Accumulation Experiments with Stochastic Cooling in the ESR C. Dimopoulou T. Katayama I. Meshkov D. Möhl F. Nolden G. Schreiber A. Sidorin R. Stassen M. Steck H. Stockhorst G. Trubnikov

Aim of the Experiment Accumulation of pbars will be needed in HESR due to missing RESR HESR allows no usual rf stacking Therefore „time domain“ stacking is needed GSI‘s ESR can serve for prototype experiment with limited performance available barrier bucket system available stochastic cooling system 5.10.2010 F. Nolden

Time domain stacking (ESR) one revolution (500 ns) Stored beam Intensity Kicker rise and fall time (50 ns) Injected beam Time Phase 5.10.2010 F. Nolden

Synchrotron Motion in a (Barrier) Bucket energy deviation Hamiltonian Potential depends on integrated voltage only! kinetic energy term deviation from synchronous phase Height of separatrix is 5.10.2010 F. Nolden

Experimental Procedure Fixed barrier bucket Moving barrier bucket Sinusoidal bucket (unstable fix point inj.) Sinusoidal bucket with „normal“ cavity (unstable fix point inj.) Bunched Beam Stochastic Cooling 5.10.2010 F. Nolden

Rf Hardware Barrier buckets require low Q cavities „Broadband“ ESR cavity limited to 150 V „Normal“ ESR cavity (sinusoidal voltage) can deliver up to 5 kV Barrier voltages from AWG output with limited No. of points (limited duration) 5.10.2010 F. Nolden

Unstable Fixed Point Injection (sinusoidal rf voltage) Strong cooling needed! potential Shallow potential well unstable fix point Stable fix point voltage 5.10.2010 F. Nolden

Overlapping half sine waves 5.10.2010 F. Nolden

Rf forms: awg input Voltage ratio: 1.0 Frequency ratio: 2.5 Potential depth ratio: 2.5 Separatrix height ratio: 1.6 5.10.2010 F. Nolden

RF shape and dp/p range 5.10.2010 F. Nolden

Comparison: max. energy deviation Barrier bucket yields shorter zone for accumulated beam at injection But: higher density gives problems for stochastic cooling 5.10.2010 F. Nolden

injection oscilloscope trace beam profile monitor Signal injected new beam Stored beam with space in between Ringing leads to transverse heating d/dt (Injection kicker signal) 5.10.2010 F. Nolden

Stochastic cooling hardware System bandwith 0.9-1.7 GHz Longitudinal, horizontal and vertical systems First test with bunched beam 5.10.2010 F. Nolden

Stochastic Cooling Spectrogramm p/p=6*10-4 p/p=13*10-4 13.2 s 5.10.2010 F. Nolden

Accumulation with „overlapping sines“ Imax = 320 µA Nmax = 5.6 * 107 5.10.2010 F. Nolden

Beam loss due to „empty“ injections Beam loss due to kicks! 5.10.2010 F. Nolden

Injection into unstable fix point 5.10.2010 F. Nolden

Importance of Transverse Phase Space Injection kicker throws out part of the beam (main error sources: ringing, timing jitter) Injection kicker excites transverse oscillations in rest of beam (non-ideal rise and fall properties) Beam loss without horizontal cooling 5.10.2010 F. Nolden

Effect of horizontal cooling Emittance growth due to injection kicks long. stoch. cooling kicker at high dispersion (D>6 m) Courtesy: H. Stockhorst 5.10.2010 F. Nolden

Experimental procedures We performed the following experiments: Injection into unstable fix point (sine) Injection with 2 overlapping sines Injection with moving barrier (problems due to non-adiabatic movement) Unstable fix point injection with normal rf cavity 5.10.2010 F. Nolden

Comparison ESR/HESR ESR: injection from long machine (SIS18) into short machine (ESR) HESR: injection from short machine (CR) into long machine (HESR) Less problems with kicker ringing in HESR HESR will have a dedicated bb rf system Possibly stronger stochastic cooling (higher bandwidth) 5.10.2010 F. Nolden

Preliminary Experimental Result The proof of principle of the scheme was successful. Accumulation curves were similar in all experiments. The stochastic cooling system worked with every kind of bunched beam The quantitative evaluation is still under way. It would be too early to conclude which method is preferrable for HESR accumulation. 5.10.2010 F. Nolden