FLAIR meeting, GSI

March 15-16 2004

Positron Ring for

Antihydrogen Production

A.Sidorin

for LEPTA collaboration

JINR, Dubna

Contents1. 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-flight4.1. Direct comparison of the electric charges of proton, antiproton, electron and positron4.2. Hyperfine structure of the ground state4.3. Spectroscopy of excited states, Lamb shift measurement4.4. 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+

p~

H~

e

Electron cooling of

antiprotons

e

Electron coolingof 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

3/1252

37

16

ionth r

QCQN

“Magnetised” cooling - in absence of additional heating the equilibrium is determined by temperatureof longitudinal degree of freedom of the electrons

Antiproton beam ordering - ?Stability of the string coherent oscillations

At 20 keV maximum antiproton number is about 105

Antihidrogen flux intensity

2

11

Lpri

ilife

n

dt

dN

N

3/114.032.11

ln1

TTT

Ar

Generation rate per 1 antiproton:

To increase the positron beam density:- positron deceleration in the recombination section,- positron beam compression

B

B

aC

Nn rec

pp

pp 2

reccool B

BTT ,

- bunched positron and antiproton beams

Magnetic field in recombination (cooling) section

1. Positron (electron) beam transport

bendL R2eB

pcL

2. Suppression of IBS in positron (electron) beam -preservation of flattened distribution

3/1 en

3. “Magnetised” cooling

DR

B1 ~ 100 G B2, B3 ~ 1 kG

Magnetic field in recombination (cooling) section

Antiproton motion distortion

Larmor radius of antiprotons has to be less than recombinationsection:

at 5 MeV and Lrec = 3 m B < 1 kG at 50 keV B < 100 G

At small antiproton energy and large magnetic field one needsto adjust the recombination section with antiproton ring

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

e-gun

e-collector

p

Antiproton injection into magnetic field

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

B

Electronbeam

+V

0

TaWmoderator

Low energy positron sourcebased on Electron linac

1,00E-08

1,00E-07

1,00E-06

1,00E-05

0 100 200

Electron energy [MeV]

Po

sitr

on

yie

ld

Electron energy is ~ 200 MeVIntensity is about 108 positrons per pulseMagnetic 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 2 - 5 eV.

The flux intensity at the exit is about 1-2106 slow positrons per second

Prototype is the positron part of ATHENA

Positron trapping

Magnetic field ~ 1 kGTrapping efficiency is 60%Number of trapped positrons is about 108

Repetition period ~ 100 sec

Two basic concepts

1. 200 MeV Electron linac for positron production ~ 50 G magnetic field in the positron ring Positron ring circumference of 10 - 15 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

Collectore-gun

BDetector

e+ source

Low Energy Positron Toroidal Accumulator

General parameters of the LEPTA

Circumference, m 17.8Positron energy, keV 10.0Solenoid magnetic field, G 400Quad field gradient, G/cm 10.0Positron beam radius, cm 0.5Number of positrons 1108

Residual gas pressure, Тоrr 110

Electron cooling systemCooling section length, m 4.0Beam current, A 0.5Beam radius, cm 1.0Electron density, cm-3 1.6108

Orthopositronium flux parametersIntensity, atom/sec 110

Angular spread, mrad 1Velocity spread 1104

Flux diameter at the ring exit, cm 1.1Decay length, m 8.5

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

e+p, e+e-, p-Psrecombination

e-cooling of positronsand recombination

Positronsource

Positrontrap

Positron injectorAntihydrogen trap

(“ATHENA/ATRAP”)

Ps

H0

p

kicker

helicalquadrupole

e-gun,collector

of e-cooling

e-gun,collector

of e-targete+p, e+e-, p-Psrecombination

e-cooling of positronsand recombination

Positronsource

Positrontrap

Positron injectorAntihydrogen trap

(“ATHENA/ATRAP”)

Ps

H0

p

kicker

helicalquadrupole

e-gun,collector

of e-cooling

e-gun,collector

of e-target

Scheme of The LEPTA Type Positron Ring

6900

580

0

Facility parameters and H-bar generation#2

Positron ringRing circumference, m 25Recombination section length, m 3Positron energy in the ring, keV 10Positron beam radius in the ring, cm 0.5Magnetic field in the positron ring, G 400Magnetic field in the recombination section, G 1000Positron number 108

Antiproton ring Energy, MeV 50 5 0.1

0.02Circumference, m 52 52 36 36 Antiproton number

“normal” state 1010 107 106 106

ordered state 3.4106 1.6106 3.9105 3105

Positron energy in the recombinationsection, keV 26 2.6 0.054

0.01

Facility parameters and H-bar generation (continuation)

#2

Antihydrogen flux parametersEnergy, MeV 50 5 0.1 0.02Generation rate per 1 antiproton 110-8 2.510-8 810-8 110-

7

Flux intensity, s-1

“normal” state 100 0.25 0.08 0.1 ordered state 0.034 0.04 0.03 0.03

Angular spread “normal” state 10-4 ordered state < 10-6

Relative velocity spread “normal” state 10-4

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 Bof the length L:

x = (e · BL2) / (2pc) ,

#4.1

Charge inequality |q1+ q2| / e

ExperimentPresent Expected

TheoryParticles

1, 2

Electron / positron < 2· 10-18 <4 410

Antiproton / positron 0 ? <25 (indirect) 29

Proton / antiproton < 2· 10-18 <25 29

Proton / electron 0 ? <121 -

#4.1

“Atoms”

Position sensitive detector

CsI

CsI

CsI

B

The experiment concept

“The atoms” : H0 H-bar o-Ps

Required parameters

Magnetic field, T 10.0 10.0 2.0

Magnet length, m 10.0 10.0 10.0

Detector resolution, mcm 2.0 2.0 100.0

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 :

|qp+ qe| / e < 410-8 => 410-10 .

#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.

4.2. Hyperfine structure of the ground state

4.3. Spectroscopy of excited states, Lamb shift measurement

Hydrogen :

Hyperfine structure 2S-state / ~ 310 –

7

Lamb shift of 2P-state / ~ 210-6

ERF

#4.3 Microwave spectrometry of 22S1/2 22PJ transitions (J = 1/2, 3/2)

H-bars22S1/2

Detector

RF Cavity

tuned to transition

22S1/2 1/7 s

22 P1/2 1.52 ns

12S1//2

12S1/2

4.4. Laser spectroscopy of 12S1/2 – 22S1/2 transition

The goal of ATHENA and ATRAP experiments at CERN : / < 110-12

Life time of the metastable 22S1/2 state ~ 1/7 s ,

i.e. ( / )natural ~ 10-17 .

Experiment in traps with Hydrogen today

( / )transition ~ 10-12

What about H-bars in-flight ?

#4.4

H-bar 12S1/2

Detector

Laser beam

12S1/2 and 22S1/2 Mirrors

Laser frequensy in the particle Rest Frame (PRF):

PRF = Laser·· (1 ) ,

Two photon energy is H-bar velocity dependent : = 2 ћ - scan by vH-bar !

22S1/2

Doppler free two photon spectroscopy

of 12S1/2 22S1/2 transition

(principle scheme)

ftransition = 1. 233·1015 Hztransition = 0.12 Laser = 0.24

RF cavity

12S1/2

22S1/2 1/7 s

22P1/2

12S1/2

22S1/2 1/7 s

22P1/2

12S1/2

#4.4Doppler free spectroscopy of 12S1/2 22S1/2 transition

Experiment parameters:

Antiproton energy, MeV 50 5.0

= v/c 0.31 0.1

H-bar flux, s-1 “normal” state 100 0.25 ordered state 0.034 0.04Relative velocity spread v / v :

“normal” state 10-4

ordered state 10-6

Experiment resolution / ~ 0.1 of Doppler spread: / ~ 0.122 (v / v)

“normal” state 10-6 10 -7

ordered state 10-8 10-9

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