High-beta run at injection

Switch to hypercycle 0.45TeV_2017_HighBeta during rampdown and for the preparation to injection.

Let the machine come down to pre-injection.

Then launch a pre-cycle (yes - even if you just came down normally from 6.5 TeV) with the following variation :

PRECYCLE sequence: the two tasks containing “(HIGH BETA RUN)” in the name that concern the Q4s have to be executed:
Please step them and check that RQ4s in IP1/IP5 (8 circuits):

    1st TASK: Go back to IDLE (were ARMED)
    2nd TASK: Go back to ARMED and REF.OPENLOOP command in EQUIPSTATE gives 80 A

Conditions and setup

High beta at injection is performed with beta* of 50-90m which gives IP sizes of ~500-800 microns. Be aware of this huge size when performing IP steering (for example).

The machine is setup for collision tunes (and so is the ADT). There is no separation in IR1 and IR5, so for probes inject into non-colliding buckets. For measurements with probes move to injetion tunes (Q') and then back to collision tunes (0.31/0.32) before injecting nominal bunches.

The aperture limit of the machine in this configuration is arounf 8 sigma in IR5. It is important to have the collimators sufficiently closed to avoid that background signals cover the very tiny luminosity signal.

The BPMs can be used very easily to find collisions as the rates are very low which makes optimizations very tricky. Below an example of the IR beam position panels (Machine specials menu) for optimized beam overlap. The residual offsets determined by the BPMs are at the level of 0.2 mm which is small compared to the beam size.

As the luminosity is very low, the optimizations must be done with large steps (1 sigma) and large integration 60 s. An example is given below.

Note the rates are at the level of 0.001-0.002 when optimized with 5 colliding bunches (see below).

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