Cooled Heavy Ions in the ESR

1
Cooled Heavy Ions in the ESR
M. Steck for the ESR team K. Beckert, P. Beller,
B. Franzke, F. Nolden

• Outline
• Stochastic cooling
• Electron cooling
• Equilibrium with IBS
• Ultra-cold Beams
• Laser Cooling

2
The ESR Electron Cooler
electron beam parameters
energy 1.6 250 keV current
0.001 1 A diameter
50.8 mm gun perveance 1.95
?P collection efficiency gt 0.9998 temperature
transverse 0.1 eV longitudinal
0.1 meV
magnetic field
strength 0.015 0.2 T straightness
110-4
vacuum
210-11 mbar
3
Stochastic Cooling at the ESR
Fast pre-cooling of hot fragment beams
electrodes installed inside magnets
energy 400 (-550) MeV/ubandwidth 0.8 GHz (range
0.9-1.7 GHz) ?p/p ?0.35 ? ?p/p ?0.01
e 10 ? 10-6 m ? e 2 ? 10-6 m
combination of signals from electrodes
power amplifiersfor generation ofcorrection
kicks
4
Stochastic Cooling
Longitudinal cooling
(Schottky noise)
Cooling time
Ar18
dependent on beam intensity
5 s
Transverse cooling
(beam profile)
Ar18
Ar18
cooling time for U92 (N106) longit., vert.
0.5 s, horiz. 2.5 s
5 s
5
Combination of Stochastic and Electron Cooling
stochastic pre-cooling final electron
cooling immediately after injection
Primary Uranium beam heated in thick target
One trace every 120 ms 5.52 s in total
Accumulation of secondary beams 1) S.C. on
injection orbit 2) rf stacking 3) electron
cooling of stack
Subsequent fast electron cooling
Fast pre-cooling of large initial momentum width
Ion current mA
time s
hot secondary beams can be cooled in reduced
total time
6
Beam Quality of Cooled Beams in the ESR

• Electron cooling is more powerful for cold beams.
  
• Electron cooling allows the achievement of
  smaller momentum spread (by a factor of 5) and
  smaller emittance (by a factor of 2).
• Consequently the cooling rate (for cold ion
  beams) must be more than an order of magnitude
  higher.
• The equilibrium is a balance between the cooling
  rate and the heating rate by intrabeam scattering.

mm
106
107
7
Electron Cooled Beams in Equilibrium with IBS
by non-destructive methods (particle detectors,
profile monitor)
by destructive scraping
?p/p ? N0.3
E 400 MeV/u
horizontal radius mm
?x mm mrad
?x,y ? N0.5-0.6
?y mm mrad
vertical radius mm
Phase space volume increases with ion beam
intensity and ion charge
8
Equilibrium of Bunched Beams
comparison coasting beam - bunched beam as a
function of the line density
emittance ?x mm mrad
bunched beams show the same IBS dominated beam
parameters as coasting beams
9
Comparison Experiment (ESR) and Simulation
Simulation with BETACOOL program (black dots)
Ni28 200 MeV/u
G. Trubnikov, JINR Dubna
Magnetized kT?? 10 meV, kT? 100meV
Non-magnetized kT?? 0.2 meV, kT? 100meV
Magnetized kT?? 50 meV, kT? 100meV
Magnetized kT?? 0.2 meV, kT? 100meV
?p/p
?x
?y
Main uncertainty originates from cooling force
model
10
Observation of Ultra-cold Beam
temporal evolution of Schottky noise allows
independent determination of particle
number decay time due to REC
Reduction of momentum spread
Schottky noise power a.u.
?p/p
sudden reduction of the momentum spread for less
than about one thousand stored ions
? linear ordering in ion string
storage time min
11
Transverse Beam Size of Ultra-cold Beam
high precision measurement employing a scraper in
a dispersive section ( D ? 1 m )
lowest temperature for C6 at 4800 MeV kT??
0.26 meV kTX 0.14 meV
mm
a.u.
minimum ion temperature of the order of the
longitudinal electron temperature
mm
? magnetized cooling
scraper position mm
12
Increase of Phase Space Density
The phase space density below the transition
point is dramatically increased

• At higher intensities the cooling rate is
  slightly reduced.
• Intrabeam scattering must be absent for low ion
  beam intensity.
• The cooling rate cannot be increased
  correspondingly to the IBS heating rate.

?m-2m-1
13
Detection of Single Ions
decay of an unstable nucleus
measurement of excited states in unstable nuclei
resolution m/?m up to 1106
14
Bunched Ultra-cold Beam
V
150 s
bunch length lb2c?/?s?p/p
before heating
after heating
?s2 ?r2h?eV0(2??cp0)-1
line density (?lN/hlb) limit is the same as for
coasting ultra-cold beam
? ? 10 ions / m
15
Cooling above Transition Energy
horizontal beam profile
longitudinal Schottky signal

• ESR operation in isochronous mode
• ?t 1.38

N5105
N1108
N1108
noise power a.u.
N5105
beam energy ? 1.41 Kr36
position mm
frequency MHz
momentum spread
?f/f 10-4, ?x 10-6m
compared with Keil-Schnell limit
16
Laser Cooling of C3 in the ESR
Beam parameters before laser cooling
Electron cooling is applied for pre-cooling of
the injected beam in order to reduce the
emittance and momentum spread. The longitudinal
captured range and the transverse size of the
laser beam are limited.
!
?x?N
?Qx ? -0.005
17
Laser Cooling of C3 in the ESR
Schottky Diagnostics of Bunched Laser Cooled
Beams
C3 122 MeV/u (ß0.47) ?0(2S1/2-2P1/2)
154.82 nm
?laser/2 257.34 nm
U.Schramm, D. Habs, M. Bussmann
18
Laser Cooling of C3 in the ESR
Diagnostics of Bunched Beams
19
Laser Cooling of C3 in the ESR
Fluorescence Diagnostics
current cooling limit available laser power