Linear accelerators for nuclear physics and (other) applications Winfried Barth, GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany Helmholtzinstitut Mainz, Mainz, Germany Linear accelerators for nuclear physics and (other) applications • Overview: History and accelerator types (I) • Beam dynamics (I/II) • Heavy Ion stripping (II) • Basics/Linear Accelerators (II-III) • The GSI accelerator facility (III/IV) • LINACS for different applications (IV) Accelerator Facilities for Heavy Ion Nuclear Physics: Background and Aims • Accelerated heavy ion beams for Nuclear spectroscopy, reaction studies and nuclear astrophysics since middle of the last century • Special topic: Super Heavy Elements (SHE) => fusion reactions between medium mass ions (4-5 MeV/u) and very heavy targets (LBL, GSI and JINR (actinide targets), RIKEN (cold fusion) => nowadays: nucl. spectroscopy, lifetime measurements, nuclear chemistry of SHEs • Since mid of 1980s: medium energy ion beams (<100 MeV/u) in normal conducting cyclotrons and super conducting cyclotron facilities => fragmentation and fission of heavy projectile nuclei in thin (light) targets to produce fast exotic nuclei using In flight technology (11Li). • Rare ion beam facilities => nuclear reactions involving post accelerated short lived nuclides of particular interest for astrophysics. • Isotopes far off stability and higher space charge density exotic ion beams => ISotope On-Line Technique (ISOL), using light ion beams (20 to 1400 MeV/u) to generate radioactive nucleii by spallation, fission or fragmentation reactions in thick targets of heavy elements. Landmark results from experiments with in-flight produced super heavy elements (SHE), with exotic beams at the Synchrotron-FRagment-Separator facility (SIS-FRS), and at the Experimental Storage Ring (ESR) at GSI Darmstadt. [Reprinted from Nucl. Phys. A 701 (2002) 259, H. Geissel, G. Muenzenberg, and H. Weick, Copyright (2002), with permission from Elsevier] in-flight production method for radioactive isotopes (left) and ISotope On-Line (ISOL) production method (right). • Rare isotopes (stopped or very low energy <100 keV) are used for precision measurements of masses, moments, and symmetries. • Re-accelerated isotopes (.2-20 MeV/u) are used for detailed nuclear structure studies, high-spin studies, and measurements of astrophysical reaction rates. • Inflight produced fast isotopes (>100 MeV/u) => farthest reach from stability to the limits of existence and to the shortest life times. Requirement for stable beam and/or radioactive beam facilities (new high intensity heavy ion accelerators for further extend of possibilities for synthesis and SHE experiments... Status Quo • Since about 20 years there is a growing worldwide demand for in-flight and in ISOL facilities for the production of radioactive isotopes. • Developments in the fields of ion sources and superconducting accelerator technologies have facilitated access of many nuclear physics laboratories to exotic beams. • The new facilities will further increase the production rates and the measurement precision for exotic ions. • In-flight facilities have advantages in the field of nuclear physics, whereas ISOL facilities have their strengths in the field of nuclear astrophysics. • A new generation of in-flight facilities builds on very powerful driver accelerators covering a broad range of light to heavy primary ion beams. • For new and expanding ISOL facilities with superconducting post-accelerators, target handling, charge breeding, acceleration, and beam handling of radioactive ions are important issues. • ISOL post-accelerators are operated typically in the same energy range as machines for super-heavy element synthesis. Heavy Ion Accelerators for Nuclear Physics, Norbert Angert , Oliver Boine-Frankenheim, in book: Accelerators and Colliders, Edition: Landolt-Börnstein: Numerical Data and Functional Relationships in Science and Technology, Chapter: Heavy Ion Accelerators for Nuclear Physics, Publisher: Springer, Editors: H.Schopper, S.Meyers Particle energies Energies in eV Expected mass of > 100 GeV the Higgs boson W, Z exchange bosons 82 bzw. 93 GeV of the weak force Rest mass of the 0.938 GeV anti proton: E=mc2 eU=1.602 10-19 J=1 eV 1 keV= 103 eV Excitation energies in 1 MeV= 106 eV nuclei MeV 1 GeV= 109 eV 1 TeV= 1012 eV Ionisation energies in keV heavy atoms Ionisation energy of the 13 eV hydrogen atom TV Development of compact, high efficient, (high intensity) heavy ion linacs... 238U37+ How to shorten the lenghs of a heavy ion accelerator? Delivery of Post-Stripper HILAC (heavy ion linear accelerator) tank on Cyclotron Road (at the horseshoe curve), April 16, 1956. Mar 1983; Particle accelerator conference; Santa Fe, NM (USA): - Very complex ion sources - Ion sources to be optimized for high intensity high charge state beams - Low charge/mass ratio  High field gradient/long accelerating structure - Stripping losses  intensity requirements - Highest linac energy  stripping to the highest possible charge state for max. final beam energy ‘Plasma’ ion sources Where do the ions come from ? Ions are produced in a ionized gas (‘plasma’) In thermal equilibrium the Saha equation describes the amount of ionization in a gas  3/2 I n kT  j i  3 1027 B e kBT n n n i Ionization energy: I (j: charge state) j Highly stripped ions require high plasma temperatures and good plasma confinement. High ion currents are achieved for lower charge states ions.