LC e+ sources
By Takuya Kamitani
At Channeling e+ source Workshop
2003.Jan.17 at KEKComparison of the LC e+ sources1.4

Number of Beam-Pulses exposed [106]Target Destruction Issue
Energy density limit= 2.0 GeV*10 12 /mm 21.2

A1

10.8

GEA2

Survived targets
Cracked targets

B1

0.60.4

D1F2

D2
0.20

B2F10123

Beam Energy density per area [GeV*10412/mm 2 ]W75Re25 targets were irradiated by 20GeV, 16-nC e- beam at SLAC. Bychanging the beam spot size, theenergy density threshold for thedestruction was studied.
(S. Ecklund, SLAC-CN-128, 1981)Local volume Energy Density
SLAC Limit condition

CLIC DesignLocal volume density is more essentialfor the destruction.

Redection of energy density
by enlarging the beam spot size
[ 10^10 GeV / mm^3 ]Peak deposit-Energy density per volume

10**19eV/mm3/pulse
SLAC-limit(EGS4 simulation)

1.6

Energy density Limit
expected fromSLAC Experiment

1.2

e = 76 J/g
0.8

Recent Limit
expected from
SLC failed targete = 35 J/g
0.4

CLIC design
000.5

11.5

2Incident Beam radius [mm]2.53Multiple Target system
From http://www-project.slac.stanford.edu/lc/wkshp/snowmass2001/

A bunch train is separated into 3 sparse trains by the RF separator
 Each trains hit one of the three target - capture section system They are merged by another RF deflectorTESLA e+ source

Beam intensity in a pulse is too large
to irradiate directly the target material.
Instead, very high energy e- beam andundulator are used to generate
20 MeV photons.
Target material is very thin (0.4 X0) to
reduce the energy deposition, however,
sufficient for the low energy photons.

JLC Positron Source
DC Solenoid

Flux concentrator
RotatingConverter
TargetPositrons
PrimaryElectronsE(e-) = 10 GeV
N(e-) = 192x10^10150 Hz Rep. Rate

L-band Acceleratingstructure•W75Re25 target•Thickness 6.0 X0(=21mm)•Adibatic matching system
Bi = 7.0 T, Bf = 0.5 T•L-band capture section
up to 180 MeV•S-band Linac
up to 1.98 GeV•Pre-damping ring andMain damping ringat 1.98 GeV

Target Thickness Optimization
Target Thickness vs Positron Yield

0.2

Positron Yield (Ne+/Ne-/Ee-) [1/GeV]

Ne+/Ne-/Ee-[1/GeV]
E(e-) = 10.0 GeV
N(e-) = 192. x 10 10 /pulse

0.15

0.1

0.05

001234567

Target Thickness [x80]Total Energy Deposition
Target Thickness vs Energy Deposition Fraction
Total Energy Deposition / Beam Power

Total Energy Deposition / Beam Power

0.5

0.4

E(e-) = 10.0 GeV
N(e-) = 192. x 10 10 /pulse

0.30.20.1001234567

Target Thickness [x80]30% of Beam Power is deposited on the target

Local volume Energy density
100E(e-) = 10.0 GeV
N(e-) = 192. x 10 10 /pulse

Energy deposit density [Joule/gram]

90

Target Thickness
80= 6.0 x 070
60
50
40
30
1 target2 targets
3 targets
4 targets
SLC Limit

20
10
00

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5Incident e- beam size ( σ =σY) [mm]X

To makethe peak energy denisty
below the destruction limit,
very large spot size or multiple
target system is necessary.

Positron Yield vs Beam spot size

Positron Yield at PDR (Ne+/Ne-)

1.5

E(e-) = 10.0 GeV
N(e-) = 192. x 10 10 /pulse

1.25

Target Thickness= 6.0 x 0

34.5

10.75

0.5

0.25

00

1 target (sig-x=4.8)
2 targets (sig-x=3.2)
3 targets (sig-x=2.5)
4 targets (sig-x=2.1)
Design Yield
0.5

1

1.5

2

2.5

3.5

45

Incident e- beam size ( σ =σY) [mm]X

With large spot size, thepositron yield is lower.
Single or 2 target system
is not acceptable. At least,
3 target system isnecesarry.

Positron Yield Estimation
2020(Tracking simulation)
targetFC aperture
positrons

2000

After SBECS(PDR acceptance)Longitudinal acceptance = 24 mm
Energy acceptance = +/- 1.0 %20Particle Energy [MeV]Particle position in Radius [mm]2515Flux Concentrator
10Target

1980

1960

1940

1920

5
1900

0-808

16

2432

Distance from target exit [mm]4048

1880-50-40-30

-20

-100

10

Particle position in a bunch [mm]

 Positron Generation at target (EGS4)
 Positron Tracking in the capture section (SOLEIL)
 Positron Tracking in the e+ 1.98-GeV linac (SAD) Elimination with Pre-damping Ring acceptance(both in transverse and longitudinal phase space )Proposals to Channeling Experts
Design Goal of Channeling target for JLC
to replace W75Re25 to crystal
Comparable positron yield with
1/3 of Peak energy density

Search for the target material (crystal or hybrid)
which generates sufficient positrons andcomfirm it experimentally
 Establish the channeling simulation code whichis consistent with the experimentsTo generate sample particles for realstic yield estimation
To estimate the energy density distribution in the target