What is inside the detector in a particle accelerator??

[JADphysics]

We need E and B fields to steer and focus beams in a particle accelerator, but all the calculations we do in QFT assume (apart from the colliding particles) that we are in the vacuum state. Does this mean there are no fields at the point of interaction of two beams? i.e., are detector chambers designed to be vacuum sealed and do they shield out external E and B fields? How then do the colliding particles enter the chamber?

Thanks.

[Galron]

The emission source is inside the chamber..?

Not sure what you mean though tbh.

[JADphysics]

The emission source is inside the chamber..?

Not sure what you mean though tbh.

Sorry, I don't mean the emission chamber. The particles collide somewhere, presumably this happens at the center of the detector. What is that space? Is it a vacuum? Are there still stray fields from the accelerator ring? Does it matter if this is not a vacuum or if there are electric and magnetic fields around when the particles actually collide?

[rkrsnan]

Not only the center of the detector, but other regions like the beam pipe are kept in vacuum.
The detector set up usually consists of magnetic fields. It is used to bend the collision products and measure their momenta. The effect of this field on the interaction between particles during collision will be extremely small(if at all there is an effect).