1. Accelerator Laboratory, Physics Department (JYFL) University of Jyväskylä P.O. Box 35 (YFL) FI-40014 Jyväskylä Finland MARA recoil-mass separator at JYFL – status, instrumentation and performance modelling Jan Sarén, K. Auranen, M. Leino, J. Partanen, J. Tuunanen, J. Uusitalo and Ritu-Gamma -research group

2. 6.6.2013 INPC2013, Firenze, Jan Sarén2 Outline Overview of MARA (Mass Analysing Recoil Apparatus) Position of MARA at JYFL accelerator laboratory Motivation to build MARA Optics of charged particles MARA working principle and its optical elements Instrumentation Vacuum system, Slits and apertures, Control system Performance modelling Simplified modelling scheme Example of a fusion reaction simulated Current status and conclusions

3. 6.6.2013 INPC2013, Firenze, Jan Sarén3 Position of MARA at JYFL accelerator laboratory K130 Cyclotron MARA RITU

4. 6.6.2013 INPC2013, Firenze, Jan Sarén4 MARA (Mass Analysing Recoil Apparatus) RITU gas-filled separator MARA

5. 6.6.2013 INPC2013, Firenze, Jan Sarén5 Motivation to build MARA The gas-filled separator RITU has been used extensively over almost 2 decades to study heavy elements produced in fusion-evaporation reactions close to the proton drip-line and transfermium nuclei. In recent years interest has been increasingly pointed to the lighter nuclei in the 100 Sn region and below. RITU gas-filled separator Problems with gas-filled separator in lighter mass region: beam is difficult to separate in symmetric reactions (impossible in inverse kinematics) no mass resolution -> needs often a tag (alpha, beta, isomer,...) high counting rates at a focal plane due to other evaporation channels

6. 6.6.2013 INPC2013, Firenze, Jan Sarén6 Optics of charged particles In a presence of an electric and magnetic field the force acting on a charged particle (mass m, momentum p, velocity v and kinetic energy E k ) is the Lorentz force: A rigidity is the product of a field strength and a bending radius. Thus it tells how strong field is needed to bend charged particle with given radius of curvature. The electric rigidity and the magnetic rigidity of an ion describes the trajectory of the ion through the spectrometer. Electric rigidity:Magnetic rigidity: The electric and magnetic field can be designed so that the energy dispersion cancels (E k in both   and   ) and only the mass dispersion remains (m only in   ) → RECOIL MASS SPECTROMETER (FMA, EMMA, CAMEL, HIRA, MARA,...)

7. 6.6.2013 INPC2013, Firenze, Jan Sarén7 MARA (Mass Analysing Recoil Apparatus) Quadrupole triplet scalable angular magnification Electrostatic deflector split anode, beam dump effect of the gap on the field homogeneity Arriving JYFL in late summer 2013! Magnetic dipole inclined and rounded effective field boundaries (EFB) surface coils Focal plane after 2.0 m long drift length slit system two position sensitive detectors → tracking Target beam from K130 cyclotron Schematic view of MARA Adjustable aperture in x and y directions Adjustable aperture in x direction

8. 6.6.2013 INPC2013, Firenze, Jan Sarén8 MARA (Mass Analysing Recoil Apparatus) Realistic view of MARA

9. 6.6.2013 INPC2013, Firenze, Jan Sarén9 The MARA working principle Quadrupole triplet: point-to-parallel focus from target to the deflector point-to-point focus from target to the focal plane Deflector: separates primary beam and products separates according to energy (per charge) Magnetic dipole separates masses and cancels the energy dispersion at the focal plane Different energies Different masses

10. 6.6.2013 INPC2013, Firenze, Jan Sarén10 MARA specification Some comparison to other RMS with physical mass separation: MARA has asymmetric ion optical configuration with one electrostatic deflector (E): QQQEM Fixed energy focus (due to missing second deflector) Heavily tilted m/q focal plane Shorter than other recoil mass separators Typical angular acceptance of 10 msr Typical m/q and energy acceptance Typical resolving power

11. 6.6.2013 INPC2013, Firenze, Jan Sarén11 MARA specification

12. 6.6.2013 INPC2013, Firenze, Jan Sarén12 Transmission and acceptance studies of MARA MARA has about 20% larger solid angle acceptance than RITU. Angular acceptance is almost symmetric: ~45x55 mrad 2 while RITU acceptance is asymmetric ~25x85 mrad 2. MARA can collect only 2 or 3 charge states representing 30-45% of total. The figure below shows transmission as a function of the width of the angular distribution of products. Real transmission is smaller due to energy spread and charge distribution. MARA and RITU Transmission with central energy and charge state

13. 6.6.2013 INPC2013, Firenze, Jan Sarén13 Transmission and acceptance studies of MARA No strong coupling between horizontal and vertical angles (A and B in the figure) Strong coupling between energy deviation and angle in both x and y horizontal “angle”: A = p x /p z (~rad), vertical “angle”: B = p y /p z (~rad)

14. 6.6.2013 INPC2013, Firenze, Jan Sarén14 Instrumentation: vacuum system Gate valves (x3): after target, between deflector and the dipole and before focal plane chamber. The high voltages of the deflector requires high vacuum. Since there are very limited space between Q 3 and the deflector the triplet and the deflector will form one vacuum section. The second section is formed by the dipole and part of the tube towards the focal plane. Turbo molecular pumps and a cryo pump will be used for pumping.

15. 6.6.2013 INPC2013, Firenze, Jan Sarén15 Instrumentation: apertures and slits m/q slits ±10 cm from the FP Adjustable apertures (RED) Fixed shadowing plates (MAGENTA) Baffle structure in the dipole vacuum chamber and in the drift tube.

16. 6.6.2013 INPC2013, Firenze, Jan Sarén16 Instrumentation: Apertures and slits Due to tilted focal plane in MARA it is preferable to have two m/q slit systems before and after the focal plane.

17. 6.6.2013 INPC2013, Firenze, Jan Sarén17 Control system Key notes about MARA control system Control system can be used to control vacuum components (pressure meters and gate valves), magnet power, deflector HV, apertures and slits Implemented using programmable logic control (PLC) system Automatic conditioning of the deflector HV Uses local cyclotron control system infrastructure (Alcont) Software and hardware interlocks Manual operation can be switched on Control panel of slits and apertures MARA control system is designed and built by J. Partanen

18. 6.6.2013 INPC2013, Firenze, Jan Sarén18 Possible target area detectors In principle all detector setups used or planned to be used with RITU could be used also in conjunction with MARA. These are for example: JUROGAM Ge-detector array and SAGE electron spectrometer UoY 96 CsI crystals (20x20mm 2 ) Can be used simultaneously with JUROGAM Can be used to veto charged particle channels which enhances sensitivity in pure neutron evaporation channel.

19. 6.6.2013 INPC2013, Firenze, Jan Sarén19 First stage detector system at the focal plane Multi Wire Proportional Counter, MWPC, 1 mm wire pitch in x- and y-directions gives position, time and energy loss of a recoil Micron BB17 DSSD 128x48 mm 2 128x48 strips cooled to ~ -20°C BB17 is planned to be replaced later with a same size DSSD but having 0.67 mm strip pitch. MARA focalplane is designed to be highly modifiable and easy to maintain. Vacuum chamber around DSSD can be replaced to larger one in order to fit a planar Ge-detector or scintillation detectors inside chamber.

20. 6.6.2013 INPC2013, Firenze, Jan Sarén20 Tests with Mesytech preamplifier Micron W1-300 50x50 mm 2 16x16 strips cooled to -20°C Mesytec MPRT16 preamplifier 16 channels 4 gain settings differential output NIM-tricker output 2 TFA outputs (8 channels in one) Nutaq (Lyrtech) VHS-ADC 16 channels moving window convolution tracing of preamp signal possible 133 Ba conversion e - (FWHM ~ 11 keV) 141 Am alphas (FWHM ~ 19 keV) 252 Cf fission fragments

21. 6.6.2013 INPC2013, Firenze, Jan Sarén21 Simulation of a fusion evaporation reactions Generating a primary beam particles Slowing beam down to reaction position (TRIM/some distribution) Generating a primary beam particles Evaporating light particles independently and isotropically in CM frame using the kinetic energy distribution given by PACE4 code. The weight of the product is calculated from beam intensity, total number of events, target thickness, cross section and position weight Generating a primary beam particles Slowing and scattering products out from the target (TRIM/some distribution) Transferring products over drift length or optical element using GICOSY matrices Applying slits and apertures to particles Analysing results Development of a multipurpose graphical interface for ion-optical calculations is going on... The code will be able to use transfer matrices and fieldmaps and can simulate also gas-filled systems. First version should work this autumn. Transferring products over drift length or optical element using GICOSY matrices Applying slits and apertures to particles

22. 6.6.2013 INPC2013, Firenze, Jan Sarén22 Example reaction: 40 Ca+ 40 Ca-> 78 Zr+2n Symmetric reaction target 300  g/cm 2 Beam energy 117 MeV Cross sections from PACE4 almost 40% of products in two most abundant charge states pure neutron channel has narrower energy and angle distribution other channels produce around 6 orders of magnitudes more fusion products in total

23. 6.6.2013 INPC2013, Firenze, Jan Sarén23 Example reaction: 40 Ca+ 40 Ca-> 78 Zr+2n Most of the counting rate can be cut by one aperture (10 cm before the FP) and one barrier (10 cm after the FP) Products (RED) has been multiplied by 10 4.

24. 6.6.2013 INPC2013, Firenze, Jan Sarén24 Example reaction: 40 Ca+ 40 Ca-> 78 Zr+2n m/q spectrum calculated from realistic focal plane information (scattering and limited resolution in detectors) (bottom figure) The biggest problem is to separate isobars and other peaks which have almost the same m/q ratio Veto detector (UoYTube) for charged channels is more than welcome...

25. 6.6.2013 INPC2013, Firenze, Jan Sarén25 Example reaction: 40 Ca+ 40 Ca-> 78 Zr+2n Spatial distribution at the implantation detector 40 cm after the optical focal plane (MWPC). The choosed DSSD size of 128x48 mm 2 seems to be suitable.

26. 6.6.2013 INPC2013, Firenze, Jan Sarén26 Current status and conclusions Danfysik will deliver the electrostatic deflector late summer 2013. Minimal focal plane detection system, the 128x48 mm 2 DSSD and a MWPC, are supposed to be ready around October 2013. All vacuum chambers will be also ready that time. Transmission-, alignment- and other ion-optical tests with an alpha source will take place end of the year and commissioning with a primary beam can be estimated to start early spring 2014. We hope MARA can fulfil the expectations we have set and will be a complementary recoil separator to RITU gas-filled one.