Adjustment of angles in the cooling section with drag rate measurements

1. Adjustment of angles in the cooling section with drag rate measurements Recycler Meeting November 28, 2007 A. Shemyakin and L. Prost

2. 2 kv jump Choice of the voltage jump: 2 kV • A 2-kV voltage jump measures the drag rate close to maximum • Insensitive to energy errors • The total shift of pbar energy during several-minutes measurement still keeps the drag force near maximum • The drag rate is ~ (electron angles)-2

3. Procedure • Low-intensity pbar beam is cooled to equilibrium • Electron beam is moved to a desired offset • Electron energy is shifted • Drag rate is a linear fit to the Average Momentum as a function of time HV 5min E-beam position Average pbar momentum Momentum width FWs Arden’s aggregate Dan’s program

4. Electron angles’ composition One can split the electron angles to a linear component, and everything else Dipole angles (Autotune + field adjustment in CS) Axially-symmetrical component (adjustment adjustment of solenoidal lenses upstream of the cooling section) Quadrupole (adjustment of quadrupoles) Temperature, time-dependent components, aberrations … Because of the finite pbar beam size, the drag rate in each point is affected by all three linear effects.

5. Solenoid modules BPMs Electron beam trajectory What we have tried to do (dipole component) Field adjustment with drag rate measurement in one solenoid (24-25-Oct-2007) In this set, the results were ambiguous. Most likely, we did not adjust the field as good as it used to be before the shutdown The drag rate on axis is still lower than the record value for 0.1 A.

6. What we have tried to do (solenoidal focusing) • Lenses B1 and B2 were adjusted while the pbar beam was kept at equilibrium (26-Oct-2007) • The hope was that the equilibrium momentum spread can be used as an indicator • Difficult to analyze • Most likely, the electron energy fluctuations contribute significantly • SPB01I might be too high by ~ 1A

7. What we have tried to do (quadrupoles) • YAG measurements • Clearly shown importance of quadrupole and higher components of electron angles in the cooling section • At best quadrupole settings found in YAG measurements, the drag and cooling rates are not better than without quads • Most likely reason is an ion compensation in the DC mode • Quadrupole adjustment according to drag rate measurements • -1 mm vertical offset • Change one of 6 correction quadrupoles, measure the drag rate, leave its setting in a position with the maximum rate • ~13 min/rate measurement, ~ 1 hr per quadrupole

8. Results of quadrupole adjustments (1-Nov-2007) After the adjustment, the area of good cooling increased. Most likely, the quadrupole effect had been dominant.

9. Solenoid modules BPMs Electron beam trajectory Ideal trajectory How the procedures can be improved (dipole fields) • Instead of adjusting a field in the first solenoid and measuring small changes in drag rates, • create a MULT changing simultaneously 10 X 16 = 160 dipole correctors so that the beam would still moving through centers of all BPMs and • adjust the correctors to the position of maximum drag rate

10. + = How the procedures can be improved (focusing) • If errors of solenoidal and quadrupole focusing are comparable, measuring of drag rates at one offset can be misleading. • We probably should measure the drag rates at two offsets, (X,Y) = (1.5,0) and (0,1.5) mm. • Possible scenario: • measure a change in the drag rate resulted from the change of a quadrupole current • repeat for 6 quads and 2 offsets • apply the procedure similar to that developed by Alexey for YAG measurements • Minimization of (1/drag rate)