rays, specifying repeat

Specifying a repeat of the previous set of rays.

This is relevant only for space-charge calculations.

A set of rays can be repeated in a space-charge calculation until convergence is reached.

As explained in the general notes on space-charge each set of rays is traced in the space-charge created by the previous set.

Further information on the option to repeat a set of rays or to introduce new rays (eg to introduce positive ions after an electron cathode iteration) is given in the note on iterating sets of rays.

Usually the currents would be slowly increased at successive iterations until the desired final current is reached, and would then stay at that value for a few further iterations. If this is not done -eg if the user starts with the final desired current -then the rays might diverge or misbehave in some other way.

The user chooses the number of iterations, and also chooses a multiplication factor for the currents at each iteration. For example the user might start with a current 0.1 times the desired final value, and then in the following iterations the multiplication factor might be 2, 4, 6, 10, 10 and 10 (and note that this factor multiplies the initial current, not the previous current). Then

run 1 has current 0.1 and runs in zero space-charge,

run 2 has current 0.2 and runs in space-charge of current 0.1,

run 3 has current 0.4 and runs in space-charge of current 0.2,

run 4 has current 0.6 and runs in space-charge of current 0.4,

run 5 has current 1.0 and runs in space-charge of current 0.6,

run 6 has current 1.0 and runs in space-charge of current 1.0,

run 7 has current 1.0 and runs in space-charge of current 1.0.

On the other hand the user might sometimes start with the desired final current, in which case the multiplication factor would always be 1.

See the notes on the space charge tube method and the space charge cell method for the two possible ways of assigning space charge.

Colours of the rays:

During an iterative calculation the previous rays are redrawn (for comparison) in green (colour number 2), so this colour should be avoided for the new rays.

(The green rays are redrawn without using the interpolation points.)

Return to specifying the initial ray conditions.

For users who are editing or constructing an 'input data file' without the use of the data-builder -that is, pre-processor:

But Manual editing is certainly not recommended -it is a relic from the time when the databuilder was not available All users are strongly encouraged to use the databuilder, which always gives the correct formats and which has many options for which the formats are not described or easily deduced.

CPO2D:

Typical data (including the initial specification of the set of rays), taken from the 'example' file xmpl2d12.dat, are:

set of single rays:

0.1 -10.0 -0.0100 1.0000 1. 0.016E-3 r,z,vr,vz,energy,mA

0.3 -10.0 -0.0300 0.9996 1. 0.047E-3 r,z,vr,vz,energy,mA

0.5 -10.0 -0.0499 0.9988 1. 0.078E-3 r,z,vr,vz,energy,mA

0.7 -10.0 -0.0698 0.9976 1. 0.109E-3 r,z,vr,vz,energy,mA

0.9 -10.0 -0.0896 0.9960 1. 0.140E-3 r,z,vr,vz,energy,mA

1.1 -10.0 -0.1093 0.9940 1. 0.172E-3 r,z,vr,vz,energy,mA

1.3 -10.0 -0.1289 0.9917 1. 0.203E-3 r,z,vr,vz,energy,mA

1.5 -10.0 -0.1483 0.9889 1. 0.234E-3 r,z,vr,vz,energy,mA

1.7 -10.0 -0.1676 0.9859 1. 0.265E-3 r,z,vr,vz,energy,mA

1.9 -10.0 -0.1867 0.9824 1. 0.306E-3 r,z,vr,vz,energy,mA

2.1 -10.0 -0.2055 0.9787 1. 0.328E-3 r,z,vr,vz,energy,mA

2.3 -10.0 -0.2241 0.9746 1. 0.359E-3 r,z,vr,vz,energy,mA

2.5 -10.0 -0.2425 0.9701 1. 0.390E-3 r,z,vr,vz,energy,mA

2.7 -10.0 -0.2607 0.9654 1. 0.421E-3 r,z,vr,vz,energy,mA

2.9 -10.0 -0.2785 0.9604 1. 0.452E-3 r,z,vr,vz,energy,mA

last of this set of rays

y n calculate space-charges?

0.2 mesh spacing for space-charges

repeat of previous rays