1. On the ARIEL Pre-separator
S. Saminathan, R. Baartman, TRIUMF, Vancouver, BC, Canada.
Basic Requirements
Maximal beam energy
60 keV
Maximum beam rigidity
0.544 Tm
First bending angle of the beamline
112 deg.
Second bending angle of the beamline
90 deg.
Mode of operation
achromatic
Emittance (4*RMS)
20 µm
Mass resolving power
300
Abstract
Beamline Layout
Two new independent target ion sources with a dedicated pre-separator will be built in the ARIEL facility[1] to triple the radioactive ion beam production at TRIUMF. The pre-separators are to minimize the undesired radioactive species from contaminating the further transport, including to the high resolution separator. A compact Nier-Johnson type of pre-separator has been designed to achieve a mass resolving power of 300[2]. It consists of a 112 deg. magnetic and a 90 deg. toroidal electrostatic dipole with deflection in opposite direction. It also contains electrostatic quadrupole elements in between the dipoles. The electrostatic dipole compensates the energy dispersion of the magnetic dipole. This allows an achromatic mode of operation resulting in a high mass resolving power downstream to the electrostatic deflector even for beams with a high energy spread. We present the result of beam optics calculations for the ARIEL pre-separator along with the design of the toroidal electrostatic dipole.
Figure: Layout of the pre-separator in the
target hall.
Dipole
Spec.
MB8
EB12
Radius
50 cm
45 cm
Angle
112 deg.
90 deg.
Pole gap
6 cm
5 cm
Edge angle
27.5 deg.
0 deg.
EB12
MB8
Figure : Mechanical design of the toroidal electrostatic dipole (EB12).
Target ion source
Figure : RIB beamline in the ARIEL target hall. Dashed line indicates the pre-separator beamline.
Figure: Calculated total electrostatic field (|E|) along the beam axis (from the dipole center to
exit) of the electrostatic dipole (EB12).
Figure : Pre-separator layout with calculated ion trajectories (dE = %, dM = ±0.33 %) by using the code GIOS.
Beam Envelope
Resolving Power
In the linear approximation :
Mass resolving power (Rm) at the location of mass slit (SLIT8B),
Rm = (x|δm)/(2(x|x)W) ≈ 300
Where (x|δm) = 77 cm is the mass dispersion,
(x|x) = 1.0 is the magnification, and W = cm
is the half width of the source slit (COL8A).
2. Energy resolving power (Rk) at the location of energy slit (SLIT13 ),
Rk = (x|δE)/(2(x|x)W) ≈ 327
Where (x|δE) = 77 cm is the energy dispersion,
(x|x) = 0.92 is the magnification, and W = cm is the half width of the source slit (COL8A).
Figure: At slit8B with dE = % and
dM = ±0.33 %.
Figure: At slit8B with dE = 0.33 % and
dM = ±0.33 %.
Figure: At slit13 with dE = 0.33 % and
dM = ±0.33 %.
Figure: Calculated beam envelope (2*RMS) with energy and mass dispersion for 60 keV ion beam through the pre-separator by using the code TRANSOPTR.
Figure: At slit13 with dE = % and
dM = ±0.33 %.
Figure: At slit13 with
dE = %.
Figure: At slit13 with
dE = %.
Figure: Above profiles calculated by using the code COSY INFINITY.
Merits
References
(a) It allows rejection of neighboring masses that are off energy, as can happen when a much more populous undesired isotope is stripped in the extraction region and gains less energy than the total potential difference, (b) It has an energy collimation feature, (c) The achromaticity will cancel energy-horizontal motion correlation and hence it simplifies tuning when small energy changes are being made.
L. Merminga, et al., “ARIEL:TRIUMF advanced rare isotope laboratory'‘, Proceedings of IPAC, vol.11, 2011.
S. Saminathan, R. Baartman, “ARIEL Pre-separator”, TR-DN-16-07, Internal report, TRIUMF, May, 2016.
MOPIK056, 8th International Particle Accelerator Conference, Copenhagen, Denmark, 2017 May 14