The OPAL Discussion Forum

[Norman Huang <norman-huang AT hotmail.com>]

Hi Steve,

Thanks for the tip, I've ran the test again following your suggestion and I'm seeing the correct energy. But now I'm even more confused.

It now appears to me that the average energy (at least that printed out by OPAL on the cosole) is taken directly from the value of PT. This doesn't make sense to me... Is it doing an approximation? Is there an implicit assumption that the resting mass of the particle is much smaller than the kinetic energy? In fact, I've noticed many places in the code where momentum and energy are used almost interchangeably.

I would much appreciate it if anyone could help me out with this.

Thanks,
Norman

Steve Russell <srussell AT lanl.gov> wrote:

Hi Norman,

When I run this file I get a distribution with a kinetic energy over 1000 MeV. Try changing the distribution command from

Dist1:DISTRIBUTION, DISTRIBUTION=gauss,
                    sigmax=  0.005, sigmapx=0.0, corrx=0.0,
                    sigmay=  0.005, sigmapy=0.0, corry=0.0,
                    t = 0.0, sigmat= 0.00040, pt=P0*1e9, sigmapt=0.0,corrt=0.0;

to

Dist1:DISTRIBUTION, DISTRIBUTION=gauss,
                    sigmax=  0.005, sigmapx=0.0, corrx=0.0,
                    sigmay=  0.005, sigmapy=0.0, corry=0.0,
                    t = 0.0, sigmat= 0.00040, pt=Edes*1e9, sigmapt=0.0,corrt=0.0;

I used "Edes" instead of "P0" to set the value of pt.

This at least gives the right average energy.

Regards

Steve


On 10/12/2011 04:19 PM, Norman Huang wrote:

Hi Andreas,

Following up on my request for a sample test file, I've attached the test case that we wrote to simulate a pencil beam through a single focusing quadrupole. Maybe I'm misinterpreting the input format, as the result does not match with expectation; in any case, could you take a look?

---

Here are the specs for our configuration:

Track: Drift1---->Quarupole---->Drift2

Drift1 = 10 cm
Drift2 = 122.7647 cm

Beam: Proton

Kinetic energy = 460 MeV

Magnetic rigidity = 3.45816 Tm

Initial condition:

Sigma X = Sigma Y = 0.5 cm

Sigma Px = Sigma Py = 0

r12 = r34 = 0

Quadrupole:

Pole tip field = 0.5 T

Apperture radius = 3.55 cm

Length = 20 cm

---

We still don't know what SigmaT and SigmaPt refer to, but OPAL wouldn't run if we set them to 0. 

The expected output is an upright X-Px distribution at the end of Drift2, which we're not getting.

Thanks,

Norman

-- 
Steve Russell
Technical Staff Member
MS H851
P.O. Box 1663
Los Alamos National Laboratory
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USA
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