High precision tune and coupling measurements and tune/coupling feedback in RHIC

Abstract

Precision measurement and control of the betatron tunes and betatron coupling in RHIC are required for establishing and maintaining both good operating conditions and, particularly during the ramp to high beam energies, high proton beam polarization. While the proof-of-principle for simultaneous tune and coupling feedback was successfully demonstrated earlier, routine application of these systems has only become possible recently. Following numerous modifications for improved measurement resolution and feedback control, the time required to establish full-energy beams with the betatron tunes and coupling regulated by feedback was reduced from several weeks to a few hours. A summary of these improvements, select measurements benefitting from the improved resolution and a review of system performance are the subject of this report.

Stabilization of betatron tune in Indus-2 storage ring

“…This figure shows that without the feedback, betatron tune is shifted and it crosses the 3rd, 4th and 5th order resonance lines [9]. The equations of these resonance lines are −ν x +2ν y = 3, (7) 4ν x −ν y = 31, (8) 2ν x +3ν y = 37, (9) 3ν x +ν y = 34.…”

“…The measured tune value (ν x , ν y ) is subtracted from desired tune value (ν xREF , ν yREF ) to obtain tune error (Δν x , Δν y ). PI control rule is applied to multiply the tune error and the inverse of the premeasured tune transfer matrix to calculate the required changes in the quadrupole power supply currents [7,8]. For small changes of excitation currents of quadrupoles, the variation of tunes depends linearly on the current increments.…”

Application of independent component analysis to ac dipole based optics measurement and correction at the Relativistic Heavy Ion Collider

“…The beta-beat response matrix method using quadrupoles in interaction regions and arcs was applied to reduce peak beta-beat in both planes to approximately 10% to facilitate arc beta-beat correction. The computed horizontal closed orbit bumps were then applied by the closed orbit feedback system [20]. Figure 11 shows the computed horizontal closed orbit required for arc beta-beat correction.…”

Analysis of failed ramps during the RHIC FY09 run

“…A "session" refers to a period of time dedicated to accelerating beams to full energies ("ramp development"). During the FY09 run, each and every ramp was performed using tune and coupling feedback [3,4]. Since this was the first time this important feedback-based control of beams was routinely used operationally, ramp development experience was carefully documented and analysed as described in the remainder of this report.…”