Transcript Slides - Agenda INFN

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
Accelerator Laboratory, Physics Department (JYFL)
University of Jyväskylä
P.O. Box 35 (YFL)
FI-40014 Jyväskylä
Finland
Outline
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Overview of MARA (Mass Analysing Recoil Apparatus)
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Position of MARA at JYFL accelerator laboratory
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Motivation to build MARA
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Optics of charged particles
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MARA working principle and its optical elements
Instrumentation
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Vacuum system,
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Slits and apertures,
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Control system
Performance modelling
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Simplified modelling scheme
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Example of a fusion reaction simulated
Current status and conclusions
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Position of MARA at JYFL accelerator laboratory
MARA
RITU
K130 Cyclotron
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MARA (Mass Analysing Recoil Apparatus)
MARA
RITU
gas-filled
separator
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Motivation to build MARA
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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 100Sn region and below.
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
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RITU gas-filled separator
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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 Ek) 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 (Ek in both E and B) and only the mass dispersion remains (m only in B) →
RECOIL MASS SPECTROMETER (FMA, EMMA, CAMEL, HIRA, MARA, ...)
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MARA (Mass Analysing Recoil Apparatus)
Schematic view of MARA
Adjustable aperture in x
direction
Focal plane
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Magnetic dipole
Quadrupole
triplet
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after 2.0 m long
drift length
slit system
two position
sensitive
detectors →
tracking
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scalable angular
magnification
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inclined and rounded
effective field boundaries
(EFB)
surface coils
Electrostatic deflector
split anode, beam dump
 effect of the gap on the field
homogeneity
 Arriving JYFL in late summer 2013!
Adjustable aperture in x
and y directions

Target
beam from
K130 cyclotron
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MARA (Mass Analysing Recoil Apparatus)
Realistic view of MARA
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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
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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
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MARA specification
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Transmission and acceptance studies of MARA
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MARA has about 20% larger solid angle acceptance than RITU.
Angular acceptance is almost symmetric: ~45x55 mrad2 while RITU
acceptance is asymmetric ~25x85 mrad2.
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
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Transmission and acceptance studies of MARA
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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 = px/pz (~rad),
vertical “angle”: B = py/pz (~rad)
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Instrumentation: vacuum system
The high voltages of the deflector requires high vacuum. Since there are
very limited space between Q3 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.
Gate valves (x3): after target, between deflector and the
dipole and before focal plane chamber.
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Instrumentation: apertures and slits
Baffle structure in the
dipole vacuum chamber
and in the drift tube.
Adjustable apertures (RED)
m/q slits
±10 cm from
the FP
Fixed shadowing plates (MAGENTA)
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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.
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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
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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 (20x20mm2)
Can be used simultaneously with JUROGAM
Can be used to veto charged particle channels
which enhances sensitivity in pure neutron
evaporation channel.
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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
2
 128x48 mm
 128x48 strips
 cooled to ~ -20°C
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.
BB17 is planned to be
replaced later with a same
size DSSD but having 0.67
mm strip pitch.
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Tests with Mesytech preamplifier
Mesytec MPRT16 preamplifier
 16 channels
 4 gain settings
 differential output
 NIM-tricker output
 2 TFA outputs (8 channels in one)
Micron W1-300
2
 50x50 mm
 16x16 strips
 cooled to -20°C
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Ba conversion
e- (FWHM ~ 11 keV)
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alphas
(FWHM ~ 19 keV)
Nutaq (Lyrtech)
VHS-ADC
 16 channels
252Cf
 moving window
fission
convolution
fragments  tracing of
preamp signal
possible
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Simulation of a fusion evaporation reactions
Generating a
primary beam
particles
Slowing beam
Generating
down to
a reaction
primary
position
beam
(TRIM/some
particles
distribution)
Evaporating light particles
Generatingand isotropically
independently
primary
inaCM
frame using the kinetic
energy
distribution given by
beam
PACE4 code. The weight of the
particles
product is calculated from beam
Slowing and
Generating
scattering
products
out
a primary
frombeam
the target
(TRIM/some
particles
distribution)
intensity, total number of events,
target thickness, cross section
and position weight
Analysing
results
Applying slits
and apertures
to particles
Applying slits
and apertures
to particles
Transferring
products over
drift length or
optical element
using GICOSY
matrices
Transferring
products over
drift length or
optical element
using GICOSY
matrices
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.
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Example reaction: 40Ca+40Ca->78Zr+2n
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Symmetric reaction
target 300 mg/cm2
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
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Example reaction: 40Ca+40Ca->78Zr+2n
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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 104.
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Example reaction: 40Ca+40Ca->78Zr+2n
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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...
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Example 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 mm2 seems to
be suitable.
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Current status and conclusions
Danfysik will deliver the electrostatic deflector late summer 2013.
Minimal focal plane detection system, the 128x48 mm2 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.
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