GAMMA BASED POSITRON SOURCE OPTIONS FOR ILC Klaus Floettmann DESY

transcript

K. Floettmann KEK, Nov. 13-15, 2004

GAMMA BASED POSITRON SOURCE OPTIONS FOR ILC

Klaus Floettmann

Contents:

§ Basics of gamma based sources

§ Status of work

§ Who wants to Do What?

Conventional vs. Gamma Based Source

Target

Photons 10-20 MeV

Electrons 0.1-10 GeV

Primary Beam Capture Optics

thin target: 0.4 X0

thick target: 4-6 X0

Parameters of existing and planed positron sources

rep rate# of bunches per pulse

# of positrons per bunch

# of positrons per pulse

TESLA/ILC 5 Hz 2820 2 · 1010 5.6 · 1013

NLC 120 Hz 192 0.75 · 1010 1.4 · 1012

SLC 120 Hz 1 5 · 1010 5 · 1010

DESY positron source

50 Hz 1 1.5 · 109 1.5 · 109

The Problem: Target Heating

MeV cm

1 capture efficiency

heat capacity

source area

deppos

Number of Positrons / Source Area

Example of the rotating target for TESLA:

0.8 m diameter

1250 revolutions per minute

52 m/s on the circumference

4 cm in a pulse train of 0.8 ms

Conceptual design for a rotating feed-through:“A Megawatt Electron Positron Conversion Target – A Conceptual Design” 1st EPAC Rome 1988

Heat Capacity of the Target Material

Low Z materials have a higher heat capacity (Dulong Petit Rule)

high Z materials give a higher positron yield.

Positron Yield vs. Target Thickness for a Photon based Source

"Structural Modeling of Tesla TDR Positron Target," Werner Stein, John C. Sheppard, July 2002 (SLAC-TN-03-043)

Radiation Damage Material Test at BNL

collaborative effort of SLAC and other labs

NOTE: Gamma based sources produce significantly less neutrons than conventional sources.

How to Increase the Capture Efficiency?

Increase the acceptance of the capture optics

requires a Predamping ring with large acceptance

Improve the positron emittance

photon based positron source with thin target

Transverse momenta

conventional source

thin target source

Comments concerning the DR design

Present situation: on energy acceptance is ok, off energy acceptance is too small

• improve off energy acceptance

• investigate possibilities to reduce the energy spread by scraping or removing correlations

Better communication between DR people and positron people is required

• assumed positron distributions seem to be too pessimistic sometimes

• realistic distributions should be used as input

Operation of a gamma based positron source without predamping ring should be possible

Undulator Based Positron Source

• Undulator length depends on the integration into the system, i.e. the distance between undulator exit and target which is required for the beam separation:

• ~ 50-150 m

Integration of the Source into the BDS of TESLA

Auxiliary and Commissioning source

“Conceptual Design of a Positron Pre-Accelerator for the TESLA Linear Collider” TESLA-99-14“Conceptual Design of a Positron Injector for the TESLA Linear Collider” TESLA-00-12

Low energy operation

50 100 150 160 200 250Electron energy (GeV)

safety margin

used positrons

5 Hz operation2.5 Hz operation

Low energy operation

0.0E+00

5.0E+33

1.0E+34

1.5E+34

2.0E+34

2.5E+34

3.0E+34

3.5E+34

4.0E+34

100 150 200 250 300 350 400 450 500

Ecm (GeV)

) scaling (fundamental)

nominal5 Hz operation

2.5 Hz luminosityoperation

High-energy optimised sourceLow-

energy optimised source

NOTE: Higher currents are possible at lower energy if the source is integrated into the BDS (limited by DR)

Auxiliary and Commissioning Source

500 MeV electron source provides low intensity (~1%) e+ source but same bunch train• commissioning source

• standby source for MD when e- system is down• e-e- and physics options source

Design of the Positron Preaccelerator

The capture optics

low frequency (L-band)

Ø large iris radius

Ø long wave length

Adiabatic Matching Device - AMD

Very basic design considerations by BINP Novosibirsk (internal report):

• long pulse seems to be possible

• problem is to achieve the required field quality

NC High Gradient Cavities (solenoid focusing)

Design by INR Troitsk

Optical functions in the Separator Section

• separation of photons, positrons and

electrons

• longitudinal collimation of the positron bunches

• transverse collimation can be done in the

solenoid section

aim for no particle loss during injection into

NC Low Gradient Cavities (triplet focusing)

Design by INR Troitsk

Phase Space at the exit of the Preaccelerator

Positron Transfer Line

Acceleration to 5 GeV in SC Cavities

Polarized Positron Sources

For the production of polarized positrons circularly photons are required.

Methods to produce circularly polarized photons of 10-60 MeV are:

• radiation from a helical undulator

• Compton backscattering of laser light off an electron beam

Why polarized positrons

Physics potential beyond the scope of this workshop but we can gain a factor of two in the interaction rate (eff. luminosity) by using

polarized electron and positron beams

Polarization Transfer in Pair Production

Super Conducting Design

• Ribbon-wire wound in a double helix

Current

Polarization vs. Emission angle

Model of the Prototype Helical Undulator at Daresbury

Compton Backscattering based Positron Source

GLC Polarized Positron Source Design

Multi Collision Point Layout

GLC Collision Region

10 collision sections, with 20 collision points each:

200 collision points

E-166 Demonstration Experiment for a Polarized Positron Source

About 47 members from 17 institutions:

Brunel, CERN, Cornell, DESY, Daresbury, Durham, Jefferson, Humboldt, KEK, Princeton, South Carolina, SLAC, Tel Aviv, Tokyo M.U., Tennessee, Wasada, Yerevan

• Final Focus Test Beam (FFTB) at SLAC with 50 GeV Electrons.

• 1 m long helical undulator produces circular polarized radiation of up to 10 MeV.

Undulator Parameter for Polarized Positron Source

Parameter TESLA E-166

Length ~150 m 1 m

Beam 200 GeV 50 GeV

Period 14 mm 2.4 mm

B-field 0.7 T 0.76 T

Energy of first Harmonic

20 MeV 9.6 MeV

Positrons/bunch 3 · 1010 2 · 107

Pulsed Undulator for E-166

• Inner diameter 0.89 mm

• Magnetic field: 0.76 T

• Pulsed current: 2.3 kA

• Rate 30 Hz

• Conversion of photons to positrons in 0.5 X0 Ti-target• Measurement of polarization of photons and positrons by Compton transmission method• Expected polarization ~50%

• E166 is a demonstration of production ofpolarized positrons for future linear colliders

• Uses the 50 GeV FFTB at SLAC• Approved by SLAC in June 2003• All components or prototypes work properly• Installation of total experiment in FFTB tunnel in

August 2004• First data taking run in October 2004• Second data taking in February 2005

Experiment@KEK

1.) Production of polarized γ‘s and polarized e+

• pol. γ: finished 2002

• pol e+: underway

2.) Polarimetry

• polarimetry of short pulse & high intensity γ rays established

• same method applicable for polarized positrons

Who wants to Do What? (to be completed)

ASIA• contributions to E166

• conceptual design for a polarized positron source for ILC (simulation study) KEK: Y. Kurihara, T. Okugi, J. Urakawa, K. Yokoya, T. Omori Tokyo Metropolitan Univ.: K. Dobashi National Institute of Radiological Sciences: I. Sakai Waseda Univ.: T. Aoki, M. Washio, T. Hirose Sumitomo Heavy Industries: A. Tsunemi

• experimental production of polarized positron at ATFKEK: Y. Kurihara, T. Okugi, J. Urakawa, T.Omori Tokyo Metropolitan Univ.: A. Ohashi National Institute of Radiological Sciences: M. Nomura, M. Fukuda Waseda Univ.: I. Yamazaki, K. Sakaue, T. Saito, R. Kuroda, M. Washio, T. Hirose

Europe• EuroTEV (s. talk by E. Elsen)

• contributions to E166

• interest to continue work on preaccelerator: beam dynamics, structures, diagnostics INR Troitsk: V. Paramonov

• synergies with FEL work at DESY: NC structure design, code development, beam dynamics

USA• E166

SLAC, collaborators: John Sheppard et al.

• conceptual positron source design SLAC, collaborators: John Sheppard et al.

• material tests SLAC and collaborators: John Sheppard et al.

• more from SLAC ??????

• beam dynamics simulations/experiment ANL: Wei Gei et al. Fermilab: Philippe Piot et al.

Workshop Announcement

'Workshop on Positron Sources for the International Linear Collider‘

This workshop will discuss relevant issues for positron production for the ILC

Daresbury Laboratory

11th to 13th April 2005

http://www.astec.ac.uk/id_mag/ID-Mag_Helical_ILC_Positron_Production_Workshop.htm

GAMMA BASED POSITRON SOURCE OPTIONS FOR ILC Klaus Floettmann DESY

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