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Cooling Experiments at COSYin preparation for HESR
COOL 09, August 30th to September 4th, 2009
Dieter Prasuhn
August 31st, 2009 2COOL 09 in Lanzhou
Outline
Introduction to the COSY Facility
The HESR
Recent Cooling Experiments at COSY
Future Developments
August 31st, 2009 3COOL 09 in Lanzhou
The Accelerator Facility
COSY accelerates (polarized) protons and deuterons between 300/600 and 3700 MeV/c
4 internal and 3 external experimental areas
Electron cooling at low momentaStochastic cooling at high momenta
August 31st, 2009 4COOL 09 in Lanzhou
The Electron Cooler
Design Values
Electron energy up to 100 kV
Electron current up to 3 A
August 31st, 2009 5COOL 09 in Lanzhou
Stochastic CoolingHardware
2 Pickup-Tanks, 4m long, cooled to 20 K2 Kicker-Tanks, 2 m long
Frequency range: 1.0-1.8 GHz1.8-3.0 GHz
Adjustable delays for different ion velocities above β=0.85
Longitudinal Notch FilterCooling with the vertical system in „Sum-Mode“
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The HESR at FAIR
August 31st, 2009 7COOL 09 in Lanzhou
Artist’s view of
High Energy Storage RingHESR
August 31st, 2009 8COOL 09 in Lanzhou
Basic Data of HESR
Circumference 574 mMomentum (energy) range1.5 to 15 GeV/c (0.8-14.1 GeV)Injection of (anti-)protons from RESR at 3.8 GeV/cMaximum dipole field: 1.7 TDipole field at injection: 0.4 TDipole field ramp: 0.025 T/sAcceleration rate 0.2 (GeV/c)/s
August 31st, 2009 9COOL 09 in Lanzhou
Electron cooling
Electron energy range: 450 keV to 4.5 MeVElectron current up to 1 A
Allows cooling of anti-protons between1.5 GeV/c and 8.9 GeV/c
Beam Cooling in the HESR
August 31st, 2009 10COOL 09 in Lanzhou
Stochastic cooling(optimized for momenta above 3.8 GeV/c)
2 systems with 2-4 GHz and 4-6 GHzSeparate systems for radial, vertical and longitudinal phase spaceIndependent cooling per plane to adjust beam properties to the experimental requirements
August 31st, 2009 11COOL 09 in Lanzhou
Main common features of COSY and HESR
Electron coolingStochastic coolingInternal targets
August 31st, 2009 12COOL 09 in Lanzhou
August 31st, 2009 13COOL 09 in Lanzhou
Internal Target Experiments at COSY
ANKE:
• Dipol spectrometer• Polarized target• Cluster target• Solid state target
WASA:
• Solenoidal field• Pellet target
August 31st, 2009 14COOL 09 in Lanzhou
Internal Target Experiments at HESR
PANDA
• Solenoidal field• Forward dipol magnet• Pellet target• Cluster target
August 31st, 2009 15COOL 09 in Lanzhou
Studies at COSY for HESR
Prototype hardware tests
Beam – Target interaction- With stochastic cooling- With barrier bucket- Combination of barrier bucket and stochastic cooling
Electron cooling- Phase space density limits- Beam feed-back- Phase space manipulation
August 31st, 2009 16COOL 09 in Lanzhou
Prototype hardware tests at COSY
Barrier Bucket tests in COSY
One cavity one gapFilled with VitroPerm 500F Very compact design (length of cavity without gap: 28 cm). The length form flange to flange including the COSY gap: 50cm.
• Single sinus 5*f0 (2.5MHz) generated by 20 harmonics -> ~20% gap in antiproton beam
• Standing bucket• Voltage: 600V
1. Barrier bucket cavity
August 31st, 2009 17COOL 09 in Lanzhou
The principle of the Barrier Bucket
-0.1-0.08-0.06-0.04-0.02
00.020.040.060.080.1
0.0 0.5 1.0 1.5 2.0 2.5
Phasensonde mitBBAWG Signal
Barrier Bucket voltage
-0.1
-0.08
-0.06
-0.04
-0.02
0
0.02
0.04
0.06
0.08
0.1
0 0.5 1 1.5 2
time / µs
a.u.
beam-phase monitor with BBbeam-phase monitor with RF
August 31st, 2009 18COOL 09 in Lanzhou
2. Stochastic cooling electrodes
August 31st, 2009 19COOL 09 in Lanzhou
Inner part with coupling structures
Printed loop couplersSlot couplers
August 31st, 2009 20COOL 09 in Lanzhou
Longitudinal pickup (protons, 1.69 GeV/c, 5E10)
1958. Harmonics 1959. Harmonics
August 31st, 2009 21COOL 09 in Lanzhou
Slot coupler as transversal pickup:Beam centered / out of center
Betatron sidebands
only low beta-functions atinstallation point
August 31st, 2009 22COOL 09 in Lanzhou
Slot ring coupler as BPM
long. Spectrum vs BPM 5
02468
101214
-30 -20 -10 0 10 20
Position [mm]
Am
plitu
de [µ
V]
Noise level
August 31st, 2009 23COOL 09 in Lanzhou
Studies of Beam Target Interaction
• Only with stochastic cooling
• Only with RF or barrier bucket
• With the combination of stochastic cooling and RF
August 31st, 2009 24COOL 09 in Lanzhou
August 31st, 2009 25COOL 09 in Lanzhou
August 31st, 2009 26COOL 09 in Lanzhou
August 31st, 2009 27COOL 09 in Lanzhou
Advantage of the barrier bucket
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Electron Cooling Experiments at COSY• At low energies• Beam life time studies• Dynamic aperture calculations
August 31st, 2009 29COOL 09 in Lanzhou
PAX at COSYThe beam time for beam acceptance studies gaveus new insight into loss mechanisms within COSY
The electron beam size limits the dynamicacceptance of COSYThe beam lifetime (dynamic aperture) is stronglytune dependantInitial losses due to the electron cooling can bereduced by slowly increasing the electron current
August 31st, 2009 30COOL 09 in Lanzhou
Initial losses
Beam Intensity vs. Time
00.10.20.30.40.50.60.70.80.9
1
0 5 10 15 20
time / s
BC
T / V
BCT (20 ms injection)BCT (10 ms injection)
H_0-rate vs time
0123456789
10
0 5 10 15 20time / s
H_0
rate
/ ar
b. u
nits
H_0-Rate (20 ms injection)
H_0-Rate (10 ms injection)
Initial losses disappear at smaller injected proton beam emittance
Explanation:Protons outside the electron beam see a non-linear focussing by the electron beam
August 31st, 2009 31COOL 09 in Lanzhou
Recent studies to overcome initial losses:
Electron cooled beam
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0 20 40 60 80 100time / sec
Beam
Inte
nsity
/arb
. uni
ts
0.0
0.5
1.0
1.5
2.0
2.5
3.0
H_0
sig
nal /
arb
. uni
ts
August 31st, 2009 32COOL 09 in Lanzhou
Electron cooled beam
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0 20 40 60 80 100time / sec
Beam
Inte
nsity
/arb
. uni
ts
0.0
0.5
1.0
1.5
2.0
2.5
3.0
H_0
sig
nal /
arb
. uni
ts
August 31st, 2009 33COOL 09 in Lanzhou
Electron cooled beam
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0 20 40 60 80 100time / sec
Beam
Inte
nsity
/arb
. uni
ts
0.0
0.5
1.0
1.5
2.0
2.5
3.0
H_0
sig
nal /
arb
. uni
ts
August 31st, 2009 34COOL 09 in Lanzhou
Beam life time in the presence of a cluster target (1014 cm-2)
beam lifetime vs. ecool current
0.0200.0400.0600.0800.0
1000.01200.01400.01600.01800.02000.0
0 50 100 150 200 250 300 350 400 450 500e_cool current / mA
1/e-
beam
life
time
/ s
lifetime target on / s
August 31st, 2009 35COOL 09 in Lanzhou
Explanation for the life time results
• Without electron beam the measured beam life time is consistentwith the full geometrical acceptance of COSY and the targetrelated loss rates
• The electron beam is smaller than the proton beam. Now thebeam life time can only be explained with a reduced dynamicacceptance
• The dynamic acceptance corresponds to the acceptance of theelectron beam.
• The non linear space charge of the electron beam excitesresonances of higher order and reduces the dynamic acceptance.
August 31st, 2009 36COOL 09 in Lanzhou
Future Developments at COSY
• Investigations of Time-of-Flight stochastic coolingTalk on Tuesday morning
• Installation of the proposed 2 MeV electron coolerTalk by Juergen Dietrich on Friday morning
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