Energy Spread Measurement in the TESLA Extraction Line

1
Energy Spread Measurement in the TESLA Extraction
Line

• Nick Walker - DESY

2
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?

3
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
4
Extraction Line Optics
5
Extraction Line Apertures
6
What do we want to measure?
red Elt140 GeV
disrupted beam for a design head-on collision
7
What we see at QED2
8
What we see at QED2
Vertical Distribution
Integrated
4 orders of magnitude in signal
-42mm 1
9
Estimating Energy Distribution
First we need the dispersion relation(from
simulation)
Use fit to map y measurementsto energy
blue reconstructed red actual
10
Estimating Energy Distribution
misleading really only a relative
measurement (will need precision spectrometer to
locate edge)
Actual Measured Error Emean 241.529 241.525 2?10-
5 ERMS 13.87 13.09 3?10-3
Emittance of disrupted beam will cause
significant error if we need to get accurate
measurements around energy peak (i.e. 250
GeV) AND thats not all
11
Simulation representsBest 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?