UMD, College Park, Maryland, USA
The University of Maryland Electron Ring (UMER) is a machine designed to study high-intensity beam physics. With the application of axial fields to the bunch ends, we are able to keep a beam with an injected tune shift of 1.0, bunched over multiple turns. This is feasible with the application of tailored fields to optimally match the space-charge self-fields while minimizing the excitation of longitudinal space-charge waves. With this scheme, we have been able to extend the number of turns at the University of Maryland Electron Ring (UMER) by a factor of ten. Without the use of longitudinal focusing, head and tail effects begin to dominate, especially with the higher current beams. Time resolved measurements of the peak correlated energy spread have shown in some cases a change in the overall spread of 1.8% for the 0.6 mA beam, from the injected beam energy.
Diamond, Oxfordshire, United Kingdom
SLAC, Menlo Park, California, USA
CERN, Geneva, Switzerland
Radio Frequency noise induced bunch lengthening can strongly affect the Large Hadron Collider performance through luminosity reduction, particle loss, and other effects. Models and theoretical formalisms demonstrating the dependence of the LHC longitudinal bunch length on the RF station noise spectral content have been presented*,**. Initial measurements validated these studies and determined the performance limiting RF components. For the existing LHC LLRF implementation the bunch length increases with a rate of 1 mm/hr, which is higher than the intrabeam scattering diffusion and leads to a 27% bunch length increase over a 20 hour store. This work presents measurements from the LHC that better quantify the relationship between the RF noise and longitudinal emittance blowup. Noise was injected at specific frequency bands and with varying amplitudes at the LHC accelerating cavities. The experiments presented in this paper confirmed the predicted effects on the LHC bunch length due to both the noise around the synchrotron frequency resonance and the noise in other frequency bands aliased down to the synchrotron frequency by the periodic beam sampling of the accelerating voltage.
*T. Mastorides et.al., "RF system models for the LHC with Application to Longitudinal Dynamics,"
**T. Mastorides et.al., "RF Noise Effects on Large Hadron Collider Beam Diffusion"
Fermilab, Batavia, USA
ANL, Argonne, USA
During the design of the 60.635 MHz RFQ for the ATLAS efficiency and intensity upgrade*, we have established a new full 3D approach for the electromagnetic and beam dynamics simulations of a RFQ. A Detailed full 3D model (four meter long) including vane modulation was built and simulated using CST Microwave Studio, which is made possible by the ever advancing computing capabilities. The approach was validated using experimental measurements on a prototype 57.5 MHz RFQ**. The effects of the radial matchers, vane modulation and tuners on the resonant frequency and field flatness have been carefully studied. The full 3D field distribution was used for beam dynamics simulations using both CST Particle Studio and the beam dynamics code TRACK***. In the final design we have used trapezoidal modulation instead of the standard sinusoidal in the accelerating section of the RFQ to achieve more energy gain for the same length, following the leading work of the Protvino group****. In our case, the output energy increased from 260 keV/u to 295 keV/u with minimal change in the beam dynamics.
* P.N. Ostroumov et al, Proceedings of LINAC-2010
** P.N. Ostroumov et al, Proceedings of LINAC-2006
*** TRACK @ http://www.phy.anl.gov/atlas/TRACK
**** O.K. Belyaev et al, Proceedings of LINAC-2000
ESS Bilbao, Bilbao, Spain
Bilbao, Faculty of Science and Technology, Bilbao, Spain
University of the Basque Country, Faculty of Science and Technology, Bilbao, Spain
ESS-Bilbao, Zamudio, Spain
Imperial College of Science and Technology, Department of Physics, London, United Kingdom
STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom
The Bilbao Accelerator RFQ is aimed to accelerate a 75 mA proton beam from 75 keV to 3 MeV, while keeping the beam both transversely and longitudinally focused, and presenting a minimum emittance growth. We report on the current status of the project, mainly focusing on the Beam Dynamics aspects of the design. Several particle simulations are carried out with RFQSIM, GPT and TRACK codes, in order to study the particle transmission of the RFQ under several circumstances, such as different current levels, vane geometry changes due to thermal stress, and different input beam characteristics obtained by changing the LEBT operation settings.