Ion Beam Bunchingor: Beam Handling with/for Ion Traps
How to match production schemes and ion traps efficiently?
F. Herfurth - Ion Beam Bunching
Introduction
– Scope of this lecture– Production of exotic ions– “Typical” exotic ion trap facility
F. Herfurth - Ion Beam Bunching
Experiments with Exotic Ions
Exotic Ions- radioactive = short lived
- (heavy) highly charged ions (HCI)- antimatter
Experiments in Traps- precision spectroscopy (K. Blaum, F. Herfurth)- (heavy) highly charged ions (HCI) (J. Créspo)
- antimatter (N. Madsen, C. Surko)- watching them decay (F. Herfurth)
This Lecture
F. Herfurth - Ion Beam Bunching
Production & Preselection of radioactive Ions – ISOL & Fusion Techn.
Target wheel
Primary beaml@ 1..10 MeV/u
Fusion productswith about 100 keV/u
SHIPTRAPJYFLTRAP
Fusion products selected in flight by velocity
Fission, Spallation and Fragmentation products selected by m/q
ISOLTRAPTITAN, SPIRAL2-Trap
8
8
20
20
50
50
126
82
82
28
28
Dipole magnet
Target – Ion source
Proton beam1 .. 1.4 GeV
F. Herfurth - Ion Beam Bunching
Production & Preselection of radioactive Ions – Fragmentation in Flight
Fragmentation products from heavy beams selected by m/q and Z
LEBITMATS
8
8
20
20
50
50
126
82
82
28
28
Primary beam@ 100 to 1000 MeV/u
„Thi
n“ T
arge
t
FRS
F. Herfurth - Ion Beam Bunching
Production of radioactive Ions
p
fusion
Target
projectile
60 keVup to 400 MeV/u
Kinetic Energyafter the reaction
~100 keV/u
F. Herfurth - Ion Beam Bunching
Production of Heavy, Highly-Charged Ions
– stripping of all Electrons at high Energy– fast, efficient– up to 106 bare Uranium Nuclei per pulse but at 400 MeV/u
U72+ @ 1 GeV/u
Au
f
oi
l U92+ @ 400 MeV/u
F. Herfurth - Ion Beam Bunching
Production of Heavy, Highly-Charged Ions
– stripping of all Electrons by energetic Electron Beam→ J. Créspo
U1+ @ eV U92+ @ eV
time
Intense, energetic Electron Beam
F. Herfurth - Ion Beam Bunching
How to get these Ions into a Trap?
Why is it a problem?
Production energy >> trap potential
(We try to capture the results of an explosion in a card box)
Great variety of energies and species after production (It's a mess)
Exotic ions are rare!
(Just a few per measurement shall be enough)
They are delicate. (Some decay quickly and some dislike matter)
F. Herfurth - Ion Beam Bunching
How to get those Ions into a Trap?
Solutions:
Production energy >> trap potential
Decelerate/Stop in matter and/or electrically.
Great variety of energies and species after production Cooling and Purification using trap-specific properties.
Exotic ions are rare! Be efficient!
They are delicate. Be fast and handle them carefully!
F. Herfurth - Ion Beam Bunching
Trap Facilities for Exotic Ions
ISOLTRAPSHIPTRAPMATSand others(see talk tomorrow)
HITRAP
Production Beam Preparation (incl. Bunching)
Bunching required
F. Herfurth - Ion Beam Bunching
“Bunching” vs. “Chopping”
Club
people
people
People pass in groups periodically Sooner or later everybody passes
People pass in groups periodically Some are diverted :-(
Traffic Light
F. Herfurth - Ion Beam Bunching
“Bunching” vs. “Chopping”
Chopper
ions
ions
Ions are grouped (bunched) and then transported further in those bunches
The ion beam is interrupted for a certain time during which no transport takes place
Buncher
F. Herfurth - Ion Beam Bunching
RFQ Cooler & Buncher
– Principle– World wide– Example facilities
F. Herfurth - Ion Beam Bunching
RFQ cooler & buncher
• Linear Paul trap i.e. radial RF, long. DC• Gas filled (at low pressure ~ sub mbar)
- Used first in chemistry for reaction studies. D. Gerlich. “Inhomogeneous RF fields: a versatile tool for the study of processes with slow ions” Adv. Chem. Phys. 82, 1–176 (1992)
- Brought to nuclear physics applications by R. B. Moore from McGill, Montreal
RF drive
Upseudo
Ulong - DC
F. Herfurth - Ion Beam Bunching
RFQs for short-lived Ions in the World
ISOLDE/CERN
TRIGA/Mainz
SPIRAL II/CaenLEBIT/MSU
TITAN/TRIUMF TRIμP
Riken
Jyväskylä
ISOLTRAP/CERN
CPT/ArgonneSHIPTRAP/GSI
Oak Ridge
LPC/CaenLanzhou
F. Herfurth - Ion Beam Bunching
• Continuous beam cooling (COLETTE for MISTRAL, now at TRIGA Mainz, ISCOOL)
• Beam accumulation and bunching (ISOLTRAP, JYFLTRAP, LEBIT, TITAN ...)
Beam and Bunch creation (Louvain, JYFL, SHIPTRAP, CPT, LEBIT, SLOW-RI)
“Stop” and Bunch using RFQ cooler&buncher
F. Herfurth - Ion Beam Bunching
The ISOLTRAP RFQA beam accumulator and buncher
F. Herfurth - Ion Beam Bunching
F. Herfurth - Ion Beam Bunching
Ion Puls Properties
longitudinal emittance
transversal emittance
overall efficiency (ISOLDE beam)
F. Herfurth - Ion Beam Bunching
Cooling Time
Changing buffer gas pressure:
10-3
10-2
0
2
4
6
co
ol
in
g
ti
me
[
ms
]
Helium pressure [mbar]
133Cs
39K
F. Herfurth - Ion Beam Bunching
Be aware of RF heating- cooling stops working when M
ion- ~ M
gas
(but you need microscopic model to realize)
Resonant charge exchange (neutralization)- can't cool He+ ions with He buffer gas
Buffer-gas cooling Limits in RFQs
K+
K+see example
He
at 0
.02
mba
rA
r at
0.0
05 m
bar
F. Herfurth - Ion Beam Bunching
The JYFL Cooler/buncher
Buffer gas cell, pHe ~ 0.1 mbar
DecelerationCollisional cooling in an
RF-quadrupole Acceleration
Beam in Beam out
40 kV
Turbo pump500 l/s
Turbo pump1300 l/s
Turbo pump900 l/s
High vacuum 10-6 mbar
Intermediate vacuum 10-4 mbar Electrodes
HV isolator
IGISOL E ~40 keV, � E ~100 eVIGISOL E ~40 keV, � E ~100 eV
Buncher: Accumulation time 10 ms -10 s
(Typically 100 ms - 1 s)
FWHM 15 � s bunches
Buncher: Accumulation time 10 ms -10 s
(Typically 100 ms - 1 s)
FWHM 15 � s bunches
A dual mode beam cooler/buncher
DC-cooler: E ~ 40 keV, � E < 1 eV
Transmission, on-line > 60%
DC-cooler: E ~ 40 keV, � E < 1 eV
Transmission, on-line > 60%
A. Nieminen et al., Nucl. Instrum. Methods Phys. Res., A 469, 244 (2001).
F. Herfurth - Ion Beam Bunching
The ISOLDE Cooler “ISCOOL”A modern multi-purpose continuous mode beam cooler
I Podadera et al., Nucl. Phys. A 746 (2004) 647c and E. Mane et al., Eur. Phys. J. A - DOI 10.1140/epja/i2009-10828-0
F. Herfurth - Ion Beam Bunching
The LEBIT RFQ
Deceleration- few keV to few 10 eV
accumulation &bunching
μ - RFQ
Injection & cooling
RF1
RF1
RF2 RF2
DC1
DC1
DC2DC2
Cross - section
extraction
• Separation of cooling and bunching
• Regions with different buffer gas pressure
• Linear ion trap with novel electrode system
• Cryogenic system (80K)
S. Schwarz et al., Nucl. Instr. Meth. B204 (2003) 474
Advanced technology – Separation of functions
F. Herfurth - Ion Beam Bunching
Advantages of a Cold RF Trap
-2.0 -1.0 0.0 1.0 2.0-3000
-2000
-1000
0
1000
2000
3000
vx [
m/s
]
x [mm]
-2.0 -1.0 0.0 1.0 2.0-3000
-2000
-1000
0
1000
2000
3000
vx [
m/s
]
x [mm]
T = 300 KT = 300 K T = 80 KT = 80 K
Transverse phase space, 23Na ion cloud in trap (simulated)
� 95% = � 1.45 m2/s � 95% = � 0.41 m2/s
Transverse emittance� 95% ~ 4.9 � mm mrad @ 2keV
- Considerable emittance reduction
- Increased buffer gas density – lower gas load to the pumps
- Cleaner environment – longer storage time
S. Schwarz et al., Nucl. Instr. and Meth. B 204 (2003) 474
F. Herfurth - Ion Beam Bunching
The next Generation• Separation of cooling, bunching and mass separation
e.g. W. Plass et al.
(SHIPTRAP)
• Different solutions to solve the DC – RF coupling challenge
• Improved control of RF and DC
rectangular RF drive – TITAN (TRIUMF)
phase controlled switching and precise amplitude control – W. Plass et al.
Includes mass resolving power and extremely short bunches
F. Herfurth - Ion Beam Bunching
The next Generation● Go to higher particle number
from nA to � A
● Present devices: Vpseudo
~ 10 eV – limits the current to nA
• Simulations done – mean field and PIC approach
Accepting higher Ion currents (� A)
F. Herfurth - Ion Beam Bunching
Space Charge Simulation vs. Exp.
“Mean field”-code: (FH & SCS)RF + Buffer gas collisions + Coulomb interaction
T. Kim, R.B Moore, McGill, MontrealBeam size as a function of beam current ψιελδσ beam temperature assuming no space charge
Agreement for spatial distribution (0 - 1.2 nA)
& slow rise of beam temperature
0.8 2.3� 95% [� mm mrad @ 60 keV]
T. Kim (PhD thesis),
1 � A simulation:URF = 15 kV, fRF = 5 MHz, Ez = 10 V/cm
� 95% ∼ 3 � mm mrad @ 60 keV
• Cs+ in N2 at 8·10-2 mbar
• r0 = 6.9 mm
• 0.7 MHz, 300 V
• Axial drag field Ez = 1 V/cm
Slope = 17.0(3) meV/nAT. Kim exp.: 15(3)
Offset = 44.3(3)T. Kim exp.: 42(3)
F. Herfurth - Ion Beam Bunching
The SPIRAL II High Current RFQ
- First experimental tests: R.B. Moore, O. Gianfrancesco,
Nucl. Instr. and Meth. B 204 (2003) 557–562
- Device realized and being tested: R. Boussaid et al.
Accepting higher Ion currents (� A)
VRF < 10 kVF < 8 MHz
F. Herfurth - Ion Beam Bunching
Performance of linear RFQ - Buncher
efficiency up to 80%
cooling time ~ ms
bunch length > 70 ns
capacity ~ 104..5, nA’s improving
mass separation Some but improving
present
F. Herfurth - Ion Beam Bunching
Penning Traps to cool and bunch
– Advantagesstorage capacity, mass selectivity
– Examples areREXTRAP@ISOLDE; ISOLTRAP, JYFLTRAP, SHIPTRAP, CPT …
F. Herfurth - Ion Beam Bunching
REXTRAPBuffer gas filled cylindrical Penning Trap
F. Herfurth - Ion Beam Bunching
Storage Capacity
F. A
mes
et a
l. / N
ucl.
Inst
r. an
d M
eth.
A 5
38 (
2005
) 17
Cyclotron Frequency
F. Herfurth - Ion Beam Bunching
Mass Resolving Power
In buffer gas filled preparation trap In UHV precision trap
Rauth et al., Phys. Rev. Lett. 100, 012501 (2008)
Rauth et al. EPJ ST 150, 329 (2007)
147Er
147Ho147Dy
147Dy+I.S.
G.S.
No.
of
ion
s
Mea
n T
OF
/ �s
Excitation frequency / Hz Detuning frequency / Hz
SHIPTRAP measurements
F. Herfurth - Ion Beam Bunching
Heavy, Highly – Charged Ions
– Production at high energy (stripping electrons off sending 400 MeV/u ionsthrough a foil)
– To get them into Traps:The HITRAP facility
– Challenges:• Extremely high energy• Cooling of HCI
F. Herfurth - Ion Beam Bunching
HITRAP @ GSI
Beam that will be available to users:
type A/q < 3 (U92+ ...)ions/pulse 105
energy keV/q ... meV/qenergy spread ≥ 0.3 meV
Test Ion Source - EBIT:
Up to bare KAny element (charge breeding)105 per pulse and second
F. Herfurth - Ion Beam Bunching
The HITRAP Energy Range
F. Herfurth - Ion Beam Bunching
To the Experiments
DDBIH
Cooler Trap
7m
HITRAP – A linear Decelerator
RFQ
Beam Type A/q < 3 (U92+ ...)
Ions/Pulse 105
Energy keV/q ... meV/q
Energyspread ≥ 0.3 meV
Be
am
f
ro
m
ES
R
F. Herfurth - Ion Beam Bunching
RF Bunching
Gap UGap
time/2�
ions
Ele
ctro
de
Ele
ctro
de
Typical frequency: 100 MHz i.e. ns bunches
F. Herfurth - Ion Beam Bunching
RF Bunching @ HITRAP
Gapions
Ele
ctro
de
Ele
ctro
de
Typical frequency: 100 MHz i.e. ns bunches
F. Herfurth - The linear Decelerator Facility HITRAP
ee--ee--
UU92+92+
HITRAP – LEBT & Cooler Trap
4 MeV/u 0.5 MeV/u 6 keV/u
• catch the ions in flight
• cool them with combined electron and resistive cooling to ~ 4 Kelvin
F. Herfurth - The linear Decelerator Facility HITRAP
HITRAP – LEBT & Cooler Trap
4 MeV/u 0.5 MeV/u 6 keV/u
4 M
eV/u
• trap installed in magnet – offline injection tests ongoing
• Extensive calculations done – resistive cooling possible but slower than expected
F. Herfurth - The linear Decelerator Facility HITRAP
• in Coulomb collisions, ions transfer in Coulomb collisions, ions transfer energy to eenergy to e--
• electrons are rapidly cooled by electrons are rapidly cooled by synchrotron radiation to 4.2 Ksynchrotron radiation to 4.2 K
Approximations:Approximations:• instantaneous conversion Einstantaneous conversion Eionion → T → Tee
• no ion-ion collisionno ion-ion collision• isotropic eisotropic e-- distribution distribution
Warning: radiative recombination!Warning: radiative recombination!
Conclusions:Conclusions:ee-- cooling down to 10 eV possible within ~ cooling down to 10 eV possible within ~ 1 s and 10-20% ion losses1 s and 10-20% ion losses
* = G. Zwicknagel, in „Non-neutral Plasma Physics VI“, eds. M. Drewsen, U. Uggerhoj, H. Knudsen, AIP Conference Proceedings, 862, 281 (2006)
Electron cooling*Electron cooling*
F. Herfurth - The linear Decelerator Facility HITRAP
Resistive cooling of an ion cloud
H. Häffner et al., Eur. Phys. J. D 22, 163 (2003)
CoM
internal motionsτ ~ 5 s
(experiment)
internal motionsτ ~ 0.52 s
B
q/m
B
q/mΔqimage=0 !
z
• cooling of Center of Mass motion N times faster• “invisible” internal modes?
→ asymmetric coupling and nonlinear contributions to image charge
F. Herfurth - The linear Decelerator Facility HITRAP
Spectrogram of 30 C5+ from our PIC code
PhD
thes
is G
. Mae
ro
F. Herfurth - The linear Decelerator Facility HITRAP
U92+ in the HITRAP cooler TrapSimulations with:
• 105 U92+
• Symmetric coupling
• Utrap = 100 V (trap depth)
• Axial oscillation frequency 400 kHz
yields a cooling time tail � ~ 3.7 s !
F. Herfurth - Ion Beam Bunching
Ion Beam Bunching – Handling of rare Ions
– Traps are indispensable (both, Paul and Penning)
– The technical challenges are enormous
– A number of interesting experiments wouldn't be possible without → Tomorrow's Talk