[neutron-mc] Chopper_fermi arguments

[Granroth, Garrett E.]

Dickon,
	For simulating the SNS Fermi chopper instruments ARCS and
SEQUOIA, I 
	have found that I get the correct phasing for 	

	phase=(L1)/(sqrt(E)*SE2V)+toffset;
	
	Where L1 is the distance from the moderator to the chopper, E is
the
	energy of desired neutron, and toffset accounts for the time 
	difference between t=0 and the time when the moderator has the
highest
	probability of emitting a neutron of energy E. 

	Hopefully this helps.

Garrett 

Garrett Granroth
Instrument Scientist
Spallation Neutron Source 
Oak Ridge National Laboratory
P.O. Box 2008 MS 6474
Oak Ridge TN 37831
Phone: 865-576-0900
Fax: 865-241-5177
email: granrothge at ornl.gov


-----Original Message-----
From: Champion, JDM (Dickon) [mailto:D.Champion at rl.ac.uk] 
Sent: Wednesday, August 06, 2003 7:26 AM
To: 'neutron-mc at neutron.risoe.dk'
Subject: [neutron-mc] Chopper_fermi arguments

Hi

i am testing the soon to be officially released ISIS moderator modules
with
the Chopper_fermi module of Andrew Garrett.  
I was wondering how the Phase Angle is precisely defined? I have been
looking at the code but it is not obvious to me. i can get reasonable
results if i put the time of the selected energy to reach the far wall
of
the cylinder in the x=0 plane, but i would like to know what the module
is
expecting.

thank you for any help in this matter

dickon

Dr Dickon Champion 
ISIS Facility 
R3 Room 1-49 
Rutherford Appleton Laboratory 
Chilton 
OX11 0QX 
  
Tel : 01235 446043 (Office) 
      07939 084159 (Mobile) 

Fax : 01235 445720 

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