Abstracts Brochure - CERN

TUPCH — Poster Session 27-Jun-06 16:00 - 18:00
Laser-based Beam Diagnostic for the Front End Test Stand (FETS) at RAL
High power proton accelerators (HPPA) are
required for several future projects like spallation
sources or a neutrino factory. Compared
with existing machines the beam
power therefore has to be increased by a fac-
C. Gabor (IAP) D.A. Lee (Imperial College of Science and Technology,
Department of Physics) A.P. Letchford (CCLRC/RAL/ISIS)
J.K. Pozimski (CCLRC/RAL)
tor of 30. The Front end test stand at RAL is being built to demonstrate that a chopped Hminus beam of 60 mA at
3 MeV with 50 pps and sufficiently high beam quality, as required for all proposed Proton drivers, can be built. For
the test stand a comprehensive set of beam diagnostics is also required. Due to the high beam energy and power
non destructive diagnostic methods are favorable. Hminus beams offer the possibility to use intense laser light to
detach the additional electron and use the produced particles for beam diagnostics. The principle is appropriate to
determine the transversal beam density distribution as well as the transversal and longitudinal beam emittance in
front and behind the RFQ. A detailed layout of the beam diagnostics including a discussion of the predicted spatial
and temporal resolution and the dynamic range of the proposed devices will be presented.
Layout of the Diagnostic Sections for Emittance and Energy Spread Measurements at the
European XFEL
High brightness electron bunches are necessary
at the European XFEL to obtain high C. Gerth, M. Roehrs, H. Schlarb (DESY)
gain and saturation in the SASE process during
a single pass through a long undulator. Special online diagnostic and feedback tools have to be developed to
monitor and stabilise the relevant beam quantities with sufficient precision along the accelerator. Collective effects
such as space-charge forces and coherent synchrotron radiation in bunch compressor magnets, and transverse wake
fields in the superconducting cavities may lead to a longitudinal deformation of the electron bunches. The longitudinal
charge distribution, slice energy spread and slice emittance are the most critical parameters for the SASE process.
These parameters can only be determined by means of time-resolved techniques. The layout of the two diagnostic
sections, located downstream of the magnetic chicanes for bunch compression, is discussed. Emphasis is put on
design considerations for slice emittance and energy spread measurements.
Principles of longitudinal beam diagnostics with coherent radiation
The Kramers-Kronig dispersion relation connects
the real and imaginary part of a re- O. Grimm (DESY)
sponse function under very general assumptions.
It is used in the context of accelerator physics for longitudinal bunch diagnostics as a phase retrieval technique:
the modulus of the complex form factor (the Fourier transform of the charge distribution) is accessible experimentally,
and the missing phase then (partially) reconstructed to allow an inversion of the Fourier transform. Contrary to real
and imaginary part, the connection between modulus and phase is not unique anymore due to the possibility of zeros
of the form factor in the complex frequency plane that cannot be measured. This paper gives a mathematically explicit,
step-by-step derivation of the phase reconstruction technique for bunch diagnostics, and it explains the problem of
zeros and their practical effect with some examples. The intention is not utmost mathematical rigour, but a clear,
accessible explanation of all steps involved.
165
TUPCH019
TUPCH020
TUPCH021