feat: add front support to BarrelImaging Calorimeter (#608)

### Briefly, what does this PR introduce?
Adds the 0.5 cm aluminum front support 

### What kind of change does this PR introduce?
- [ ] Bug fix (issue #__)
- [x] New feature (issue #__)
- [ ] Documentation update
- [ ] Other: __

### Please check if this PR fulfills the following:
- [ ] Tests for the changes have been added
- [ ] Documentation has been added / updated
- [ ] Changes have been communicated to collaborators

### Does this PR introduce breaking changes? What changes might users
need to make to their code?
No.

### Does this PR change default behavior?
No.

---------

Co-authored-by: akshaya <[email protected]>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

compact/definitions.xml

@@ -544,7 +544,7 @@ Service gaps in FW direction (before endcapP ECAL) and BW direction (before endc
     <constant name="EcalEndcapN_rmin"               value="9.*cm"/>    <!-- Currently fix value hardcoded -->
     <constant name="EcalEndcapN_rmax"               value="63.*cm"/>   <!-- Currently fix value hardcoded -->
 
-    <constant name="EcalBarrelRegion_thickness"     value="38.*cm"/>
+    <constant name="EcalBarrelRegion_thickness"     value="40.*cm"/>
     <constant name="EcalBarrel_rmin"                value="max(81.*cm, CentralTrackingRegion_rmax + BarrelPIDRegion_thickness + BarrelExtraSpace_thickness)"/> <!-- FIXME hardcoded max -->
     <constant name="EcalBarrel_inner_margin"        value="2*cm"/>
     <constant name="EcalBarrel_rmax"                value="EcalBarrel_rmin + EcalBarrelRegion_thickness"/>

compact/ecal/barrel_interlayers.xml

@@ -30,7 +30,8 @@
     <constant name="EcalBarrel_Calorimeter_offset"
       value="(EcalBarrel_Calorimeter_zmax - EcalBarrel_Calorimeter_zmin)/2.0"/>
 
-    <constant name="EcalBarrel_Support_thickness"    value="3*cm"/>
+    <constant name="EcalBarrel_FrontSupportThickness" value="0.5*cm"/>
+    <constant name="EcalBarrel_BackSupportThickness" value="3*cm"/>
     <constant name="EcalBarrel_SiliconThickness"     value="500*um"/>
     <constant name="EcalBarrel_ElectronicsThickness" value="150*um"/>
     <constant name="EcalBarrel_CopperThickness"      value="100*um"/>
@@ -68,7 +69,7 @@
     <constant name="EcalBarrel_RadiatorThickness"    value="EcalBarrel_FiberZSpacing * 17"/>
     <constant name="EcalBarrel_TotalFiberLayers_num" value="12"/>
     <constant name="EcalBarrel_SectorRepeat"         value="EcalBarrelSectorsN"/>
-    <constant name="EcalBarrel_AvailThickness"       value="EcalBarrelRegion_thickness - EcalBarrel_Support_thickness"/>
+    <constant name="EcalBarrel_AvailThickness"       value="EcalBarrelRegion_thickness - EcalBarrel_BackSupportThickness - EcalBarrel_FrontSupportThickness"/>
 
     <constant name="EcalBarrel_ImagingLayerThickness" value="1.5*cm"/>
 
@@ -145,9 +146,11 @@
         </module_component>
       </module>
 
+      <support thickness="EcalBarrel_FrontSupportThickness" material="Aluminum" vis="EcalBarrelSupportVis"/>
+
       <layer repeat="1" vis="EcalBarrelLayerVis"
              thickness="EcalBarrel_ImagingLayerThickness"
-             space_before="0.*cm">
+             space_before="EcalBarrel_FrontSupportThickness">
         <barrel_envelope
           inner_r="EcalBarrel_rmin - EcalBarrel_Stave_thickness"
           outer_r="EcalBarrel_rmin + EcalBarrel_Stave_thickness"
@@ -237,7 +240,7 @@
       <sectors vis="EcalBarrelSectorVis"/>
       <layer repeat="EcalBarrelImagingLayers_num-1" vis="EcalBarrelLayerVis"
        space_between="EcalBarrel_ImagingLayerThickness + EcalBarrel_SpaceBetween"
-       space_before="EcalBarrel_ImagingLayerThickness + EcalBarrel_SpaceBetween/2.">
+       space_before="EcalBarrel_FrontSupportThickness + EcalBarrel_ImagingLayerThickness + EcalBarrel_SpaceBetween/2.">
         <slice material="SciFiPb_PbGlue" thickness="EcalBarrel_RadiatorThickness" vis="EcalBarrelFiberLayerVis">
           <fiber material="SciFiPb_Scintillator"
             sensitive="yes"
@@ -270,7 +273,7 @@
         </slice>
       </layer>
 
-      <support thickness="EcalBarrel_Support_thickness" material="Aluminum" vis="EcalBarrelSupportVis"/>
+      <support thickness="EcalBarrel_BackSupportThickness" material="Aluminum" vis="EcalBarrelSupportVis"/>
     </detector>
   </detectors>
 

src/BarrelCalorimeterImaging_geo.cpp

@@ -28,6 +28,10 @@ using namespace dd4hep;
 
 typedef ROOT::Math::XYPoint Point;
 
+// geometry helpers
+static void buildSupport(Detector& desc, Volume& mother, xml_comp_t x_support,
+                         const std::tuple<double, double, double, double>& dimensions);
+
 // barrel ecal layers contained in an assembly
 static Ref_t create_detector(Detector& desc, xml_h e, SensitiveDetector sens)
 {
@@ -176,8 +180,10 @@ static Ref_t create_detector(Detector& desc, xml_h e, SensitiveDetector sens)
       }
     }
   }
-
-  // Loop over the sets of layer elements in the detector.
+  if (x_detector.hasChild(_Unicode(support))) {
+       buildSupport(desc, sector_volume, x_detector.child(_Unicode(support)), {inner_r, layer_pos_z, x_dimensions.z(), half_dphi});
+  }
+  //Loop over the sets of layer elements in the detector.
   int layer_num = 1;
   for (xml_coll_t i_layer(x_detector, _U(layer)); i_layer; ++i_layer) {
     xml_comp_t x_layer             = i_layer;
@@ -399,4 +405,21 @@ static Ref_t create_detector(Detector& desc, xml_h e, SensitiveDetector sens)
   return sdet;
 }
 
+// simple aluminum sheet cover
+// dimensions: (inner r, position in z, length, phi)
+static void buildSupport(Detector& desc, Volume& sector_volume, xml_comp_t x_support,
+                         const std::tuple<double, double, double, double>& dimensions)
+{
+  auto [inner_r, pos_z, sector_length, hphi] = dimensions;
+  double support_thickness                   = getAttrOrDefault(x_support, _Unicode(thickness), 0.5 * cm);
+  auto   material                            = desc.material(x_support.materialStr());
+  double trd_y                               = sector_length / 2.;
+  double trd_x1_support                      = std::tan(hphi) * pos_z;
+  double trd_x2_support                      = std::tan(hphi) * (pos_z + support_thickness);
+
+  Trapezoid s_shape(trd_x1_support, trd_x2_support, trd_y, trd_y, support_thickness / 2.);
+  Volume    s_vol("support_layer", s_shape, material);
+  s_vol.setVisAttributes(desc.visAttributes(x_support.visStr()));
+  sector_volume.placeVolume(s_vol, Position(0.0, 0.0, pos_z + support_thickness / 2.));
+}
 DECLARE_DETELEMENT(epic_EcalBarrelImaging, create_detector)