new option for global field

Author: maureeungaro

gemc/gdetector/gdetectorConstruction.cc

@@ -211,6 +211,18 @@ void GDetectorConstruction::ConstructSDandField() {
 		}
 	}
 
+	// Process the global field, if requested.
+	// A global field is associated with the ROOT world volume and propagated to all daughters, so it
+	// applies everywhere a more specific per-volume field has not been installed.
+	const auto global_field_name = gopt->getScalarString(GLOBAL_FIELD_OPTION);
+	if (global_field_name != "" && global_field_name != UNINITIALIZEDSTRINGQUANTITY) {
+		if (gmagneto == nullptr) { gmagneto = new GMagneto(gopt); }
+		log->info(2, "Setting global field manager for the ROOT world volume <", ROOTWORLDGVOLUMENAME,
+		          "> with field <", global_field_name, ">");
+		g4world->setFieldManagerForVolume(ROOTWORLDGVOLUMENAME,
+		                                  gmagneto->getFieldMgr(global_field_name).get(), true);
+	}
+
 	// Load digitization plugins only when geometry has changed and only on the master thread.
 	// digiplugins_need_reload is set true by reload_geometry() and prepare_geometry_for_run()
 	// so that routine BeamOn re-initializations (which also call ConstructSDandField() on the

gemc/gdetector/gdetector_options.cc

@@ -3,6 +3,7 @@
 #include "g4system_options.h"
 #include "gdynamicdigitization_options.h"
 #include "gsd.h"
+#include "gfield_options.h"
 
 /**
  * \file gdetector_options.cc
@@ -35,6 +36,10 @@ GOptions defineOptions() {
 	goptions += gdynamicdigitization::defineOptions();
 	goptions += gsensitivedetector::defineOptions();
 
+	// Field options are consumed by GDetectorConstruction (per-volume emfield and the
+	// global_field association on the ROOT world volume), so they must be defined here too.
+	goptions += gfields::defineOptions();
+
 	return goptions;
 }
 }

gemc/gfields/gfieldConventions.h

@@ -36,6 +36,15 @@
  */
 #define GFIELD_DEFAULT_VERBOSITY "0"
 
+/**
+ * \brief Command-line option name used to associate a field with the ROOT world volume.
+ *
+ * The value is the name of a configured field (see \c gmultipoles / \c gfields). The corresponding
+ * \c G4FieldManager is installed on the ROOT world volume and propagated to all daughters, acting as a
+ * global field wherever a more specific per-volume field is not set.
+ */
+#define GLOBAL_FIELD_OPTION "global_field"
+
 
 // Error codes in the 1200 range (module-local).
 #define ERR_WRONG_FIELD_ROTATION 1201

gemc/gfields/gfield_options.cc

@@ -231,6 +231,14 @@ GOptions defineOptions() {
 	};
 	goptions.defineOption("gfields", "define a generic plugin-backed e.m. field", gfields, gfields_help);
 
+	goptions.defineOption(
+		GVariable(GLOBAL_FIELD_OPTION, UNINITIALIZEDSTRINGQUANTITY, "associate a field with the ROOT world volume"),
+		"Associates a configured electromagnetic field with the ROOT (top-level) world volume.\n \n"
+		"The value must be the name of a field defined with -gmultipoles or -gfields. The field's\n"
+		"G4FieldManager is installed on the ROOT world volume and propagated to all daughters, so it\n"
+		"applies everywhere a more specific per-volume field has not been set.\n \n"
+		"Example: -global_field=dipole1\n \n");
+
 	goptions.defineOption(
 		GVariable("fieldAt", UNINITIALIZEDSTRINGQUANTITY, "query all configured fields at x y z"),
 		"Evaluate all configured electromagnetic fields at one absolute coordinate.\n \n"