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This animation explores what kind of accelerating fields would be needed to first accelerate an extended column of uniform velocity charges and then compress the column into a very spatially narrow group. The accelerating Electric field, `E-a(x,t) , will need to be chosen so that it contains both an average E field and a spatially varying E field that accelerates the back end of the initial column more than the front end. With this velocity profile we expect that the spatial length of the column would go to zero at distance
`d_0="len"v_(avg)/(deltav)`
where len is the length of the pulse at the end of the acceleration, `v_(avg)` is the average speed of its particles, and `deltav` is the speed difference between the back and front end of the pulse. This might seem like the end of the problem but, with no other control, the pulse length will increase after `"len"_0` because the velocities of the charges are not uniform. Therefore we should place another criterion on the compression phase of the pulse-that both the member velocity difference and the member spatial difference be simultaneously zero. To do this we apply velocity change ramps of opposite sign to the leading and trailing members of the group. This results in a new value for the distance required to compress the pulse. We compute the value of the velocity change ramp needed using the following algorithm. First we compute the number of computer iterations n (same as elapsed time) needed using a given ramp to get the front and back velocities the same:`ndeltav_(Ramp)=(v_(Back)-v_(Front))/2`
Then we express the distance this `deltav_(Ramp) will compress the bunch`n(v_(Back)-v_(Front))/2=(x_(Front)-x_(Back))/2`
From this we can compute the number of iterations needed:`n=(x_(Front)-x_(Back))/(v((Back)-v_(Front))`
Then we can use n in the first equation to obtain an expression for dvRamp:`deltav_(Ramp)=(v_(Back)-v_(Front))/(2*n)=(v_(Back)-v_(Front))^2/(2(x_(Front)-x_(Back))`
To actually achieve the accelerations needed for compression, we would use time and spatially varying quadrupole electric fields since the waveform required is a sawtooth. The advantage of the final result is that, with the bunch compressed to zero width and with all going the same speed, it is easy to do further velocity changes. The parameters available are the following: