Design of a new setup for extraction of

Design of a new setup for extraction of reaction products by means of their stopping in gas and subsequent resonance laser ionization Sergey Zemlyanoy Flerov Laboratory of Nuclear Reactions Joint Institute for Nuclear Research 35 th meeting of the JINR PAC for Nuclear Physics Jan. 26 -27, 2012, Dubna.

Production of new heavy nuclei in Xe + Pb collisions

Programme Advisory Committee for Nuclear Physics 34 th meeting, 16– 17 June 2011 • • • Valery Zagrebaev presents the talk: Possibility for the production and study of heavy neutron-rich nuclei formed in multi-nucleon transfer reactions The PAC discussed the proposal of the Flerov Laboratory, presented by V. Zagrebaev, on the synthesis of heavy neutron rich nuclei formed in lowenergy multi-nucleon transfer reactions. The use of this method opens a new field of research in low-energy heavy-ion physics, namely, the production and study of new neutron rich heavy nuclei playing a key role in the r-process of nucleosynthesis. The development of an experimental setup based on the method of stopping reaction fragments in gas and on their subsequent selective resonance laser ionization is proposed. With such a method atoms of required elements can be selected. The method is already used in several laboratories for separation and study of light exotic nuclei and fission fragments. Because of the capability of selecting ions of specific atomic numbers, this set-up can also be employed in other studies, like the unknown charge distribution of the products of quasi-fission. The PAC emphasizes that the proposed experimental method is feasible. Recommendation. The PAC strongly recommends starting to work on the details of this proposal within the Flerov Laboratory right away.

During period from last PAC session it was performed • • • Detailed Laser scheme of setup. Scheme of gas part of setup, consisting of: front end system, gas cell, SPIG system, evacuation system, gas cleaning system etc. Drawings for all elements of gas part of setup The different possibilities of Setup position at FLNR U-400 M cyclotron have been considered and 2 variants developed more detailed The International Workshop on “Resonance Laser Separation of Nuclear Reaction Products” was held on 6 -7 December at Flerov Laboratory. Leading scientists in this field of research from Leuven, Jyvaskyla, GANIL, CERN, GSI, Mainz and i. Themba took part in the Workshop. During the Workshop the project on production and study of heavy neutron rich nuclei formed in multi-nucleon transfer reactions was discussed along with details of the corresponding setup. The project have been examined by the experts and got their approval.

Schematic view of setup for resonance laser ionization of nuclear reaction products stopped in gas

Setup consist of the following subsystems

The scheme of the front end of the LISA mass separator subsystem

The layout of the dual chamber laser ion source gas cell The aim: (by separating stopping and laser ionization chambers) • Increasing laser ionization efficiency at high cyclotron beam current • Increasing selectivity (collection of survival ions) Working conditions: -cyclotron – DC Exit hole diameter – 0. 5 mm/1 mm Stopping chamber – 4 cm in diameter Laser ionization chamber – 1 cm in diameter -Ion collector – DC -Lasers – transverse or longitudinal

The ion extraction from the gas cell d. E ~ 0. 7 e. V 4. 7 MHz 0 -500 V 1200 V 250 V (-210 V) 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 cm 3; • 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. Production cost of the gas cell and ion output systems is about 800 k$.

Specifications of the pump station located in the basement: -Pumping system: RUVAC WH 7000 roots pump with SCRELINE SP 630 backing pump -(from Oerlikon Leybold Vacuum Gmbn) is taken as example. Electrical power for the prepump : 3 X 380 V, 11 k. W Electrical power for the pump: 3 X 380 V, 18 k. W Weight : 1300 kg, Noise level : 80 d. B(A) - pumps to be placed in the basement with sound isolation panels -Pumping station is placed on the high voltage platform (40 k. V) 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 pump station 3 roots pump station at HV platform Isolating transformer for HV platform

The scheme of the gas handling and purification system Ar Grade 5. 5 (99. 9995%) Gas purifier Mono. Torr Phase II 3000 SAES Pure Gas, Inc. Flow meter Brooks Instrument 5860 S 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 metalsealed valves have to be used in order to reduce the outgasing and the "memory effect". The system should be bakeable up to 2000 C 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 ke. V) 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 40 о– 90 о, • 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 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). Production cost of such mass separator is about 250 k$.

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 300 A/25 V AC main input: 3 X 380 V, 18. 5 A Cooling water flow: 120 l/h, pressure drop=3 bar Vacuum system 4 turbo pumps (at front end, lens chamber, entrance of the magnet, dispersion chamber): for example Edwards STP 1003 C, Water cooled, 100 l/h per pump Two Prepumps, for example Pfeiffer MVP 160 -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 k. W

Comparison dye vs. possible Ti: Sa system Active Medium condition of aggregation Tuning range Power Pulse duration Power stability Synchronization Maintenance Dye > 10 different dyes liquid 540 – 850 nm < 15 W 8 ns decrease during operation optical delay lines renew dye solutions Ti: Sa =1 Ti: sapphire crystal solid-state 680 – 980 nm < 5 W 50 ns stable q-switch, pump power ~ none Dye Ti: Sa 2 x Dye 2 x Ti: Sa 3 x Dye 4 x Ti: Sa Dye

The (almost) optimum RILIS Laser System l – meter Nd: YAG Master clock Delay Generator Dye 2 SHG Dye 1 SHG THG Narrowband Dye RILIS Dye Laser System 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 p. A – meter

Laser system type output power, (average) main & harmonics: (2 nd ), {3 rd & 4 th}, Wt 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 Credo dye laser specification (Sirah) Nd: YAG laser specification (Edge. Wave Gmb. H) Maximal average power: 20 W at fundamental wavelength, 2 W at Maximal average power: 90 W and 36 W respectively; 2 nd harmonics; Repetition rate: 10 -15 k. Hz; Line width: 12 GHz Pulse duration: 8 -10 ns. 2 = 1. 4; Pulse duration: ~7 ns Divergence parameter of the green beam: M Electrical power 3. 6 k. W including 1. 6 k. W for the water chiller. Remote control of wavelength with stabilization to an external laser wavelength meter. Production cost of the laser system with three-step resonance ionization (combined with the corresponding optical scheme) is about 950 k$.

The layout of laser installation OT 1 -OT 9 – optical tables; Nd: YAG 1 and Nd: YAG 2 – pump lasers; DL 1 -DL 3 – dye lasers; R 1 and R 2 – racks for electronics and water chillers; M 1 -M 10, M 22 – high power mirrors for 532 nm beams; M 10 -M 15 – high power mirrors for 355 nm beams; BS 1 -BS 4 – beam splitters for 532 nm beams; M 16 -M 21, M 23 -M 25 – mirrors for dye laser beams; T 1 -T 4 – telescopic zoom expanders for 532 nm beams; T 5 and T 6 - telescopic zoom expanders for 355 nm beams; L 1 -L 6 – spherical lenses, SM 1 and SM 2 – spherical mirrors; BD 1 and BD 2 – beam dumps for IR beams; P 1 and P 2 – half-wave plates for 355 nm; RM 1 -RM 4 – return mirrors for reference beams; RP – reference plane; Al. M 1 – Al mirror; QP 1 – quartz plate; RC – reference cell

The laser system view

Rooms requirements for this setup

Possible position of SETUP at cyclotron U 400 M

Possible position of SETUP at cyclotron U 400 M

Price of the equipment for the SETUP Laser System Position Supplier Model Price/unit Euro Quantity Total cost Euro Nd: YAG laser Edge Wave Gmb. H, Germany IS-XXX 140000 2 280000 Dye laser Sirah Laser- und Plasmatechnik, Germany Credo 60000 3 180000 Stabilized He. Ne single mode laser Edmund Optics NT 59 -939 5000 1 5000 Lasers Sub-total "Lasers" Instruments and electronics Sub-total "Instruments and electronics" Optomechanics Sub-total "Optomechanics" Optics Sub-total "Optics" 465000 Wavemeter, powermeters, photodiods, CCD cameras, control electronics, etc. 38500 Optical tables, microtables, mounts, microdrives, etc. 67500 Telescopes, lenses, mirrors, prizmas, doubl-tripl. crystals, etc. 39300 Safety Sub-total "Safety" 18700 Reference chamber 30000 TOTAL: 659000

Price of the subsystems equipment for the SETUP Position Mass separator front end Price Euro Position Price Euro Isolation quarts tube, remote control needle valve, electronics, gas line towards gas cell) 15000 Backing power supplies and temperature control 5000 Electronics and mechanics for the gas cell 15000 Sub-total "Gas handling and purification system" 77000 Pumping station (roots pump, prepump, bak. pump, ) 200000 High voltage platform with isolation transformers 30000 Sub-total 290000 Laser ion source and extraction chambers 20000 Laser ion source 10000 Stabilized power supply Sextu. Pole ion guide (SPIG) structure 5000 Electronics and mechanics SPIG (RF, DC pow. suppl. ) 12000 Pumps for the extr. chamb. 30000 Sub-total 47000 Lens chamber 20000 Diagnostics (mov. Faraday cup and prism, electronics) Accelerator beam transport system Movable Faraday Cup, movable or rotable energy degraders, electronics 12000 Remote control vacuum valves, turbo molecular pump with baking pump 25000 Sub-total "Accelerator beam transport system" 37000 Dispersion chamber and Detection system Dispersion chamber 20000 10000 Turbo molecular and baking pumps pressure gauges and meters 25000 Power supply, high voltage insulator 12000 Tape station for radioactive isotopes 20000 Pumps for the lens chamber 30000 Gamma, beta or alpha detectors 40000 Current meter (noise level< 1 p. A) 8000 Oil-free pumping station 17000 Beam diagnostics (Faraday cup, needle scanner, adjustable diaphragm in the focal plane) 15000 Sub-total 80000 Detectors and housing for stable beam 8000 Sub-total"Dispersion chamber and Detection system" Gas purifier, gas flow meter, valves, electro polished tubes, pressure gauges and meters 40000 128000 Dipole magnet Gas handling and purification system 80000 Total 739000

Financial plan, k$ 2012 Laser system 2013 600 390 Front end system 265 Pump station 145 2014 240 Gas purification 100 Separator, detection 250 Total 600 800 590 Total: 1990 k$

Working plan Laser Front Pump system end system station prepa ration moun ting startu p prepa ration moun ting Gas purification startu p Separator, detection prepa ration 2012 2013 2014 2015 starting experiments moun ting startu p

Report of the Experts • on the FLNR project on production and study of heavy neutron rich nuclei formed in multi-nucleon transfer reactions by means of their stopping in gas cell and subsequent resonance laser ionization • The International Workshop on “Resonance Laser Separation of Nuclear • Reaction Products” was held on 6 -7 December at Flerov Laboratory of Nuclear Reactions JINR. Leading scientists in this field of research from • Leuven, Jyvaskyla, GANIL, CERN, GSI, Mainz, i. Themba and Troitsk took part in the Workshop and made contributions on the current status of these investigations in their centers. During the Workshop the FLNR project on production and study of heavy neutron rich nuclei formed in multi-nucleon transfer reactions was discussed along with details of the corresponding setup for extraction of reaction products by means of their stopping in gas cell and subsequent resonance laser ionization. The project was undergone an examination by the experts and got their approval. The discussion on the details of the project has been initiated by the decision of the JINR PAC on Nuclear Physics in June 2011. • Experts made a number of recommendations on detailed parts of the project and optimal choosing of setup components: type and initial configuration of laser system, construction of front-end system and gas cell, importance of adequate gas purifying system etc. • It was stressed by experts the following: • The proposed physics program is rather ambitious. These studies allow investigating unexplored area of heavy neutron rich nuclei, helping to understand the r-process of astrophysical nucleogenesis near the last “waiting point”. The method proposed for production of heavy neutron rich nuclei, namely, the low-energy multi-nucleon transfer reactions, looks promising and adequate; the calculated cross sections of these reactions look quite realistic. • The setup proposed, its configuration and components are quite feasible and correspondent the problem. Analogous setups already successfully operated in some facilities for another investigations and reactions type. – The chosen laser system (YAG + DYE) with following extension to (YAG +Ti. Sa) allow performing an efficient ionization of new neutron rich isotopes, giving the possibility of their selection by atomic number and even by isomers. – Gas cell with indicated main parameters (pressure 100 -500 mbar of Ar (He), double chambers) will provide efficient stopping and guiding of reaction products to mass separator. – Basic mass separator parameters (with the resolution not less than 1500) fulfill the goal of isotope separation by mass. • The total efficiency of setup could be of order from few to tens percent. • The setup definitely could be build up during the period not exceeding 3 years (depending on financial schedule). • Required funding of amount ~2 M$ looks absolutely feasible and reasonable. The all experts strongly recommend constructing this setup at FLNR JINR. Many of experts show an interest to participate in realization of this project and forthcoming experiments. Proponents: V. Zagrebaev, S. Zemlyanoi and E. Kozulin Experts: Michael Block (GSI, Darmstadt, Germany) Valentine Fedosseev (CERN, Switzerland) Iouri Koudriavtsev (KUL, Leuven, Belgium) Nathalie Lecesne (GANIL, Caen, France) Vyacheslav Mishin (ISAN, Troitsk, Russia) Iain Moore (JYFL, Jyväskylä, Finland) Herve Savajols (GANIL, Caen, France) Klaus Wendt (Institut für Physik Johannes Gutenberg-Universität, Mainz, Germany)

On 24 January 2012 the design of setup for extraction of reaction products by means of their stopping in gas and subsequent resonance laser ionization have been considered by Technical Council of Flerov Laboratory of Nuclear Reactions, JINR and approved.

Conclusion • At target thickness 0. 3 mg/cm 2, ion beam of 0. 1 pm. A 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 IS RAN Troitsk: Vyacheslav Mishin FLNR: V. Zagrebaev, S. Zemlyanoi, E. Kozulin, and others

People involved into developing and discussion of this SETUP project

Supplementary

r-process and heavy neutron rich nuclei (1) difficult to synthesize (2) difficult to separate

Production of NEW heavy nuclei in the region of N=126 (Zagrebaev & Greiner, PRL, 2008) “blank spot”

IGISOL – Ion Guide Isotope Separation on line Time profiles of laser-ionized stable Ni filament He + Laser beams target 3 -10 mg/cm 2 + SPIG + Ni-58 from the filament 40 k. V cyclotron beam mass separator Weak beam, 1 n. A, 1 ms Delay time - down to 10 ms (He) Refractory elements - ! 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 Strong beam, 1 u. A, 20 ms ~1994

Setup position at U-400 M cyclotron

Required beams of accelerated ions (the ion beams available at FLNR are well satisfied our requirements) Ions: 16, 18 О, 20, 22 Ne, … 48 Ca, 54 Cr, … 86 Kr, 136 Xe, 238 U (i. e. , quite different depending on the problem to be solved). Beam energies: 4, 5 – 9 Me. V/nucleon (slightly above the Coulomb barrier) Beam intensity: not restricted (up to 1013 pps). Beam spot at the target: 3– 10 mm in diameter (not very important). Beam emittance: 20 p mm mrad. Targets: different, including actinides Th, U, Pu, Am, Cm.

The setup consists of the following elements (units) - front end system including: gas cell, system for extraction of the cooled ion beam, electrostatic system for final formation and acceleration of the ion beam (800 k$) - laser system (950 k$) - mass-separator (250 k$) - system for delivery and cleaning of the buffer gas inside the gas cell, - vacuum system, - high voltage and radio frequency units, - diagnostic and control systems for the ion beam.

Schematic view of setup for resonance laser ionization of nuclear reaction products stopped in gas

Laser System Max. Rep. Rate – 200 Hz Excimer lasers Dye lasers SHGs Reference cell Yu. Kudryavtsev, SMI 06, March 2728, 2006 Towards LIS, 15 m 4/20

Towards mass separator Energy (e. V) LISOL Laser Ion Source 4 SPIG – 210 V Exit hole Target (~ mg/cm 2) 0 Cyclotron beam Ar 500 mbar Ar/He from gas purifier Ion source selectivity - Laser ON/OFF: 30 -80 for proton-induced fission reactions 100 -200 for fusion evaporation reactions Filament Gas cell for fusion reactions Laser beams Thermalisation in a buffer gas cell (500 mbar Ar/He) • Neutralisation (>99%) • Resonant laser ionization: Z-selection (isomer) • Extraction using gas flow, transport using RF ion guide • Mass separation: A/Q selection Plasma created in the cell does not allow to collect not neutralized ions and causes recombination of laser-produced ions Pulsed operation mode Cyclotron on off on Laser Separator on