Multichannel vector field control module for LLRF control of superconducting cavities

TLDR: The MFC (Multichannel Field Control) module is a 33- channel, FPGA based down-conversion and signal processing board in a single VXI slot, with 4 channels of high speed DAC outputs, which provides additional computational and control capability for calibration and implementation of more complex control algorithms.

Abstract: The field control of multiple superconducting RF cavities with a single Klystron, such as the proposed RF scheme for the ILC, requires high density (number of RF channels) signal processing hardware so that vector control may be implemented with minimum group delay. The MFC (Multichannel Field Control) module is a 33- channel, FPGA based down-conversion and signal processing board in a single VXI slot, with 4 channels of high speed DAC outputs. A 32-bit, 400MHz floating point DSP provides additional computational and control capability for calibration and implementation of more complex control algorithms. Multiple high speed serial transceivers on the front panel and the backplane bus allow a flexible architecture for inter-module real time data exchanges. An interface CPLD supports the VXI bus protocol for communication to a SlotO CPU, with Ethernet connections for remote in system programming of the FPGA and DSP as well as data acquisition.

Figures

Figure 4: 14-bit ADC SNR

Figure 3: MFC board

Figure 5: 8 ch ADC - Process gain and Crosstalk

Figure 1: MFC Board Overview

Frequently asked questions

Q1. What is the main component of the MFC board?

There are 4 DAC channels for RF outputs and multiple high speed serial transceivers on the front panel and the backplane bus to allow a flexible architecture for inter-module real time data exchanges. 

Q2. What is the purpose of the MFC board?

The MFC board is an FPGA based 33 channel downconversion and signal processing module designed for vector control of multiple cavities with a single Klystron such as the proposed RF scheme for the ILC[1]. 

Q3. What is the purpose of the floating point DSP?

A floating point DSP provides additional computational capability for calibration and implementation of more complex control algorithms. 

Q4. What is the function of the MFC board?

Downconversion is performed by multiplying the data with an 18 bit scaled and offset Cosine/Sine table to provide a composite gain plus rotation. 

Q5. What is the phase of the beam and cavity phase?

Reference signals for the beam and cavity phase (one for each cryomodule with 8 cavities each) are processed in 4 of the auxiliary channels. 

Q6. What is the noise floor of the MFC board?

For this test the authors fed a signal at 13MHz IF and +4dBm into one channel on the MFC board and observed the 13MHz component in adjacent channels.