1

Status of LEPTA projectLow Energy Positron Toroidal

AccumulatorE.Boltushkin, V.Bykovsky, A.Kobets, Y. Korotaev, V.Lokhmatov,

I.Meshkov, R.Pivin, I.Seleznev, A.Sidorin, A.Smirnov, G.Trubnikov, S.Yakovenko

JINR, Dubna

COOL’05

2

Goals of the LEPTA project

• Dynamics of coupling motion in the stellatron• Electron cooling of positrons• Positronium generation in flight • Positronium physics• Electron cooling with circulating electron beam• Feasibility study of antihydrogen generation in

flight

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septum

kicker

cooling section

positroniumdetector

positron trap

Design of the LEPTA

22Na→106 e+ per sec

10 6×100sec=10 8e +

10 4 Ps per sec

e-gun

collector

4

General parameters of the ring

8.52Positronium decay length, m1.1Beam diameter at the exit of the ring, cm1⋅10−4Velocity spread1Angular spread, mrad1⋅104Intensity, atom/s

Design of positronium beam parameters1*10-10Residual gas pressure, Тоrr1*108Number of positrons in the ring

1.62

Length of the helical quadrupole, m and number of steps of the helix

0 - 20Helical quadrupole gradient, G/cm1.45Radius of the toroidal solenoids, m300 - 1000Longitudinal magnetic field, G1 - 10Particle energy, keV17.2Circumference , m

5

13th April 2004 had done tracking of the electron cooling system

helical quadrupolee-gun

collector

6

Beam diagnostic tools and correction coils disposition

Horizontal PU

diaphragms

kicker

Helical quadrupole

Electron gun

Verticalcorrector

Horizontal corrector

septumVertical PU

DL

D = 79 mm, L = 126 mm

7

Formation of closed orbit

in the case when the quadrupole is switched off

10 µs

voltage on the kicker plate

Signal from BCM

kicker is on kicker is off

gun is on

gun is off

2.5 µsPU signals of injected beam

gun is on kicker is off

0.5 µs

kicker is off

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Helical quadrupole“stellarator windings”

-6 -4 -2 0 2 4 68.0

8.5

9.0

9.5

10.0

10.5

11.0

grad

ient

[G

/cm

]

x [cm]

22

dcNIG⋅

=π

Quadrupole Length L = 160 cm

Helix step h = 80 cm

Cross section of the quadrupoleis similar to Panofsky lens

Uniform gradient magnetic fieldinside aperture

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Test of the helical quadrupole

LQ0≈ϕ

,

20

2

0 2kBGQ ≡

0 5 10 15 200

20

40

60

80

100

120

140 B=533 G B=400 G B=267 G

beam

rota

tion

angl

e [d

egre

es ]

helical qudrupole current [A]

x

y

φ

Quadrupole axis

Quadrupole isswitched offQuadrupole is

switched on

quadrupole current, АB

eam

rota

tion

angl

eφ,

degr

ees

G – magnetic field gradient

h – helix stepk=2π/h

results at different magnetic fields

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one peculiarity of the closed orbit formation in the focusing system with

longitudinal magnetic field and helical quadrupole

- 6 - 4 - 2 2 4 6x

- 2

2

4

6

8

10

12y

αx

φx

δx

- 12 - 10 - 8 - 6 - 4 - 2 2x

- 6

- 4

- 2

2

4

6

y

αy

φyδy

g, G/cm

7.5

9.0

1217

g, G/cm

7.5 9.0 12 17

simulation results in drift approximation

horizontal corrector → vertical displacement vertical corrector → horizontal displacement

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Quadrupole was upgraded

030≤simulatedϕ

00 18030 <≤ erimentalexpϕ

Quadrupole length L = 160 cm, helical step h = 80 cm .

Quadrupole is switched on First circulating

10th September 20042.5 µs

The design angle rotation was not suffusion for optimum machine setting.

revolutionfrequency

slow mode frequency

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Betatrone tune of the slow mode

0 10 20 30 40 50 600.0

0.1

0.2

0.3

0.4

0.5 8.2 keV

2.3 keV

revolution

slowslow f

fQ =

5 µs

10 20 30 40 50Iqadrupole

0.1

0.2

0.3

0.4

0.5

QslowQuadrupole length L = 140 cmHelix step h = 80 cm

Fourier analysis

Qslow

Iqudrupole, A

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Betatrone tune was measured with excitation of the slow moderesonance using of the external sin signal applied to PU

20 40 60 80Iqadrupole

- 1.5

- 1

- 0.5

0.5

1

1.5

Spur€€€€€€€€€€€€€€€

2½ Sp

IQ

10 20 30 40 50 60Iqadrupole

0.2

0.4

0.6

0.8Qslow

π⎟⎠⎞

⎜⎝⎛=

21

21arccos SpQslow

h – helix step

L eff =2h

L eff <2h

Qslow

I quadrupole

adiabatic entrance and exit changeof the effective length of the quad

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Beam life time

0 2 4 6 8 100

5

10

15

20

25

Life

tim

e [m

s]

Energy [kev]

Magnetic field 350 G Magnetic field 510 G10 µs

“Killer” pulse wasapplied to the kicker plate

signal from PU

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ND – number of regions with perturbed magnetic fieldC – ring circumference, a – beam radiusB – magnetic field, D – the length of the region with perturbed magnetic field∆B/B – the amplitude of the magnetic field perturbation

K ≈ 4000 – numerical coefficientε - electron energy, c – the speed of lightP – residual gas pressure, nTorr, b – aperture

Vacuum lifetime 2

22 ⎟⎠⎞

⎜⎝⎛⋅

ε⋅=τ

mceBb

mcPK

vacuum

Magnetic field lifetime

⎪⎭

⎪⎬⎫

⎪⎩

⎪⎨⎧

ε⋅⋅⎟

⎠⎞

⎜⎝⎛ ∆⋅

ε⋅⎟⎟

⎠

⎞⎜⎜⎝

⎛⋅⎟

⎠⎞

⎜⎝⎛⋅⋅=τ

− 2

2

2

2

222 2exp21 mcmceBD

BB

mceBDmc

ab

cC

N DB

1

Bvacuumtotal

11−

⎟⎟⎠

⎞⎜⎜⎝

⎛+=ττ

τ

Lifetime vs EnergyExperimental results and theoretical fitting

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0

2

4

6

8

10

12

14

0 2 4 6 8 10Энергия, кэВ

врем

я жиз

ни, м

сек

Р = 50 нТоррР = 250 нТорр

0 2 4 6 8 100

5

10

15

20

2525

0

τ_tot1 ε( )

τ_tot2 ε( )

100 ε

25

20

15

10

5

00 2 4 6 8 10

Energy, keV

B1 = 350 GP1 = 30 nTorrB2 =510 G, P2 =60 nTorr

0 2 4 6 8 100

2

4

6

8

10

12

1414

0

τ _tot1 ε( )

τ _tot2 ε( )

100 ε

14

12

10

8

6

4

2

00 2 4 6 8 10

Energy, keV

Experimental results and theoretical fitting

Lifetime vs Energy

B = 350 G

P1 = 50 nTorr

P2 = 120 nTorr

∆B/B~20%

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results of the LEPTA ring testwith electron beam

7*10-8Residual gas pressure of, Torr

22Life time at 4 keV, ms

3*1010Number of circulating particles

0.5Efficiency of injection

10Injection current, mA

0.1 – 0.43«Slow» betatron tune

32 – 57Current of the quadrupole, A

1- 10Energy of the circulating beam, keV

300 – 510Longitudinal magnetic field, G

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5253

6 67

1 4

6 6 7

88

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The positron injector is under assembling

1-positron source 22Na, 2-positron trap, 3-transport section to the ring, 4-radioactive protection shield, 5-vacuum chamber for pumping and diagnostics, 6-ion pump, 7-turbo molecular pump, 8-valve, 9-liquid helium

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Design parameters of the positron injector

1⋅10−9Residual gas pressure, Tor

100Accumulation time, s300Injection pulse duration, ns

1⋅10-4Momentum spread1⋅108Number of positrons in injection pulse

0.5Beam radius, cm

1500Longitudinal magnetic field in the trap, G400Longitudinal magnetic field, G10.0Positron injection energy, keV

6,2Length, m

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Positron energy spectrum

10-1 100 101 102 103 104 105 106 10710-9

10-8

10-7

10-6

10-5

10-4

10-3

10-2

Positron energy, eV

Moderated positrons

energy spectrum of

emitted positron

from 22Na

Posi

tron

yie

ld

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Positron source

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Cryogenic test T = 6.9 K, moderator – frozen Ne

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Assembling of the positron trap

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Solenoid and vacuum chamber of the positron trap is assembled

90

100

110

120

130

140

150

160

170

180

0 10 20 30 40 50 60 70 80 90 100 110 120

Шаг

B(Гс)

∆B/B=0,017

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Nearest plans

1 Improvement of magnetic field quality in LEPTA ring.

2 Test and tuning of electron cooling system with continuous beam.

3 Test of positron trap with electrons

4 Assembling of positron injector

5 Electron cooling of positrons and positromium generation

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LEPTA team is very grateful to our colleagueswho supported the project efficiently:

Gerry Jackson & John Peoples, FermilabRudolf Maier, Walter Oelert, Jurgen Dietrich, Hans Stockhorst, FZJIlan Ben-Zvi, BNLTakeshi Katayama, RIKENAkira Noda, Kyoto University

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Assembling of the LEPTA ring is completed

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Spectrum measurement Beam energy 2.2 keVInjection current 5 mARevolution frequency corresponding to injection energy 1.58 MHz

Self excitationfrequency is 1.35 MHz

9.6 ms

f=frevolution- fslow

Fourier amplitude of the signal from differential PU

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Beam excitationwith external sinusoidal signal(beam transfer functionmeasurement)

f = 1.451 MHz

f = 1.317 MHz

Beam energy 2.2 keVInjection current 5 mARevolution frequency corresponding to injection energy 1.58 MHz

32 ms

32 ms