Radoslaw Rybaniec

Measuring and minimizing interrupt latency in Linux-based embedded systems

Paper describes performance of embedded real-time system controlled by Linux. Interrupt latency is taken into account as a main measured parameter in further considerations. To improve and minimize systems interrupt latency two separate approaches were evaluated. Obtained results proved that its possible to build a hard real-time system based on a modified Linux kernel.

MicroTCA.4-Based RF and Laser Cavities Regulation Including Piezocontrols

In this paper, we present an universal solution for radio frequency (RF) and laser cavities regulation, including piezocontrols and drivers based on MicroTCA.4 electronics. The control electronics consists of an Analog to Digital Converter-advanced mezzanine card (AMC) with an analog rear transmission module (RTM) to downmix and measure the RF signals and a low cost AMC-based Field Programmable Gate Array mezzanine card carrier for fast data processing and digital feedback operation connected to an RTM piezodriver. For the RF cavity regulation, the piezodriver includes additional inputs to use piezoelements as active force sensors. The fine tuning of the laser is carried out using a cavity fiber stretcher. The coarse tuning of the supported optics is done using a piezomotor-driven linear stage. Both channels can be operated using digital feedback controllers. First, results from continuous wave operation of the RF field controller and the cavity active resonance control with the piezotuners are demonstrated. The laser lock application performance using both fine and coarse channel feedbacks is shown and briefly discussed.

Experience with Single Cavity and Piezo Controls for Short, Long Pulse and CW Operation

We present a compact RF control system for superconducting radio frequency (SCRF) single cavities based on MicroTCA.4 equipped with specialized advanced mezzanine cards (AMCs) and rear transition modules (RTMs). To sense the RF signals from the cavity and to drive the high power source, a DRTM-DWC8VM1 module is used equipped with 8 analog field detectors and one RF vector modulator. Fast cavity frequency tuning is achieved by piezo-actuators attached to the cavity and a RTM piezo-driver module (DRTMPZT4). Data processing of the RF signals and the real-time control algorithms are implemented on a Virtex-6 and a Spartan-6 FPGAs within two AMC’s (SIS8300-L2V2 and DAMC-FMC20). The compact single cavity control system was tested at Cryo Module Test Bench (CMTB) at DESY. Software and firmware were developed to support all possible modes, the short pulse (SP), the long pulse (LP) and CW operation mode with duty cycles ranging from 1% to 100%. The SP mode used a high power multi-beam klystron at high loaded quality factor (QL) of 3 · 106. For the LP mode (up to 50% duty cycle) and the CW mode a 120 kW IOT tube was used at QL up to 1.5 · 107. Within this paper we present the achieved performance and report on the operation experience on such system.

FPGA based RF and piezo controllers for SRF cavities in CW mode

Modern digital low level radio frequency (LLRF) control systems used to stabilize the accelerating field in facilities such as Free Electron Laser in Hamburg (FLASH) or European X-Ray Free Electron Laser (E-XFEL) are based on the Field Programmable Gate Array (FPGA) technology. Presently these accelerator facilities are operated with pulsed RF. In future, these facilities should be operated with continuous wave (CW) which requires significant modifications on the real-time feedbacks realized within the FPGA. For example, higher loaded quality factor of the cavities when operated in a CW mode requires sophisticated resonance control methods. However, iterative learning techniques widely used for machines operated in pulsed mode are not applicable for CW. In addition, the mechanical characteristic of the cavities have now a much more important impact on the choice of the feedback scheme. To overcome the limitations of classical PI-controllers novel realtime adaptive feed forward algorithm is implemented in the FPGA. Also, the high power RF amplifier which is an inductive output tube (IOT) for continuous wave operation instead of a klystron for the pulsed mode has major impact on the design and implementation of the firmware for regulation. In this paper, we report on our successful approach to control multi-cavities with ultra-high precision (dA/A<;0.01%, dphi<;0.02 deg) using a single IOT source and individual resonance control through piezo actuators. Performance measurements of the proposed solution were conducted at Cryo Module Test Bench (CMTB) facility.

MicroTCA.4 based Single Cavity Regulation including Piezo Controls

We want to summarize the single cavity regulation with MTCA.4 electronics. Presented solution is based on the one MTCA.4 crate integrating both RF field control and piezo tuner control systems. The RF field control electronics consists of RTM for cavity probes sensing and high voltage power source driving, AMC for fast data processing and digital feedback operation. The piezo control system has been setup with high voltage RTM piezo driver and low cost AMC based FMC carrier. The communication between both control systems is performed using low latency link over the AMC backplane with data throughput up to the 3.125 Gbps. First results from CW operation of the RF field controller and the cavity active resonance control with the piezo tuners are demonstrated and briefly discussed. INTRODUCTION The 1.3 GHz superconducting radio frequency (SCRF) cavities of modern linear accelerators like FLASH and European X-Ray Free Electron Linac (XFEL) are operated in short pulse (SP) mode with 1300 μs RF-pulse and repetition rate up to 10 Hz at high loaded quality factor (QL) above 3·10. During SP operation of the cavity, the 650 μs of RF-pulse can be efficiently used to accelerate up to 27.000 number of bunches per second (averaged over 10 successive RF pulses) with minimum bunch spacing of 222 ns and maximum charge per bunch of 1 nC. Since the bandwidth of the cavity resonator operated in SP mode is 433 Hz for FLASH and 283 Hz for XFEL (QL=4.6·10) with nominal operating gradient of 23.6 MV/m, the dominating effect of the RF field disturbance is Lorentz force detuning (LFD). As LFD is repetitive from pulse to pulse, adaptive feedforward methods for active compensation using piezo tuners can be applied [1]. For the continuous wave (CW) mode of operation of SCRF cavity at quality factor of more than 1.5·10 (5 times less bandwidth), the unpredictable microphonics becomes the main RF field disturbance source. In order to achieve stable acceleration of 100.000 number of bunches per second with nominal operating gradient of 7 MV/m (CW operation scenario for XFEL machine), the RF field stability requirements better than 0.01% for the amplitude and 0.01 degrees for the phase are the real challenge. Therefore, new control algorithms need to be developed and evaluated for the real environment conditions. Nowadays higher numbers of high energy research centers are switching from multi cavity (MC) to single cavity approach (SCA) operation. The SCA solution is giving a possibility of establishing in a short time a small facilities where the high current and low emittance (below 1 mm x mrad) CW electron beam at 2 ps rms bunch duration are the main goals for the experiment, i.e. Berlin Energy Recovery Linac Project bERLinPro at Helmholtz Zentrum Berlin (HZB). SUPERCONDUCTING RF CAVITY OPERATION IN CW MODE In order to operate SCRF cavity in CW mode, the several limitations need to be taken into account [2]. First of all the heat load at 2 K (1.8 K) shouldn’t exceed 20 W when considering single cryomodule (CM) consisted of 8 cavities. Heating of the higher order modes (HOM) couplers must not cause quenching of the cavity. Due to the fact all end-groups are cooled by means of heat conduction. The cryo plant capacity needs to be doubled due to increased dynamic heat load (max. 16 W for single CM). Finally, the CW high power RF sources need to be applied. The most promising solutions are Inductive Output Tubes (IOTs) with nominal output power of 120 kW or Solid State Power Amplifiers (max. output power of 3.8 kW per device). When considering all above constraints the following operating conditions for CW mode are defined (FLASH and XFEL):  Accelerating field gradient per cavity Eacc ~ 7 MV/m.  Nominal loaded Q of input coupler QL ~ 1.5·10  Maximum peak RF power per cavity ~ 3.8 kW  Maximum number of bunches per second ~ 100.000  Minimum spacing between bunches ~ 10 μs  Nominal/ Maximum charge per bunch ~ 0.1/ 0.5 nC  Nominal beam current ~0.010 mA. MICROPHONICS AND PIEZO TUNERS The cavities are detuned by external mechanical forces microphonics. The CW operated cavity with high loaded quality factor of order of 1.5·10 and narrow bandwidth of 87 Hz is very susceptible to disturbances of this kind. The first measurements carried out from XFEL CM installed in Cryo Module Test Bench (CMTB) facility at DESY show vacuum pumps as the main source of microphonics. As seen in Figure 1 the disturbance caused by vacuum pumps has dominant frequency of approx. 50 Hz with varying amplitude and phase. In addition slowly varying operating conditions such as helium pressure fluctuations can also cause detuning of the cavities. The peak-peak microphonics of more than 10 Hz can strongly modulate resonance frequency of 1.3 GHz of the cavity, especially when operated at gradient of 7 MV/m and ___________________________________________ † konrad.przygoda@desy.de THOAA03 Proceedings of IPAC2016, Busan, Korea ISBN 978-3-95450-147-2 3152 C op yr ig ht