ECFA-DESY workshop, NIKEF 1 st April, 2003Nick Walker, DESY Energy Spread Measurement in the TESLA Extraction Line Nick Walker - DESY

ECFA-DESY workshop, NIKEF 1 st April, 2003Nick Walker, DESY Introduction Question: can we accurately measure the energy spread (RMS) or energy distribution of the beam using a profile monitor in the current TDR extraction line First ‘peek’ at problem What do we really need for the physics?

ECFA-DESY workshop, NIKEF 1 st April, 2003Nick Walker, DESY Extraction Line Concept strong final doublet electrostatic separator thin-bladed septum strong dipoles strong chromaticity of FD in conjunction with large disrupted emittance and energy spread will cause us problems

ECFA-DESY workshop, NIKEF 1 st April, 2003Nick Walker, DESY Extraction Line Optics ‘best’ (?) location linear dispersion

ECFA-DESY workshop, NIKEF 1 st April, 2003Nick Walker, DESY Extraction Line Apertures Ø120 mm strong dipole magnet

ECFA-DESY workshop, NIKEF 1 st April, 2003Nick Walker, DESY What do we want to measure? Angles at IPEnergy Distribution red: E<140 GeV disrupted beam for a design head-on collision

ECFA-DESY workshop, NIKEF 1 st April, 2003Nick Walker, DESY ~65% of beam ~35% of beam has y  5mm What we see at QED2 projection

ECFA-DESY workshop, NIKEF 1 st April, 2003Nick Walker, DESY What we see at QED2 Vertical DistributionIntegrated  42mm = 1% ~4 orders of magnitude in signal

ECFA-DESY workshop, NIKEF 1 st April, 2003Nick Walker, DESY Estimating Energy Distribution First we need the dispersion relation (from simulation) linear dispersion blue: reconstructed red: actual Use fit to map y measurements to energy

ECFA-DESY workshop, NIKEF 1 st April, 2003Nick Walker, DESY Estimating Energy Distribution ActualMeasuredError E mean  10  5 E RMS  10  GeV Emittance of disrupted beam will cause significant error if we need to get accurate measurements around energy peak (i.e. 250 GeV) AND that’s not all… misleading: really only a relative measurement (will need precision spectrometer to locate edge)

ECFA-DESY workshop, NIKEF 1 st April, 2003Nick Walker, DESY Simulation represents Best Possible Case realistic beams (not design collisions) error in calibration curve for y-energy –how to do this (non-linearity a problem?) –Is simulation good enough? effects of magnet misalignments and beam jitter: –within bunch train (fast feedback) –train to train (5Hz) How to measure? –laser wire (scan range?) –mechanical wire (survivability?) What do we really need to measure?