Initial Values for Magnet Trimming Resistors
C H Gough
Introduction
This Note is one of a series, documenting the development of the five Storage Ring Kicker systems for the SLS. The pulser current was found to depend upon which magnet was used. Note 7 found that parallel resistance trimming of the magnets was highly effective to compensate for the different chamber resistances.
This Note finalises the choice of trimming resistor values.
Effect of Resistor Inductance
Fig.1 Basic circuit.
Fig.2a Effect of inductance in series with trimming resistor on measured current. The inductance is assumed to scale with the required resistance, so these curves are for 0, 5 and 10nH/. The vertical axis is proportional, so "1m" corresponds to 1 part per
thousand.
Fig.2b Effect of inductance in series with trimming resistor on the magnetic field.
Resistor Values for Parallel Trimming
The results are shown in Table 1. The minimum trimming resistance for Magnet 2 was chosen to give a reserve of 5ppt trimming range on this magnet. The other magnets have considerably lower resistance values and correspondingly tighter tolerances.
Magnet / Chamber DCR of Chamber Trimming Resistor
M1/C4 0.849 23.10.1
M2/C2 0.734 150.02
M3/C3 0.837 25.00.2
M4/C1 0.926 15.950.07
M5/C6 0.843 24.00.15
Table 1. Parallel trimming resistors with estimated tolerances.
Conclusions
The trimming resistance should have an inductance below 5nH/.
