1. R.A. Gough, J.R. Alonso: Workshop on Underground Accelerators Tucson, Oct 27-28, 2003 1 Accelerators (<1 MeV/n) for Low-Energy Measurements Workshop on Underground Accelerators for Nuclear Astrophysics October 27-28, 2003 Jose Alonso, Rick Gough Lawrence Berkeley National Laboratory

2. R.A. Gough, J.R. Alonso: Workshop on Underground Accelerators Tucson, Oct 27-28, 2003 2 Outline Types of accelerators suitable for low-energy nuclear astrophysics applications Other system components Existing and possible new configurations Important questions to be addressed –REQUIREMENTS

3. R.A. Gough, J.R. Alonso: Workshop on Underground Accelerators Tucson, Oct 27-28, 2003 3 Types of Accelerators For low energy, linacs are generally considered more “straight forward” than circular machines There are various schemes to apply kinetic energy: - radio frequency (rf), induction, or static potential drop A dc electrostatic accelerator is a potential-drop type of linac with typical voltages up to several MV -Offers easy and continuous energy variation -Superior energy dispersion:  E/E ~10 -4 compared to room temp. rf linacs or RFQs (~10 -2 ), SCRF linacs ( 10 -3 ) -Energy dispersion determined by dc power supply voltage regulation

4. R.A. Gough, J.R. Alonso: Workshop on Underground Accelerators Tucson, Oct 27-28, 2003 4 Power Supply Types for DC Accelerators  Van de Graaff (including pelletron) – low current but capable of reaching terminal potentials > 10 MV  Cockcroft-Walton – uses a ladder network to build voltage up to ~1 MV  Dynamitron – a “shunt-fed” type Cockcroft-Walton that has higher current capability and provides voltages to a few MV  External transformer – high current capability but high voltage limited by breakdown between windings  Coaxial transformer – a high current (50 mA) and high voltage (2.5 MV) design under development

5. R.A. Gough, J.R. Alonso: Workshop on Underground Accelerators Tucson, Oct 27-28, 2003 5 Tandem Configuration Higher beam energies Ion source at ground Requires negative ion source which limits current and ion species but +V+V Strip to q+ in high voltage dome E/A = V  (q+1)/A

6. R.A. Gough, J.R. Alonso: Workshop on Underground Accelerators Tucson, Oct 27-28, 2003 6 Van de Graaff / Pelletron S-Series NEC Pelletron (1 - 5 MV) Pelletron charging principle Open air systems for lower beam energies (1 - 500 keV) National Electrostatics Corporation

7. R.A. Gough, J.R. Alonso: Workshop on Underground Accelerators Tucson, Oct 27-28, 2003 7 Ultra high precision energy… TUNL, ca 1980??

8. R.A. Gough, J.R. Alonso: Workshop on Underground Accelerators Tucson, Oct 27-28, 2003 8 Traditional Linac Injectors Open air electrostatic systems used as traditional linac injectors – require lots of space, largely being replaced by RFQs RFQs are compact and efficient – tunability and low  E/E problematic for this application 2.5 MeV H – RFQ built by LBNL for SNS 500 kV open-air injector at Livermore

9. R.A. Gough, J.R. Alonso: Workshop on Underground Accelerators Tucson, Oct 27-28, 2003 9 Dynamitrons -used to produce x-rays, protons, electrons, and low-Z ions for TREE & space radiation effects -pulsed or dc operation -energies from 0.2 - 2.8 MeV -< 10 mA of electrons -hundreds of microAmps of positive ions Dynamitron from Boeing Radiation Effects Lab shown w/cover removed Require high pressure gas ( SF 6 ) Dynamitron was used as HILAC injector and is in use at Argonne for radioactive beam studies

10. R.A. Gough, J.R. Alonso: Workshop on Underground Accelerators Tucson, Oct 27-28, 2003 10 High Current Accelerator Development at LBNL  25 mA protons 2.5 MV CW ESQ accelerator for BNCT (spin-off application) 2 MV pulsed ESQ accelerator for fusion energy (base program) coaxial transformer power supply 0.6A K +

11. R.A. Gough, J.R. Alonso: Workshop on Underground Accelerators Tucson, Oct 27-28, 2003 11 Then there’s always…

12. R.A. Gough, J.R. Alonso: Workshop on Underground Accelerators Tucson, Oct 27-28, 2003 12 Types of Beam Focusing Electric field lens  Aperture lens – strength decreases with beam energy  Electrostatic quadrupole (ESQ) – strength increases with beam energy Magnetic field lens (best at high beam energy)  Magnetic solenoid lens  Magnetic quadrupoles

13. R.A. Gough, J.R. Alonso: Workshop on Underground Accelerators Tucson, Oct 27-28, 2003 13 ElectroStatic Quadrupole (ESQ) Focusing  Provides strong focusing for high beam current  Suppresses secondary electrons  Reduces longitudinal average voltage gradient to accommodate insulators ESQ module for 4 parallel beams Basic ESQ module

14. R.A. Gough, J.R. Alonso: Workshop on Underground Accelerators Tucson, Oct 27-28, 2003 14 LUNA: Pace-setter in the field III Terminal potential50 kV400 kV TechnologyElectrostaticElectrostatic (Cockcroft-Walton) Ripple5x10 -4 (25eV)4eV Long-term stability1x10 -4 (5eV)5eV/hr Measured  E 72eV SourceDuoplasmatron (  E ~ 20eV) RF Ions 3 He, 400µA p, d p, 750µA 4 He LUNA Collaboration, INFN, Gran Sasso

15. R.A. Gough, J.R. Alonso: Workshop on Underground Accelerators Tucson, Oct 27-28, 2003 15 Surface Laboratories LENA - TUNL Bochum Notre Dame ISAC, TRIUMF … others? ~1 MeV electrostatic Spectrometers Careful attention to unavoidable backgrounds

16. R.A. Gough, J.R. Alonso: Workshop on Underground Accelerators Tucson, Oct 27-28, 2003 16 Possible HI Solution for Underground Lab Low power, permanent magnet ECR ion source mounted on the terminal of a 2.5 MV Van de Graaff could provide cw ion beams from hydrogen to argon at 0.5 MeV/nucleon Demonstrated performance: commercial permanent magnet ECR ion sources can produce Ar 9+ at greater than 100 eµA Utilize lower charge states for lower energy ranges Beams from gaseous elements straightforward; beams from solids more challenging but possible Integration of ECR and Van deGraaff technologies has been demonstrated, but not available as commercial off-the-shelf item Requirement: 50 eµA up to 0.5 MeV/nucleon protons to argon E / A = 9 / 40 x 2.5 = 0.56 MeV / amu

17. R.A. Gough, J.R. Alonso: Workshop on Underground Accelerators Tucson, Oct 27-28, 2003 17 ECR in Electrostatic Accelerators ISL Hahn-Meitner Institute Berlin ECR Ion Source in HV terminal JAERI Tandem Tokai Research Establishment, Japan Ar 8+ 2eµA at 112 MeV

18. R.A. Gough, J.R. Alonso: Workshop on Underground Accelerators Tucson, Oct 27-28, 2003 18 Maximum beam energies? (rest-frame, to determine accel. potential) Range of energies needed? (tunability, energy precision) Short / long term energy stability (high voltage control, ripple) Energy spread? (ion source temperature or RF accelerator design) Ion species needed? Purity of ion species? – heavy ions with q/A = 0.5 likely to have contaminants – molecular, charge-state ambiguities What beam currents are required? What are the beam current stability requirements? Important Questions for Accelerator Design - I

19. R.A. Gough, J.R. Alonso: Workshop on Underground Accelerators Tucson, Oct 27-28, 2003 19 Beam-on-target requirements? (spot size…) Duty factor (CW or pulsed? Is RF structure OK?) Noise constraints? – could x-rays beyond some energy interfere w/ exp. signals? – are accelerator-produced neutrons a background problem? Site constraints? – space, access, power, utilities, special safety issues... Configuration flexibility? – may be necessary to have more than one accelerator system to meet all requirements Important Questions for Accelerator Design-II