# Presentation: 456U5RSC65JCABWK55TRDSJ5XYMOZFKV

## A Possible Test in the FFTB of Undulator Based Positron Sources Friday May 10, 2002R. Pitthan and J. Sheppard

## Contacts

- Roger Carr, SSRL
- Max Cornacchia, SSRL
- Ralph Nelson, SLAC RP
- Roman Tatchyn, SSRL
- Helmut Wiedemann, SSRL
- Klaus Flöttmann, DESY
- Alexander Mikhailichenko, Cornell
- Yuri Batygin, SLAC NLC
- Vinod Bharadwaj, SLAC LCLS/NLC
- Artem Kulikov, SLAC PEPII
- David Schultz, SLAC NLC
- Maria Caturla, LLNL
- Werner Stein, LLNL

## .

## Positron Sources for Linear Colliders

**Positron Sources for Linear Colliders**

## NLC Positron Production

**NLC Positron Production**

## NLC Positron Source

- N+ = 1.8x1014 e+/s
- 6.2 GeV e- drive beam
- 4.5 R.L. WRe targets
- Needs 3 separate targets to handle peak stress
- Acceptance = 0.03 m-rad (0.045 m-rad preDR)
- Yield =1
- Cumbersome at best;
- Problematic wrt Train Uniformity
- “Detailed” engineering required for train assembly scheme

## Tesla, Unpolarized(K. Flöttmann)

- Planar wiggler ~100 m

## Tesla Positron Source

- N+ = 2.8x1014 e+/s
- 1.34 cm period planar undulator
- K=1
- L= 100 m
- 160 GeV < E- < 250 GeV
- 0.4 R.L Ti-alloy target
- Acceptance = 0.048 m-rad
- Yield =1
- Question operability at lower end of electron energy range
- Not Polarized in the Tesla Baseline
- (Polarization as a possible upgrade path)

## Decision to put development of NLC conventional e+ source on hold so as to investigate the feasibility of a polarized positron source for the NLC

- Looking into the use of a K=1 helical undulator and 150 GeV NLC primary electron beam; keeping options open

- Direction of Present NLC Positron Effort

## Slide 10

## Production Issues

- Photon Production:
- 	flux, , polarization, field, gap, and length
- 	Electron beam dilutions: , E, e, 	depolarization
- 	(xw = 4.3 nm; w = 2 rad)
- 	 (x = 20 m; x’ = 0.2 rad)
- 	(E=3 GeV (1.2%), e=0.15% w (0.05%w/o)
-       xw/o errors; = 2/1x10-3 x/y w/ errors
- Collimation: not so important for unpolarized positron  	         production
- Target:Yield, emittance
- 	Material Choice and thickness
- 	Power handling: peak and average
- 	Incident photon beam size

## Production Issues

- Collection:
- 	Adiabatic Matching Device: different 	optimization from electron based production due 	to broader positron spectrum
- 	Concerned about beam loading in the initial 	capture region prior to e+/e- separation because of 	large particle flux, including the presence of 	electrons (this is also an issue in the 	conventional design)
- Diagnostics:
- 	Not much to say; this is more interesting in the 	case of polarized positron production; bad energy 	range for polarimetry; very difficuly to test
- Overall Proof of Principle:
- 	Every reason to expect the basic e- to  to e+
- 	conversion to work as imagined; polarized e+
- 	production will benefit from a demonstration

## NLC Polarized Positron System and e- Main Linac Layout

- NLC Polarized Positron System and e- Main Linac Layout

## NLC Polarized Positron System Layout

## NLC Polarized Positron Source Systems Layout

## NLC Polarized Positron Target Station Layout

## What’s Going On? What’s the Status?

- Undulator: K=1,** ********u** = 1.4-0.7 cm, helical
- Search for an Optimization: Eb, ******u**, K,target material and thickness, collection scheme
- Photon Beam Specification
- Target Studies: Ti-alloy: hydro and radiation damage launched at LLNL
- Effect on primary electron beam studies, begun; thinking about commissioning and operating scenarios
- Open also to compton based photon sources (lasers and FELs)

**What’s Going On? What’s the Status?**

## NLC Polarized Positron Photon Beam Specification

**NLC Polarized Positron Photon Beam Specification**

## Use of a Microundulator to Study Positron Production

**Use of a Microundulator to Study Positron Production**

## An Immodest Proposal

- Measure the yield, spectrum, and polarization of both the photons and positrons

**An Immodest Proposal**

- Do this in the next 22-42(?) months in the FFTB enclosure:
- Proof of Principle Demonstration
- Validate Codes
- Develop  Spin Diagnostics
- Develop e+ Spin Diagnostics
- Maybe Get a Surprise (better not)

## What’s the Big Idea?

_**Goals:**_
- demonstrate the viability of undulator based positron production, both polarized and unpolarized
- measure the yield, spectrum, and polarization gammas and  positrons.
- design (steal, borrow) conversion, collection, and detection systems
- validate the microundulator-photon production codes
- Many opportunities for collaboration amongst collider laboratories, and including experimenters from both the colliding physics and the fixed target physics communities who are experts in polarimetry.  The discussion should include plans for the development of such a collaboration.

## What are the Possibilities (1)?

**What are the Possibilities (1)?**
- SLAC single bunch electron beam: *N**e* = 1x1010 *e**-**/bunch,*
*E**e** = 50 *GeV*, *and* ****x**=****y**= *1.5x10-5*m-rad*
- For a helical undulator with

## What Are the Possibilities (2)?

- In this energy region, *h****Y**p*, the yield of positrons  from ’s incident on 0.4 r.l. of Ti, is about 0.025 e+/photon.
- For N- = 1x1010 e- per bunch, the expected yield of e+ is then

**What Are the Possibilities (2)?**

## Positron Polarization as a function of Positron Energy

## Positron Spectra for Different Ti Target Lengths

## Positron Polarization for Different Ti Lengths

## Positron Polarization for Different Ti Lengths

## What Does the Hardware Look Like?

**What Does the Hardware Look Like?**

## FFTB Beams

- Size <50 m to thread through a narrow sub-mm-gap undulator
- Divergence < 1/

- Critical parameters in red

## What is Required

** **A fully modeled experiment which simulates 	results and identifies hardware requirements
-  Beam line design to determine accelerator 	hardware specifications
-  Cost and schedule development
-  Acceptance of proposal and release of funds
-  Construction, Installation, Checkout, and 	Commissioning
-  Do experiment and compare with simulations

## Collaboration Building

-  Determine Institutional Interest
-  Discuss Who Contributes What
-  What is required to get 	commitments
-  When can commitments be made
-  When and where do we meet again 	and for what purpose?

## Summary

- No Summary, Just Discussion.