Beam thermalization in a large gas catcher

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS

卷:463

Article; Proceedings Paper

Sumithrarachchi, C. S.¹  Morrissey, D. J.^1,2  Schwarz, S.¹  Lund, K.¹  Bollen, G.⁴  Ringle, R.¹  Savard, G.³  Villari, A. C. C.⁴ 

[1] Michigan State Univ, Natl Superconducting Cyclotron Lab, E Lansing, MI 48824 USA

[2] Michigan State Univ, Dept Chem, E Lansing, MI 48824 USA

[3] Argonne Natl Lab, 9700 S Cass Ave, Argonne, IL 60439 USA

[4] Michigan State Univ, Facil Rare Isotope Beams, E Lansing, MI 48824 USA

关键词: Gas catcher;    Thermalized beam;   

DOI  :  10.1016/j.nimb.2019.04.077

来源: Elsevier

【 摘 要 】

Thermalization of fast ions in a buffer gas provides a method to transform the high-energy, exotic beams produced by projectile fragmentation at the National Superconducting Cyclotron Laboratory (NSCL) into low-energy beams. The process includes slowing down the fast exotic beams in solid degraders combined with momentum compression and removal of the remaining kinetic energy by collisions with a buffer gas. The original beam thermalization area for mass measurements at the NSCL was reconfigured to accommodate a new momentum compression beam line, a large radio-frequency (RF) gas catcher constructed by Argonne National Lab and a low-energy beam transport system. A large variety of exotic isotopes produced by projectile fragmentation and selected by the A1900 fragment separator was thermalized in the 1.2 m long gas catcher filled with helium at approximately 100 mbar. The ions were guided to an extraction nozzle with a combination of electrostatic and RF potentials and ejected by the gas flow. A novel RF ion guide was used in a differential pumping system to remove the helium and transport the ions into ultrahigh vacuum. Finally, the ions were accelerated to 30 kV for transport to various experiments. The distribution of the thermalized ions among chemical adducts is one of the operational challenges. The important steps implemented to minimize the production of the chemical adducts in the gas catcher are discussed. The operational status of the facility and some example results from characterization of the gas catcher operation with K-37 and K-47 beams are presented.

【 授权许可】

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