feat(target): implement 2026 BDF target design

README.md

@@ -34,7 +34,7 @@ quantity explicit at the point where it is written.
 | Subsystem | Status | Description |
 |-----------|--------|-------------|
 | [Cavern](subsystems/Cavern/README.md) | Complete | World volume with subtracted rock cavities |
-| [Target](subsystems/Target/README.md) | Complete | 19 W slabs with Ta cladding in Inconel vessel |
+| [Target](subsystems/Target/README.md) | Complete | 2026 BDF target: 33 W disks in grooved steel core with jacket and endcap |
 | [MuonShield](subsystems/MuonShield/README.md) | Approximate | 6 stations, box approximations of arb8 shapes |
 | [NeutrinoDetector](subsystems/NeutrinoDetector/README.md) | Approximate | Veto + Si/W target + HCAL with individual scintillating fibres |
 | [Magnet](subsystems/Magnet/README.md) | Approximate | Iron yoke with box-shaped coils (should be tubes) |

subsystems/Target/README.md

@@ -5,8 +5,11 @@ The Target subsystem contains the SHiP proton target and its associated shieldin
 ## Overview
 
 The proton target is where the 400 GeV/c proton beam from the SPS interacts to produce
-hidden sector particles. The target consists of tungsten slabs with tantalum cladding,
-housed in a helium-filled vessel, surrounded by copper and iron shielding.
+hidden sector particles. This implements the 2026 BDF target design, extracted from
+CATIA model `ST1A07710_01_AB.02`: solid tungsten disks held in a steel core with
+serpentine helium cooling grooves, surrounded by a steel jacket with flanges and a
+domed rear endcap, all inside a pressurised-helium container. Copper and iron
+shielding surround the target.
 
 ## Geometry Structure
 
@@ -16,55 +19,73 @@ target_vacuum_box (Vacuum, 160×227.1×300 cm)
 ├── top_shielding (Copper, 160×60×300 cm)
 ├── bottom_shielding (Copper, 160×54.5×300 cm)
 ├── shielding_pedestal (Iron, 107×15×217 cm)
-└── TargetArea
-    ├── TargetVessel (Inconel718, tube r=20-20.8 cm, z=171.04 cm)
-    ├── TargetVesselFront (Inconel718, disk r=20.8 cm, z=0.8 cm)
-    ├── TargetVesselBack (Inconel718, disk r=20.8 cm, z=0.8 cm)
-    └── HeVolume (PressurisedHe90, tube r=20 cm, z=171.04 cm)
-        ├── target_enclosure (Steel316L)
-        └── 19× CladdedTarget_N (Tantalum, r=12.5 cm)
-            └── TargetCore_N (Tungsten, r=12.35 cm)
+├── he_volume (PressurisedHe90, tube r=23.7 cm, z=-3.78..150.97 cm)
+│   ├── 33× core_N (Tungsten disks, r=12.5 cm; core_33 r=15.7 cm)
+│   ├── core_steel (Steel316L, polycone with He grooves subtracted)
+│   ├── jacket (Steel316L, tube r=21.7-22.5 cm)
+│   ├── flange_front (Steel316L, r=19.5-22.5 cm)
+│   ├── front_window (Steel316L, disc r=14.1 cm, 8 mm)
+│   ├── front_nose (Steel316L, r=14.1-19.5 cm)
+│   ├── cover_ring1, cover_ring2 (Steel316L, cover-plate bore rings)
+│   ├── flange_back (Steel316L, r=22.5-23.7 cm)
+│   └── endcap (Steel316L, 8 mm domed shell as polycone)
+└── cover_plate (Steel316L, 60×65×2 cm plate minus the He container bore)
 ```
 
+All target z coordinates are measured from the front face of the first disk, which is
+the SHiP global origin.
+
+## Tungsten disks
+
+33 solid tungsten disks (no cladding), radius 125 mm except the 455 mm rear block
+(radius 157 mm), separated by 4 mm helium slits (5 mm after disks 25 and 26). Total
+length 1460 mm, of which 1330 mm tungsten.
+
+Thickness sequence (mm): 30, 10, 15×8, 9, 11, 12, 13, 13, 16, 20, 20, 21, 30, 40,
+55, 73, 106, 276, 455.
+
+## Steel core, cooling grooves, jacket and endcap
+
+- **Core** (z 7.2–1443.7 mm): the two clamp halves of the CAD model merged into one
+  axisymmetric polycone; bore r=125 mm (stepping to 157 mm at z=1005 mm around the
+  rear block), outer r=207 mm with a front step to r=195 mm (inside the front flange)
+  and a rear step to r=190 mm.
+- **He cooling grooves**: 61°-wide arcs (r 125→153 mm) in the bore, centred on the
+  vertical axis and staggered in z between the upper half (12.2–57, 95–153, 191–257,
+  300–464, 559–933.2 mm) and the lower half (45–104.7, 142.7–200.7, 238.7–334.7,
+  385.7–1005 mm), plus a 49°-wide top groove (r 157→182 mm, z 1005–1441.7 mm) around
+  the rear block. Together with the inter-disk slits they form the serpentine helium
+  flow path. Implemented as tube-segment subtractions; the removed volume fills with
+  the parent helium.
+- **Jacket**: 8 mm steel tube (r 217–225 mm, z 55.2–1198.7 mm) with front flange
+  (r 195–225 mm, z −23.8–55.2 mm) and rear flange (r 225–237 mm, z 1198.7–1263.7 mm);
+  the r 207–217 mm gap between core and jacket is a helium annulus.
+- **Upstream closure**: the vessel bore is closed by a dished beam window integral to
+  the front flange part, simplified to a flat disc (r 141 mm, z −33.5–−25.5 mm) that
+  preserves the 8 mm of steel on the beam axis; a nose ring (r 141–195 mm,
+  z −35.8–−23.8 mm) connects the window rim to the flange. An external cover plate
+  (600×650×20 mm, z −37.8–−17.8 mm, stepped bore r 196/226 mm, asymmetric about the
+  beam axis: +250 mm above, −400 mm below) is modelled as two bore rings inside the
+  helium container plus a rectangular box-minus-tube outside it.
+- **Rear endcap**: 8 mm shell (cylinder r 229–237 mm, z 1263.7–1413.7 mm) closed by a
+  domed head approximated as a polycone (three cone segments and an apex disc,
+  ending at z=1509.7 mm).
+
+Simplifications relative to the CAD model: bolt lugs, key-ways, pipe stubs, fasteners
+and survey hardware are omitted; the flange/jacket boundary is placed at the end of
+the core front step (55.2 mm instead of the CAD's stepped flange bore at 64.2 mm); the
+beam window dishing is dropped and the window spacer pads are omitted.
+
 ## Materials
 
 | Component | Material | Density (g/cm³) |
 |-----------|----------|-----------------|
 | Vacuum box | Vacuum | 1.205e-6 |
 | Shielding | Copper | 8.96 |
 | Pedestal | Iron | 7.87 |
-| Vessel | Inconel718 | 8.19 |
-| Enclosure | Steel316L | 7.99 |
+| Disks | Tungsten | 19.3 |
+| Core, jacket, flanges, window, cover plate, endcap | Steel316L | 7.99 |
 | He volume | PressurisedHe90 | 0.00212 |
-| Cladding | Tantalum | 16.65 |
-| Core | Tungsten | 19.3 |
-
-## Target Slabs
-
-The target consists of 19 tungsten slabs with tantalum cladding. The slab thicknesses
-increase along the beam direction to account for the hadronic shower development.
-
-| Slab | Cladding Z (cm) | Core Z (cm) | Position Z (cm) |
-|------|-----------------|-------------|-----------------|
-| 1 | 4.5 | 4.2 | -77.07 |
-| 2 | 1.8 | 1.5 | -73.47 |
-| 3 | 1.7 | 1.4 | -71.27 |
-| 4 | 1.7 | 1.4 | -69.12 |
-| 5 | 1.8 | 1.5 | -66.92 |
-| 6 | 1.9 | 1.6 | -64.62 |
-| 7 | 2.1 | 1.8 | -62.17 |
-| 8 | 1.9 | 1.6 | -59.72 |
-| 9 | 2.1 | 1.8 | -57.27 |
-| 10 | 2.4 | 2.1 | -54.57 |
-| 11 | 2.8 | 2.5 | -51.52 |
-| 12 | 3.3 | 3.0 | -48.02 |
-| 13 | 4.1 | 3.8 | -43.87 |
-| 14 | 5.6 | 5.3 | -38.57 |
-| 15 | 8.8 | 8.5 | -30.92 |
-| 16 | 17.2 | 16.9 | -17.44 |
-| 17 | 28.7 | 28.4 | +6.01 |
-| 18 | 28.8 | 28.5 | +35.44 |
-| 19 | 28.8 | 28.5 | +64.92 |
 
 ## Position in World
 
@@ -86,5 +107,6 @@ GeoPhysVol* target = factory.build();
 
 ## References
 
-- GDML source: `gdml/ship_geometry.gdml`
+- CATIA model: `ST1A07710_01_AB.02` (July 2026)
+- FairShip implementation of the same design: ShipSoft/FairShip#1361
 - SHiP Technical Proposal: CERN-SPSC-2015-016

subsystems/Target/include/Target/TargetFactory.h

@@ -9,6 +9,7 @@
 
 class GeoPhysVol;
 class GeoLogVol;
+class GeoShape;
 
 namespace SHiPGeometry {
 
@@ -17,12 +18,27 @@ class SHiPMaterials;
 /**
  * @brief Factory for the Target (proton target and shielding) geometry
  *
- * The target consists of:
+ * Implements the 2026 BDF target design, extracted from CATIA model
+ * ST1A07710_01_AB.02 and simplified to axisymmetric shapes:
  * - Vacuum box containing shielding and target assembly
  * - Copper proximity, top, and bottom shielding
  * - Iron shielding pedestal
- * - Inconel718 target vessel with helium-filled interior
- * - 19 tungsten target slabs with tantalum cladding
+ * - Helium container (HeVolume) holding:
+ *   - 33 solid tungsten disks (no cladding); the last disk (rear block)
+ *     has a larger radius
+ *   - steel core (the two clamp halves modelled as one axisymmetric
+ *     polycone) with serpentine He cooling grooves subtracted
+ *   - steel jacket tube with front and rear flanges; the gap between
+ *     core and jacket is a He annulus
+ *   - upstream beam window (dished membrane simplified to a flat disc
+ *     preserving the 8 mm of steel on the beam axis) with its nose ring,
+ *     and the bore rings of the upstream cover plate
+ *   - domed rear endcap (8 mm shell, dome approximated as a polycone)
+ * - Upstream cover plate (rectangular, asymmetric about the beam axis),
+ *   the part outside the He container
+ *
+ * All target z coordinates are measured from the front face of the first
+ * disk, which is the SHiP global origin.
  */
 class TargetFactory {
    public:
@@ -43,14 +59,13 @@ class TargetFactory {
     GeoPhysVol* createTopShielding();
     GeoPhysVol* createBottomShielding();
     GeoPhysVol* createShieldingPedestal();
-    GeoPhysVol* createTargetVessel();
-    GeoPhysVol* createTargetVesselFront();
-    GeoPhysVol* createTargetVesselBack();
-    GeoPhysVol* createTargetEnclosure();
     GeoPhysVol* createHeVolume();
+    const GeoShape* createSteelCoreShape();
 
-    // Unit conversion helper (GDML uses cm, GeoModel uses mm)
+    // Unit conversion helpers
     static constexpr double cm = GeoModelKernelUnits::cm;
+    static constexpr double mm = GeoModelKernelUnits::mm;
+    static constexpr double deg = GeoModelKernelUnits::degree;
 
     // Target vacuum box dimensions (half-sizes)
     static constexpr double s_vacuumBoxHalfX = 80.0 * cm;
@@ -90,52 +105,123 @@ class TargetFactory {
     static constexpr double s_pedestalPosY = -51.55 * cm;
     static constexpr double s_pedestalPosZ = 15.0 * cm;
 
-    // TargetArea position within vacuum box
+    // TargetArea position within vacuum box: the target frame (z = 0 at the
+    // front face of the first disk) sits at this offset in the vacuum box
     static constexpr double s_targetAreaPosY = 14.45 * cm;
     static constexpr double s_targetAreaPosZ = -43.25 * cm;
 
-    // Target vessel
-    static constexpr double s_vesselRmin = 20.0 * cm;
-    static constexpr double s_vesselRmax = 20.8 * cm;
-    static constexpr double s_vesselHalfZ = 85.52 * cm;
-    static constexpr double s_vesselPosZ = 79.32 * cm;
-
-    // Target vessel end caps
-    static constexpr double s_vesselCapRadius = 20.8 * cm;
-    static constexpr double s_vesselCapHalfZ = 0.4 * cm;
-    static constexpr double s_vesselFrontPosZ = -6.6 * cm;
-    static constexpr double s_vesselBackPosZ = 165.24 * cm;
-
-    // HeVolume
-    static constexpr double s_heVolumeRadius = 20.0 * cm;
-    static constexpr double s_heVolumeHalfZ = 85.52 * cm;
-    static constexpr double s_heVolumePosZ = 79.32 * cm;
-
-    // Target enclosure
-    static constexpr double s_enclosureRmin = 12.51 * cm;
-    static constexpr double s_enclosureRmax = 19.2 * cm;
-    static constexpr double s_enclosureHalfZ = 79.32 * cm;
-    static constexpr double s_enclosureCutoutHalfX = 8.0 * cm;
-    static constexpr double s_enclosureCutoutHalfY = 14.0 * cm;
-
-    // Target slabs (common parameters)
-    static constexpr double s_claddingRadius = 12.5 * cm;
-    static constexpr double s_coreRadius = 12.35 * cm;
-    static constexpr int s_numSlabs = 19;
-
-    // Target slab data arrays (half-lengths in Z, positions in Z)
-    static constexpr std::array<double, 19> s_claddingHalfZ = {
-        2.25 * cm, 0.9 * cm,  0.85 * cm,  0.85 * cm, 0.9 * cm,  0.95 * cm, 1.05 * cm,
-        0.95 * cm, 1.05 * cm, 1.2 * cm,   1.4 * cm,  1.65 * cm, 2.05 * cm, 2.8 * cm,
-        4.4 * cm,  8.6 * cm,  14.35 * cm, 14.4 * cm, 14.4 * cm};
-    static constexpr std::array<double, 19> s_coreHalfZ = {
-        2.1 * cm,  0.75 * cm, 0.7 * cm,  0.7 * cm,   0.75 * cm, 0.8 * cm, 0.9 * cm,
-        0.8 * cm,  0.9 * cm,  1.05 * cm, 1.25 * cm,  1.5 * cm,  1.9 * cm, 2.65 * cm,
-        4.25 * cm, 8.45 * cm, 14.2 * cm, 14.25 * cm, 14.25 * cm};
-    static constexpr std::array<double, 19> s_slabPosZ = {
-        -77.07 * cm, -73.47 * cm, -71.27 * cm, -69.12 * cm, -66.92 * cm, -64.62 * cm, -62.17 * cm,
-        -59.72 * cm, -57.27 * cm, -54.57 * cm, -51.52 * cm, -48.02 * cm, -43.87 * cm, -38.57 * cm,
-        -30.92 * cm, -17.44 * cm, 6.01 * cm,   35.44 * cm,  64.92 * cm};
+    // ---- 2026 BDF target (CATIA ST1A07710_01_AB.02) ----
+    // All z values below are in the target frame (z = 0 at disk-1 front face).
+
+    // HeVolume: container for disks, steel core, jacket, flanges, beam
+    // window, cover-plate bore rings and endcap
+    static constexpr double s_heRadius = 237.0 * mm;
+    static constexpr double s_heZMin = -37.8 * mm;   // upstream face of the cover plate
+    static constexpr double s_heZMax = 1509.7 * mm;  // downstream end of rear endcap
+    static constexpr double s_heCentreZ = 0.5 * (s_heZMin + s_heZMax);
+
+    // Tungsten disks: [z start, z end] per disk; 4-5 mm He slits in between
+    static constexpr int s_numDisks = 33;
+    static constexpr double s_diskRadius = 125.0 * mm;
+    static constexpr double s_lastDiskRadius = 157.0 * mm;  // rear block
+    static constexpr std::array<std::array<double, 2>, s_numDisks> s_diskZ = {{
+        {0.0 * mm, 30.0 * mm},    {34.0 * mm, 44.0 * mm},    {48.0 * mm, 56.0 * mm},
+        {60.0 * mm, 68.0 * mm},   {72.0 * mm, 80.0 * mm},    {84.0 * mm, 92.0 * mm},
+        {96.0 * mm, 104.0 * mm},  {108.0 * mm, 116.0 * mm},  {120.0 * mm, 128.0 * mm},
+        {132.0 * mm, 140.0 * mm}, {144.0 * mm, 152.0 * mm},  {156.0 * mm, 164.0 * mm},
+        {168.0 * mm, 176.0 * mm}, {180.0 * mm, 188.0 * mm},  {192.0 * mm, 200.0 * mm},
+        {204.0 * mm, 212.0 * mm}, {216.0 * mm, 224.0 * mm},  {228.0 * mm, 237.0 * mm},
+        {241.0 * mm, 252.0 * mm}, {256.0 * mm, 268.0 * mm},  {272.0 * mm, 285.0 * mm},
+        {289.0 * mm, 302.0 * mm}, {306.0 * mm, 322.0 * mm},  {326.0 * mm, 346.0 * mm},
+        {350.0 * mm, 370.0 * mm}, {375.0 * mm, 396.0 * mm},  {401.0 * mm, 431.0 * mm},
+        {435.0 * mm, 475.0 * mm}, {479.0 * mm, 534.0 * mm},  {538.0 * mm, 611.0 * mm},
+        {615.0 * mm, 721.0 * mm}, {725.0 * mm, 1001.0 * mm}, {1005.0 * mm, 1460.0 * mm},
+    }};
+
+    // Steel core (two clamp halves modelled as one axisymmetric piece)
+    static constexpr double s_coreZMin = 7.2 * mm;
+    static constexpr double s_coreZMax = 1443.7 * mm;
+    static constexpr double s_coreBoreR1 = 125.0 * mm;      // matches disks 1..32
+    static constexpr double s_coreBoreR2 = 157.0 * mm;      // matches the rear block
+    static constexpr double s_coreBoreStepZ = 1005.0 * mm;  // bore radius change
+    static constexpr double s_coreOuterR = 207.0 * mm;
+    static constexpr double s_coreFrontOuterR = 195.0 * mm;  // front, inside the flange
+    static constexpr double s_coreFrontZMax = 55.2 * mm;     // end of front step
+    static constexpr double s_coreRearOuterR = 190.0 * mm;   // rear, inside rear flange
+    static constexpr double s_coreRearZMin = 1233.7 * mm;    // start of rear step
+
+    // Serpentine He cooling grooves: arcs in the bore, centred on the vertical
+    // axis, staggered between the upper and lower half; He flows between them
+    // through the inter-disk slits
+    static constexpr double s_grooveRmin = 120.0 * mm;  // below bore: clean subtraction
+    static constexpr double s_grooveRmax = 153.0 * mm;
+    static constexpr double s_groovePhiWidth = 61.0 * deg;
+    static constexpr std::array<std::array<double, 2>, 5> s_groovesTop = {{
+        {12.2 * mm, 57.0 * mm},
+        {95.0 * mm, 153.0 * mm},
+        {191.0 * mm, 257.0 * mm},
+        {300.0 * mm, 464.0 * mm},
+        {559.0 * mm, 933.2 * mm},
+    }};
+    static constexpr std::array<std::array<double, 2>, 4> s_groovesBottom = {{
+        {45.0 * mm, 104.7 * mm},
+        {142.7 * mm, 200.7 * mm},
+        {238.7 * mm, 334.7 * mm},
+        {385.7 * mm, 1005.0 * mm},
+    }};
+    // Groove around the rear block (upper half only), ends 2 mm before the
+    // core rear face
+    static constexpr double s_rearGrooveRmin = 152.0 * mm;  // below bore R2
+    static constexpr double s_rearGrooveRmax = 182.0 * mm;
+    static constexpr double s_rearGroovePhiWidth = 49.0 * deg;
+    static constexpr double s_rearGrooveZMin = 1005.0 * mm;
+    static constexpr double s_rearGrooveZMax = 1441.7 * mm;
+
+    // Jacket tube and flanges; He annulus between core (207) and jacket (217).
+    // The flange bore matches the core front step, so the flange/jacket
+    // boundary is placed at the end of the step. The flange proper starts at
+    // the cover-plate step; upstream of it the outer radius is the r 195
+    // nose that slides into the cover-plate bore.
+    static constexpr double s_jacketRmin = 217.0 * mm;
+    static constexpr double s_jacketRmax = 225.0 * mm;
+    static constexpr double s_jacketZMin = s_coreFrontZMax;
+    static constexpr double s_jacketZMax = 1198.7 * mm;
+    static constexpr double s_flangeFrontRmin = 195.0 * mm;
+    static constexpr double s_flangeFrontZMin = -23.8 * mm;  // cover-plate step
+    static constexpr double s_noseZMin = -35.8 * mm;         // upstream face of the vessel
+    static constexpr double s_flangeRearRmax = 237.0 * mm;
+    static constexpr double s_flangeRearZMax = 1263.7 * mm;
+
+    // Beam window: dished membrane closing the bore, simplified to a flat
+    // disc preserving the 8 mm of steel on the beam axis; the r 141-195 nose
+    // ring connects the window rim to the flange
+    static constexpr double s_windowRmax = 141.0 * mm;
+    static constexpr double s_windowZMin = -33.5 * mm;
+    static constexpr double s_windowZMax = -25.5 * mm;
+
+    // Upstream cover plate (600 x 650 x 20 mm, stepped bore r 196/226 mm,
+    // asymmetric about the beam axis: +250 mm above, -400 mm below): the
+    // part within the He container is modelled as two bore rings, the
+    // rectangular remainder as a box-minus-tube outside it
+    static constexpr double s_coverRing1Rmin = 196.0 * mm;
+    static constexpr double s_coverRing2Rmin = 226.0 * mm;
+    static constexpr double s_coverZMax = -17.8 * mm;
+    static constexpr double s_coverPlateHalfX = 300.0 * mm;
+    static constexpr double s_coverPlateHalfY = 325.0 * mm;
+    static constexpr double s_coverPlateHalfZ = 10.0 * mm;
+    static constexpr double s_coverPlateOffsetY = -75.0 * mm;  // plate centre below the axis
+
+    // Rear endcap: 8 mm shell, cylindrical section closed by a domed head;
+    // polycone planes (z, rmin, rmax) approximating the dome with three cone
+    // segments and an apex disc
+    static constexpr std::array<std::array<double, 3>, 6> s_endcapPlanes = {{
+        {1263.7 * mm, 229.0 * mm, 237.0 * mm},
+        {1413.7 * mm, 229.0 * mm, 237.0 * mm},
+        {1450.0 * mm, 212.0 * mm, 223.0 * mm},
+        {1480.0 * mm, 142.0 * mm, 166.5 * mm},
+        {1505.0 * mm, 0.0 * mm, 67.0 * mm},
+        {1509.7 * mm, 0.0 * mm, 67.0 * mm},
+    }};
 };
 
 }  // namespace SHiPGeometry