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The ESS_moderator_long_2001 Component

Identification

• Site:
• Author: KL, February 2001
• Origin: Risoe
• Date:

Description

Produces a time-of-flight spectrum, from the ESS parameters
Chooses evenly in lambda, evenly/exponentially decaying in time
Adapted from Moderator by: KN, M.Hagen, August 1998

Units of flux: n/cm^2/s/AA/ster
(McStas units are in general neutrons/second)

Example general parameters (general):
size=0.12 l_low=0.1 l_high=10 dist=1.6 xw=0.19 yh=0.15 freq=16.67
branchframe=0.5

Example moderator specific parameters
(From F. Mezei, "ESS reference moderator characteristics for ...", 4/12/00:
Defining the normalised Maxwellian
M(lam,T) = 2 a^2 lam^-5 exp(-a/lam^2); a=949/T; lam in AA; T in K,
the "pulse integral" function
iexp(t,tau,d) = 0                              ; t<0
tau (1-exp(-t/tau))            ; 0d ,
and the long pulse shape function
I(t,tau,n,d) = (iexp(t,tau,d)-iexp(t,tau/n,d)) n/(n-1)/tau/d ,

the flux distribution is given as
Phi(t,lam) =  I0 M(lam,T) F(t,tau,n)
+ I2/(1+exp(chi2 lam-2.2))/lam*F(t,tau2*lam,n2)  )

c1: Ambient H20, long pulse, coupled
T=325 tau=80e-6 tau1=400e-6 tau2=12e-6 n=20 n2=5 d=2e-3 chi2=2.5
I0=13.5e11 I2=27.6e10    branch1=0.5 branch2=0.5

c2: Liquid H2, long pulse, coupled
T=50 tau=287e-6 tau1=0 tau2=20e-6 n=20 n2=5 d=2e-3 chi2=0.9
I0=6.9e11 I2=27.6e10    branch1=0 branch2=0.5

Debugged intensively against Mezei note (4/12 2000) and VitESS @ Rencurel 2006.
The output is now neutrons / second, not as previously neutrons / pulse.

%VALIDATION
Validated against VitESS and Mezei note (4/12 2000) @ Rencurel 2006

Input parameters

Links

• Source code for ESS_moderator_long_2001.comp.

[ Identification | Description | Input parameters | Links ]