Fill the bore of the RB24 pumping modules in caveRB24 with vacuum

This fixes air instead of vacuum in the bore of the VMABC pumping modules at z = 8.7 m and 18.8 m.

- The module is an assembly of hollow parts with no vacuum volume, so its 28 cm bore was cave air.
- A vacuum tube at the inner radius of the transition tube and RF contact now fills it, from one end to the other.
- It is placed beside the two copies in caveRB24 only. In the barrel copy the aluSideA pipe runs through the bore.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: sawenzel

Detectors/Passive/src/Pipe.cxx

@@ -1591,6 +1591,15 @@ void Pipe::ConstructGeometry()
   z = kRB24VMABCRBT1L / 2. + newRB24B1BellowUndL + kRB24VMABBEConTubeL1 + kRB24VMABBEConTubeL2 - kRB24VMABCCTL + 1.;
   voRB24VMABCRB->AddNode(voRB24VMABRFCT, 1, new TGeoTranslation(0., 0., z));
 
+  // Vacuum in the bore, from the transition tube to the end of the RF contact, at the inner radius
+  // of both. Placed beside the copies in caveRB24 only: in the barrel the aluSideA pipe runs through it.
+  const double kRB24VMABCVacZ0 = -kRB24VMABCRBT1L / 2. - 1.;
+  const double kRB24VMABCVacZ1 = z + kRB24VMABCCTL;
+  const double kRB24VMABCVacZc = (kRB24VMABCVacZ0 + kRB24VMABCVacZ1) / 2.;
+  TGeoVolume* voRB24VMABCVac = new TGeoVolume(
+    "RB24VMABCVac", new TGeoTube(0., 6.3 / 2., (kRB24VMABCVacZ1 - kRB24VMABCVacZ0) / 2.), kMedVacNF);
+  voRB24VMABCVac->SetVisibility(0);
+
   //
   // Assembling RB24/1
   //
@@ -1612,6 +1621,7 @@ void Pipe::ConstructGeometry()
   // VMABC close to compensator magnet
   z = -kRB24cCuTubeL / 2. - (kRB24VMABCL - kRB24VMABCRBT1L / 2) + 1.;
   voRB24C->AddNode(voRB24VMABCRB, 2, new TGeoTranslation(0., 0., z));
+  voRB24C->AddNode(voRB24VMABCVac, 2, new TGeoTranslation(0., 0., z + kRB24VMABCVacZc));
   // <-
 
   // Bellow
@@ -1714,6 +1724,7 @@ void Pipe::ConstructGeometry()
 
   z = -2. * (kRB243CuTubeL + kRB24B1L) - (kRB24VMABCL - kRB24VMABCRBT1L / 2) + 1.;
   voRB243->AddNode(voRB24VMABCRB, 3, new TGeoTranslation(0., 0., z));
+  voRB243->AddNode(voRB24VMABCVac, 3, new TGeoTranslation(0., 0., z + kRB24VMABCVacZc));
 
   z = -kRB24cCuTubeL / 2 - kRB24VMABCL - kRB242CuTubeL - 1.2;
   voRB24C->AddNode(voRB243, 1, new TGeoTranslation(0., 0., z));