diff --git a/run.py b/run.py
index 21d6585..33131a7 100644
--- a/run.py
+++ b/run.py
@@ -10,7 +10,7 @@
 import pprint
 FILEPATH= pathlib.Path(yaml_directory.__file__).parent.resolve()
 #FP= pathlib.Path(__file__).parent.resolve()
-def run_simulation_server(name, monitor_overview, measurement_noise_level):
+def run_simulation_server(name, monitor_overview, measurement_noise_level, number_of_particles):
     if name == "diag0":
         devices = load_relevant_controls(
             os.path.join( FILEPATH, "DIAG0.yaml")
@@ -25,7 +25,7 @@ def run_simulation_server(name, monitor_overview, measurement_noise_level):
         raise ValueError(f"Unknown virtual accelerator name: {name}")
 
     PVDB = create_pvdb(devices)
-    va = get_virtual_accelerator(name, monitor_overview, measurement_noise_level)
+    va = get_virtual_accelerator(name, monitor_overview, measurement_noise_level, number_of_particles)
     server = SimServer(PVDB)
     driver = SimDriver(server=server, devices=devices, virtual_accelerator=va)
 
@@ -54,7 +54,16 @@ def run_simulation_server(name, monitor_overview, measurement_noise_level):
         help="If provided, adds realistic noise to measurements. See `simulation_server.virtual_accelerator.utils.add_noise` for details.",
     )
 
+    parser.add_argument(
+        "--number_of_particles",
+        type=int,
+        default=0,
+        help="If provided, limits the number of particles to this amount.",
+    )
+
     args = parser.parse_args()
+
+    print("args.number_of_particles ", args.number_of_particles)
     run_simulation_server(
-        args.name, args.monitor_overview, args.measurement_noise_level
-    )
\ No newline at end of file
+        args.name, args.monitor_overview, args.measurement_noise_level, args.number_of_particles
+    )
diff --git a/simulation_server/factory.py b/simulation_server/factory.py
index 0abb39a..ce86327 100644
--- a/simulation_server/factory.py
+++ b/simulation_server/factory.py
@@ -10,7 +10,7 @@
 LCLS_LATTICE = pathlib.Path(os.environ.get("LCLS_LATTICE", "/sdf/group/ad/sw/scm/repos/optics/lcls-lattice/cheetah"))
 
 
-def get_virtual_accelerator(name, monitor_overview=False, measurement_noise_level=None):
+def get_virtual_accelerator(name, monitor_overview=False, measurement_noise_level=None, number_of_particles=0):
     """
     Create an instance of VirtualAccelerator for a given beamline.
 
@@ -26,6 +26,8 @@ def get_virtual_accelerator(name, monitor_overview=False, measurement_noise_leve
     measurement_noise_level: float, optional
         If provided, adds realistic noise to measurements.
         See `simulation_server.virtual_accelerator.utils.add_noise` for details.
+    num_particles: int, optional
+        If provided, limits the number of particles to this amount.
 
     Returns
     -------
@@ -60,6 +62,10 @@ def get_virtual_accelerator(name, monitor_overview=False, measurement_noise_leve
         mapping_file = os.path.join(FILEPATH, "mappings", "lcls_elements.csv") 
         lattice_file = os.path.join(LCLS_LATTICE,"nc_hxr.json")
 
+    if number_of_particles > 0:
+        incoming_beam.particles = incoming_beam.particles[:number_of_particles]
+        incoming_beam.survival_probabilities=incoming_beam.survival_probabilities[:number_of_particles]
+
     return VirtualAccelerator(
         lattice_file=lattice_file,
         initial_beam_distribution=incoming_beam,
diff --git a/start.sh b/start.sh
index 59af758..fc3082d 100755
--- a/start.sh
+++ b/start.sh
@@ -12,11 +12,12 @@ else
     export LCLS_LATTICE=$1
 fi
 
- 
+
 NAME="${2:-diag0}"
 OVERVIEW="${3:-False}"
 NOISE="${4:-0.0}"
+NUM_PARTICLES="${5:-0}"
 
 # Start the server
 echo "Starting server..."
-python3 run.py --name $NAME --monitor_overview $OVERVIEW --measurement_noise_level $NOISE
\ No newline at end of file
+python3 run.py --name $NAME --monitor_overview $OVERVIEW --measurement_noise_level $NOISE --number_of_particles $NUM_PARTICLES