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
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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
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13th April 2004 had done tracking of the electron cooling system
helical quadrupolee-gun
collector
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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
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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