Towards an Undulator Based NLC Positron Source

Transcription

1 Towards an Undulator Based NLC Positron Source Tuesday June 26, 2002 LCD Meeting, SLAC R. Pitthan and J. Sheppard

2 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 2

3 Concepts 3

4 Change in Direction of NLC Positron Effort Put development of NLC conventional e+ source on hold Use resources to investigate the feasibility of a polarized positron source for the NLC Look into the use of a K 1 helical undulator and 150 GeV NLC primary electron beam for polarized positron production Because of drawback of coupling e + production to primary e -, investigate other options: back scattered laser (Compton) short-period novel undulator on dedicated beam 4

5 NLC Polarized Positron System Layout 5

6 NLC Polarized Positron Target Station Layout 6

7 Codes: Undulator: What s Going On? What s the Status? MatLab files, EGS4-Pol, BeamPath K 1, u = cm, helical Search for Optimization: E b, u, K, target material and thickness, collection scheme Photon Beam Specification Target Studies: Ti-alloy: hydro and radiation damage study launched at LLNL Effect on primary electron beam, studies begun; commissioning and operating scenarios Open also to Compton based photon sources (lasers and FELs) 7

8 Use of a Microundulator to Study Positron Production We had a discussion at LC02 to explore the possibilities of using a microundulator and the damped, 50 GeV SLAC beam in the FFTB to study positron production. Expectedly warm response from all e+ folks 8

9 An Immodest Proposal Use the SLAC 50 GeV, low emittance beam in conjunction with a 1-2 mm period helical undulator to demonstrate undulator based production of polarized positrons for linear colliders Measure the yield, spectrum, and polarization of both the photons and positrons 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) 9

10 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. Efforts for the development of such a collaboration underway. 10

11 FFTB Beams Size <50 m to thread through a narrow submm-gap undulator Divergence < 1/ Parameter Units TESLA NLC FFTB E b GeV N - /bunch - 3x x10 9 1x10 10 N bunch /pulse Pulses/s Hz K u u cm E c10 MeV N/m/e Y + % L u m N + /pulse - 8.5x x x10 7 N + /bunch - 3x x x10 7 Polarization % E b N b x = y x y x, y x', y' D σ D x σ x' 1 γ GeV e - m-rad m m rad m rad rad 50 1x x ,10 20 Critical parameters in red 11

12 Positron Polarization as a Function of Positron Energy 12

13 Positron Polarization as a Function of Positron Energy 13

14 Positron Spectra for Different Ti Target Lengths 14

15 Positron Polarization for Different Ti Lengths 15

16 Positron Polarization for Different Ti Lengths 16

17 What Does the Hardware Look Like? 17

18 What is Required A fully modeled experiment which simulates results and identifies hardware requirements Beam line designto 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 18

19 2.4 mm 0 SC, bifilar helical undulator prototype: A. Mikhailichenko Cornell Univ., 5/21/02 19

20 2.4 mm 0 SC, bifilar helical undulator prototype: A. Mikhailichenko Cornell Univ., 5/21/02 20

21 2.4 mm 0 Pulsed Cu helical undulator prototype: A. Mikhailichenko Cornell Univ., 5/29/02 21

22 Experimental Anchor Point Needed Since there is no experimental data on polarization (or loss) in scattering, propose a Testbeam Experiment in Sector 0 (the Ladder Experiment): Scatter the SLAC polarized electron e - beams by different r.l. Ti targets, measure relative polarization in the E- 158 Møller Spectrometer. Projected relative accuracy 1% (Chudakov). 22

23 EPOLEGS4: Polarized e- thru Different Targets 23

24 EPOLEGS4: Polarized e- thru Different Targets 24

25 EPOLEGS4: Polarized e- thru Different Targets 25

26 What s Going On? Need viable polarimetry for demonstration Proposal by Summer s End (2002) Thoughts on Depolarization via ionization loss? (Multiple scatter does not look to be a problem) Is electron experiment useful? Is demonstration required? What if NLC produces partially polarized e+? 26

27 Summary No Summary, Just Discussion. 27