FLAIR meeting, GSI March Positron Ring for Antihydrogen Production A.Sidorin for LEPTA collaboration JINR, Dubna

Contents 1. Antihydrogen in-flight 2. LEPTA – the positron storage ring with electron cooling of positrons and particle “magnetization” 3. Scheme of the Antihydrogen Generator based on the LEPTA type ring 4. Possible experiments with antihydrogen in-flight 4.1. Direct comparison of the electric charges of proton, antiproton, electron and positron 4.2. Hyperfine structure of the ground state 4.3. Spectroscopy of excited states, Lamb shift measurement 4.4. Laser spectroscopy of 1S – 2S transition 5. Status of the LEPTA project 6. Conclusion

1. Antihydrogen in-flight Basic idea: G.Budker, A.Skrinsky,Uspekhi Fyz. Nauk, 124 (1978) 561

Antiproton ring e+e+ p~p~ H~H~ e  Electron cooling of antiprotons e  Electron cooling of positrons The facility general scheme Positron ring

Antihydrogen flux quality Angular and velocity spread is determined by the antiproton beam parameters - deep cooling of antiprotons “Magnetised” cooling - in absence of additional heating the equilibrium is determined by temperature of longitudinal degree of freedom of the electrons Antiproton beam ordering - ? Stability of the string coherent oscillations At 20 keV maximum antiproton number is about 10 5

Antihidrogen flux intensity Generation rate per 1 antiproton: To increase the positron beam density: - positron deceleration in the recombination section, - positron beam compression - bunched positron and antiproton beams

Magnetic field in recombination (cooling) section 1. Positron (electron) beam transport 2. Suppression of IBS in positron (electron) beam - preservation of flattened distribution 3. “Magnetised” cooling B 1 ~ 100 G B 2, B 3 ~ 1 kG

Magnetic field in recombination (cooling) section Antiproton motion distortion Larmor radius of antiprotons has to be less than recombination section: at 5 MeV and L rec = 3 m B < 1 kG at 50 keV B < 100 G At small antiproton energy and large magnetic field one needs to adjust the recombination section with antiproton ring

Scheme of The Electron Cooler at Large B: Beams Injection / Extraction

Magnetic field in positron source 1. Positron source based on Electron linac: low magnetic field 2. Positron source based on Radioactive isotope: large magnetic field

Electron beam Ta - convertor W - foils Positron flux Low energy positron source based on Electron linac

Electron energy is ~ 200 MeV Intensity is about 10 8 positrons per pulse Magnetic field < 100 G

Positron source based on radioactive isotope Positron source and moderation The efficiency of this type moderator lies in the range from 0.2 to 0.5%. The positron energy spread at the exit of moderator is about eV. The flux intensity at the exit is about 1-2  10 6 slow positrons per second Prototype is the positron part of ATHENA

Positron trapping Magnetic field ~ 1 kG Trapping efficiency is 60% Number of trapped positrons is about 10 8 Repetition period ~ 100 sec

Two basic concepts MeV Electron linac for positron production ~ 50 G magnetic field in the positron ring Positron ring circumference of m Positron energy of about 1 keV Positron deceleration to ~ 10 eV in the recombination section 2. Positron production using radioactive isotope ~ 500 G magnetic field in the positron ring Positron energy of about 10 keV Positron beam compression and deceleration in the recombination section Matching of the antiproton beam with recombination section “LEPTA - type” ring

2. LEPTA – the positron storage ring with electron cooling of positrons and particle “magnetization” I.Meshkov, A.Skrinsky, NIM A379 (1996) 41 ; NIM A391 (1997) 205 I.Meshkov, A.Sidorin, NIM A391 (1997) 216

e + trap Septum Cooling section Quadrupole Collector e-gun BB Detector e + source Low Energy Positron Toroidal Accumulator

General parameters of the LEPTA Circumference, m17.8 Positron energy, keV10.0 Solenoid magnetic field, G400 Quad field gradient, G/cm10.0 Positron beam radius, cm0.5 Number of positrons 1  10 8 Residual gas pressure, Тоrr1  10  Electron cooling system Cooling section length, m4.0 Beam current, A0.5 Beam radius, cm1.0 Electron density, cm  10 8 Orthopositronium flux parameters Intensity, atom/sec1  10  Angular spread, mrad1 Velocity spread1  10  4 Flux diameter at the ring exit, cm1.1 Decay length, m8.5

3. Scheme of the Antihydrogen Generator based on the LEPTA type ring

Scheme of The LEPTA Type Positron Ring

Facility parameters and H-bar generation #2 Positron ring Ring circumference, m 25 Recombination section length, m 3 Positron energy in the ring, keV 10 Positron beam radius in the ring, cm 0.5 Magnetic field in the positron ring, G 400 Magnetic field in the recombination section, G 1000 Positron number 10 8 Antiproton ring Energy, MeV Circumference, m Antiproton number “normal” state ordered state 3.4     10 5 Positron energy in the recombination section, keV

Facility parameters and H-bar generation (continuation) #2 Antihydrogen flux parameters Energy, MeV Generation rate per 1 antiproton 1     Flux intensity, s -1 “normal” state ordered state Angular spread “normal” state ordered state < Relative velocity spread “normal” state ordered state 10 -6

4. Possible experiments with antihydrogen in-flight I.Meshkov, Phys. Part. Nucl. 28 (1997) 496

4.1. Direct comparison of the electric charges of proton, antiproton, electron and positron - – Test of CPT Theorem The experiment concept : Detection of a displacement  x of "neutral" atoms, when they travel in a transverse magnetic field B  of the length L:  x = (  e · B   L 2 ) / (2pc),

#4.1 Charge inequality |q 1 + q 2 | / e Experiment Present Expected Theory Particles 1, 2 Electron / positron < 2· <  4   4   10 Antiproton / positron 0 ? <  2   5 (indirect) 2   9 Proton / antiproton < 2· <  2   5 2   9 Proton / electron 0 ? <  1   21 -

#4.1 “Atoms”  Position sensitive detector CsI  BB The experiment concept “The atoms” : H 0 H-bar o-Ps Required parameters Magnetic field, T Magnet length, m Detector resolution, mcm

One of the goals of the LEPTA project is the experiment EPOCC (Electron/Positron Charge Comparison) - direct comparison of the electric charges of proton, antiproton, electron and positron to exceed the present accuracy of the charge difference by two orders of magnitude : |q p + q e | / e 4  #4.1

An achievable resolution (  /  ) HFS < 3·10 – 8 Antiproton magnetic moment from (  /  ) HFS : Absolute value:  a /  a < 2·10 – 5 (presently 3·10 – 3 ) Difference with proton: |  p +  a | < 1·10 – 7 The method: Atomic interferometer with sextupole magnets Hyperfine structure of the ground state

4.3. Spectroscopy of excited states, Lamb shift measurement Hydrogen : Hyperfine structure 2S-state  /  ~ 3  10 – 7 Lamb shift of 2P-state  /  ~ 2  10 -6

E RF #4.3 Microwave spectrometry of 2 2 S 1/2  2 2 P J transitions (J = 1/2, 3/2) H-bars 2 2 S 1/2 Detector RF Cavity tuned to transition 2 2 S 1/2   1/7 s 2 2 P 1/2   1.52 ns 1 2 S 1//2 12S1/212S1/2

4.4. Laser spectroscopy of 1 2 S 1/2 – 2 2 S 1/2 transition The goal of ATHENA and ATRAP experiments at CERN :  /  < 1  Life time of the metastable 2 2 S 1/2 state ~ 1/7 s, i.e. (  /  ) natural ~ Experiment in traps with Hydrogen today (  /  ) transition ~ What about H-bars in-flight ?

#4.4 H-bar 1 2 S 1/2 Detector Laser beam 1 2 S 1/2 and 2 2 S 1/2 Mirrors Laser frequensy in the particle Rest Frame (PRF):  PRF =  Laser ·  · (1   ), Two photon energy is H-bar velocity dependent :  = 2 ћ   - scan by v H-bar ! 2 2 S 1/2 Doppler free two photon spectroscopy of 1 2 S 1/2  2 2 S 1/2 transition (principle scheme) f transition = ·10 15 Hz transition = 0.12  Laser = 0.24  RF cavity 1 2 S 1/2 2 2 S 1/2   1/7 s 2 2 P 1/2 1 2 S 1/2

2 2 S 1/2   1/7 s 2 2 P 1/2 1 2 S 1/2 #4.4 Doppler free spectroscopy of 1 2 S 1/2  2 2 S 1/2 transition Experiment parameters: Antiproton energy, MeV  = v/c H-bar flux, s -1 “normal” state ordered state Relative velocity spread  v / v : “normal” state ordered state Experiment resolution  /  ~ 0.1 of Doppler spread:  /  ~ 0.1  2  2  (  v / v) “normal” state ordered state

5. Status of the LEPTA project

October 2003: 3/4 of the ring is assembeled and traced with pulsed electron beam

6. Conclusion For technical design of the positron ring one needs: Experimental study of the particle dynamics in a ring with longitudinal magnetic field Experimental study of electron cooling of positrons Choice of the installation concept providing best conditions for experiments