Ultracolod Photoelectron Beams for ion storage rings

1

Ultracolod Photoelectron Beamsfor ion storage rings

CSR E-Cooler

TSR (magnetic)

e-target

e-c

oole

r

CSR (electrostatic)

Elab: 100-4000 eV

Current - 2 mA Lifetime - 24 h kT < 1.0 meV kT|| = 0.02 meV

Electron-ion collision spectroscopy

D. A. Orlov, C. Krantz, A. Shornikov, A. Wolf

Elab : 10-1eV

• Low e-energies: => low current (100-1µA) => higher kT||

• e-transport by B => slow ions distorted

Cooling at eV-energies - it is a challenge!

Electron cooling

TSR E-target

Extremely high resolution is demonstrated!

DR of Sc18+

1 ve = vi

2 ve ≠ vi

6 meV

Max-Planck-Institut für Kernphysik, 69117, Heidelberg, Germany

Dmitry Orlov, MPI-K, PESP-08 2

cold electrons

OUTLINE1

HOW TO: cold e-beams

2 E-cooling

Collision resolution

6Cooling of CF+ ions

at TSR by 53 eV photoelectrons

7Manipulation with

0.1-10 eV e-beams at TSR target

4Why?

ElectrostaticCryogenic Storage Ring

3electron collision

spectroscopy @ TSR (keV)

5e-beams of eV energies,

CSR cooler


300 K 90 K

Energy distributions of photoelectrons“2D”-measurement

(E|| , E)

EF

E vac

ThermocathodevacuumT=1300-1500 K

kT=110-120 meV

Cold electrons. How to (A): Photocathode kTC = 10 meV

Fully activated cathode: QY= 15-35%

QYeff=1 %

Laser: 1W @ 800 nm9 (transmission) 2W @ 532 nm (reflection)E-current: 0.1- 2.5 mALifetime : >24 h

D.A. Orlov et al., APL, 78 (2001) 2721;

Suppression

Suppression

Strong energy and impulse relaxations Energy spreads of about kT

E vac

E F

E c

(CsO)

E v

GaAs vacuum

T= 80 K

Suppression

Suppression

kT=10 meV

Thermocathode kTC > 100 meV

4

Cold electrons. How to make them colder (B):

1. Magnetic expansion

C

guide

kTkT

B

B

0B

0 (high field) B

guide(low field)

2. Acceleration

Reduction of kT

Reduction of kT||

heatingplasmaeU

TkkT C

2

22

||

= 20

Thermocathode kT = 5-6 meV

Photocathode kT = 0.5 meV

kT|| = 0.02-0.1 meV

Phase-space conservation

v║

E

ΔE

ΔE

Δv Δv'

U0

5

Cold electrons. How o keep them cold (C):

4/12/1100015

12.6

U

V

d

mm

mA

IGBB

3/12/16/1

110

10001561

mA

I

meV

kT

U

V

d

mmGB c

g

High magnetic field is required

1. To avoid beam divergence

2. To suppress TLR

3. To provide adiabatic transport

2/1

1000

10067

V

U

B

GmmC

e

e

e

low current high currenthigh current +magnetic field

keeping dT|| / dZ < 5 μeV/m :e

e

B

rc

ne-1/3

rc << ne-1/3

B

e

R

λc << R

λc

Typical transition lengths R=100 mm

2/1

1000316

V

UGBg1.0

RC


cold electrons1

HOW TO: cold e-beams



7Manipulation with


4Why?


3electron collision



CSR cooler

2 E-cooling



Principle of Electron Cooling10-3

2

3

068

3

e

mcC

eion

2/3

220

cM

Tk

LZn

MC

e

eB

Ce

ion

TSR

e-cooling


Electron-ion collision resolution

rEv

V║

V

Recombination velocity

Flattened electron distribution

kT║≪ kT

||2 2ln16)2ln( kTEkTE r

0

0.2

0.4

0.6

0.8

1

0.002 0 0.002 0.004 0.006 0.008 0.01

Rat

e, a

.u

C M en e rg y, eV

U -U , Vc o o l

0 2 4 6 5 3 1 -2 -1

U = 1 0 0 0 Vco o l

k T

k T ||

= 1 m eV

= 0 .0 1 m eV

Real resonance position

DR

rat

e co

effi

cien

t

ve = v

i

Tk

m

Tk

m

Tk

m

Tk

mf edeee

d 2exp

2exp

22),(

2

||

2||

2

||

3, df dd

For high energies Er:


cold electrons1HOW TO:

cold e-beams



7Manipulation with


4Why?



CSR cooler

2 E-cooling


3electron collision



~0.2 ... 8 MeV/uDetectors

(ions and neutrals)

e-target

Interaction section 1.5m

Electron gun withmagnetic expansion

≈10...90

Adiabaticacceleration

Collector

TSR dipole

Movable ion detector

Neutrals detector

Ion beam

e-

e-source

Electron collision spectroscopy.TSR electron target.

Dmitry Orlov, MPI-K, PESP-08

-e

Aq +

Electron captureresonance

nℓ

(Aq +)* + nℓ

( A(q -1)+ )**= + e ( A(q -1)+ )*

nℓ

ProductdetectionE

res

Electron collision spectroscopyon multi-charged ions

Dmitry Orlov, MPI-K, PESP-08

Core excitation energies ΔE (2s–2p)

(2p3/2

10d5/2

)J = 4

(2p3/2

10d3/2

)J = 2

(2p3/2

10d3/2

)J = 3

Electron target

PRL, 100, 033001 (2008)

Photocathode

~ 0.02 meV T||

T┴

= 1.0 meV

45Sc18+

TSR – 4 MeV/u

E

EnΔE

core

1s2 2p3/2

1s22s(1s2 2p

3/2 nℓ'

j )

J

Eres

= 44.30943(20) eV (±0.2 meV, 4.6 ppm)

n = 10

100 meV

(<1% few body QED)


direct& indirectprocess

Dissociative recombination of HD+: rate spectrum

Electron collision energy (milli-eV)

Re

com

bin

atio

n r

ate

co

effi

cie

nt (

10

-9 c

m3

s-1)

kT ~ 2 meV(CRYRING data)

Model cross section withkT ~ 0.5 meV, kT

|| ~ 0.02 meV

TSR e-target with cryo-photocathode

HD+ (1sσ, v = 0, J ) + e → HD** (1sσ nℓλ , v'J' ) → H(n) + D(n' )

PRL 100, 193201 (2008)

Rotational resolution (DR rate)

-e

+ eAB + -

B*A +

(AB +)* + nℓ = AB **

Vibration v=0 -> 1 0.15 eVRotation j=0 -> 1 4.5 meV


Dissociative recombination of HF+: 2D imaging

Electron - Target

~ 12 m

vbeam (~MeV)

~cm

detector surface

Pro

bab

ilit

y (n

orm

aliz

ed)

d2D [mm]

Rotational resolution

Particle distance, mm60 2 4 8 10

EKER – ECM-kT, milli-eV50 20 50 100

PRELIMINARY

HF+ (X 2, v=0 ,J ) + e- HF**(V 1+) H(n=2) + F(2P3/2,1/2)

HF**(V 1+)

v=0

J=0,1,2,….

H(n=2) + F(2P3/2)



cold e-beams



7Manipulation with



CSR cooler

2 E-cooling


3electron collision


4Why?



Electrostatic Cryogenic Storage Ring at 2 K

Reaction microscope

Ion injection

E-target

Diagnostic section

neutrals CSR

Clusters, biomolecules

(M up to few 1000 amu)

ELECTROSTATIC

Storage Rings

(no mass limitation)

Ring Circumference

34 m

Straight Section Length

2.5 m

Energy Range 20 - 300

keV

Maximum Beta h/v

12/6 m

Maximum Dispersion

2.1 m

Tunes Qh/Qv 2.59/2.65

XHV (n<103 cm-3)

M= 1-100(1000) amu

Electrostatic Storage Ring

T=10 (2K)

Electron collision energy (milli-eV)

Re

com

bin

atio

n r

ate

co

effi

cie

nt (

10-9

cm

3 s

-1)

kT ~ 2 meV(CRYRING data)

Model cross section withkT ~ 0.5 meV, kT

|| ~ 0.02 meV

TSR e-target with cryo-photocathode

T< 10 K is required

after some second storage

after production in the ion source

Boltzmann distribution (300 K @ TSR)

rotational quantum state

vibrational quantum stateHD+ + e- H + D



cold e-beams



7Manipulation with



CSR cooler

2 E-cooling


3electron collision


4Why?



Features of low-energy e-beams (A)

2/32/3

10011

V

U

Perv

PmAPUI

1. Low voltage Low current @ density

2/3

220

cM

Tk

LZn

MC

e

eB

Ce

ionCOOL

High-perveance?

28028

0.281.8

0.03

0.10.0021.63001000.30.015.1300323.20.45430030.70.0211201102.11653001

Electron density

[10 6 cm -3]

Electron current

[mA]

Electron energy

[eV]

Ion energy[keV]

Ion mass[amu]

Cooling time (cold beam)

[s]P=1 μPerv

kBTe=1.0 meV

Lc=3.3

C=0.028


Features of low-energy e-beams (B)

Photoelectron source Low T║

2. Low voltage High kT||

3. High Bguid

Better for slow electrons Strong ion deflection

heatingplasmaeU

TkkT C

2

22

||

Electron energy W, eV

thermocathode

photocathode

1e-06

1e-05

1e-04

10 100

1e-03

{avoid beam divergence; suppress TLR; adiabatic transport}

2/1

100

1002.21

V

U

B

GmmC


New Concept for the CSR Electron Cooler/Target

toroid merging Dipole merging

1-2 G 30 G

We need to cool 20 keV protons Bmin≈20 G


Ion track

General view

New Concept for the CSR Electron Cooler/Target

Electron energy 160-1(or below) eV

Cooling solenoid length

1065 mm

Cooling solenoid radius

130 mm

Max. magnetic field 150 Gauss

Toroid bending radius

200 mm

Merging box solenoid

Racetrack 330x540 mm, length 350 mm

Merging box vertical dipoles

Racetrack 268x360

Merging Box

toroid merging Dipole merging

1-2 G

ZkeV

WAGB ion

C

1

20130

30 G

We need to cool 20 keV protons Bmin≈20 G


Adiabatic electron transport

1

z

B

Bz

Z

L

T

Adiabatic criterion

2

3028

G

BeVBECScaling rule for critical energy

Finite element analysis with TOSCA code

Cross-sections of Heating of paraxial beam

EeB

meL

22 - Larmor length

1.0

z

B

Bz

Z

LHeating start at app.

Adiabatic motion

Transverse temperature

cathbb

TkTk

For modeled field geometry

15 20 25 30 35 40 45 50 55 60 65 120 150 180 210 240

1

10

EC

30 Gauss

kTT

R ,

me

V

Beam energy, eV

60 Gauss

EC

initial kTTR

= 0.5 meV

kTcath

= 10 meV

= 20

1234567

0

30

60

90

120

150

180

210

240

270

300

330

1234567

Etr, meV

Ra

diu

s, m

m

0.5416

0.5448

0.5480

0.5512

0.5545

0.5577

0.5609

0.5641

0.5673

Electron energy 20 eV, B = 30 G

Etr~0.02meV

Results of e-tracking calculation (TOSCA code)

kT┴0



cold e-beams

7Manipulation with



CSR cooler

2 E-cooling


3electron collision


4Why?





Low-energy cooling of CF+ cooling by 53 eV electrons

vC,total

vF,total

vbeam

vC

d3D d2D

C

F

vbeam

CF +

Detectorsurface

ve

vC

vF

e-

vC,total

vF,total

vbeam

vC

d3D d2D

C

F

vbeam

CF +

Detectorsurface

vC,total

vF,total

vbeam

vC

d3D d2D

C

F

vbeam

CF +

Detectorsurface

ve

vC

vF

e-

Themocathode, September 2006, 0eV, 12-30 s

Photocathode, March 2007, 0eV, 12-30 s

CF

CF

Electron-target

Photocathode T~ 1.0 meV

I = 0.34 mA

ne=3∙106 cm-3

x [mm]-10 0 10 20 30 40 50 60 70

y [

mm

]

-10

0

10

20

30

40

50

hh3Entries 59917Integral 5.991e+004

hh3Entries 59917Integral 5.991e+004

0

10

20

30

40

50

60

70

80

Center of mass distribution

Photocathode

Themocathodecenter-of-mass

12-30 sEcm = 0 eV

center-of-mass12-30 s

Ecm = 0 eV


CF+– cooling time

2

4

6

8

10

0

5

10

15

20

25

0 2 4 6 8 10 12

FWH

My,

mm

0

0 2 4 6 8 10 12 6 0 2 4 8 10 12

x=1.8 s

Cooling time, s

FWH

Mx,

mm

55

1 mm

1 mm

Cooling time, s

0

0

Y, m

mX

, mm

55

y=1.4 s

vC,total

vF,total

vbeam

vC

d3D d2D

C

F

vbeam

CF +

Detectorsurface

ve

vC

vF

e-

vC,total

vF,total

vbeam

vC

d3D d2D

C

F

vbeam

CF +

Detectorsurface

vC,total

vF,total

vbeam

vC

d3D d2D

C

F

vbeam

CF +

Detectorsurface

ve

vC

vF

e-

C F

Y, m

m

X, mm

TSR

Photocathode, March 2007

• Current: 0.34 mA• B-expansion: 20• ne=3∙106 cm-3

• T┴ =1.0 meV cool < 2 s

Detector (X/Y): σ 0.4 / 0.3 mm

Ion beam: X Y

ε 2.5∙10-3 0.9∙10-3 mm∙mrad

σ 200 37 μm ΔP/P 2.5∙10-5 2.5∙10-5

x=1.8 s

y=1.4 s

1 mm

1 mm



cold e-beams


CSR cooler

2 E-cooling


3electron collision


4Why?




7Manipulation with



Manipulation with magnetized eV-electrons

Wcathode

Wemission

Wmetal

SC

Ekin

V0

V

Wmetal

SCEF

EDC, log. scale

Ekin

Cathode

Drift tubes

TSR target

Cathode

Collector



Ekin = q(V0V)(WmetalWemission)SC

1. Work function difference

2. Space charge at the cathode

3. Space charge SC(Ie, V) in the interaction region can be calculated independently.

Wcathode

Wemission

Wmetal

SC

Ekin

V0

V

Wmetal

SCEF

EDC, log. scale

Ekin

Cathode

Drift tubes

To collector

TSR target

Drift tubesCathode

Collector

Ekin ≠ q(V0V)

29



EF

Wemission

V0

V

Wmetal

SC

Ekin

To collectorDrift tubesCathode

Cathode

Drift tubes

Collector

V0=20 V

Ie=3µA

Ie=40 pA

(WmetalWemission)SCEkin

A

B

A

B

30



EF

Wemission

V0

V

Wmetal

SC

Ekin

To collectorDrift tubesCathode

Cathode

Drift tubes

Collector

V0=20 V

Ie=4.5 µA

Ie=40 pA

(WmetalWemission)SCEkin

A

A

Ekin, eV 2.3 1.4 1.0 0.48

I, μA 34.5 21.3 13.2 4.5P, μPerv 9.8 12.5 12.8 13.6


1HOW TO:

cold e-beams


CSR cooler

2 E-cooling


3electron collision


4Why?




7Manipulation with


THANK YOU !

Questions?



Electron beam formation – adiabaticity

adiabaticity: dB/dz, dE/dz small against cyclotron length

2/1

100

1002.21

V

U

B

GmmC

Bg

Cathode, -100 V Extraction electrode, 0 V

80

50

φ=100

CathodeEntrance,

extraction electrode

80 G

320 G

40 G

Typical transition lengths 100 – 200 mm ζ=0.1-0.2 2/1

100100

V

UGBC

Higher adiabaticity Low energies


Acceleration sectionAcceleration section

CollectorCollectorToroidToroid

TSR dipoleTSR dipole

Interaction Interaction sectionsection

electron beam

Ion beam

Correction dipolesCorrection dipoles

RailsRails

Electron target at TSR

PreparationPreparationchamberchamber

(photocathode)(photocathode)

Documents

Ultracolod Photoelectron Beams for ion storage rings