• F.B. Bouly, J.-L. Biarrotte, C. Joly
  IPN, Orsay

An Accelerator Driven System (ADS) for transmutation of nuclear waste requires a high power proton beam (several MWs) to reach the necessary spallation efficiency. Due to the induced thermal stress to the subcritical core, the high-power proton linac will have to fulfil stringent reliability requirements to minimise the number of unwanted beam trips (> 1 sec.) per operation cycle. In view of the construction of the MYRRHA ADS demonstrator, in Mol (Belgium), beam dynamic analyses were carried out to evaluate the fault tolerant capability of the superconducting linac, in the particular case of a radiofrequency (RF) cavity failure. This analysis was coupled with simulations on the RF behaviour of 700 MHz superconducting cavitiy as well as its tuning and feedback loop systems. Such considerations led to the development of a prototypical digital Low Level RF (LLRF) system to control the cavity phase and accelerating field, especially in the case of fast cavity retuning for failure compensation. In this paper we summarize the work which has been performed so far toward the development of such a fault-tolerant RF linac.

• J. Branlard, B. Chase, E. Cullerton, P.W. Joireman, V. Tupikov
  Fermilab, Batavia

The High Intensity Neutrino Source (HINS) R&D program requires super conducting single spoke resonators operating at 325 MHz. After coupler installation, these cavities are tested at the HINS-SRF facility at Fermilab. The LLRF requirements for these tests include support for continuous wave and pulsed mode operations, with the ability to track the resonance frequency of the tested cavity. Real-time measurement of the cavity loaded Q and Q0 are implemented using gradient decay techniques, allowing for Q0 versus Eacc plots. A real time cavity simulator was also developed to test the LLRF system and verify its functionality.

• P. Varghese, B. Barnes, J. Branlard, B. Chase, E. Cullerton, P.W. Joireman, V. Tupikov
  Fermilab, Batavia

A LLRF control and data acquisition system for the 8-cavity Cryo-Module 1 at the ILCTA has been implemented using three , 33-channel MFC boards in a VXI mainframe. One card each is dedicated for the cavity probes for vector control , forward power and reverse power measurements. The system is scalable to 24 cavities or more with the commissioning of Cryo-Modules 2 and 3 without additional hardware. The signal processing and vector control of the cavities is implemented in a FPGA and a high speed data acquisition system with upto 100 channels stores data in external SDRAM memory. The system supports both pulsed and CW modes with a pulse rate of 5Hz. Acquired data is transferred between pulses to auxiliary systems such as the piezo controller through the slot0 controller. The design of the system is described and the performance of the vector control system is evaluated.

• T. Kobayashi
  JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
• M. Ikegami
  KEK, Ibaraki

The function of the chopped beam loading compensation was implemented into the digital feedback/feed-forward control system of the J-PARC Linac LLRF system to stabilize the ACS cavity fields for the 400-MeV upgrade. The beam test of the chopped beam loading compensation was performed with the present 324-MHz cavity sysmte. Consequently the chopped beam loading was successfully compensated and that this system is valid.

• M.T. Crofford, T.W. Hardek, S.W. Lee, M.F. Piller
  ORNL, Oak Ridge, Tennessee
• J.A. Ball, T.L. Davidson
  ORNL RAD, Oak Ridge, Tennessee

The Spallation Neutron Source (SNS) has been operating since the first neutrons were produced on April 29, 2006. During the last several years the beam energy has been methodically ramped-up and outlying issues solved to improve system reliability. During the beam studies a temperature dependence has been discovered with the Low-Level RF systems. The effect is small but readily observable as increased beam losses. The temperature dependence has been studied both in the accelerator and in the laboratory and the sensitive components identified. A prototype solution that replaces the temperature dependent components of the Low-Level RF System has been designed and is in initial testing. Preliminary results of the laboratory tests have been encouraging. Accelerator tests are planned after installation during the December 2010 maintenance cycle.

• S.W. Lee, J.A. Ball, T.L. Davidson, S.L. Jones
  ORNL RAD, Oak Ridge, Tennessee
• M.T. Crofford, T.W. Hardek
  ORNL, Oak Ridge, Tennessee

The Spallation Neutron Source (SNS) High-Power Protection Module (HPM) provided interlocks and fast shutdown for the RF system to protect the accelerating structures and high power RF (HPRF) Distribution System. The HPM has required some functionality upgrades since the start of beam operations and an upgrade to the HPM test stand was required to support these added features. The HPM test stand currently verifies functionality, RF channel calibration, and measurement of the speed of shutdown to ensure the specifications are meet. The upgraded test stand was implemented in a single FPGA to allow for future growth and flexibility. Work is currently progressing on automation of the test stand to better perform the required module calibration schedule.

• G. Jug, C.J. Bocchetta, A. Kosicek
  I-Tech, Solkan

Control of bunch arrival time, energy and trajectory of particle beams in linear accelerators is mandatory to reach performance goals and is carried out using different sub-systems. For optimal control and especially for accelerators aiming at the highest level of performance, for example FELs, these systems should be considered as a whole and work together. At Instrumentation Technologies such systems have been developed and tested on the field. Precise control of amplitude and phase of the accelerating felds is performed with the Libera LLRF, a digital RF stabilization system that is couple to Libera SYNC a very low jiiter master oscillator distribution system. The Libera Brilliance Single Pass system provides high resolution position information that allows accurate control of trajectories through critical machine sections such as bunch compression modules and FEL modulators and radiators. These systems are described in detail in the paper with examples from field measurements.

• Y.S. Lee, J.-S. Chai
  SKKU, Suwon
• K.R. Kim, K.-H. Park
  PAL, Pohang, Kyungbuk

The low level RF (LLRF) control system for PLS is being upgraded to improve the performance of the system. The LLRF control system under development consists of FPGA, and high speed ADC and DAC as well as analog front-end devices which process the signal from cavity and to RF high power system. In addition, it utilizes digital signal processing technology based on FPGA. In order to optimize the accelerating electric field in the cavity, it is required to maintain field stability less than ±1% in amplitude and 1° in phase. And the resonance condition of the cavity should be monitored and controlled. The various digital signal processing theories such as digital filters, Cordic, PI control enable to meet these requirements and to control the feedback signal less than a microsecond. The LLRF control system is also equipped with the Ethernet by the cPCI. The preliminary design study on the LLRF control system for PLS superconducting cavity will be described in this paper.

• T. E. Plawski, C. Hovater
  JLAB, Newport News, Virginia

A digital low level radio frequency (RF) system typically incorporates either a heterodyne or direct sampling technique, followed by fast ADCs, then an FPGA, and finally a transmitting DAC. This universal platform opens up the possibilities for a variety of control algorithm implementations. The foremost concern for an RF control system is cavity field stability, and to meet the required quality of regulation, the chosen control system needs to have sufficient feedback gain. In this paper we will investigate the effectiveness of the regulation for three basic control system algorithms: I&Q (In-phase and Quadrature), Amplitude & Phase and digital SEL (Self Exciting Loop) along with the example of the Jefferson Lab 12 GeV cavity field control system.

• C. Hovater, T.L. Allison, R. Bachimanchi, G.E. Lahti, J. Musson, T. E. Plawski, C. Seaton, D.J. Seidman
  JLAB, Newport News, Virginia

To support the CEBAF energy upgrade from 6 GeV to 12 GeV, the RF control system is being modernized to control the high gradient high QL superconducting cavities. The new system incorporates a heterodyne transceiver along with I&Q sampling to measure and control magnitude and phase. A low-cost Altera FPGA is used to digitally implement the cavity control algorithms. One of the features of the system is a digital self excited loop to track the cavity over large Lorentz detuning (800 Hz) during turn on. The system has successfully completed preliminary development and is now moving into the production stage of the project. This paper discusses the design, modeling, testing and production of the new RF control system and associated peripheral systems (cavity interlocks, and resonance control).

• A. Fabris, P. Craievich, P. Delgiusto, F. Gelmetti, M.M. Milloch, A. Milocco, F. Pribaz, A. Rohlev, C. Serpico, N. Sodomaco, R. Umer, L. Veljak, D. Wang
  ELETTRA, Basovizza

FERMI@Elettra is a single-pass FEL user-facility covering the wavelength range from 100 nm (12 eV) to 4 nm (310 eV) and is located next to the third-generation synchrotron radiation facility Elettra in Trieste, Italy. The first electron beam from the photocathode electron rf gun and injector system was extracted in August 2009. Commissioning and installation of the remaining linac and linac systems are continuing and will alternate through this year . The linac is based on normal conducting S-band technology. It uses fifteen 3 GHz 45 MW peak RF power plants powering the gun, the accelerating structures, and the RF deflectors, and when completed will be able to deliver greater than 1.5 GeV electron beams to the FEL undulator system. This paper provides a summary of the installation activities and discusses the performances results of the main subassemblies both during the initial checkouts and through the commissioning of the accelerator.

• H.-J. Kwon, Y.-S. Cho, J.-H. Jang, D.I. Kim, H.S. Kim, K.T. Seol, Y.-G. Song
  KAERI, Daejon

A 100MeV proton accelerator is developed by the Proton Engineering Frontier Project (PEFP). As a front part, a 20MeV linac has been installed and operated at Korea Atomic Energy Research Institute (KAERI) site. Among the components for the 100MeV accelerator, some parts were installed and tested by using 20MeV linac. One modulator for a 100MeV linac was installed to drive two klystrons simultaneously which were used for a 20MeV linac. Various operating parameters such as a long term voltage fluctuation and control performance are checked during operation. Also a LLRF system for 100MeV linac which was modified from the 20MeV system was installed and tested. In this paper, the operation characteristics of the 20MeV linac are presented especially from the viewpoint of the newly installed components such as a modulator and LLRF system.

• E.R. Harms, J. Branlard, G.I. Cancelo, K. Carlson, B. Chase, E. Cullerton, A. Hocker, P.W. Joireman, T. Kubicki, J.R. Leibfritz, A. Martinez, M.W. McGee, Y.M. Pischalnikov, J. Reid, W. Schappert, K.R. Treptow, V. Tupikov, P. Varghese, T.J. Zmuda
  Fermilab, Batavia

Capture Cavity II is the first operational component at the SRF Beam Test Facility now under construction at Fermilab. This 9-cell 1.3 GHz cavity, previously operated in another venue on the Fermilab site, was transported to this facility in early 2009. We will summarize its transport and operation in its new (permanent) home compared to previous performance and also present results of studies, particularly Low Level RF, microphonics/vibration, and Lorentz force de-tuning compensation that have been recently carried out with it.

• R.C. Webber, T.N. Khabiboulline, R.L. Madrak, T.H. Nicol, L. Ristori, W.M. Soyars, R.L. Wagner
  Fermilab, Batavia

A new superconducting RF cavity test facility has been commissioned at Fermilab in conjunction with first tests of a 325 MHz, β = 0.22 superconducting single-spoke cavity dressed with a helium jacket and prototype tuner. The facility is described and results of full gradient, CW cavity tests with a high Qext drive coupler are reported. Sensitivities to Q disease and externally applied magnetic fields were investigated. Results are compared to bare cavity results obtained prior to hydrogen degassing and welding into the helium jacket.