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| WEPP060 |
Abort Gap Cleaning Using the Transverse Feedback System: Simulation and Measurements in the SPS for the LHC Beam Dump System
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2656 |
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- A. Koschik, B. Goddard, W. Höfle, G. Kotzian, D. K. Kramer, T. Kramer
CERN, Geneva
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The critical and delicate process of dumping the beams of the LHC requires very low particle densities within the 3 microseconds of the dump kicker rising edge. High beam population in this so-called 'abort gap' might cause magnet quenches or even damage. Constant refilling due to diffusion processes is expected which will be counter-acted by an active abort gap cleaning system employing the transverse feedback kickers. In order to assess the feasibility and performance of such an abort gap cleaning system, simulations and measurements with beam in the SPS have been performed. Here we report on the results of these studies.
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| THPC121 |
LHC Transverse Feedback System and its Hardware Commissioning
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3266 |
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- W. Höfle, P. Baudrenghien, F. Killing, Y. A. Kojevnikov, G. Kotzian, R. Louwerse, E. Montesinos, V. Rossi, M. Schokker, E. Thepenier, D. Valuch
CERN, Geneva
- E. V. Gorbachev, N. I. Lebedev, A. A. Makarov, S. Rubtsun, V. Zhabitsky
JINR, Dubna, Moscow Region
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A powerful transverse feedback system ('damper') has been installed in LHC. It will stabilise coupled bunch instabilities in a frequency range from 3 kHz to 20 MHz and at the same time damp injection oscillations originating from steering errors and injection kicker ripple. The transverse damper can also be used as an exciter for purposes of abort gap cleaning or tune measurement. The power and low-level systems layout are described along with results from the hardware commissioning. The achieved performance is compared with earlier predictions and requirements for injection damping and instability control. Requirements and first measurements of the performance of the low-level system are summarized. The chosen approach for the low-level system using advanced FPGA technology is very flexible allowing implementation of future upgrades of the signal processing without changing the hardware.
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| THPC122 |
Digital Signal Processing for the Multi-bunch LHC Transverse Feedback System
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3269 |
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- W. Höfle, P. Baudrenghien, G. Kotzian, V. Rossi
CERN, Geneva
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For the LHC a VME card has been developed that contains all functionalities for transverse damping, diagnostics and controlled bunch by bunch excitation. It receives the normalized bunch by bunch position from two pick-ups via Gigabit Serial Links (SERDES). A Stratix II FPGA is responsible for resynchronising the two data streams to the bunch-synchronous clock domain (40.08 MHz) and then applying all the digital signal processing: In addition to the classic functionalities (gain balance, rejection of closed orbit, pick-up combinations, one-turn delay) it contains 3-turn Hilbert filters for phase adjustment with a single pick-up scheme, a phase equalizer to correct for the non-linear phase response of the power amplifier and an interpolator to double the processing frequency followed by a low-pass filter to precisely control the bandwidth. Using two clock domains in the FPGA the phase of the feedback loop can be adjusted with a resolution of 10 ps. Built-in diagnostic memory (observation and post-mortem) and excitation memory for setting-up are also included. The card receives functions to continuously adjust its parameters as required during injection, ramping and physics.
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| THPP113 |
Emittance Growth at LHC Injection from SPS and LHC Kicker Ripple
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3629 |
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- B. Goddard, M. J. Barnes, L. Ducimetière, W. Höfle, G. Kotzian
CERN, Geneva
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Fast pulsed kicker magnets are used to extract beams from the SPS and inject them into the LHC. The kickers exhibit time-varying structure in the pulse shape which translates into small offsets with respect to the closed orbit at LHC injection. The LHC damper systems will be used to damp out the resulting betatron oscillations, to keep the growth in the transverse emittance within specification. This paper describes the results of the measurements of the kicker ripple for the two systems, both in the laboratory and with beam, and presents the simulated performance of the transverse damper in terms of beam emittance growth. The implications for LHC operation are discussed.
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| THPP114 |
LHC Transverse Feedback Damping Efficiency
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3632 |
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- G. Kotzian, W. Höfle
CERN, Geneva
- E. Vogel
DESY, Hamburg
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A simulation model has been developed to predict the damping efficiency of the LHC transverse feedback system in the presence of coupled bunch instabilities and under realistic assumptions for the injection error. The model tracks both the centre of gravity of a bunch and the r.m.s beam size during and after injection. It includes the frequency characteristic of the transverse feedback system. Nonlinearities in the beam optics will cause the bunches to filament and lead to an increase of the transverse emittance after injection. The resistive wall instability reduces the effectiveness of the transverse feedback by slowing down the damping process. Possibilities for enhancing the performance of the feedback system by signal processing schemes are outlined.
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