1 Ultracolod Photoelectron Beams for ion storage rings CSR E-Cooler TSR (magnetic) e-target e-cooler CSR (electrostatic) E lab : eV Current - 2 mA Lifetime - 24 h kT  < 1.0 meV kT || = 0.02 meV Electron-ion collision spectroscopy D. A. Orlov, C. Krantz, A. Shornikov, A. Wolf E lab : 10-1eV Low e-energies: => low current (100-1µA) => higher kT || e-transport by B => slow ions distorted Cooling at eV-energies - it is a challenge! Electron cooling TSR E-target Extremely high resolution is demonstrated! DR of Sc v e = v i 2 v e ≠ v i 6 meV Max-Planck-Institut für Kernphysik, 69117, Heidelberg, Germany

Dmitry Orlov, MPI-K, PESP-08 2 cold electrons OUTLINE 1 HOW TO: cold e-beams 2 E-cooling Collision resolution 6 Cooling of CF+ ions at TSR by 53 eV photoelectrons 7 Manipulation with eV e-beams at TSR target 4 Why? Electrostatic Cryogenic Storage Ring 3 electron collision TSR ( keV) 5 e-beams of eV energies, CSR cooler

Dmitry Orlov, MPI-K, PESP-08 3 EFEF E vac Thermocathode vacuum T= K kT= meV Cold electrons. How to (A): Photocathode kT C = 10 meV Fully activated cathode: QY= 15-35% QY eff =1 % Laser: 800 nm9 (transmission) 532 nm (reflection) E-current: mA Lifetime : >24 h D.A. Orlov et al., APL, 78 (2001) 2721; Suppression Strong energy and impulse relaxations Energy spreads of about kT E vac E FE F E cE c (CsO) E vE v GaAs vacuum T= 80 K Suppression kT=10 meV Thermocathode kT C > 100 meV

4 Cold electrons. How to make them colder (B): 1. Magnetic expansion B 0 (high field) B guide (low field) 2. Acceleration Reduction of kT  Reduction of kT ||  = 20 Thermocathode kT  = 5-6 meV Photocathode kT  = 0.5 meV kT || = meV Phase-space conservation v║v║ E ΔE Δv Δv' U0U0

5 Cold electrons. How o keep them cold (C): High magnetic field is required 1. To avoid beam divergence 2. To suppress TLR 3. To provide adiabatic transport e e e low current high current high current + magnetic field keeping dT || / dZ < 5 μeV/m : e e B rcrc n e -1/3 r c << n e -1/3 B e R λ c << R λcλc Typical transition lengths R=100 mm

Dmitry Orlov, MPI-K, PESP-08 6 cold electrons 1 HOW TO: cold e-beams 6 Cooling of CF+ ions at TSR by 53 eV photoelectrons 7 Manipulation with eV e-beams at TSR target 4 Why? Electrostatic Cryogenic Storage Ring 3 electron collision TSR ( keV) 5 e-beams of eV energies, CSR cooler 2 E-cooling Collision resolution

Dmitry Orlov, MPI-K, PESP-08 7 Principle of Electron Cooling TSR e-cooling

Dmitry Orlov, MPI-K, PESP-08 8 Electron-ion collision resolution V║V║ VV Recombination velocity Flattened electron distribution kT ║ ≪ kT  Real resonance position DR rate coefficient v e = v i For high energies E r :

Dmitry Orlov, MPI-K, PESP-08 9 cold electrons 1 HOW TO: cold e-beams 6 Cooling of CF+ ions at TSR by 53 eV photoelectrons 7 Manipulation with eV e-beams at TSR target 4 Why? Electrostatic Cryogenic Storage Ring 5 e-beams of eV energies, CSR cooler 2 E-cooling Collision resolution 3 electron collision TSR ( keV)

Dmitry Orlov, MPI-K, PESP ~ MeV/u Detectors (ions and neutrals) e-target Interaction section 1.5m Electron gun with magnetic expansion  ≈ Adiabatic acceleration Collector TSR dipole Movable ion detector Neutrals detector Ion beam e-e- e-source Electron collision spectroscopy. TSR electron target.

- e A q + Electron capture resonance nℓ (A q + )* + nℓ ( A (q -1)+ )** = + e ( A (q -1)+ )* nℓ Product detection E res Electron collision spectroscopy on multi-charged ions

Core excitation energies ΔE (2s–2p) (2p 3/2 10d 5/2 ) J = 4 (2p 3/2 10d 3/2 ) J = 2 (2p 3/2 10d 3/2 ) J = 3 Electron target PRL, 100, (2008) Photocathode ~ 0.02 meV T || T┴T┴ = 1.0 meV 45 Sc 18+ TSR – 4 MeV/u E EnEn ΔE core 1s 2 2p 3/2 1s 2 2s (1s 2 2p 3/2 nℓ' j ) J E res = (20) eV (±0.2 meV, 4.6 ppm) n = meV (<1% few body QED)

Dmitry Orlov, MPI-K, PESP direct & indirect process Dissociative recombination of HD + : rate spectrum HD + (1sσ, v = 0, J ) + e → HD** (1sσ nℓλ, v'J' ) → H(n) + D(n' ) PRL 100, (2008) Rotational resolution (DR rate) - e + e AB + - B*B* A + (AB + )* + nℓ = AB ** Vibration v=0 -> eV Rotation j=0 -> meV

Dmitry Orlov, MPI-K, PESP Dissociative recombination of HF + : 2D imaging Electron - Target ~ 12 m v beam (~MeV) ~cm detector surface Probability (normalized) d 2D [mm] Rotational resolution Particle distance, mm E KER – E CM -kT, milli-eV PRELIMINARY HF + (X 2 , v=0,J ) + e - HF ** (V 1  + ) H(n=2) + F( 2 P 3/2,1/2 ) HF ** (V 1  + ) v=0 J=0,1,2,…. H(n=2) + F( 2 P 3/2 )

Dmitry Orlov, MPI-K, PESP cold electrons 1 HOW TO: cold e-beams 6 Cooling of CF+ ions at TSR by 53 eV photoelectrons 7 Manipulation with eV e-beams at TSR target 5 e-beams of eV energies, CSR cooler 2 E-cooling Collision resolution 3 electron collision TSR ( keV) 4 Why? Electrostatic Cryogenic Storage Ring

Dmitry Orlov, MPI-K, PESP Electrostatic Cryogenic Storage Ring at 2 K Reaction microscope Ion injection E-target Diagnostic section neutrals CSR Clusters, biomolecules (M up to few 1000 amu) ELECTROSTATIC Storage Rings (no mass limitation) Ring Circumference34m Straight Section Length2.5m Energy Range keV Maximum Beta  h /  v 12/6m Maximum Dispersion2.1m Tunes Q h /Q v 2.59/2.65 XHV (n<10 3 cm -3 ) M= 1-100(1000) amu Electrostatic Storage Ring T=10 (2K) T< 10 K is required after some second storage after production in the ion source Boltzmann distribution (300 TSR)      rotational quantum state vibrational quantum state HD + + e -  H + D

Dmitry Orlov, MPI-K, PESP cold electrons 1 HOW TO: cold e-beams 6 Cooling of CF+ ions at TSR by 53 eV photoelectrons 7 Manipulation with eV e-beams at TSR target 5 e-beams of eV energies, CSR cooler 2 E-cooling Collision resolution 3 electron collision TSR ( keV) 4 Why? Electrostatic Cryogenic Storage Ring

Dmitry Orlov, MPI-K, PESP Features of low-energy e-beams (A) 1. Low voltage Low density High-perveance? Electron density [10 6 cm -3 ] Electron current [mA] Electron energy [eV] Ion energy [keV] Ion mass [amu] Cooling time (cold beam) [s] P=1 μPerv k B T e =1.0 meV Lc=3.3  C =0.028

Dmitry Orlov, MPI-K, PESP Features of low-energy e-beams (B) Photoelectron source Low T ║ 2. Low voltage High kT || 3. High B guid Better for slow electrons Strong ion deflection {avoid beam divergence; suppress TLR; adiabatic transport}

Dmitry Orlov, MPI-K, PESP New Concept for the CSR Electron Cooler/Target toroid merging Dipole merging 1-2 G 30 G We need to cool 20 keV protons B min ≈20 G

Dmitry Orlov, MPI-K, PESP Ion track General view New Concept for the CSR Electron Cooler/Target Electron energy160-1(or below) eV Cooling solenoid length 1065 mm Cooling solenoid radius 130 mm Max. magnetic field150 Gauss Toroid bending radius 200 mm Merging box solenoid Racetrack 330x540 mm, length 350 mm Merging box vertical dipoles Racetrack 268x360 Merging Box toroid merging Dipole merging 1-2 G 30 G We need to cool 20 keV protons B min ≈20 G

22 Adiabatic electron transport Adiabatic criterion Scaling rule for critical energy Finite element analysis with TOSCA code Cross-sections of Heating of paraxial beam - Larmor length Heating start at app. Adiabatic motion Transverse temperature For modeled field geometry Results of e-tracking calculation (TOSCA code) kT ┴ 0

Dmitry Orlov, MPI-K, PESP cold electrons 1 HOW TO: cold e-beams 7 Manipulation with eV e-beams at TSR target 5 e-beams of eV energies, CSR cooler 2 E-cooling Collision resolution 3 electron collision TSR ( keV) 4 Why? Electrostatic Cryogenic Storage Ring 6 Cooling of CF+ ions at TSR by 53 eV photoelectrons

Dmitry Orlov, MPI-K, PESP Low-energy cooling of CF + cooling by 53 eV electrons Themocathode, September 2006, 0eV, s Photocathode, March 2007, 0eV, s CFCF CFCF Electron-target Photocathode T  ~ 1.0 meV I = 0.34 mA n e =3∙10 6 cm -3 Photocathode Themocathode center-of-mass s E cm = 0 eV center-of-mass s E cm = 0 eV

Dmitry Orlov, MPI-K, PESP CF + – cooling time TSR Photocathode, March 2007 Current: 0.34 mA B-expansion: 20 n e =3∙10 6 cm -3 T ┴ =1.0 meV  cool < 2 s Detector (X/Y): σ 0.4 / 0.3 mm Ion beam: X Y ε 2.5∙ ∙10 -3 mm∙mrad σ μm ΔP/P 2.5∙ ∙10 -5  x =1.8 s  y =1.4 s 1 mm

Dmitry Orlov, MPI-K, PESP cold electrons 1 HOW TO: cold e-beams 5 e-beams of eV energies, CSR cooler 2 E-cooling Collision resolution 3 electron collision TSR ( keV) 4 Why? Electrostatic Cryogenic Storage Ring 6 Cooling of CF+ ions at TSR by 53 eV photoelectrons 7 Manipulation with eV e-beams at TSR target

Dmitry Orlov, MPI-K, PESP Manipulation with magnetized eV-electrons W cathode W emission W metal SC E kin V0V0 V W metal SC EFEF EDC, log. scale E kin Cathode Drift tubes TSR target Cathode Collector

Dmitry Orlov, MPI-K, PESP Manipulation with magnetized eV-electrons E kin = q(V 0  V)  (W metal  W emission )  SC 1. Work function difference 2. Space charge at the cathode 3. Space charge SC(I e, V) in the interaction region can be calculated independently. W cathode W emission W metal SC E kin V0V0 V W metal SC EFEF EDC, log. scale E kin Cathode Drift tubes To collector TSR target Drift tubes Cathode Collector E kin ≠ q(V 0  V)

29 Manipulation with magnetized eV-electrons E kin = q(V 0  V)  (W metal  W emission )  SC EFEF W emission V0V0 V W metal SC E kin To collector Drift tubes Cathode Drift tubes Collector V 0 =20 V I e =3µA I e =40 pA (W metal  W emission ) SC E kin A B A B

30 Manipulation with magnetized eV-electrons E kin = q(V 0  V)  (W metal  W emission )  SC EFEF W emission V0V0 V W metal SC E kin To collector Drift tubes Cathode Drift tubes Collector V 0 =20 V I e =4.5 µA I e =40 pA (W metal  W emission ) SC E kin A A E kin, eV I, μA P, μPerv

Dmitry Orlov, MPI-K, PESP HOW TO: cold e-beams 5 e-beams of eV energies, CSR cooler 2 E-cooling Collision resolution 3 electron collision TSR ( keV) 4 Why? Electrostatic Cryogenic Storage Ring 6 Cooling of CF+ ions at TSR by 53 eV photoelectrons 7 Manipulation with eV e-beams at TSR target THANK YOU ! Questions?

Dmitry Orlov, MPI-K, PESP-08 32

Dmitry Orlov, MPI-K, PESP Electron beam formation – adiabaticity adiabaticity: dB/dz, dE/dz small against cyclotron length BgBg Cathode, -100 VExtraction electrode, 0 V φ= 10 0 Cathode Entrance, extraction electrode 80 G 320 G 40 G Typical transition lengths 100 – 200 mm ζ= Higher adiabaticity Low energies

Dmitry Orlov, MPI-K, PESP Acceleration section Collector Toroid TSR dipole Interactionsection electron beam Ion beam Correction dipoles Rails Electron target at TSRPreparationchamber(photocathode)