[ Identification | Description | Input parameters | Output parameters | Links ]
ESS_moderator_long
ComponentProduces 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=2 xw=0.06 yh=0.12 freq=50 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
Name | Unit | Description | Default |
---|---|---|---|
size | m | Edge of cube shaped source | |
l_low | AA | Lower edge of lambda distribution | |
l_high | AA | Upper edge of energy distribution | |
dist | m | Distance from source to focusing rectangle; at (0,0,dist) | |
xw | m | Width of focusing rectangle | |
yh | m | Height of focusing rectangle | |
freq | Hz | Frequency of pulses | |
T | K | Temperature of source | |
tau | s | long time decay constant for pulse tail 1a | |
tau1 | s | long time decay constant for pulse tail 1b | |
tau2 | s | long time decay constant for pulse, 2 | |
d | s | pulse length | |
n | 1 | pulse shape parameter, 1 | |
n2 | 1 | pulse shape parameter, 2 | |
chi2 | 1/AA | lambda-distribution parameter in pulse 2 | |
I0 | flux | integrated flux, 1 (in flux units, see above) | |
I2 | flux | Flux, 2 (in flux units, see above) | |
branch1 | 1 | limit for switching between two time structures in distribution 1 (only for coupled water, else = 1) | |
branch2 | 1 | limit for switching between distribution 1 and 2. (default value 0.5) | |
branch_tail | 1 | limit for switching between pulse and tail (suggested value: tau/d) | |
branchframe | 1 | limit for switching between 1st and 2nd pulse (if only one pulse wanted: 1) |
Name | Unit | Description | Default |
---|---|---|---|
M | |||
F | |||
l_range | |||
w_mult |
ESS_moderator_long.comp
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[ Identification | Description | Input parameters | Output parameters | Links ]
Generated automatically by McDoc, Peter Willendrup <peter.willendrup@risoe.dk> / Wed Oct 8 18:18:16 2008