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

ICFA-HB20042 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-HB20043 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-HB20044 E-beam position Space charge field of the e-beam Current Temperature Neutralization Measured parameters (e-beam)

ICFA-HB20045 Measured parameters (ions) Beam current Position along the orbit Momentum Momentum spread Profile Emittance Tune BTF

ICFA-HB20046 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-HB20047 Cooler Synchrotron COSY -COSY accelerates (polarized) protons and deuterons between 300 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-HB20048 COSY-Cooler

ICFA-HB20049 COSY-Cooler Electron energy: Up to 100 kV Electron current: A Operating at: 24,5kV mA

ICFA-HB e + trap Septum Cooling section Quadrupole Collector e-gun BB Detector e + source LEPTA

ICFA-HB LEPTA Electron gun

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

ICFA-HB 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…) Diagnostics in the cooler section

ICFA-HB COSY BPMs

ICFA-HB 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) Diagnostics in the cooler section

ICFA-HB Example of H 0 -profile measurement at COSY Calculated from the measured H 0 - Profiles Emittance [  m rad] Beam radius [mm] horizontal vertical Proton beam current

ICFA-HB 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. Diagnostics in the cooler section

ICFA-HB 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 f rev again, repeat the procedure several times shifting the e-beam in both directions from the initial position.

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

ICFA-HB 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-HB Ionization profile monitor е-е- H+H+ Proton beam +  Y X Detector for ions Detector for electrons (optional) 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-HB IPM at COSY

ICFA-HB Beam Profiles measured in COSY Electron cooled proton beam Profile measurement The proton beam is not cooled 1,3·10 9 particles in the ring, 45 MeV.

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

ICFA-HB 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-HB Example of the beam spectrum at COSY Vertical delta signal

ICFA-HB Vertical BTF

ICFA-HB Transverse stability diagram Imaginary part [relative units] ZZ Real part [relative units]

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

ICFA-HB Transverse BTF at COSY Beam current: 3,2 mA 2,5 mA

ICFA-HB 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-HB Thank you