TriSol a major upgrade of the TwinSol RNB facility

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TriSol: a major upgrade of the TwinSol RNB facility

P.D. O’Malley, T. Ahn, D.W. Bardayan, M. Brodeur, S. Coil, J.J. Kolata1,∗

Dept. of Physics and Astronomy, University of Notre Dame, Notre Dame, IN 46556,

United States

Abstract

We report here on the recent upgrade of the TwinSol radioactive nuclear beam

(RNB) facility at the University of Notre Dame. The new TriSol system in-

cludes a magnetic dipole to provide a second beamline and a third solenoid

which acts to reduce the size of the radioactive beam on target.

Keywords: Radioactive ion beams, Solenoid spectrometer

1. Introduction

The ﬁrst radioactive nuclear beam setup [1] at the University of Notre Dame,

used from 1987-1995, was replaced by the TwinSol facility [2, 3, 4, 5, 6, 7] which

became operational in 1998. Both of these were the result of a collaboration

between the University of Notre Dame and a group at the University of Michigan

headed by Prof. F. D. Becchetti.

∗Corresponding author

Email address: jkolata@nd.edu (J.J. Kolata)

1Emeritus professor

Preprint submitted to Journal of L

X Templates October 7, 2022

arXiv:2210.01950v2 [physics.acc-ph] 6 Oct 2022

Figure 1: (Color online) The TwinSol radioactive nuclear beam facility. Figure from Ref. [7].

TwinSol (Fig.1) consists of a pair of 30 cm bore, 6T superconducting solenoids

contained within low-loss cryostats (<0.1 LHe/h) having a holding time of >2

months. The solenoids are air-core (hence no iron yokes) and are operated in

persistent mode. As a result, their magnetic ﬁelds do not suﬀer from hysteresis

and scale exactly with the applied currents. However, the ﬁelds extend to a

large distance (up to 0.1 T at 2 m on axis at maximum ﬁeld) and this must

be accounted for both in computing the required magnet current and in safety

concerns for those working near the magnets when they are energized.

Referring to Fig.1 above, a variable aperture (0-30 mm dia.) at the crossover

point between the two solenoids provides momentum analysis and therefore a

degree of isotope separation. In some cases, an absorber foil was also located

there to provide further separation via diﬀerential energy loss. Most of the

early experiments were carried out in the small scattering chamber close to the

second solenoid. In this location, the beam spot size was typically 5-6 mm full

width at half maximum (FWHM). However, in later experiments involving neu-

tron or γ-ray detection, a shielding wall consisting of borated water followed

by concrete blocks was inserted as shown. Experiments were also carried out

in the larger scattering chamber illustrated, or in other apparatus such as the

prototype active-target time projection chamber (pAT-TPC) [8] from Michigan

State University (MSU) or the neutron array described in [9].

The primary target was initially situated within an ISO-100 cross, followed

by an ISO-200 cross containing an entrance aperture and a Faraday cup having

an outer diameter of 2.5 cm. Typically this setup accepted particles scattered

between 3◦and 6◦in the laboratory (lab) frame, although larger collimators ac-

cepting up to 11◦were available if needed. However, more recently the ISO-100

cross was replaced by a 30 cm dia. chamber to provide room for a moveable

target system holding 4 gas targets [10], and also the ability to place silicon (Si)

detectors around the target for certain experiments. In this conﬁguration, the

angular acceptance of the system is between 2◦and 5.25◦in the lab. For most

experiments, the primary target is a 2.5 cm long gas cell containing 2H or 3He

gas at atmospheric pressure (though solid targets are occasionally used). The

gas-cell windows are typically 4 µm Ti foils. A list of the many publications

carried out with TwinSol during its nearly 25 years of existence can be found

here: http://notredame.box.com/s/9w79ctrizr3ol8ac1pow9bckm5sa73bu.

2. TriSol

A further recent change in the setup shown in Fig.1 was the removal of the

neutron shielding wall shown and extension of the beam line through a 1.25 m

thick high-density concrete shielding wall into an adjacent area. This modiﬁca-

tion provided additional isolation from neutron and γ-ray background coming

from the primary target and more room to attach ancillary equipment such as

the β-decay station described in Ref.[11]. Unfortunately, at this location the

ion optics resulted in a beam spot size of 25 mm FWHM or greater. While

acceptable for some experiments, this was problematic for others which resulted

in the ﬁrst impetus to design an upgrade which would produce improved RNBs.

Additionally, the “St. Benedict” ion trap [12] requires a dedicated beam line.

Hence, reaction studies with exotic beams or other experiments including addi-

tional lifetime measurements could only be continued if two lines were available.

Therefore, a small XY steering magnet followed by a magnetic dipole were in-

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摘要：

TriSol:amajorupgradeoftheTwinSolRNBfacilityP.D.O'Malley,T.Ahn,D.W.Bardayan,M.Brodeur,S.Coil,J.J.Kolata1,Dept.ofPhysicsandAstronomy,UniversityofNotreDame,NotreDame,IN46556,UnitedStatesAbstractWereporthereontherecentupgradeoftheTwinSolradioactivenuclearbeam(RNB)facilityattheUniversityofNotreDame.Then...

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TriSol a major upgrade of the TwinSol RNB facility

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