ERL2013 - List of Authors (Evtushenko, P.E.)

Paper

Title

Page

WG402

Time-Resolving Laser Wire for Large Dynamic Range Measurements - Design Considerations

P.E. Evtushenko, M. Marchlik
JLAB, Newport News, Virginia, USA

Funding: Work supported by US DOE office of Basic Energy Sciences under the early career program; DOE award number FWP#JLAB-BES11-05
Better diagnostics and understanding of beam halo are needed for high average current CW SRF electron linacs. Here longitudinal beam halo upstream of the linac evolves in to transverse halo downstream of the linac. A diagnostic for measurements longitudinal phase space distribution with large dynamic range (LDR) is needed for proper setup of an injector and better understanding of beam halo formation. In addition, one of unsolved ERL's diagnostic problems is the transverse beam size monitoring of a high average current, few MeV energy beam. We present our design for a Thomson scattering based CW laser wire system for LDR transverse beam profile measurements. It is designed to be used with CW beam starting with an average current of about 150 mkA, but can, as it is non-destructive and non-intercepting, be use at any average current. When implemented in a dispersive section it can be used for energy distribution measurements. Using a short pulse laser adds time resolution to the diagnostic. Combining time and energy resolution, the system will allow measurements of the longitudinal phase space distribution while keeping the LDR due to the counting nature of the detection scheme.

Slides WG402 [1.148 MB]

WG404

Optical System with Image Intensifier and Spatial Filters for Large Dynamic Range Transverse Beam Profile Measurements

P.E. Evtushenko
JLAB, Newport News, Virginia, USA

Funding: Work supported by US DOE office of Basic Energy Sciences under the early career program; DOE award number FWP#JLAB-BES11-05
We have previously reported * on transverse beam profile measurements where dynamic range (DR) was increase by a factor of 100 from typical 500 to about 5.0·10⁺⁴. It was shown that for non-equilibrium beam with non-Gaussian transverse distribution the RMS beam size can depend significantly on the DR used for calculations. Consequently, measured emittance and Twiss parameters depend on the DR as well. For the optical system used in * diffraction limits the DR at the level slightly above the 5.0·10⁺⁴ used in measurements. For further increase of the DR spatial filters needs to be used in a way similar to original solar coronagraph ** and its application to the synchrotron radiation measurements ***. To increase overall sensitivity to allow large dynamic range measurements with low duty cycle tune-up beam, our systems includes an image intensifier. On contrary to a coronagraph-like scheme, where central bright part of the distribution is not measured, our systems is intended for simultaneous, complete distribution measurements including the bright core and low amplitude halo, which is needed for proper beam size measurements. Here design considerations for the system are presented.
* P. Evtushenko et al., in Proceedings of FEL2012
** B. F. Lyot, Month. Notice Roy. Ast. Soc, p580, 99 (1939)
*** T. Mitsuhashi, "Beam halo observation by coronagraph", Proceedings of DIPAC05

Slides WG404 [1.745 MB]

WG501

Experience with Unwanted Beam at Jefferson Lab

P.E. Evtushenko
JLAB, Newport News, Virginia, USA

We attempt to review operational experience of Jefferson Lab accelerators related to beam halo and beam loss. We divide the beam halo in to four categories based on its origins. These are: 1 – beam halo evolving due to non-linear beam dynamics, 2 – beam due to the field emission in LINAC cavities and in the electron source, 3 – beam due to the drive laser “ghost” pulses, which are the laser pulses present in the system due to finite extinction ration of the electro-optical cells used to reduce the repetition rate of the drive laser, 4 – beam due to the scattering of the drive laser in its transport system and on the cathode as well as due to parasitic light in reaching the cathode. Independent of its source the beam loss can be acute with relatively high intensity, which is sufficient to damage accelerator components within a very short time, and chronic with much lower intensity that does not prevent accelerator operation but can cause damage in a long term. The acute beam loss must be mitigated by the machine protection system. The chronic beam loss is partially mitigated (to acceptable level) by limiting the accelerating gradient of the LINAC and the electron gun, but ultimately can be improved by building accelerator components with onset of the field emission at higher gradient and understanding of the beam dynamic with a very high dynamic range in mind.

Slides WG501 [3.566 MB]