Intense Slow Positron Source - SLAC National Accelerator ... · Intense Slow Positron Source...

Nov-14-2003 SLAC EPAC

P. Pérez & A. Rosowsky 1

Intense Slow Positron Source

•Introduction•Science & Frontier Technology •Production of e+

•Competition•Proposal•Request to EPAC

10 MeVrhodotron

target - collector

moderator - buffer gas - trap e+

~ 14 m



Introduction

• Our motivation: detect deviation from gravity inPs or Hbar free-fall

– make a beam of anti-atoms (≠CERN expts.)– use few pbar (expensive)– use many e+ EC ~ eV , D EC ~ 1.5 meV

• e+ factory : today’s proposal

• New applications outside this field for Ne+ > 109 s-1



Making anti atoms• Radiative Recombination (RR) ne ≤ 10 8 cm –3

p + + e – H p – + e + Hbar

• Laser Induced Radiative Recombination (LIRR)p + + e – + hν H + 2hν p – + e + + hν Hbar + 2hν

• 3 Body reactions (3BDY) ne ≥ 10 9 cm –3

p + + e – + e ± H * + e ± p – + e + + e ± Hbar * + e ±

e + + e – + e ± Ps * + e ±

• Charge exchange with Positronium (CXPS)p + + Ps H + e + p – + Ps Hbar + e –

H + Ps H – + e + Hbar + Ps Hbar+ + e –

Matter Anti-matter

SLA

CC

ER

N



p+ + Ps H + e+

C.M.

20 KeV p– (lab) 10 –15 cm2

H + Ps H − + e+

20 KeV p (lab) 10−17 cm2

1014 Ps at/cm3 10– 4 Hbar +

per incident antiproton

N.Yamanaka & Y. Kino, Phys. Rev. A 65, 062709 P.K. Biswas, J.Phys. B: At. Mol. Opt. Phys. 34 (2001) 4831



Transform all e+ into Ps in less than 1 ns via 3 body reaction: e + + e – + e ± Ps * + e ±

1014 Ps at/cm3

10– 4 Hbar +

per incident antiproton

20 KeV p ± + Ps target

H/p = Hbar/p– = 0.1

In same Ps target

H + Ps H – + e +

Hbar + Ps Hbar++ e–

H–/H = Hbar+/Hbar =10-3

density (cm-3)

Lif

etim

e (s

)

1 meV

direct annihilation

5 meV20 meV

10-14

10-13

10-12

10-11

10-10

10-9

10-8

10-7

10-6

10-5

10-4

10-3

10-2

10-1

1

10

10 2

10 3

1010

1011

1012

1013

1014

1015

0.1 ns

1 ns

Plasma temperature

we will be here !

ATHENA 2.5 108 cm-3

e+lif

etim

e in

pla

sma

(s)

1012 1014

plasma density (cm-3)



Layout scheme

Positronium target :

Few 1012 e ± inside 10-2 cm3

=> Ps density ~ 1014 cm-3

Greaves-Surko traps Target :

aerogel / Si cristal

H, H – or Hbar, Hbar+ ï Free fall expt.

L = 1 cmS = 1 mm2

« = 1200 mm

e– trap

( ~ eV )

e+ trap

( ~ eV )

p+ or p– trap

( ~20 keV )

several minutes to fill e+ trap



Greaves-Surko trap

Ne moderator: Ec < 1 MeV eV

N2 buffer gas : eV meV

Penning Malmberg trap

Rotating wall

ATHENA : 108 e+

UC San Diego

(7K)

Project to store 1015

within 3 years 1012 1013 e+



Fundamental Physics expts

• Gravity experiment possible with Ps only– High Rydberg states of Ps can live ~ 1ms – produce thermal Ps atoms (3 km/s max speed) then excited

with Doppler-free two photon techniques – Ps atoms focused by mirror and converge on 1 mm spot– deflection expected from gravity is 50 mm on a 10 m scale – rate of slow positrons needed in order to achieve a 5 s

measurement in a week of run is ~ 109 s-1

• BEC Ps• 511 KeV g ray laser• 3D imaging of molecules

A. P. Mills & P.M. Platzman publications



Other research & Applications

• e+ e – plasmas Astrophysics– Feed stellarator for low energy neutral plasma study– Relativistic plasmas study on ms to s time scales

• Cold & bright e+ beams materials study– High speed electronics and chips (PALS)– Positron microscopy

• Filling of portable trap with 1012 e+ commercial use (UCSD design)

• « advanced futuristic » projects : energy storage, USAF shuttle propulsion…



e+ Production and Collection

• Beam energy/intensity : 10 MeV 2~10 mA

• Target geometry : thin foil at grazing incidence ( 3 degrees)

• Probability of first interaction (e+ & Xrays)

• Thermal effects : Xrays leak + IR slab effect

• Large angle collection and selection < 1 MeV



Target (2)Y

Z

X

e−

LINAC 10 MeV

Tungsten target

20 mm x 20 mm x 50 µm

e− beam section

1 mm x 20 mm

3 degree

e+

e+e+

e+

Study energy deposit as a function of incidence angle

Thickness = D

equivalent thickness: D’ = D / sin 30

30

D’

D



Kinetic energy at target exit

positrons electrons

Energy (GeV) Energy (GeV)



Energy versus angle

Production point

Kinetic energy (GeV)

At target exit

Kinetic energy (GeV)

angl

e



x

dump

e+

e- B B

B

e+

e+

target

target

Magnetic Bulb



Collection Setup

HELMOLTZ GUIDING TUBE��

��

��

��

TARGET

QUADRUPOLE

DUMP

MAGNET H2

WALL SHIELD

MAGNET H1

20 cm 50 cm 40 cm 1 m

count e+ here



Simulation and engineering

x

z

10 cm

x

z

10 cm

10 cm



Positrons

x

y

z



electrons

x

z

10 cm



3D view



e+ position in (y , z) planes

X = 3 cm X = 200 cm

Before 4-poles



energy versus radius at x = 200 cm

Rad

ius

(cm

)

Energy (GeV)

positrons

Energy (GeV)

electrons



Positrons radius at x = 200 cm

Radius (cm)

Kinetic energy < 1 MeV

Radius (cm)

All kinetic energies



Target

e- soldering test on

Tungsten 50 mm

40 kV / 20 mA on 20 mm2

not perforated at 15 mA

Working hypothesis: 1 k W / cm2 3100 K

Test with high intensity beam from IBA foreseen T rise, evaporation…



Target (2)Y

Z

X

e−

LINAC 10 MeV

Tungsten target

20 mm x 20 mm x 50 µm

e− beam section

1 mm x 20 mm

3 degree

e+

e+e+

e+

Study energy deposit as a function of incidence angle

Thickness = D

equivalent thickness: D’ = D / sin 30

30

D’

D



Target (3)

track length (cm)

1

10

10 2

10 3

10 4

-0.5 0 0.5 1 1.5 2 2.5 3

30

900

e- track length inside targets of 1mm equivalent thickness

0.480.53900

0.110.1130

rms<L> ( cm) ( cm)



Energy Deposit in 1cm2 Target

E=10MeV puissance deposee pour 1mA de e-

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

0 1000 2000 3000 4000 5000

Simulation with GEANT/EGS

E=10MeV courant d e- pour 1kW de puissance deposee

10-1

1

10

10 2

0 1000 2000 3000 4000 5000

D’(mm) D’(mm)

E(e-) = 10 MeV

Pow

er (W

)

30

900

Deposited power for 1 mA

900

30

IMAX for 1 kW deposited

Cur

rent

(mA

)

4.5 kW/mA

1.7 kW/mA

0.59 mA

0.22 mA



30

E=10MeV nombre de e+ de moins de 1 MeV a l avant pour 107 e- sur la cible

0

1000

2000

3000

4000

5000

6000

7000

8000

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000

E=10MeV nombre de e+ a l avant pour 107 e- sur la cible

0

2500

5000

7500

10000

12500

15000

17500

20000

22500

25000

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000

30

Production Rate (1)

D’(mm) D’(mm)

107 electrons on 1 cm2 target

900

900

Ne+

Ee+<1 MeVe+ forward

Ne+

~ 15000 / 107 = 1.5 10-3

~ 3500 / 107 = 3.5 10-4



Production Rate (2)

E=10MeV taux de e+ a l avant pour 1kW depose dans la cible

0

1000

2000

3000

4000

5000

6000

7000

8000

x 10 9

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000

E=10MeV taux de e+ de moins de 1 MeV a l avant pour 1kW depose dans la cible

0

200

400

600

800

1000

1200

1400

1600

1800

2000

x 10 9

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000

D’(mm) D’(mm)

Ne+

(s-1

)

X 109

Power deposited in 1 cm2 target = 1 kW

900 900

X 109

Ne+

(s-1

)

30 30

Ee+<1 MeVe+ forward

1.4 1012

0.6 1012



Production

0

10

20

30

40

50

60

70

80

90

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5x 10

-2

0.552.50.25 mA900

1.14.60.58 mA30

Ne+(<1MeV)Ne+Imax

in units of 1012 s-1

For 1 cm2 of target

D’ = 1mm

Limit 1 kW / cm2

Ee+ (MeV)1 2 3 4 5

Normalization to same number of e- generated

900

30

0.58 mA 2.3 mA for 4 cm2



Collection efficiency

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.2 0.4 0.6 0.8 1 1.2 1.40

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.2 0.4 0.6 0.8 1 1.2 1.4

Fraction of e+ at exit plane inside circle of radius 5 or 2 cm centered on axis

r = 5 cm r = 2 cm

E < 600 KeV

E < 1 MeV

transverse radius of e+ source at target level (cm)

e 5 e2

slit shaped beam

2 x 2 cm

1 x 4 cm

with quad

no quad



Collected Positron Rates (2m from target)

e+ produced as much as possible near axis is best for production and collection

1.360%E < 600 KeV

2.752%E <1 MeV

4.220%forward

e+ ratee5Rcoll= 5 cm

0.630%E < 600 KeV

1.120%E <1 MeV1.68%forward

e+ ratee2Rcoll= 2 cm

(e+ rates in units of 1012 s-1)

0

10

20

30

40

50

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

all e+ at exit plane

R < 5 cm

R < 2 cm

E (MeV)



Electron and photon fluxes

• Beam and coils on same axis

• Target and downstream coils on same axis

e-

e-

Two possible setups with same e+ output



Fluxes of electrons and photons

0

1

2

3

4

5

6

7

8

9

10

0 50 100 150 200 250 300

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

200 210 220 230 240 250 260 270 280

0

1

2

3

4

5

6

7

8

9

10

0 50 100 150 200 250 300

0

0.025

0.05

0.075

0.1

0.125

0.15

0.175

0.2

0.225

0.25

200 210 220 230 240 250 260 270 280

X (along coils axis) (cm) X (along coils axis) (cm)

Pow

er (k

W)

Pow

er (k

W)

Setup 1 Setup 2

110 W80 W45 W10 WSetup 21.5 kW450 W140 W5 WSetup 1

R = 4 cmR = 3 cmR = 2 cmR = 1 cmI = 2.3 mA

plot

s fo

r 1 m

A

at exit plane



-.01 -.005 0.0 0.005 0.01

-.01

-.005

0.0

0.005

0.01

Postprocessor/Zgoubi NoDate... Z (m) vs. Y

A very first design of a 2D expander/uniformizer

b(m

)

x (m)

F. Meot and T. Daniel,

NIM, A 379 (1996) 196-205.

Z (m

)

Y (m)



Design differences (1)

1.5 eV e+

Proposed design

e-

converter

MeV e+

trap

Ne moderator

e-dump

converter moderator

E (2-5 kV)

extraction lenses

MeV e+

trap

EPOS design + trap

E(decel.)

1.5 eV e+

W

7K10- 2Neonroom10- 4Tungsten

temperatureefficiency

Rossendorf / Aarhus



Original EPOS design:40 MeV, 0.25 mA, ~CW LinacPt or W moderator, 3.5 mm Pt targetNeutron activationCollection efficiency before trap 20%Expected Rate before trap 1.6 108 s-1

0.8 1082m3mnoW2.510

RatewallLActiv.Mod.I(mA)E (MeV)

10102m3mnoNe2.510

1.6 1083m30myesPt0.2540

Proposed design:

10 MeV, 2.5 mA, CW

Ne Moderator, thin W target

Collection efficiency before trap 20%

Expected rate before trap 1.1 1010 s-1At 10 MeV, 2.5 mA1mm target = 0.8 108 s-1

Design differences (2)



Other designsThermal neutron capture: 113Cd(n,g)114Cd s = 26000 barn !!By nuclear research reactor FRM2 in Munich (Germany) can reach 1010s-1

Building size:

40 m x 40 m x 30 m



• Gravity and spectroscopy with Ps H Hbar

• Astrophysics “in vitro”

• 3D molecule imaging

• Ps BEC and 511 KeV Laser

• Applied technology : positron microscope

Scientific Goals



Proposal: best ingredients ..

• e+ facility : Ne+ > 109 s-1

• fundamental interaction physics : HEP lab

• e – beam expertise and beam research

• SR radiation control infrastructure

• Interdisciplinary lab

• Location near trap development

10 MeVrhodotron

target - collector

moderator - buffer gas - trap e+

~ 14 m



Ressource Impacts

• Building :– new ~ 2.5 M$ – refurbished ~ x00 k$

• e- machine :– Rhodotron ~ 2.5 M$ – Linac ~ 300 k$

• Infrastructure :– 250 kW – Water cooling – Radiation control, safety …

• Target-collection• Injection

~ 400 k$

• Parallel project UC San Diego

– Moderator

– Buffer gas

– trap ~ 500 k$



• EPAC feed back:– encourage TDR for june 2004 EPAC

Requests

• Winter workshop:– Start interdisciplinary community– Start SLAC - Saclay project collaboration– Trigger other institutes interest

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