Linear accelerators for nuclear physics and applications Winfried Barth, GSI Helmholtzzentrum für

149 Pages·2015·15.89 MB·English

by  Barth, Winfried Dr.

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.