Exotic Beam Production and Facilities II

1. Exotic Beam Production and Facilities II • Brad Sherrill, Michigan State University • Lecture I • The Rare Isotope Accelerator Concept • Some history and background • The status of exotic beam plans in the USA • Lecture II • Methods of exotic beam production • Production mechanisms (e.g. fragmentation) • Current world situation for exotic beams

2. Target/Ion Source Driver Production Mechanisms • In-flight Separation • ISOL – Isotope Separation On-Line • Neutron induced fission (2-step target) Fragment Separator Driver Accelerator beam Beams used without stopping Post Acceleration Gas cell catcher/ion source Post Acceleration Neutrons Driver Post Acceleration

3. Advantages/Disadvantages of ISOL/In-Flight In-flight: GSI RIKEN NSCL GANIL • Provides beams with energy near that of the primary beam • For experiments that use high energy reaction mechanisms • Luminosity (intensity x target thickness) gain of 10,000 • Individual ions can be identified • Efficient, Fast (100 ns), chemically independent separation • Production target is relatively simple • Good Beam quality (p mm-mr vs. 30 p mm-mr transverse) • Small beam energy spread for fusion studies • Can use chemistry (or atomic physics) to limit the elements released • 2-step targets provide a path to MW targets • High beam intensity leads to 100x gain in secondary ions ISOL: HRIBF ISAC SPIRAL ISOLDE 400kW protons at 1 GeV is 2.4x1015 protons/s

4. Production Methods – Low Energy • (p,n) (p,nn) etc. • Ep < 50 MeV • Used for the production of medical isotopes. • Selective, large production cross sections (100 mb), and intense (500 mA) primary beams. • Used at HRIBF(ISOL), LLN (ISOL), ANL (in-flight) and Notre Dame (in-flight), Texas A&M (in-flight) • Fusion • Low energy 5-15 MeV/A and “thin” targets • Selective with fairly large production cross sections. • Used at ANL(in-flight), JYFL (Jyväskylä)

5. Example of production by fusion • High, specific production cross sections • Example: 58Ni(3He,n)60Zn, EHe = 100 MeV • Production cross section from ALICE: 100 mb • 4 g/cm2 target • Yield of 60Zn is 3x107/pmA (LBL 88-inch has 10 pmA of 3He) • Heavier beams can have larger cross sections, but require thinner targets.

6. Low Energy - Continued • Transfer reactions • Significant cross section between 10 - 50 MeV/A (this energy range implies thin targets, mg/cm2) • High production of nuclei near stability. • Multi-nucleon reactions can be used to produce rare or more neutron rich nuclei, e.g. GSI mass separator had a program to study neutron rich f-p shell nuclei using neutron transfer. • Deeply inelastic reactions • Deep inelastic - much of the KE of the beam is deposited in the target. • Was used to first produce many of the light neutron rich nuclei • Is used to study neutron rich nuclei since the products are “cooler” and fewer neutrons are evaporated than in fusion reactions.

7. Production Mechanisms – High Energy • Fragmentation (NSCL, GSI, RIKEN, GANIL) • Projectile fragmentation of high energy (>50 MeV/A) heavy ions • Target fragmentation of a target with high energy protons or light HIs. In the heavy ion reaction mechanism community these are called intermediate mass fragments. • Spallation (ISOLDE, TRIUMF-ISAC) • Name comes from spalling or cracking-off of target pieces. • One of the major ISOLDE mechanisms, e.g. 11Li made from spallation of Uranium. • Fission (technically not only high energy) • There is a variety of ways to induce fission (photons, protons, neutrons (thermal, low, high energy) • The fissioning nuclei can be the target (HRIBF) or the beam (GSI/MSU/RIKEN). • Coulomb Breakup • At beam velocities of 1 GeV/n the equivalent photon flux as an ion passes a target is so high the GDR excitation cross section is many barns.

8. Fission Cross Sections Low energy fission can lead to higher yields for certain nuclides. This is the basis of the electron driver upgrade of the HRIBF.

9. HRIBF eBeam Upgrade • Bremsstrahlung from the electron beam induces photo-fission in a uranium carbide target system with a thickness of ~35 g/cm2 • A 50 kW, 100 MeV electron beam incident on such a target would generate a total uranium fission rate 25 times greater than a 20 μA, 50 MeV proton beam. • In addition, the yield of neutron-rich species is shifted much farther from stability than for proton induced fission. • This would result in a factor of 1,000 to 10,000 increase in beam intensities at HRIBF http://www.phy.ornl.gov/hribf/initiatives/electrons/

10. Terminology for High Energy Reactions The fragment could emit nucleons (fragmentation) and/or fission Projectile Fragment See the lectures of D Bazin Intermediate Mass Fragment/ Target Fragment Spallation Product ABRABLA - A. R. Junghans, K.-H. Schmidt et al, Nucl. Phys. A 629 (1998) 635

11. Overview of the In-Flight Technique Example: The NSCL Coupled Cyclotron Facility 100 pnA 86Kr 5 kW Beam power 65% of the 78Ni is transmitted 8 msr Dp = 5% Wedge location D = 5 cm/% R = 2500 p/Dp Morrissey and Sherrill: Euroschool Lectures

12. Multiple stages of separation Higher energy provides cleaner separation. H. Geissel et al. NIM B

13. LISE++ Simulation Code The code operates under Windows and provides a highly user-friendly interface. It can be downloaded freely from the following internet address: http://www.nscl.msu.edu/lise O. Tarasov et al.

14. Facility Specifications 78Ni from 86Kr No secondary reactions Tony Nettleton

15. Fragmentation at 400MeV/u Momentum distrib. Relatively ‘easy’ due to small phase space 100Sn 200W • Angles ≤ ± 20 mrad • Momentum ± 3 - 8 % M. Hausmann, T. Nettleton

16. In-Flight Fission at 400 MeV/u More challenging due to larger phase space 132Sn 76Ni • Angles ± 40 - 60 mrad • Rigidity ± 6 - 10 % • Plus correlations due to fission kinematics M. Hausmann, T. Nettleton

17. NSCL Coupled Cyclotron Project Cyclotrons – up to 200 MeV/u Operational – will study N=82 nuclei and nuclei along the neutron drip line up to mass 30. ECR Experimental Areas

18. Particle Identification

19. Beams Produced with CCF/A1900

20. GSI Current RNB Facility • Production of 100Sn and 78Ni • Hundreds of new masses and isotopes, …

21. Cold Fragmentation Studied at GSI J. Benlliure, K.-H. Schmidt, et al. Nuclear Physics A 660 (1999) 87 197Au + Be at 950 A MeV 5

22. The GSI FAIR Facility Layout from J. Nolen ANL

23. RIKEN Radioactive Ion Beam Factory from J. Nolen ANL

24. RIKEN RIBF Heavy-ion accelerator system An ion source current of 32 p-μamps is required to reach uranium beam goal.

25. Targets and Production Mechanisms from J. Nolen ANL

26. Production is only one part of the equation H. Ravn I = s Ib Tuseableediffedeseeffeis_effeaccel_eff • s - production cross section • Ib - beam intensity • Tuseable - usable target thickness • ediff – diffusion efficiency • edes – desorption efficiency • eeff – effusion efficiency • eis_eff - ionization efficiency • eaccel_eff - acceleration efficiency target

27. ISOLDE CERN PSB 1 GeV protons 2 mA Intensities up to 1011 pps Accelerate to 3.0 MeV/u http://isolde.web.cern.ch/ISOLDE/

28. SPIRAL at GANIL http://www.ganil.fr/spiral/index.html

29. GANIL SPIRAL-2 Completion ~2011

30. ISAC Radioactive Beam Facility - ISOL Beams are produced by 500 MeV protons from TRIUMF cyclotron. 2x10922Na/s ISAC-II underway

31. ISAC-2 overview ISAC has a fixed 500-MeV proton beam driver with 50-kW power.

32. Texas A&M Upgrade Project • Radioactive beams to 50 MeV/u • Difficult isotopes from the ion-guide http://cyclotron.tamu.edu/

33. EURISOL 5 MW Proton LINAC http://www.ganil.fr/eurisol/index.html

34. Overview of the RIA Concept

35. Forces in gas catcher system • A combination of forces working together is required to obtain • Fast extraction times over the full volume • High efficiency over the full volume • Tolerance to high intensity from J. Nolen ANL

36. 350 MeV/u 130Cd range width Range FWHM (atm-m) Resolving Power Momentum Compensation M. Amthor 130Cd FWHM = 32 atm-m 4He Diagram: H. Weick et al., NIM B 164-165 (2000) 168 FWHM = 0.93 atm-m 4He Above: Range compression of 350 Mev/u 130Cd produced from 500 MeV/u 136Xe (MOCADI simulation)

37. First nuclear physics experiment with thermalized beams from fast beam fragmentation T1/2 = 440 ms R = 2106 dm/m < 10-8 Gas Stopping in use at the NSCL 9.4 T Penning trap system mass measurements LEBIT project beam from A1900 Many systematic studies:L. Weissman et al., NIM A522 (2004) 212, NIM A531 (2004) 416, Nucl. Phys. A746 (2004) 655c, NIM A540 (2005) 245. 92 MeV/U 38Ca/37K efficiency Degrader thickness mm

38. RIA prototype gas catcher tested at GSI Bragg peak from 56Ni beam Bragg peak from 54Co beam Bragg peak from 52Fe beam GSI experiment S258 Savard(ANL), Scheidenberger (GSI) et al. ~ 50 % of radioactive ions stopped in the gas catcher were extracted as a radioactive ion beam! 54Co 52Fe ANL, GSI, KUL, MSU, RIKEN, …

39. ANL Upgrade based on 252Cf Fission Guy Savard, ANL

40. ANL ATLAS upgrade: CARIBU

41. Yields from the ANL Upgrade Guy Savard, ANL

42. 160 140 He+ 120 radial dimension (mm) 100 80 60 500 0 100 200 300 400 axial dimension (mm) SRIM & PIC calculation by M.Facina He+ created by a 100 pps 38Ca beam in 760 Torr Stopping volume  75 cm3 Ionization  1.7 x 106 IP/ion

43. Cyclotron Gas Stopper Concept Gas-filled weakly-focusing cyclotron magnet w/ RF guiding techniques at end-of-range Features/Expectations: Low gas pressure  long stopping path  fast drift & extraction Separate He+ from rare ions  minimal space-charge Exotic atom studies in a cyclotron trap for antiprotons, pions, and muons L.M. Simons, Hyperfine Interactions 81 (1993) 253 Proposal for a cyclotron ion guide with RF carpet I. Katayama, M. Wada, Hyperfine Interactions 115 (1998) 165 A Study of Gas-Stopping of Intense Energetic Rare Isotope Beams G. Bollen, D.J. Morrissey, S. Schwarz, NIM A550 (2005) 27

44. degrader Initial Stopping Calculations Energy loss or Ionization density Beam simulations of ions in gas-filled weak-focusing magnet by Bollen Top view 10 mbar He Stopped-ion distribution lies inside dashed circle 100 MeV/A Br [ 2.6 mm Al ] 610 MeV Br Field Bmax = 2 T, n = 0.2 High space-charge and stopped-ion regions are separated ! Intensity limits > 108/s

45. NSCL Stopping Cyclotron (Under Design) Superconducting magnet system Bmax = 2 T, n = 0.2, rinj = 0.7 m High Energy Beam D.Lawton, A.Zeller (NSCL)

46. Beam Simulation including Injection One Trajectory in ‘real’ field F. Marti (NSCL) Energy vs. Position degrader 100 MeV/A 79Br on 2.6mm Al  610 MeV 78Br

47. Minimizing extraction time Simulations of ion motion on RF carpets in 2 Tesla field RF 400V; 1.5MHz DC gradient 20V/cm Spacing 1 mm, 0.5 mm thick Low gas pressure (10 mbar compared to 200 - 1000 mbar in present systems) Time for collection onto carpet and transport out of gas stopper < 5 ms !

48. NSCL Reacceleration Stage Options Stage I: 3 MeV/u Reaccelerated beam area Stage II: 12 MeV/u

49. You ask: Should I switch fields? • Construction of a 1 B$ facility in the US in the next 5 years is unlikely • There are positive signs (3rd on the DOE list of facility priorities; congressional mandate of RIA; highest NSAC priority) that something on the scale of 600 M$ will happen • This is a very active field world-wide • NSCL, TRIUMF, HRIBF, ANL, T A&M, etc. • Upgrades at NSCL, ANL, HRIBF • Large scale international facilities: FAIR, RIBF, SPRIRAL II, EURISOL, … • There are exciting, important questions to answer

50. Additional Material