Jan Sarén K Auranen M Leino J Partanen J Tuunanen J Uusitalo and RituGamma research group 662013 INPC2013 Firenze Jan Sarén 2 Outline Overview of MARA M ass A nalysing ID: 815343
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Slide1
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
Slide26.6.2013INPC2013, Firenze, Jan Sarén
2Outline
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
Slide36.6.2013INPC2013, Firenze, Jan Sarén
3Position of MARA at JYFL accelerator laboratory
K130 Cyclotron
MARA
RITU
Slide46.6.2013INPC2013, Firenze, Jan Sarén
4MARA (Mass Analysing Recoil Apparatus)
RITU
gas-filled
separator
MARA
Slide56.6.2013INPC2013, Firenze, Jan Sarén
5Motivation 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
Slide66.6.2013INPC2013, Firenze, Jan Sarén
6Optics 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
E
and
B
) and only the mass dispersion remains (
m
only in
B
) → RECOIL MASS SPECTROMETER (FMA, EMMA, CAMEL, HIRA, MARA, ...)
Slide76.6.2013INPC2013, Firenze, Jan Sarén
7MARA (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
Slide86.6.2013INPC2013, Firenze, Jan Sarén
8MARA (Mass Analysing Recoil Apparatus)
Realistic view of MARA
Slide96.6.2013INPC2013, Firenze, Jan Sarén
9The 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
Slide106.6.2013INPC2013, Firenze, Jan Sarén
10MARA 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
Slide116.6.2013INPC2013, Firenze, Jan Sarén
11MARA specification
Slide126.6.2013INPC2013, Firenze, Jan Sarén
12Transmission 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
Slide136.6.2013INPC2013, Firenze, Jan Sarén
13Transmission 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)
Slide146.6.2013INPC2013, Firenze, Jan Sarén
14Instrumentation: 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.
Slide156.6.2013INPC2013, Firenze, Jan Sarén
15Instrumentation: 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.
Slide166.6.2013INPC2013, Firenze, Jan Sarén
16Instrumentation: 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.
Slide176.6.2013INPC2013, Firenze, Jan Sarén
17Control 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
Slide186.6.2013INPC2013, Firenze, Jan Sarén
18Possible 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.
Slide196.6.2013INPC2013, Firenze, Jan Sarén
19First 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.
Slide206.6.2013INPC2013, Firenze, Jan Sarén
20Tests 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
Slide216.6.2013INPC2013, Firenze, Jan Sarén
21
Simulation of a fusion evaporation reactions
Generating a primary beam particles
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
Slide226.6.2013INPC2013, Firenze, Jan Sarén
22Example reaction: 40Ca+40Ca->78Zr+2n
Symmetric reaction
target 300
m
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
Slide236.6.2013INPC2013, Firenze, Jan Sarén
23Example reaction: 40Ca+40Ca->78Zr+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
.
Slide246.6.2013INPC2013, Firenze, Jan Sarén
24Example reaction: 40Ca+40Ca->78Zr+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...
Slide256.6.2013INPC2013, Firenze, Jan Sarén
25Example reaction: 40Ca+40Ca->78Zr+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.
Slide266.6.2013INPC2013, Firenze, Jan Sarén
26Current 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.