cRIO as a hardware platform for Machine Protection.

cRIO as a hardware platform for Machine Protection.

W. BloklandS. Zhukov

OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY

Introduction

The Beam Instrumentation Group at the Spallation Neutron Source is responsible to measure aspects such as losses, charge and position of the accelerating particle beam.

Some of these measurements are tied to the Machine Protection System (MPS) and must be able to turn the accelerator off. The requirements can be: Turn the machine off before the next pulse (SNS: < 15ms) Turn the machine off within the pulse (SNS: 10-1000µs)

Additional requirements can be: Use a hardware (analog or digital) solution to implement the abort function

The cRIO platform supports both a Software (Real-Time) and Hardware (FPGA) implementation of Machine Protection Aborts

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Beam Loss MonitorOne unique instrument for use in a test facility. Similar to a

standard Beam Loss Monitor but resources to modify existing systems was scarce. cRIO was identified as viable alternative.

RF Test Facility Beam Loss Monitor Specifications Sample 12 channels at 100kHz Alarm in 20usec when integrated beam loss is above threshold Control and read back HV power supplies voltages Send test pulse to test Photo Multiplier Tubes

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Feature VME cRIO

Sample rate 100kS/s 100kS/s

Resolution 24 16

MPS Analog FPGA

Analog Channels 16 12-16

Hardware Cost* $29k $12k-13k* CPU, Crate, Power supply, ADC, DAC, DIO


Beam Loss Monitor cRIO

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Not needed anymore, we have at least two ways of running EPICS on cRIO without gateways


Beam Loss Monitor software

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Three different pieces of hardware but one programming environment:

• LabVIEW FPGA (on cRIO backplane)point-by-point processing of the data such as integration and comparison to threshold, baseline correction, and LED enable

• LabVIEW Real-time (in Controller)Implements the real-time calculations such as Rads/sec (This can also be done on the FPGA if needed for Beam Abort)

• LabVIEW for Windows (separate PC)Implements the gateway to the EPICS-based control system.


LabVIEW Programming Environment

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Integrated programming environment for both RT and FPGA programming Single vendor! No dealing with multiple vendors to solve problems. Same programming constructs for both RT and FPGA EPICS is supported FPGA code must be compiled and this takes time: 10 min – 40 minutes

loop

sequence

Only FPGA specific: Access to cRIO Analog In


Sequential versus point-by-point

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The LabVIEW FPGA programming environment brings the FPGA into the same realm as CPU programming!!!

- Caveat: FPGA programming increases in complexity when programming in single cycle loops (aka full speed)

Sequentialprocessing


Sequential versus point-by-point

acquisition

10 µs

processing

data

TransferTo RT

data

First Abort option in 10-20us

beam

point-by-point (pipelined) processing


Beam Loss Monitor Diagram

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Impressive: Adding PMT test feature required minimal code and development

time


Beam Loss Monitor cRIO

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BLM IOC CPU with EPICSBLM IOC CPU with EPICS

BLM AmplifiersBLM AmplifiersBLM cRIOBLM cRIO

HV Power supplyHV Power supply

RF Cavity Video System PXI crateRF Cavity Video System PXI crate


Beam Loss Monitor VME Rack

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VME Controller,Digitizer, Digital IO, Custom Timing CardCustom Analog Card

VME Controller,Digitizer, Digital IO, Custom Timing CardCustom Analog Card

Abort System ModulesAbort System Modules

Power SupplyPower Supply

HV modulesHV modules

Analog Front-endAnalog Front-end


ScrapersThin foils scrapes the beam halo in HEBT of SNS. The scraped particles are collected by collimators. Need

an MPS to prevent excessive power being dumped into collimator. There are 2-4 foils per collimator. The secondary electron emission presents itself as current source that is measured.

HEBT Scraper Specifications Sample 4 channels at 200kHz Trip the beam in 20usec when integrated beam loss is above threshold for one foil Trip the beam if 1s average of sum over all foils (for particular collimator) is above threshold (total

power on collimator) Communicate with AFE boards (over serial port, 115kbit/s RS-485) to check amplifier health, HV The Trips have to be generated by hardware (FPGA) Since the signal is AC coupled (due to HV bias applied to the foil) alleviate signal droop

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* CPU, Crate, Power supply, ADC, DAC, DIO


cRIO implementation (under development) Space saving: 3U per collimator

Modularity: one IOC fails, corresponding scrapers must be retracted, but the other can be used

All sorts of digital correction: baseline, droop etc

20uS requirement met: is limited by current driver speed 10uS

Communication can be done in FPGA or RT (drag and drop will work)

All sorts of rolling averages (1s)easy to implement


Comparison Sample-by-sample processing fitted requirements very well and got rid of

issues such as:• Sequential processing bottlenecks: Waveform acquisition takes 2 ms, then the

transfer to slot zero, then processing. This must fit within 16.6msec. Balancing act between digitizing speed, backplane data transfers and CPU processing. FPGA can process data point-by-point without data transfers.

• Separate hardware board to perform Abort functions. An analog board with integrator and analog threshold is used to implement an abort within 20 µs. FPGA can set alarm in each 10 µs cycle.

cRIO Hardware integration takes care of low-level drivers• Our projects requirements matched very well with cRIO capabilities and no FPGA

hardware knowledge was required• EPICS integration is available

VME approach is standard in accelerators• Custom timing decoding card and software is available• Experienced people• EPICS integration is standard

No special FPGA knowledge required

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Future

Scrapers 3 IOCs (Feb 2011)

Beam power on Beam Line Dump using cRIO

Replacement of BLM VME hardware? (more fantasy than future)

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cRIO as a hardware platform for Machine Protection.

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