1 BROOKHAVEN SCIENCE ASSOCIATES Plans for Low-Level Radio Frequency Hengjie Ma NSLS II RF Group NSLS-II ASAC Review, March 26, 2009

2 BROOKHAVEN SCIENCE ASSOCIATES Outline Low-level radio frequency system requirement Implementations Cavity field controller Phase reference scheme and LLRF frequencies Preliminary plan for system integration Status of LLRF R&D Rev. 1, 2 controller prototypes and test results LLRF standard frequency synthesizer Master oscillator phase noise test set Conclusions

3 BROOKHAVEN SCIENCE ASSOCIATES Low-level RF System Requirement Functions of Low-level RF System Provide a RF reference for accelerator/experiments (Master Oscillator) Regulates cavity field for required RF stability Monitors RF powers to provide equipment protections Provide RF signal data for operation and archiving.

4 BROOKHAVEN SCIENCE ASSOCIATES Low-level RF System Requirement Basic LLRF functionalities – 1 of 4 Master Oscillator MHz ± 10 kHz – physics and user experiments require that the RF master oscillator must meet the following requirements ; Phase jitter: << 0.16 deg. RMS, from 500 Hz to 50 kHz *, Frequency tuning range : > +/- 30 kHz, Frequency resolution: < 1 Hz (at least) ** * An equivalent phase noise power density of -87dBc/Hz from 0.5 to 50 kHz, it also a total phase noise budget for the RF system. ** E. Weihreter, J. Rose, “Some comments on the choice of rf master generators for NSLS II,” Technical note, October, 2007

5 BROOKHAVEN SCIENCE ASSOCIATES Low-level RF System Requirement Basic LLRF functionalities – 2 of 4 Cavity Field Controller – RF stability is also subject to the total phase error budget of 0.16 deg. RMS(PDR). The basic requirement for the field control thus includes Wideband * feedback control (P-I, or “fast feedback”) for reducing cavity shunt impedance, thus reducing transient beam loading and suppressing Robinson instability, linearizing RF PA reduce other random perturbations in the system (such as noise in high-power RF ). * A successful implementation of a wideband feedback control to a large degree depends on the amount of loop delay in the system, as the product of loop gain K p and bandwidth ω 1/2 is subject to a constraint set by the loop delay τ as

6 BROOKHAVEN SCIENCE ASSOCIATES Low-level RF System Requirement Basic LLRF functionalities – 3 of 4 Cavity Field Controller Delayed-feedback loops (such as Turn-by-Turn), Cavity resonance/tuning control (frequency loop) Sufficient number of RF input channels for allowing to implement various feedback loops, and monitoring the high-power RF. RF reference / Cavity field pickup (s)* Forward / reflected power at cavity input * Forward / reflected power at PA output Forward / reflected power at circulator load port Forward / reflected power at PA input* Beam pickup(s) * * required signal inputs, minimum 7 channels.

7 BROOKHAVEN SCIENCE ASSOCIATES Low-level RF System Requirement Basic LLRF functionalities – 4 of 4 The RF operations also require additional functionalities, including Exception-handling and equipment protections (interlocks) Synchronism with machine events (timing, trigger I/Os) Output frequency variation (off standard RF) capability – for facilitating cavity testing/conditioning, or RF system transfer function measurements. Signal waveform data viewing and archiving ( data streaming, buffers) Communication ports to local/remote computer host for controls and data transfer.

8 BROOKHAVEN SCIENCE ASSOCIATES Low-level RF System Implementation Cavity field controller implementation – 1 of 3 An all-digital, FPGA implementation is chosen for Concurrent processing Short DSP latency, More signal I/O Flexibility

9 BROOKHAVEN SCIENCE ASSOCIATES Controller implementation – 2 of 3 Peripheral around FPGA 14-bit resolution for RF I/O (to meet the 0.16 deg. precision requirement *) Low-level RF System Implementation * S. Simrock, “Digital low-level RF controls for the future superconducting Linac colliders,”, PAC05

10 BROOKHAVEN SCIENCE ASSOCIATES Cavity field controller implementation – 3 of 3 Direct Digital Synthesis (DDS) of LLRF output signal is chosen for having a precision linear control and greater dynamic range on the output (vs. an analog vector modulator). Performance is proven, Basic principle of FPGA implementation is the same as of a standard DDS; Given Phase increment size = 2 N here, N= 3, jump size M=5, and F clk =80MHz (LLRF clock). Thus, synthesized IF frequency Low-level RF System Implementation

11 BROOKHAVEN SCIENCE ASSOCIATES Phase reference scheme & LLRF frequencies – 1 of 2 Choose 500MHz RF as reference for Straightforward phase comparison Allows differential measurement Choice of LLRF processing frequencies Intermediate Freq. IF = 50MHz 1st LO = RF + IF = 550MHz (SR, BR) 2 nd LO = 5*RF = 2500MHz (LINAC) 2 nd LO = 2*RF = 1000MHz (Landau) Considerations for the freq. choice include the compatibility with the proven FPGA LLRF design LLRF4 (LBNL), or FCM (SNS). Low-level RF System Implementation

12 BROOKHAVEN SCIENCE ASSOCIATES Phase reference scheme & LLRF frequencies – 2 of 2 Same field controller hardware is used in SR, BR, and LN. 3GHz (in LINAC) and 1.5GHz (in Landau) are down converted to standard 500MHz first, then converted to 50MHz IF with 550MHz LO as in Storage Ring and Booster LINAC : 3000MHz – 2500MHz (2 nd LO) = 500MHz Landau: 1500MHz – 1000MHz (2 nd LO) = 500MHz Low-level RF System Implementation

13 BROOKHAVEN SCIENCE ASSOCIATES Phase noise performance of Possible Master Oscillator Total RMS jitter estimated < 4.3e-4(rad.) = deg. (1 Hz~100 kHz) << 0.16 deg Frequency variation step size : Hz Phase continuity maintained during frequency change Model: Agilent MHz Frequency offset1Hz10Hz100Hz1kHz10kHz100kHz SSB phase noise (dBc) Low-level RF System Implementation

14 BROOKHAVEN SCIENCE ASSOCIATES Preliminary plan for system integration LLRF is organized in clusters for the sub-systems (SR, BR and LN etc.). In each cluster, devices are centered around a master concentrator (under development in Controls) in a star configuration, connected by high-speed serial links. The Gbps up/down links of the concentrators are connected together in a ring configuration, providing a capability of inter-sub-system communication, and also a method to merge LLRF into the accelerator controls infrastructure. Much of the details is TBD at this time. Low-level RF System Implementation

15 BROOKHAVEN SCIENCE ASSOCIATES LLRF R&D Status - summary 1 st generation digital LLRF controller board has been designed. Two versions (Rev1, Rev.2) haven been designed and fabricated. Rev.1 is intended for in-lab tests and development. One sample was constructed, and is being characterized. Rev.2 is intended for supporting the near-term RF development activities, including the booster cavity frequency tuning tests, and field tests (CLS planned). Four samples are being constructed. LLRF standard frequency synthesizer - designed / constructed. Master Oscillator phase noise test set - designed/constructed.

16 BROOKHAVEN SCIENCE ASSOCIATES LLRF R&D Status – field controller Rev. 1 cavity field controller under test – verified functions of IF ADC/DAC, TTL trigger I/O, MATLAB API(w/ help from staff of Controls)

17 BROOKHAVEN SCIENCE ASSOCIATES LLRF R&D Status – field controller Rev. 1 cavity field controller: IF input channel characterization The ADC channel under test is driven by a 50 MHz Sine-wave input and a 40 MHz clock, produced by two low-noise crystal oscillators. The SNR of ADC input channels is a critical factor that limits the performance of a digital LLRF. Test results indicate that the -73dB SNR spec. of the ADC device is generally met, and with a measured spurious-free – dynamic range of -81dB. (analyzed from 4M samples of 50 MHz IF signal)

18 BROOKHAVEN SCIENCE ASSOCIATES LLRF R&D Status – field controller Rev. 1 cavity field controller: IF input channel characterization An important part of the ADC SNR is the close-in phase noise from ADC aperture jitter: The test result shows that on this Rev.1 controller prototype, the measured ADC’s aperture jitter’s contribution to the phase noise is ~ deg RMS. (4M samples) Input channel distortion was also checked (with 2-tone input for IM).

19 BROOKHAVEN SCIENCE ASSOCIATES LLRF R&D Status – field controller Rev. 1 cavity controller: directly digital synthesized 50MHz output spectrum purity was also checked (more quantifying tests)

20 BROOKHAVEN SCIENCE ASSOCIATES LLRF R&D Status – field controller Rev.2 version has been designed and fabricated with improvement in: Addition of integrated - RF-IF up/down conversion, Enhanced device cooling, Standard 1U 19” chassis packaging, 4 samples are being made for supporting RF development tasks.

21 BROOKHAVEN SCIENCE ASSOCIATES LLRF R&D Status – Frequency standards LLRF coherent frequency standard All LLRF frequencies used in LLRF, 10, 40, 50, 80, 500, and 550MHz, are derived from a common ULN 10MHz time-base of MO, maintaining the coherency, synchronism, and phase relationship.

22 BROOKHAVEN SCIENCE ASSOCIATES LLRF R&D Status – Frequency standards LLRF coherent frequency standard and MO phase noise correlation test set have been designed and constructed..

23 BROOKHAVEN SCIENCE ASSOCIATES Conclusion and Near-term Goals The LLRF plans address both the near-term needs, and a path for future upgrades and expansions. The test on the 1 st generation LLRF field controller has yield some promising results, and both the controller prototype and MO system provide a good development platform. The near-term goals include finishing the Rev.2 controller hardware, fabrication, and testing, Develop the Rev.2 software/firmware necessary for supporting RF development activities (may need assistance from Controls) Start studying the issues in the control timing/synchronization, communication between the front-end and the concentrators, and interface with control infrastructure (working with Controls)

24 BROOKHAVEN SCIENCE ASSOCIATES Acknowledgement TEAM RF JAMES ROSE (group leader), HENGJIE MA JOHN CUPOLO, JORGE OLIVA, ROBER SIKORA, NATHAN TOWNE(contractor)