Diagnostics for intense e-cooled ion beams

1. Diagnostics for intense e-cooled ion beams by Vsevolod Kamerdzhiev Forschungszentrum Jülich, IKP, COSY ICFA-HB2004, Bensheim, October 19, 2004

2. Content • Objects of diagnostics • What is an electron-cooled ion beam from the diagnostics point of view? • Parameters to be measured and corresponding diagnostic methods. • Diagnostics for electron-cooled beams, difficulties and advantages. ICFA-HB2004

3. Objects of diagnostics • Electron beam • High beam power • Beam pipe is inside the solenoid • Electron-cooled ion beam • Intensities differ in orders of magnitude • High beam density • Small transverse dimensions • Small momentum spread ICFA-HB2004

4. Measured parameters (e-beam) • E-beam position • Space charge field of the e-beam • Current • Temperature • Neutralization ICFA-HB2004

5. Measured parameters (ions) • Beam current • Position along the orbit • Momentum • Momentum spread • Profile • Emittance • Tune • BTF ICFA-HB2004

6. Interceptive methods or not? • Interceptive methods • Not suitable for a circulating beam (operation) • Any probe will melt when inserted in the dc electron beam • Not interceptive methods • Often indirect measurements • Suitable for (high current) rings ICFA-HB2004

7. Cooler Synchrotron COSY • COSY accelerates (polarized)protonsanddeuterons between300 and 3700 MeV/c for p 535 to 3700 MeV/c for d • Kicker extraction, stochastic extraction • 4 internal and 3 external experimental areas • Electron cooling at low energy • Stochastic cooling at high energies ICFA-HB2004

8. COSY-Cooler ICFA-HB2004

9. COSY-Cooler Electron energy: Up to 100 kV Electron current: 0.2 - 3 A Operating at: 24,5kV 100-250 mA ICFA-HB2004

10. LEPTA LEPTA Ps LEPTA Septum e+ trap Collector e-gun e+ source Quadrupole Cooling section Detector B ICFA-HB2004

11. LEPTA Electron gun ICFA-HB2004

12. Parameters of e-cooled ion beam Longitudinal Schottky spectra, uncooled and cooled proton beam • Small transverse size/emittance • High density • Small momentum spread • During e-cooling the ion beam is dc • Often unstable ICFA-HB2004

13. Diagnostics in the cooler section • Pick-ups (at least two) are needed inside the cooling section to measure the position of both beams. • To measure the position of the e-beam longitudinal modulation must be applied • Large dynamic range of preamplifiers (variable gain) • Difficulties in mechanical design, bad service possibilities (COSY, LEPTA…) ICFA-HB2004

14. COSY BPMs ICFA-HB2004

15. Diagnostics in the cooler section • Count rate of the particles recombinating in the cooler section can be used to find optimum alignment of the electron and ion beams and for fine tuning the energy of the electron beam. • Measurement of the profile of recombination particles (e.g. MWPC) is the easiest way to determine the ion beam profile (only during cooling process) ICFA-HB2004

16. Example of H0-profile measurement at COSY Emittance [m rad] Calculated from the measured H0- Profiles Beam radius [mm] Proton beam current horizontal vertical ICFA-HB2004

17. Diagnostics in the cooler section • Looking at the  signals of the pick-up located in the cooling section in frequency domain gives useful information about residual gas ions oscillating in the cooler section. • Such a pick-up can be used also as a clearing electrode (experience at COSY, I.Meshkov, A.Sidorin). Applying ac-voltage to the clearing electrodes makes it possible to kick out the trapped ions, provided the frequency corresponds to resonant the frequency of a particular ion species. ICFA-HB2004

18. Space charge field To measure the space charge parabola of the electron beam a low intensity cold ion beam can be used. In this case the ion beam is used as a probe which scans the e-beam. Procedure: Inject ion beam in the machine, cool it, measure the revolution frequency of the ion beam, make a parallel shift of the e-beam using the cooler magnetic system, measure the frev again, repeat the procedure several times shifting the e-beam in both directions from the initial position. ICFA-HB2004

19. Temperature of the e-beam • Longitudinal temperature can be derived from the Schottky spectrum of the cooled ion beam • Beam heating effects should be taken into account • Transverse temperature can be measured by the pepper pot method • Only in the pulsed mode • Requires complex mechanical design ICFA-HB2004

20. The idea of T-measurement The electrons move in the longitudinal magnetic field. Method based on the measurement of transverse Larmor radius Pulse duration – 20-50 s The optical analysis of the electron beam temperature, V. Golubev et all., Proceedings of the Workshop on Beam Cooling and Related Topics, 1993. ICFA-HB2004

21. Profile of the ion beam Can be based on: • Ionization of residual gas • Laser induced luminescence • Laser induced photo-neutralization • Light radiation of residual gas, exited by the beam particles • Wire scanner ICFA-HB2004

22. Detector for electrons (optional) е- + Proton beam  H+ Detector for ions Y X Ionization profile monitor If collecting the electrons additional magnetic field is required. Position sensitive detectors are usually based on the MCPs. For dense beams MCP life time is a crucial issue. IPMs are installed in: TSR, SPS, COSY,RHIC… ICFA-HB2004

23. IPM at COSY ICFA-HB2004

24. Beam Profiles measured in COSY Profile measurement Electron cooled proton beam The proton beam is not cooled 1,3·109 particles in the ring, 45 MeV. ICFA-HB2004

25. Experience with IPM at COSY • For the W&S anode high amplification factor is necessary • Use of two MCPs in chevron geometry • High electron density in the second MCP • Short life time of the MCPs • Limitations on beam current • Protection screen is installed • Triggering of the MCP power supply is applied • Using an MCP with a phosphor screen is probably the best way to build a position sensitive detector for IPM ICFA-HB2004

26. Laser profile monitor • Laser induced luminescence (for ions) in connection with laser cooling (ASTRID…) • Watching the light using a camera • Photo-neutralization for H- beam (LANL, BNL, ORNL…) • A tightly focused laser beam is directed transversely through the beam, causing photo-neutralization. • Scanning the ion beam with the laser and simultaneously measure the beam current ICFA-HB2004

27. PM based on light radiation of residual gas, exited by the beam particles ICFA-HB2004

28. Spectral analysis of the beam signals • -signals of a pick-up in frequency domain give a lot of information • Exiting the beam und measuring the betatron frequencies gives the tune • Stability information can be obtained using the Beam Transfer Function (BTF) method • Electron cooling improves S/N ratio ICFA-HB2004

29. Example of the beam spectrum at COSY Vertical delta signal ICFA-HB2004

30. Vertical BTF ICFA-HB2004

31. Imaginary part [relative units] Real part[relative units] Z Transverse stability diagram ICFA-HB2004

32. Longitudinal BTF at COSY For different proton beam currents: 0,8 mA 2,7 mA 4,5 mA ICFA-HB2004

33. Transverse BTF at COSY Beam current: 3,2 mA 2,5 mA ICFA-HB2004

34. Summary • Electron cooling gives much better S/N ratios • Schottky diagnostics is a very powerful method • Schottky spectra of an e-cooled ion beam might be strongly distorted • BTF, longitudinal and transverse • Online BTF measurement should be further developed • Profiles of an e-cooled ion beam are difficult to measure • Better resolution is needed • Life time of MCPs • For new machines diagnostic must be planed together with the machine design ICFA-HB2004

35. Thank you ICFA-HB2004