1. 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

2. 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
F. Nolden

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

4. 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
F. Nolden

5. 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
F. Nolden

6. 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)
F. Nolden

7. Unstable Fixed Point Injection (sinusoidal rf voltage)
Strong cooling needed!
potential
Shallow potential well
unstable fix point
Stable fix point
voltage
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8. Overlapping half sine waves
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9. Rf forms: awg input Voltage ratio: 1.0 Frequency ratio: 2.5
Potential depth ratio: 2.5
Separatrix height ratio: 1.6
F. Nolden

10. RF shape and dp/p range
F. Nolden

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

12. 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)
F. Nolden

13. Stochastic cooling hardware
System bandwith GHz
Longitudinal, horizontal and vertical systems
First test with bunched beam
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14. Stochastic Cooling Spectrogramm
p/p=6*10-4
p/p=13*10-4
13.2 s
F. Nolden

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

16. Beam loss due to „empty“ injections
Beam loss due to kicks!
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17. Injection into unstable fix point
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18. 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
F. Nolden

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

20. 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
F. Nolden

21. 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)
F. Nolden

22. 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.
F. Nolden