Electron Cooling Electron Cooling Plans for future electron cooling - PowerPoint PPT Presentation

Electron Cooling Electron Cooling Plans for future electron cooling needs PS BD/AC 25 th January 2001 PS Days 2001 Slide 1

What is electron cooling? What is electron cooling? • Means to increase the phase space density of a stored ion beam. • Mono-energetic cold electron beam is merged with ion beam which is cooled through Coulomb interaction. • Electron beam is renewed and the velocity spread of the ion beam is reduced in all three planes. 25 th January 2001 PS Days 2001 Slide 2

Analogy with gas B gas A the mixing of T 2 T 1 gases T 3 ion electron beam beam kT = 1/2M V 2 Two gases of different 2 kT = 1/2m v temperatures T1 an T2 tend to an equilibrium temperature T3 As the electron beam is continuously renewed, the ion beam temperature tends 1/2 to the electron beam tempera V = v(m /M ) The velocity spread is reduce by a factor (m/M) 1/2 25 th January 2001 PS Days 2001 Slide 3

Electron cooling setup Electron cooling setup 25 26 27 28 29 1 2 3 4 20 21 22 23 24 5 6 7 8 13 14 15 16 17 18 19 9 10 11 12 • Electron gun: thermocathode, Pierce shield, accelerating anodes – final current given by Child’s Law: I = ρ V 3/2 – the parameter ρ is the perveance and is given by 7.3 μ P (r/d) 2 • Interaction section • Collector • The whole system is immersed in a longitudinal field 25 th January 2001 PS Days 2001 Slide 4

Cooling time Cooling time • Electron cooling theory gives : θ 3 A τ ∝ γ β 5 4 η 2 I e Z – where θ is the relative difference in angle between the ions and electrons ( θ i - θ e ), [ θ i = √ ( ε / β )] – the parameter η = L cooler /L machine – and I e is the electron current. 25 th January 2001 PS Days 2001 Slide 5

Electron cooling at CERN Electron cooling at CERN • Improve the quality of low energy ion beams – many experiments on LEAR and AD not possible without electron cooling – used to cool (anti)protons, H - , oxygen, and lead ions – first electron cooling device to be used routinely on a storage ring • Increase of the duty cycle of the machine – cooling time much less than what can be obtained with stochastic cooling at low energies (< 310 MeV/c) • In the future LHC requests a variety of ions 25 th January 2001 PS Days 2001 Slide 6 – the proposed injection scheme requires fast cooling times and stacking

54+ cooling and Results of Pb 54+ cooling and Results of Pb stacking in 1997 stacking in 1997 • Stacking at the 2.5 Hz Linac 8 Beam Intensity [E8 ions] L in a c I I I r e p r a te : 2 .5 H z I o n b e a m e n e r g y : 4 .2 M e V /u E le c tr o n e n e r g y : 2 .3 5 k e V 9 2 repetition rate 3 6 1 2 5 1 1 6 . 6 . E le c tr o n c u r r e n t : 1 0 5 m A 0 6 . 6 . 3 . 9 6 . 6 7 8 5 . 5 5 5 5 . 9 3 . 5 3 1 . 5 3 8 4 . 7 3 • Saturation effect on the 4 . b e a m life tim e : 6 .5 s 8 8 . 4 3 3 2 . 3 accumulated intensity due to 1 4 2 . 2 7 3 A v e r a g e a c c u m u la te d in te n s ity : 6 E 8 io n s 1 . vacuum degradation and beam P e a k in te n s ity : 7 .1 E 8 io n s 0 loss 2 4 6 8 10 12 Time [s] • Cooling times of 200 ms obtained 14 machine 7-96 1/th[ms-1] 12 machine4-96:1/th[ms] with an electron current of 120 machine1-96:1/th[ms] 10 machine1-97:1/th[ms] mA machine97:1/th[ms] 1/ [s-1] 8 • missing a factor of 2 in cooling 6 time and in accumulated 4 2 intensity 0 0 50 100 150 200 250 300 350 400 Ie [mA] 25 th January 2001 PS Days 2001 Slide 7

How to decrease the cooling How to decrease the cooling time? time? τ ∝ η θ 3 ⋅ I e • Make the cooler longer • Change the lattice parameters at the cooler • Ensure a perfect alignment of electron and ion beams • Increase the electron current 25 th January 2001 PS Days 2001 Slide 8

Cooling Time Vs. L and Ie Ie Cooling Time Vs. L and Compare measurements made with the standard machine lattice in 1996 (L ecool = 1.5m) and in 1997 (L ecool = 3m ). machine 1 ecool 3m,1.5m 10 9 8 Inverse transverse cooling time of 88.86 MeV/c/u Pb 54+ ions as 7 1/th[s-1] 6 a function of electron beam 5 intensity for 1.5m and 3m setup. 4 m achine1-97:1/th[m s] 3 m achine1-96:1/th[m s] 2 1 Ie[mA] 0 0 50 100 150 200 250 300 350 400 25 th January 2001 PS Days 2001 Slide 9

Cooling Time Vs. Lattice Cooling Time Vs. Lattice Parameters Parameters Cooling times for 300 MeV/c protons Vs. different β values at the cooler 40000 M ach1 M ach97 35000 M ach97-1 M ach97-2 30000 cooling-down time [ms] 25000 20000 15000 14 m achine 7-96 1/th[m s-1] 10000 12 m achine4-96:1/th[m s] m achine1-96:1/th[m s] 5000 10 m achine1-97:1/th[m s] m achine97:1/th[m s] 1/ [s-1] 0 8 -25 -20 -15 -10 -5 0 5 10 15 position [m m ] 6 Cooling times for 300 MeV/c protons 4 Vs. different values of D at the cooler 2 Comparison of inverse cooling times for 88.86 MeV/c/u 0 Pb 54+ ions Vs. I e for all tested machine optical settings 0 50 100 150 200 250 300 350 400 Ie [m A ] 25 th January 2001 PS Days 2001 Slide 10

Obtaining higher electron beam Obtaining higher electron beam currents currents EC EA EA EC θ = 45 0 δ = 1.5 cm r C δ δ 2a = 1 cm 2a 2a Anode Anode θ φ = Δ U r C = 0.707 cm φ = Δ U Cathode Cathode φ = 0 φ = 0 I II P = P I = 0.82 microperv II P II = 6.1 microperv 7 . 5 P I To have P I = 6.1 microperv δ = 0.54 cm would be necessary • Analytical studies of diodes in space charge regime have shown that a convex spherical diode has a higher perveance than a planar diode • However the beam emitted from a convex cathode is divergent and hence has large transverse velocities. • STRONG SOLENOIDAL AXIAL FIELD is needed (>1000 G) 25 th January 2001 PS Days 2001 Slide 11

Example Example angle θ θ = 45 Gun with convex spherical cathode of half- -angle = 45 0 0 . . Gun with convex spherical cathode of half Simulation with the program SSAM/CERN. Simulation with the program SSAM/CERN. Gun geometry provided by A.Shemyakin/FNAL. Gun geometry provided by A.Shemyakin/FNAL. U a = 3kV , I = 0.92A , P = 5.6 microperv B = 2000 Gauss Beam diameter = 1 cm a= 0.5 cm 45 0 25 th January 2001 PS Days 2001 Slide 12

Gun perveance measurements at Fermilab. (Experimental error bars are not given.) 3/2 Child's law fit on data: I coll = P gun U cath P gun = 6.1 μ perv 600 550 Collector current I coll , mA 500 450 400 350 300 250 200 150 100 50 0 0 250 500 750 1000 1250 1500 1750 2000 2250 Cathode Voltage U cath , V 25 th January 2001 PS Days 2001 Slide 13

Electron beam expansion Electron beam expansion • Convex cathodes are generally small in size and need a strong axial magnetic field – electron beam is smaller than the injected ion beam – not compatible with insertion in the storage ring • Cure: decrease the axial field adiabatically such that the electron beam size is larger than the ion beam and also the field in the toroids and cooling section does not perturb the machine. E B B B = ⇒ = = ⇒ = // t const r r const E E o 2 o r B B B o // o 25 th January 2001 PS Days 2001 Slide 14

Requested ions for LHC Requested ions for LHC Pb In Kr Ar O He A 208 115 84 40 16 4 Z 54 37 29 16 4 1 β inj c .095 .095 .095 .095 .095 .095 V ecool kV 2.32 2.32 2.32 2.32 2.32 2.32 I mA 200 220 200 400 400 400 ρ μ P 1.79 1.97 1.79 3.58 3.58 3.58 β ej c .25 .42 .35 .185 .3 .35 V ecool kV 16.8 52.1 34.5 8.98 24.67 34.5 I mA 600 1000 1300 800 3000 2000 25 th January 2001 PS Days 2001 Slide 15

Required performance of a new Required performance of a new ecooler ecooler • Electron energy range: 2 keV to 55 keV • Electron currents between 100 mA and 3 A (maximum perveance of 4 μ P) • Electron beam diameter of 3.5 cm in the interaction region (variable?) • Transverse energies less than 100 meV • Good beam alignment • Minimum perturbation to the machine (closed orbit, coupling, vacuum) 25 th January 2001 PS Days 2001 Slide 16

Parameters for a “ “state of the art state of the art” ” Parameters for a cooler cooler • Electron beam: – convex cathode, diameter approx. 20 mm – high perveance (4 μ P), variable intensity (multiple anodes) and variable energy • Magnetic field: – Bgun = 0.6 T, Bdrift = 0.075 T [Bgun/Bdrift=8] – variable B field will give an expansion factor of 2.83 • ebeam diameter = 56 mm, transverse energy = 12.5 meV 25 th January 2001 PS Days 2001 Slide 17

Parameters for a “ “state of the art state of the art” ” Parameters for a cooler (contd contd.) .) cooler ( • Efficient collection ( Δ I/I<10 -4 ) of the electron beam • Cooling length of 3m • Closed orbit and coupling compensation • Associated diagnostics 25 th January 2001 PS Days 2001 Slide 18

Where are we now? Where are we now? • Theoretical work for the design of a new gun and collector • Linear testbench is being commissioned – spare gun and collector for AD – test of the high perveance electron gun • Tests at other laboratories (MSL, MPI Heidelberg, GSI) – beam expansion, optimum lattice parameters • New ideas – hollow gun – open collector 25 th January 2001 PS Days 2001 Slide 19

That’ ’s All For Now s All For Now That 25 th January 2001 PS Days 2001 Slide 20