircase 20 % off), the finite tube
+  with closed and through slits to 6 %.
+- `benchmarks/rnet_driver.py`: R_net of the BUG driver (helical coil, Faraday shield with
+  24 slits, optional EMS with supports) on reduced grids, with the cut cells cached.
+- `InductiveField3D(cut_cell_samples=...)`: the sampling of the cut cells' crossings.
+
 - Method cards (methodcard) on the equations of the models: the reactions, the global model
   (cusps, wall areas, gas temperature, the steady state), the OpenCR rates, the neutralizer
   (beam, Knudsen profile, pumping, fractions, sources, fixed point), the 0D RF driver
@@ -264,6 +277,9 @@ format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 
 ### Fixed
 
+- The auxiliary-space preconditioner's coarsest multigrid level could be exactly singular
+  (two coarse nodes reaching one fine node through a gap in a conductor); a relative
+  diagonal shift of 1e-10 keeps it regular.
 - The docstrings' `:func:`, `:class:` and `:meth:` roles are code spans, which the API pages
   render.
 

benchmarks/rnet_driver.json

@@ -0,0 +1,111 @@
+{
+ "results": [
+  {
+   "variant": "bug",
+   "h": 0.004,
+   "r_net": 0.2664038792549869,
+   "resistances": {
+    "coil": 0.07089950205981722,
+    "shield": 0.1955043360682568
+   },
+   "inductance": 4.11169189604374e-06,
+   "power_balance": -1.5437805556128836e-07,
+   "unknowns": 1116650,
+   "iterations": 758,
+   "setup_seconds": 443.21280483300507,
+   "seconds": 382.2669253750064,
+   "tolerance": 0.0001,
+   "driver": {
+    "plasma_radius": 0.1185,
+    "length": 0.17,
+    "shield_wall": 0.008,
+    "slits": 24,
+    "slit_width": 0.002,
+    "slit_margin": 0.01,
+    "coil_radius": 0.1385,
+    "turns": 6,
+    "pitch": 0.02,
+    "wire_radius": 0.004,
+    "lead_radius": 0.155,
+    "lead_side": 0.01,
+    "feed_gap": 0.01,
+    "ems_distance": null,
+    "ems_wall": 0.008,
+    "box_half": 0.17,
+    "box_end": 0.22,
+    "frequency": 1000000.0
+   }
+  },
+  {
+   "variant": "bug",
+   "h": 0.0034,
+   "r_net": 0.2855851383706187,
+   "resistances": {
+    "coil": 0.0679426879710528,
+    "shield": 0.21764246298162943
+   },
+   "inductance": 4.102877478409794e-06,
+   "power_balance": 4.405713682764656e-08,
+   "unknowns": 1830128,
+   "iterations": 860,
+   "setup_seconds": 418.28152704099193,
+   "seconds": 1394.2107854999922,
+   "tolerance": 0.0001,
+   "driver": {
+    "plasma_radius": 0.1185,
+    "length": 0.17,
+    "shield_wall": 0.008,
+    "slits": 24,
+    "slit_width": 0.002,
+    "slit_margin": 0.01,
+    "coil_radius": 0.1385,
+    "turns": 6,
+    "pitch": 0.02,
+    "wire_radius": 0.004,
+    "lead_radius": 0.155,
+    "lead_side": 0.01,
+    "feed_gap": 0.01,
+    "ems_distance": null,
+    "ems_wall": 0.008,
+    "box_half": 0.17,
+    "box_end": 0.22,
+    "frequency": 1000000.0
+   }
+  },
+  {
+   "variant": "coil",
+   "h": 0.004,
+   "r_net": 0.07035406989410348,
+   "resistances": {
+    "coil": 0.07035458043107835
+   },
+   "inductance": 6.841778988157454e-06,
+   "power_balance": 7.256680041978214e-06,
+   "unknowns": 1152314,
+   "iterations": 638,
+   "setup_seconds": 0.4532764999894425,
+   "seconds": 687.7985254580126,
+   "tolerance": 1e-05,
+   "driver": {
+    "plasma_radius": 0.1185,
+    "length": 0.17,
+    "shield_wall": 0.008,
+    "slits": 24,
+    "slit_width": 0.002,
+    "slit_margin": 0.01,
+    "coil_radius": 0.1385,
+    "turns": 6,
+    "pitch": 0.02,
+    "wire_radius": 0.004,
+    "lead_radius": 0.155,
+    "lead_side": 0.01,
+    "feed_gap": 0.01,
+    "ems_distance": null,
+    "ems_wall": 0.008,
+    "box_half": 0.17,
+    "box_end": 0.22,
+    "frequency": 1000000.0
+   }
+  }
+ ]
+}