How do particle accelerators change fast enough

[azaharak]

Hi all


How do the computers that control the magnets in a particle accelerator, make their changes fast enough to propel the charged particles at almost the speed of light, specifically with all those electronic latencies.

Is the course of the collision computer entirely beforehand, so the computers/electronics know what to do as opposed to sensing the particles positioning and changing in response?


Thanks to everyone in advance

 

[hamster143]

Particles being accelerated travel along precomputed trajectories. No sensing/adjusting is required.

 

[rcgldr]

In the case of a linear acceleration, each successive section is increasingly longer, reducing the rate a which the sections have to change their fields.

There's no sensing or reacting to particles, instead, charged particles are injected into the acceleration with the assumption that one or more of those charged particles will end up in the correct window of time for the pre-programmed cycling of the sections of the accelerator.

 

[Vanadium 50]

Particles being accelerated travel along precomputed trajectories.

True.

No sensing/adjusting is required.

Not true. There are beam pickups (and more specialized tools, like loss monitors) that inform the operators on the state of the beam. What is true is that these adjustments are done over a period of many turns (for a circular machine), and what matters is the deviation from the pre-computed reference orbit.

 

[Bob S]

I presume you are referring primarily to circular accelerators.
In circular accelerators with strong focusing (quadrupoles) and higher order magnets (sextupoles, octupoles), the orbit of a particle with a specific longitudinal momentum is well-defined. When an RF-field is applied to accelerate the particle, the currents in all the magnets are slowly ramped up to accommodate the higher energy particles. Beam position monitors (BPMs) are used to constantly monitor the beam position. In the Fermilab Tevatron, there are close to 300 beam position monitors around the 6,283-meter circumference that monitor the beam position to about 0.1 mm in the 75-mm diameter aperture.
If a particle gains too much energy in the RF accelerating cavity, the particle's velocity and orbit change such that the particle gains less energy in the RF cavities, thus correcting the energy offset. This is known as longitudinal stability. If a particle has a transverse offset in either position or angle, the quadrupoles refocus the particle to oscillate about the central orbit. This is known as transverse stability.

Bob S