14 th January 2004BDI daySlide 1 ELECTRON COOLING STATUS Why electron cooling? –LHC requirements, implications for LEIR, results of 1997 cooling & stacking experiments. Optimum parameters for the LEIR cooler. –Technical considerations, design specification. Cost & manpower. Schedule. –Where we are, where we are going. Summary.

14 th January 2004BDI daySlide 2 Why electron cooling? LHC requirements for Pb ions: –Luminosity L = 1x10 27 cm -2 s -1. –Number of ions per bunch = 7x10 7. –Normalised emittance of 1.5  m. Implications for LEIR: –1.2x10 9 ions accumulated and cooled in 1.6 s at 4.2 MeV/u. –Acceleration to 72 MeV/u. –At extraction 0.9x10 8 ions to the PS with an of emittance < 0.7  m. Only a storage ring with fast electron cooling can meet these requirements.

14 th January 2004BDI daySlide 3 Cooling experiments with Pb ions. Cooling and stacking tests made between 1994 and –Short periods in 1994 and –Dedicated run in 1997 with a specially prepared machine. Investigated: –Ion beam lifetime. –Cooling time as a function of various parameters. –Stack equilibrium emittance and emittance growth. –Stacking at Linac III repetition rate of 2.5 Hz. Results well documented –“Experimental Investigation of Electron Cooling and Stacking of Lead Ions in a Low Energy Accumulation Ring”, Particle Accelerators, Vol. 63 pp

14 th January 2004BDI daySlide 4 What did we learn from the tests? Ion beam lifetime. –Strong dependence of the lifetime on the charge state and electron current. –Measured rate coefficients cannot be explained by radiative recombination. DIELECTRONIC RECOMBINATION SEEMS TO BE THE DOMINANT EFFECT (STILL A PUZZLE FOR ATOMIC PHYSICISTS). THREE-BODY RECOMBINATION? VACUUM EFFECTS? USE CHARGE STATE IMPROVE VACUUM IN THE MACHINE. Cooling times. –Near linear increase of the cooling rate as a function of electron current. –Expected gain due to increased cooler length did not show up. –Strong influence of the lattice parameters on the cooling process. ELECTRON BEAM SPACE-CHARGE INCREASES THE DRIFT VELOCITY. ELECTRON BEAM UNSTABLE ABOVE 120 mA. ALIGNEMENT TOLERANCES CRITICAL. INTERMEDIATE VALUES OF  ARE BETTER & FINITE VALUE OF D INCREASES THE COOLING RATE.

14 th January 2004BDI daySlide 5 What did we learn from the tests? Equilibrium emittance fits the LHC requirement and emittance growth is not an issue. Stacking principle demonstrated and is compatible with the filling scheme. Factor of 3 missing in the total accumulated intensity in 1.6 s. –COOLING TIME LIMITED BY THE PERORMANCE OF THE GUN. –INTENSITY LIMITED BY LOSSES DUE TO CHARGE EXCHANGE AND ELECTRON-ION RECOMBINATION. 3.5x10 8

14 th January 2004BDI daySlide 6 Parameters for the LEIR cooler Choice of parameters based on the results from the experiments, our experience of operating electron cooler devices (LEAR/LEIR, AD) for more than 12 years and collaborations with other accelerator laboratories (MSL Stockholm, MPI Heidelberg). Electron energy range from 2 keV to 40 keV. High perveance gun (6  P at 2.3 keV => Ie = 600 mA). Variable electron beam density. Cold electron beam, E t <100 meV, E // <1 meV. Adiabatic expansion. Maximum cooling length possible. 3m? Homogeneous magnetic guiding field (  B t /B // <10 -4 ). Efficient collection of the electron beam (  I e /I e <10 -4 ). –Electrostatic deflector plates.

14 th January 2004BDI daySlide 7 Adiabatic expansion solenoid 90 o toroid to bend the electron beam onto the ion beam High perveance, variable density gun2.5m cooling section Electron beam collector The LEIR electron cooler Integrated closed orbit distortion correction

14 th January 2004BDI daySlide 8 Vacuum system & power supplies The vacuum system must follow the stringent criteria applied for the LEIR machine. –316LN stainless steel, hydroformed bellows. –NEG coated vacuum chamber, NEG cartridges close to the gun and collector where there is a high gas load. –The whole system will be bakeable at 350 o C. High voltage power supplies. –gun (40kV/10mA), control (-/+ 2kV,5mA), grid (6kV,5mA) –suppressor (6kV,5mA), collector (5kV,5A), electrostatic bends (4x 6kV,5mA) –Common spares with AD electron cooler, use existing HT infrastructure. Cathode heating power supply(20V,5A). Magnetic elements –3 power supplies needed for the gun/collector solenoids, toroids and cooling solenoids. –All standard CERN power supplies (1000A,200V & 500A,100V). –26 small (10A,70V) power supplies for steering coils.

14 th January 2004BDI daySlide 9 Cost & manpower Infrastructure and a lot of material from the LEAR installation will be reused. Manpower needs (FTE): – cat 2, 1 cat 3, 0.5 IS – cat 2, 1.3 cat 3, 1.5 IS. – cat 2, 1.3 cat 3, 1 IS. –TOTAL : 4.8 cat 2, 3.6 cat 3 & 3 IS over 3 years ItemCost (kSFr)Responsible Design160BINP Gun, collector Magnets Support frame1200BINP Vacuum chambers Vacuum system (incl. Bake out, pumps etc.) 550CERN Power supplies (HT,DC)530CERN Electrical installation100 Cooling installation50 Controls50CERN Related instrumentation120CERN Industrial support240 TOTAL3000

14 th January 2004BDI daySlide 10 Schedule, where we are Technical specifications made in 2001/2002. –LEIR electron cooler conceptual study, PS/BD/Note –Specifications for the LEIR electron cooler magnetic components, PS/BD/Note –General mechanical parameters for the LEIR electron cooler, PS/BD/Note Design/feasibility study completed by BINP in April –Modifications requested at the September meeting. –Vacuum specifications made by AT/VAC group, waiting for final drawings of vacuum components. Addendum to the CERN-Russian Federation Agreement (“Skrinsky II”) approved in June Construction of the solenoids (“pancakes”) started at BINP. Vacuum material ordered. Power supplies ordered (PO group). ECEB (bld 233) refurbished.

14 th January 2004BDI daySlide 11 Schedule, where we are going 1 st half of 2004 –Delivery of material to BINP, production of solenoids, vacuum elements, electron gun and collector. –Magnet measurements and adjustments. July, August 2004 –Tests in Novosibirsk. Vacuum leak tests. Ultra-high vacuum not needed at this stage. Generation of electron beam with characteristics needed for Pb 54+ ions (2.3 keV, 600mA variable density {x10 less in the centre}electron beam, electron beam collection inefficiency <10 -4 ). Test at higher energy (40 keV, 3A). September 2004 –Delivery to CERN. October 2004 – March 2005 –Vacuum elements cleaned and prepared, remounting, magnet measurements, bakeout of complete system to reach ultimate vacuum, commissioning with beam, ready for cooling.

14 th January 2004BDI daySlide 12 Summary The design of the new cooler is technically sound. –The different ideas/techniques that we will use have been demonstrated on existing coolers. –However the LEIR cooler will be the first to incorporate them all on one device. More variables to deal with. Commissioning a little more complicated. –Cooling with a variable density electron beam has yet to be demonstrated. Keep a close eye on the results from IMP Lanzhou, China (2004). Backup solution? Use the gun as a “classical” high perveance gun i.e. no variable density. Schedule is tight and leaves little room for important delays.

14 th January 2004BDI daySlide 13 Some photos of the IMP cooler

14 th January 2004BDI daySlide 14 The electron gun Convex thermionic cathode at high voltage. Cathode radius = 14mm. Control electrode shapes the electron beam density. –Equivalent perveance of 6  P on the border and a factor of 10 less in the centre. Grid electrode determines the intensity. The gun is immersed in a strong longitudinal field (2.35 kG).

14 th January 2004BDI daySlide 15 Electron beam profiles with control electrode potentials U c = 0V, +100V, +200V, +350V, +400V, +600V, grid potential U g =500V and cathode potential U cath = 1000V. Variable density profiles V c = -100 V

14 th January 2004BDI daySlide 16 Adiabatic expansion Needed for: –Adapting the electron beam size to the injected beam size for optimum cooling. –Reducing the magnetic field in the toroids, thus reducing the closed orbit distortion. –Reducing the transverse thermal temperature of the electron beam. B o =0.235T, B=0.075T, r o =14mm => r=24.8mm B o =0.235T, B=0.075T, E o =100meV => E=32meV

14 th January 2004BDI daySlide 17 The electron beam collector Suppressor electrode slows down the primary electrons at the collector entrance. Magnetic field is reduced to spread out the electrons on the collector surface. Surface on which the electrons are collected is water cooled.

14 th January 2004BDI daySlide 18 The electrostatic bend Electrons experience a centrifugal force in the toroid. This drift can be compensated by an additional magnetic field in the opposite direction. Reflected and secondary electrons however are excited by this field and can oscillate between the gun and collector before being lost. Complete compensation is obtained by superimposing an electric field on the magnetic field

14 th January 2004BDI daySlide 19 Closed orbit perturbation correction The vertical magnetic field component of the toroids induce a horizontal perturbation on the closed orbit. Correction dipole placed in the toroid.