##### 15 July 2016, M. Aiba

#### The application performs a measurement of the offset between a quadrupole and neighbouring BPM.

## About

The centre of a quadrupole is found by varying the quadrupole excitation current. The beam trajectory downstream of the quadrupole is affected by down-feed dipole component except when the beam is going through the centre. Therefore, the measurement is two-dimensional scan, i.e., the knobs are the beam position at the neighbouring BPM and the quadrupole excitation current. The soft offset of the BPM (BPM:OFFS-X/Y) is varied, and the beam is centred by a feedback (see Orbit Tool). The feedback loop should be configured and closed before the measurement is started.

## The Panel

How to enable a measurement:

- Choose Quadrupole. Then the neighbouring BPM is automatically shown in GUI.
- Choose BPM to measure the trajectory change.
- Input or read the beam energy at the quadrupole. This value is used to compute how much the quadrupole current should be varied to obtain reasonable trajectory change. Therefore, it is not necessary to input exact number.
- Choose Horizontal or Vertical plane to measure.
- Set measurement range.
- And finally push 'Start measurement'.