diff --git a/python/cosmotool/smooth.py b/python/cosmotool/smooth.py
index b28d329..a377ed6 100644
--- a/python/cosmotool/smooth.py
+++ b/python/cosmotool/smooth.py
@@ -6,7 +6,37 @@ import h5py as h5
 import numpy as np
 import weakref
 
-def smooth_particle_density(position, velocities=None, radius=1e6, boxsize=None, resolution=128, center=None ):
+def smooth_particle_density(
+           position,
+           velocities=None,
+           radius=1e6,
+           boxsize=None, 
+           resolution=128,i
+           center=None, tmpprefix=None ):
+  """Use adaptive smoothing to produce density and momentum fields.
+
+  Parameters:
+  position   : numpy array NxQ
+               the particle positions
+               if Q==3, only positions. Q==6 means full space phase
+  velocities : Optional numpy array Nx3. 
+               It is only optional if the above Q is 6.
+  radius     : float
+               Maximum radius to which we need to compute fields
+  boxsize    : float
+               Size of the box for the generated fields
+  resolution : int
+               Resolution of the output boxes
+  center     : list of 3 floats
+               Center of the new box. It depends on the convention 
+               for particles. If those are between [0, L], then [0,0,0]
+               is correct. If those are [-L/2,L/2] then you should set
+               [L/2,L/2,L/2].
+  tmpprefix  : string
+               prefix of the temporary directory that will be used.
+               It needs to have a lot of space available. By default
+               '/tmp/ will be typically used.
+  """
   if len(position.shape) != 2:
      raise ValueError("Invalid position array shape")
 
@@ -19,7 +49,7 @@ def smooth_particle_density(position, velocities=None, radius=1e6, boxsize=None,
     raise ValueError("Need a boxsize")
 
   cx,cy,cz=center
-  with TemporaryDirectory() as tmpdir:
+  with TemporaryDirectory(prefix=tmpprefix) as tmpdir:
     h5_file = os.path.join(tmpdir, 'particles.h5')
     with h5.File(h5_file, mode="w") as f:
       data = f.create_dataset('particles', shape=(position.shape[0],7), dtype=np.float32)