IPAC2012 - List of Authors (Molloy, S.)

Paper	Title	Page
WEEPPB008	HOM Coupler Optimisation for the Superconducting RF Cavities in ESS	2182
	R. Ainsworth Royal Holloway, University of London, Surrey, United Kingdom R. Calaga CERN, Geneva, Switzerland S. Molloy ESS, Lund, Sweden
	The European Spallation Source (ESS) will be the world’s most powerful next generation neutron source. It consists of a linear accelerator, target, and instruments for neutron experiments. The linac is designed to accelerate protons to a final energy of 2.5 GeV , with an average design beam power of 5 MW, for collision with a target used to produce a high neutron flux. A section of the linac will contain Superconducting RF (SCRF) cavities designed to resonate at 704 MHz. Dangerous beam induced modes in these cavities may make the beam unstable and increase the cryogenic load and so couplers are usually installed to provide damping. Previous studies have shown potential designs are susceptible to multipacting, a resonant process which can absorb RF power and lead to heating effects. This paper will show how a coupler suffering from multipacting has been redesigned to limit this effect. Optimisation of the RF damping is also discussed.

THPPC082	Control Performance Improvement by Using Feedforward in LLRF	3476
	R. Zeng, D.P. McGinnis, S. Molloy ESS, Lund, Sweden A.J. Johansson Lund University, Lund, Sweden
	The LLRF design is ongoing at ESS (European Spallation Source). One major task of LLRF is to overcome a variety of perturbations such as klystron droop and ripple, Lorentz detuning and beam loading. These perturbations can be well suppressed by classical PI (proportional-integral) controller in feedback loop, but at a cost of raising risk of instability and consuming power overhead for overshoot. Since ESS is a green project focusing on energy efficiency, we will hence investigate in this paper some feedforward and advanced adaptive algorithms to deal with these perturbations, so as to improve the control performance and reduce the power overhead.

THPPC083	Investigation of Feedback Control for Klystron Ripple	3479
	R. Zeng, D.P. McGinnis, S. Molloy ESS, Lund, Sweden A.J. Johansson Lund University, Lund, Sweden
	At ESS (European Spallation Source), there might be potentially serious droop and ripple because of long RF pulse more than 3 ms. It is important for us to know to what extent the droop and ripple affects the klystron output, and how much we can tolerate. The variations of the phase and amplitude of klystron output due to the change in klystron cathode voltage is investigated in this Paper. The mechanism and the effectiveness of the feedback control to suppress the variations are given. To understand the limitation of the feedback, both proportional controller and proportional-integral controller used in feedback loop are simulated and analyzed respectively for superconducting cavity and normal conducting cavity. The tolerances of the droop and ripple in cathode voltage under feedback control are shown according to the data and results obtained.

Paper

Title

Page

HOM Coupler Optimisation for the Superconducting RF Cavities in ESS

2182

R. Ainsworth
Royal Holloway, University of London, Surrey, United Kingdom
R. Calaga
CERN, Geneva, Switzerland
S. Molloy
ESS, Lund, Sweden

The European Spallation Source (ESS) will be the world’s most powerful next generation neutron source. It consists of a linear accelerator, target, and instruments for neutron experiments. The linac is designed to accelerate protons to a final energy of 2.5 GeV , with an average design beam power of 5 MW, for collision with a target used to produce a high neutron flux. A section of the linac will contain Superconducting RF (SCRF) cavities designed to resonate at 704 MHz. Dangerous beam induced modes in these cavities may make the beam unstable and increase the cryogenic load and so couplers are usually installed to provide damping. Previous studies have shown potential designs are susceptible to multipacting, a resonant process which can absorb RF power and lead to heating effects. This paper will show how a coupler suffering from multipacting has been redesigned to limit this effect. Optimisation of the RF damping is also discussed.

THPPC082

Control Performance Improvement by Using Feedforward in LLRF

3476

R. Zeng, D.P. McGinnis, S. Molloy
ESS, Lund, Sweden
A.J. Johansson
Lund University, Lund, Sweden

The LLRF design is ongoing at ESS (European Spallation Source). One major task of LLRF is to overcome a variety of perturbations such as klystron droop and ripple, Lorentz detuning and beam loading. These perturbations can be well suppressed by classical PI (proportional-integral) controller in feedback loop, but at a cost of raising risk of instability and consuming power overhead for overshoot. Since ESS is a green project focusing on energy efficiency, we will hence investigate in this paper some feedforward and advanced adaptive algorithms to deal with these perturbations, so as to improve the control performance and reduce the power overhead.

THPPC083

Investigation of Feedback Control for Klystron Ripple

3479

R. Zeng, D.P. McGinnis, S. Molloy
ESS, Lund, Sweden
A.J. Johansson
Lund University, Lund, Sweden

At ESS (European Spallation Source), there might be potentially serious droop and ripple because of long RF pulse more than 3 ms. It is important for us to know to what extent the droop and ripple affects the klystron output, and how much we can tolerate. The variations of the phase and amplitude of klystron output due to the change in klystron cathode voltage is investigated in this Paper. The mechanism and the effectiveness of the feedback control to suppress the variations are given. To understand the limitation of the feedback, both proportional controller and proportional-integral controller used in feedback loop are simulated and analyzed respectively for superconducting cavity and normal conducting cavity. The tolerances of the droop and ripple in cathode voltage under feedback control are shown according to the data and results obtained.