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

Energy Spread Measurement in the
TESLA Extraction Line
Nick Walker - DESY
Nick Walker, DESY
ECFA-DESY workshop, NIKEF 1st April, 2003
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?
Nick Walker, DESY
ECFA-DESY workshop, NIKEF 1st April, 2003
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
Nick Walker, DESY
ECFA-DESY workshop, NIKEF 1st April, 2003
Extraction Line Optics
‘best’ (?) location
Dy /  y
linear dispersion
Nick Walker, DESY
ECFA-DESY workshop, NIKEF 1st April, 2003
Extraction Line Apertures
strong dipole magnet
Ø120 mm
Nick Walker, DESY
ECFA-DESY workshop, NIKEF 1st April, 2003
What do we want to measure?
Angles at IP
Energy Distribution
red: E<140 GeV
disrupted beam for a design head-on collision
Nick Walker, DESY
ECFA-DESY workshop, NIKEF 1st April, 2003
What we see at QED2
projection
~65% of beam
~35% of beam has y<-5mm
Nick Walker, DESY
ECFA-DESY workshop, NIKEF 1st April, 2003
What we see at QED2
Vertical Distribution
Integrated
~4 orders of magnitude
in signal
-42mm = 1%
Nick Walker, DESY
ECFA-DESY workshop, NIKEF 1st April, 2003
Estimating Energy Distribution
First we need the dispersion relation
(from simulation)
Use fit to map y measurements
to energy
blue:
red:
y =27.0 - 1.08E  0.00396 E 2
reconstructed
actual
linear dispersion
Nick Walker, DESY
ECFA-DESY workshop, NIKEF 1st April, 2003
Estimating Energy Distribution
Actual
Measured
Error
Emean
241.529
241.525
210-5
ERMS
13.87
13.09
310-3
misleading: really only a
relative measurement
(will need precision
spectrometer to locate
edge)
248-250 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…
Nick Walker, DESY
ECFA-DESY workshop, NIKEF 1st April, 2003
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?
Nick Walker, DESY
ECFA-DESY workshop, NIKEF 1st April, 2003