Transcript Possibility for the production and study of heavy neutron

Gas Cell Based Laser Ion Source for Production
and Study of Neutron Rich Heavy Nuclei
(In Gas Cell Laser Ionization & Separation Setup)
Sergey Zemlyanoy
Flerov Laboratory of Nuclear Reactions
Joint Institute for Nuclear Research
Dubna
1st Topical Workshop on Laser Based Particle Sources
20-22 February 2013, CERN
Unexplored “north-east” area of the nuclear map
fusion
19 known neutron-rich isotopes
of cesium (Z = 55)
and only 4 of platinum (Z = 78).
fission
fragments
fragmentation
Above fermium (Z = 100) only
proton-rich nuclei are known.
Abundance of the element in the Universe
The 11 Greatest Unanswered Questions of Physics
(National Research Council, NAS, USA, 2002):
1. What is dark matter?
2. What is dark energy?
3. How the heavy elements from iron to uranium have been produced?
4. Do neutrinos have mass?
…
Strong neutron fluxes are expected in
core-collapse supernova explosions
or in the mergers of neutron stars.
r-process and heavy neutron rich nuclei
(1) difficult to synthesize
(2) difficult to separate
Production on NEW heavy nuclei in the region of N=126
(Zagrebaev & Greiner, PRL, 2008)
“blank spot”
82
82
Production on new heavy nuclei in the Xe + Pb collisions
Test experiment demonstrates good agreement with our expectations
Simulation of typical experiment in the laboratory frame
(1) The yield of new neutron-rich isotopes is maximal at beam energy slightly above the Coulomb barrier
(2) Desired reaction products are forward directed (no any grazing features)
Multi-nucleon transfer reactions
as a method for synthesis of heavy neutron rich nuclei
and
Stopping in the gas with subsequent resonance
laser ionization
as a method for extracting required reaction products (with a given
Z value)
IGISOL – Ion Guide Isotope Separation on line
Time profiles of laser-ionized stable
Ni-58 from the filament
Ni filament
He
+
Laser
beams
target
3-10 mg/cm2
+
SPIG
40 kV
+
cyclotron
beam
~1994
mass
separator
Weak beam,
1nA, 1ms
Delay time - down to 10 ms (He)
Refractory elements - !
Strong beam,
1uA,20ms
Laser-produced Ni ions recombine in a
plasma created by a primary beam
>99% are neutral
We have to provide for radioactive atoms:
1. Efficient laser ionization
2. Survival of laser-produced ions in a
volume around the exit hole
Schematic view of setup for resonance laser ionization
of nuclear reaction products stopped in gas
Setup consist of the following subsystems
Accelerator
beam transport
system
Detection
system
Mass separator
Ion
extraction
system
Gas cell
Mass separator
front end
Pumping
station
This part is at high
tension of 40kV
Gas handling- and
purification system
Laser system
The scheme of the front end of the GALS mass separator
subsystem
7000 m3/h
The layout of the dual chamber laser ion source gas cell
The aim: (by separating
Ar, He
from gas
purifier
Laser beams
Longitudinal
Accelerator
beam
Stopping
chamber
Target
+
+
+
500 mbar
Reaction products
Ionization
chamber
Ion
collector
+
Laser
ionization
chamber
Laser beams
Transversal
+
+
Exit hole
Ion Collector
SPIG
+
Towards mass
separator
stopping and laser
ionization chambers)
•Increasing laser ionization
efficiency at high cyclotron
beam current
• Increasing selectivity
(collection of survival ions)
Working conditions:
-cyclotron – DC
-Ion collector – DC
Exit hole diameter – 0.5mm/1mm
Stopping chamber – 4 cm in diameter
Laser ionization chamber – 1 cm in diameter
-Lasers – transverse
or longitudinal
The ion extraction from the gas cell
dE ~ 0.7 eV
4.7MHz
0-500V
1200 V
(-210 V)
250V
The SPIG consists of 6 rods (124 mm long and a diameter of 1.5
mm) cylindrically mounted on a sextupole structure with an inner
diameter of 3 mm. The distance between the SPIG rods and the
ion source is equal to 2 mm.
Front end of the LISOL mass separator
Cyclotron beam
Extraction
electrode
Gas Cell
SPIG
Gas from purifier
Gas cell and Ion-guide system
General requirements to the ion-guide systems look as follows:
• pressure in gas cell: 100–500 mbar depending on the energy of reaction products
and required extraction time;
• working gas is He or Ar (the latter looks preferably because its stopping capacity
and efficiency of neutralization are higher);
• gas purity not lower than 99,9995%;
• cell volume is about 100–200 cm3;
• vacuum in intermediate camera not worse than 10-2 mbar;
• vacuum in the entrance into the mass separator is 10-6 mbar;
Some specific requirements, stipulated by the use of the resonance laser ionization,
should also be taken into account:
• gas cell should be two-volume to separate the area of thermalization and neutralization
from the area of resonance laser ionization;
• extraction of ions from the cell and driving them into the mass separator have to be provided
by the sextupole radio-frequency system which allows one to increase
the efficiency of the setup and to perform ionization of atoms in the gas jet outside the cell;
• the input-output setup must be supplied by the system of optical windows and
by the system of explicit positioning (0.3 mm) of the gas cell, guide mirrors and prisms.
The pump station
3 roots pump station at HV platform
Isolating transformer for HV platform
Specifications of the pump station located in the basement:
-Pumping system: RUVAC WH 7000 roots pump with SCRELINE SP630 backing pump Leybold Vacuum.
Electrical power for the prepump : 3 X 380V, 11 kW
Electrical power for the pump: 3 X 380V, 18 kW
Weight : 1300 kg,
Noise level : 80 dB(A) - pumps to be placed in the basement with sound isolation panels
-Pumping station is placed on the high voltage platform (40kV) and electrical power for roots and
backing pumps comes via the isolation transformer.
- A metal fence with a door and safety switch has to be installed around the pumping station.
- Vacuum gauges and the meter have to be foreseen in the basement.
The scheme of the gas handling and purification system
Ar Grade 5.5
(99.9995%)
Gas purifier
MonoTorr Phase II 3000 SAES
Pure Gas, Inc.
Flow meter
Brooks Instrument
5860S 0.08 - 8 ln/min
Towards
gas cell
Oil-free, small
pump station
The gas purity is a key issue for efficient running of the laser ion source.
The gas handling system has to be designed to supply and to control the
gas flow into the gas cell. Electro-polished stainless steel tubes and
metal-sealed valves have to be used in order to reduce the outgasing and
the "memory effect". The system should be bakeable up to 2000C with
temperature control and be pumped by a separate small oil-free pumping
station. High-purity argon gas is additionally purified in a getter-based
purifier to the sub-ppb level.
Gas purifying system
Mass separator
All extracted ions have charge state +1 because only neutral atoms are ionized to this state
by the lasers while all “non-resonant” ions are removed by electric field before reaching
the area of interaction with laser radiation. In this case the extracted particles can be easily
separated by masses in dipole magnet.
For low-energy (30–60 keV) beams of +1 charged ions no specific requirements are needed
for the dipole magnet. It could be a standard magnet separator similar to ISOLDE II,
for example:
• Bending angle 40о–90о,
• Bending radius of about 1–1.5 m,
• Focal plane length of about 1 m,
• Rigidity of about 0.5 Т.m.
• Dipole gap about 50-60 mm
HV area
Laser ion source
chamber
Lens chamber
stable
Laser Ion Source
Detection
radioactive
Movable prism
Dispersion chamber
HV
Screen
Gas handling system
Fig. 11. Plan of the mass separator area
Mass resolution is the only critical parameter which should be about 1500.
Camera of the separator must have an optical input if collinear laser ionization
is used with the sextupole ion-guide (SPIG).
Mass separator
Most important specifications:
Magnet
Weight : 1800 kg,
Bmax :0.76 T
Cooling water flow: 400 l/h, pressure drop = 4 bar
Cooling water: 15 degrees
Magnet power supply
Weight : 250 kg
Output : max 300A/25V
AC main input: 3 X 380V, 18.5A
Cooling water flow: 120 l/h, pressure drop=3bar
Vacuum system
4 turbo pumps (at front end, lens chamber, entrance of the magnet, dispersion chamber):
for example Edwards STP1003C,Water cooled, 100 l/h per pump
Two Prepumps, for example Pfeiffer MVP160-3 can be placed in the basement
- Total flow for cooling water: min. 1000 l/h
- Compressed air to drive small actuators and vacuum valves
- Total electrical power needed : ~20 kW
Comparison dye vs. possible Ti:Sa system
Active Medium
condition of aggregation
Tuning range
Power
Pulse duration
Power stability
Dye
> 10 different dyes
liquid
540 – 850 nm
< 15 W
8 ns
decrease during operation
Synchronization
Maintenance
optical delay lines
renew dye solutions
35
Dye
Ti:S
a
2x Dye
2x Ti:Sa
3x Ti:Sa
3x Dye
4x Ti:Sa
200 300 400 500 600 700 800 900
wavelength nm
30
efficiency (%)
10.0
5.0
2.0
1.0
0.5
0.2
0.1
Ti:Sa
=1 Ti:sapphire crystal
solid-state
680 – 980 nm
<5W
50 ns
stable
q-switch, pump
power
~ none
25
20
Ti:S
a
15
10
5
0
Dye
550 600 650 700 750 800 850 900 950
wavelength (nm)
The (almost) optimum RILIS Laser System
l – meter
Nd:YAG
Master
clock
Dye 2
SHG
Dye 1
SHG
THG
Narrowband Dye
RILIS Dye Laser System
Delay
Generator
GPS/HRS
RILIS Ti:Sa Laser System
Nd:YAG
Target &
Ion Source
Ti:Sa 3
Faraday cup
Ti:Sa 2
Ti:Sa 1
SHG/THG/FHG
l – meter
pA – meter
Laser system
type
output power,
(average) main &
harmonics:
(2nd ), {3rd & 4th}, W
pulse
frequency, Hz
pulse length,
ns
wave length,
ns
Dye laser
3, (0.3)
104
10-30
213 - 850
Ti:Sapphire
2, (0.2), {0.04}
104
30-50
210 - 860
Eximer
laser
30
400
10-20
308
CVL
30-50
103-104
10-30
510.6 &
578.2
Nd:YAG
(80-100)
104
10-50
532
Nd:YAG laser specification (EdgeWave GmbH)
Maximal average power: 90 W and 36 W respectively;
Repetition rate: 10-15 kHz;
Pulse duration: 8-10 ns.
Divergence parameter of the green beam: M2 = 1.4;
Electrical power 3.6 kW including 1.6 kW for the water chiller.
Credo dye laser specification (Sirah)
Maximal average power: 20 W at fundamental wavelength, 2 W at
2nd harmonics;
Line width: 1.8 GHz
Pulse duration: ~7 ns
 Remote control of wavelength with stabilization to an external laser
wavelength meter.
The layout of laser installation
OT7
OT6
M12
M13
M16
M15
P1
T5
M8
BS2
BD1
M11
M3
BS3
T1 M1
OT2
P2
T6
M10
M9
BS1
DL 2
Nd:YAG 2
R1
DL 1
Nd:YAG 1
OT5
BS4 T3
BD2 M4
OT3
M5
L3
T4
M18
L4
M17
M2
M14
T2
L1
L2
M19
M6
BS5
SM2
OT1
M20
DL 3
OT8
L5
RC
OT4
OT9
RP
SM1
M24
R2
QP1
L6
M7
M22
M23
M21
RM1
RM2
RM3
RM4
OT1-OT9 – optical tables; Nd:YAG1 and Nd:YAG2 – pump lasers;
DL1-DL3 – dye
lasers; R1 and R2 – racks for electronics and water chillers; M1-M10, M22 – high power mirrors for
532nm beams; M10-M15 – high power mirrors for 355nm beams; BS1-BS4 – beam splitters for
532nm beams; M16-M21, M23-M25 – mirrors for dye laser beams; T1-T4 – telescopic zoom
expanders for 532nm beams; T5 and T6 - telescopic zoom expanders for 355nm beams; L1-L6 –
spherical lenses, SM1 and SM2 – spherical mirrors; BD1 and BD2 – beam dumps for IR beams; P1
and P2 – half-wave plates for 355nm; RM1-RM4 – return mirrors for reference beams; RP –
reference plane; AlM1 – Al mirror; QP1 – quartz plate; RC – reference cell
The laser system view
Rooms requirements for this setup
Possible position of SETUP at cyclotron U400M
5400
RM1a
pmM1
3000
1160
1000
OT10
Corridor
1260
M23
3500 to ion source
M25
RM1
2800
1640
W1
OT4
Mass
separator area
900
M24
1100
Laser room
Working plan
Laser
system
prepa
ration
mou
nting
Front
Pump
end system station
com
missi
oning
prepa
ration
mou
nting
com
missi
oning
prepa
ration
mou
nting
com
missi
oning
Gas
purification
Separator,
detection
prepa
ration
prepa
ration
2012
2013
2014
2015
starting experiments
mou
nting
start
up
mou
nting
com
missi
oning
Conclusion
• At target thickness 0.3 mg/cm2, ion beam of 0.1 pmA and
setup efficiency of 10% we would be able to detect
1 event per second at cross section of 1 microbarn
• It allow as to measure decay properties at least 1 new
isotope per day
• It is sufficiently not only for measurement of typical
nuclear characteristics (like half-life times, decay
schemes, etc.), but also for determining of nuclear charge
radii (and moments) with using in-source laser
spectroscopy.
People involved into developing and discussion of this SETUP
project
Leuven:
M. Huyse, Yu. Kudryavtsev, P. Van Duppen
Jyväskylä :
Juha Äystö, Iain Moore, Heikki Penttilä
CERN:
Valentin Fedosseev
GSI:
Michael Block, Thomas Kühl
GANIL:
Nathalie Lecesne, Herve Savajols
Mainz:
Klaus Wendt
Manchester:
Jonathan Billowes, Paul Campbell
iThemba LABS: Robert Bark + 2 PhD students
Egypt:
Hosam Othman
IS RAN Troitsk: Vyacheslav Mishin
FLNR JINR:
V. Zagrebaev, S. Zemlyanoi, E. Kozulin, and others
People involved into developing and discussion of this SETUP
project