Experimental Storage Ring - ESR E max = 420 MeV/u, 10 Tm, electron-, stochastic- and laser cooling
Specification of the ESR Particle detectors Re-injection to SIS Two 5 kv rf-cavities Fast Injection Schottky pick-ups Gas jet e - cooler I = 10...500 ma L = 108 m =1/2 L SIS p = 2 10-11 mbar E = 3...420 MeV/u f 1...2 MHz β = 0.08...0.73 Q h,v 2.65 Six 60 0 dipoles Bρ 10 T m Extraction
What is beam cooling? Cooling is synonymous for a reduction of beam temperature Temperature is equivalent to terms as phase space volume, emittance and momentum spread Beam cooling processes are not following Liouville s Theorem: (which neglects interactions between beam particles) In a system where the particle motion is controlled by external conservative forces the phase density is conserved Beam cooling techniques are non-liouvillean processes e.g. interaction of beam particles with other particles (electrons, photons) Benefit of beam cooling: Improved beam quality (precision experiments, luminosity increase)
Beam cooling at the ESR What is cooling? What is temperature? 3 k T 2 = 1 = m 2 v 2 = v is the velocity relative to a reference particle, which moves with an average ion-velocity. The temperature is a measure of the random movement. In an accelerator T = 2 2 = M c β p / p 2 T = M c 2 2 2 β γ ε 1 β H + 1 β V Why beam cooling? Improve of the beam quality smaller beam size and reduction of the emittance broadening of the energy better beam intensity, accumulation lifetime of the beam Kühlmethoden Stochastische Kühlung Laserkühlung Makroskopische Elektronkühlung Emittanz
Beam temperature Thermal particle motion (temperature is conserved) at rest (source) low energy high energy temperature llllllllllllllllllllllll tttttttttttttttttttt 1 2 kk BBTT = 1 2 mmvv 2 = 1 2 mmcc2 ββ 2 δδpp pp 1 2 kk BBTT = 1 2 mmvv 2 = 1 2 mmcc2 ββ 2 γγ 2 θθ 2 2
Electron cooling electron collector electron gun I: 5-500 ma v e = v ion high voltage platform E e = m e /M ion E ion magnetic field electron beam ion beam in beam frame: cold electrons interacting with hot ions e.g.: 200 kev electrons cool 400 MeV/u ions electron temperature: kk BB TT 0.1 eeee kk BB TT 0.1 1 mmmmmm superposition of a cold intense electron beam with the same velocity momentum transfer by Coulomb collisions cooling force results from energy loss in the co-moving gas of free electrons G.I. Budker, At. En. 22 (1967) 346 G.I. Budker, A.N. Skrinsky et al., IEEE NS-22 (1975) 2093
Electron cooling momentum spread Δp/p = 10-5 diameter 2 mm The ions get the sharp velocity of electrons, small size and divergence G.I. Budker, At. En. 22 (1967) 346 G.I. Budker, A.N. Skrinsky et al., IEEE NS-22 (1975) 2093
Stochastic cooling: Implementation at the ESR long. Kicker transv. Pick-up Combiner- Station transv. Kicker long. Pick-up ESR storage ring Stochastic cooling is in particular efficient for hot ion beams
Principle of stochastic cooling Self correction of ion trajectory Using a pick-up probe, the position of the ion beam is measured at a fixed position via the induced signal. A deviation of the beam from the ideal orbit can be corrected by amplification of this signal. The amplified signal is now used as a correction signal which acts on the beam at a second position (zero crossing of the betatron function) via a "kicker. The Nobel Prize in Physics 1984 Simon van der Meer 1925*, CERN This method was invented for the cooling of hot p(bar) by van der Meer. He showed that after a cooling time of τ N/C (N: particle number, C = Bandwidth of the amplifier) a momentum width of the beam of about p/p 10-3 can be achieved by stochastic cooling. Detection of the W boson from p p(bar)
Principle of laser cooling 1. Absorption of photons from a laser beam: Energy and momentum must be conserved. 2. Absorption of photons: Momentum transfer in a defined direction (directed momentum transfer). 3. No defined direction for the spontaneous emission (isotropic re-emission): Momentum transfer cancels out over many absorption-emission-cycles.
Principle of laser cooling 2-step process
Cooling D. Boutin
Cooling with the ESR
Schottky-Mass- Spectroscopy 4 particles with different m/q time
Schottky mass spectroscopy Sin(ω 1 ) Sin(ω 2 ) Fast Fourier Transform Sin(ω time 3 ) ω 4 ω 3 ω 2 ω 1 Sin(ω 4 )
Small-band Schottky Schottky mass spectroscopy frequency spectra 10 74 197 195 W 200 193 185 Pt 197 197 Bi 81+ 76+ 40.0 50.0 193 201 189 Hg 78+ Pt Hg 79+ 191 Bi 83+ 78+ 198 184 Ir Au 186 79+ 186 184 76+ Os 76+ 203 Pt Ir 77+ 193 77+ 181 198 Po 84+ 186 Bi 82+ 181 Au 77+ W 181 184 Pt 77+ Ir 77+ 191 30000 250.0 Hg Bi X q+ Os75+ 71+ 74+ Lu W Tl 201 182 Pb 81+ Tm68+ Dy Tb 64+ 147 Gd64+ 163 71+ Hf known masses unknown masses 160.0 81+ 78+ 163 Pt 156 220.0 Pt 76+ 182 Ir 182 Po 84+ 76+ Os 76+ 230.0 172 147 q+ 187 194 147 X Bi Hg 80+ 75+ Au 78+ 170 67+ Er 154 67+ Ho 210.0 Nd 60+ I 122 53+ Gd63+ A 187 83+ 193 150.0 64+ 70+ Lu 161 Dy 200.0 240.0 16 Number of channels 2 Recording time 30 sec 83+ 50000 270.0 60000 280.0 Frequency / khz / Frequency Tl 80+ Yb 77+ Ir 70+ 185 A 198 40000 77+ 161 Pt Pb 80+ Re 75+ 194 154 73+ W 66+ Ho 80+ Tl 80+ 260.0 192 185 145 191 74+ 0 10000 0240.020000 Bi 82+ 152 190.0 Hg 80+ Ir 140.0 199 152 66+ 69+ Pr 59+ 159 Eu 62+ Sm62+ Pb 82+ 143 Bi 82+ Re74+ 180.0 Dy 65+ Tb 180 65+ 55+ 196 184 177 76+ 178 136 Pt 78+ Ir 150m,g Hg 79+ 196 Cs 189 Au79+ Os 76+ 170.0 127 189 183 150 Tm 0 160.0 10 157 Er 68+ 183 Yb Pt 78+ Ta72+ Au 78+ 166 188 188 Au 79+ 175 190 197 192 Pb 82+ 168 76+ Pb 81+ 130.0 138 69+ 159 Tl 197 Hg 79+ 81+ Os 190 120.0 Tm Bi 83+ 110.0 Pb Tl 80+ 82+ 72+ 191 Hf Tl 81+ Po 83+ Au 78+ 80.0 165 196 70.0 60.0 65+ 189 100.0 195 Hg 79+ Tb 165 72+ Ta Hg 80+ 189 195 81+ 192 149 Tl 80+ 75+ Lu 200 Au 79+ mass unknown Tl 83+ Re 194 194 90.0 5 5 202 173 80.0 10 1 30.0 201 Ir massau knownpo Hg 78+ Po 84+ 80+ Re 77+ 190 68+ 75+ Hf 71+ Pt 0 68+ 2 182 187 157 3 Au 77+ 71+ 4 187 20.0 Pb 82+ 164 5 199 164 5 Pb Bi 82+ Po 84+ 205 Pb 82+ 195 Pb 80+ Er 199 204 Au 77+ 200 Po 82+ Bi 83+ 156 166 194 143m,g 6 77+ 200 188 Tl 79+ Pt 202 78+ 75+ 10.0 0 10 Intensity / arb. units Intensity / arb. units 0 193 188 Hg 79+ 168 7 Bi 81+ 72+ 198 Pb 81+ 192 190 73+ 198 Pb 81+ Tl 80+ Bi 82+ Ta 5 Hf 171 8 Hz 290.0 70000 80000 300.0 310.0 320.0 100000 90000