Figure h: varying the x beam offset
The first term was almost exclusively dedicated to running the SLAC version of guinea-pig, which is optimised for NLC-B parameters. Several approaches were tried in loading the beam files and displaying information.
These runs mostly served as a check of guinea-pig and of our understanding of its inputs and outputs, as well as a learning platform for scripting and for the root C++ framework used.
Many physical parameters were outputted, to gain visual understanding of the features, for example: energy, angular offsets, spatial coordinates of particles.
Interesting features appear when varying one parameter in a series of runs, for example:
--different centre of mass energies.
--varying the beam offset on the x axis (typically by up to a few hundred nm.)
--varying the beam offset on the y axis (typically by up to 10 nm.)
Two interesting plots are presented below, in figures h and i: we notice how the angular distribution is asymmetric when the beam offsets are varied.
Figure h: varying the x beam offset
This figure represents different parameters of the positron beam with an x-offset of 50, 100, 150, 200 and 400 nm.
The most interesting pattern to notice is that the angle of the beam to the x-axis (theta-x) has an asymmetric distribution, with two peaks. In the electron beam the distribution is the mirror image of this one. This shows that the beam polarises into two beams, separated from the centre, as its offset increases.
Notice also that the distribution in the y direction becomes more sharply peaked with higher x-offset.
Figure i: varying the beam energy
In this figure the positron beam parameters are plotted with centre of mass energies of 350, 500 and 650 GeV.
The distribution of theta-x (angle to the x-axis) becomes more sharply polarised at higher energies, and the luminosity spectrum widens, due to higher beamstrahlung.
The x and y positions distributions, sharpen at higher energies due to adiabatic damping. Adiabatic damping arises from the particles' relativistic speeds, and causes the transverse offsets of the beam to diminish as 1/√p, due to the invariance of the normalised emittance (since the 1-σ beam envelope goes as the square root of the emittance, which has a momentum term.)This means that the beams get more focussed as the particles go faster; it is one of the few processes that increases luminosity with increasing beam energy.