HIGH LEVEL PHYSICS APPLICATIONS – THE BIG PICTURE

Day 1, Lecture 2 Relation of High Level Applications to Other Systems

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Perspectives • Consider an accelerator system from the perspective of the

customers

• How does the application fit in?

• Review accelerator systems providing observables and control variables for applications

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Accelerator View: Engineer

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Engineers’ view – Real hardware and software systems that must interface and meet design requirements

Accelerator View: Accelerator Physicist

• An abstract object that performs manipulations on ideal beams under ideal conditions

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Accelerator: Operations View

• A control room with interfaces to whatever is required for seamless accelerator operation.

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Accelerator: Manager’s View

• A device that meets the promises made to the funding sponsor

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Weeks Since October 1, 2007

Inte

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ActualInternal GoalCommitment

High Level (Physics) Applications • Need to consider the many points of view of the disparate

systems that an accelerator is composed of: •  Magnets (optics) •  RF systems •  Diagnostics systems •  Timing systems •  Control systems •  Data acquisition

• All of these provide input/output to the high level applications

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EPICS View of the Data Flow

•  Here XAL would be a client •  Most “MEDM” screens are preconfigured interfaces to hardware

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MEDM MEDM Client Client Client MEDM

Server IOC IOC

Meter Power Supply Camera

IOC

Channel Access

Relation of High Level Applications to Control System and Accel. Hardware

•  The high level applications communicate with hardware through a control system •  It’s important to carefully spell out the requirements / interfaces for the control

system and the underlying hardware.

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Application level

Accelerator hardware interface

Real Time Data Link (RTDL)

XAL “device” programing layer

TCP IP network

EPICS Channel Access

Global Database

XML File

Control System

High Level (physics) Applications •  High level applications typically integrate information from multiple systems

over an extent of the accelerator •  These applications often require information about the beam (from beam

diagnostics) and perform manipulations on the beam (magnets / RF) •  They communicate with these systems through a control system •  Often a physics based model is used to provide information how to control

the beam •  Examples:

•  Orbit display and correction, orbit bumps, setting RF phase and amplitude, …

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Specify Interfaces, and all should work

•  In principle things are simple: •  Specify what you want to receive from measurement devices,

•  e.g. a measure of the horizontal beam position at some place and time and return its value in mm, with name “xyz”

•  Specify what you would like to control •  E.g. a magnet field level, in Tesla, for magnet xyz.

• Wire it all up and hit the “On” button

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What Could Go Wrong???

•  Since high level applications use information measured from many sources, it is important to understand the strengths and limitations of these sources

•  It is also important to understand the limitations of equipment you may try and control

•  There are inherent difficulties in trying to communicate quickly with many information sources – control systems are complicated and not consistently reliable.

•  Often the majority of a high level application is exception handling – responding to events that are exceptions to normal operation.

•  Let us examine some of the primary players in accelerator measurement and control

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Diagnostics - Eyes and Ears to the Beam (Provide Observables) • BPM – Beam Position Monitor measure beam position • BCM – Beam Current Monitor (current transformer) • BLM - Beam Loss Monitor

•  Ionization chamber (IC) •  Photomultiplier tube (PT)

•  Profile measurement •  Wires •  Fluorescence screens •  Residual gas stripping •  Lasers

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Beam Position Monitors

• Moving charge induces current in surrounding electrodes

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Zo

beam

electrode

BPM

• BPM

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+

++++++++ - - - - - - -

- - - - - - - Zo

R Zo

Ibeam

Zo

++++++++ - - - - - -

- - - - - -- -

Zo Reflection

R

Iwall

Beam Current Monitor (BCM)

dtdV φ−=

1/27/14 USPAS 16

φ is proportional to I I out is 1/N times I in

v R

Varying Current

Magnetic Field

Toroidal Core N turns

¡  A changing current induces a voltage on a current loop surrounding it:

BCMs

• BCMs are quite simple looking

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Controllers for diagnostics are located in racks in service buildings

•  Sometimes someone brushing against a cable can mess up things •  They have their own expert system interfaces (be careful that the

proper values are restored after re-boots!)

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Typical Analog Front End & Digitizer Block Diagram

•  There is typically a fair amount of information processing in the analog / digital conversion

•  Often there are gain settings

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-40 dB

AD602A or AD603

-10dB to +30dB

FILTER

-34dB to +26dB

ADC

40MHz or 60MHz Clock (continuous)

DAC 8 Bits

14 Bits

8 Bits

GA

IN

DAT

A

78 Ohms

SWITCHED ATTENUATOR

0dB,-20dB,-40dB

6mV to 23.4 V

AD6644 14 Bit +/- 1.1V

1.05MHz rf

REG

.

AD8131 Diff. Out

+ - +0dB

DIG

ITA

L IN

TER

FAC

E

DIGITIZER

FRONT END

Dual-amps switched

Duplicated for switched amps

7MHz Gaussian LP Filter

Example Digital Interface

•  Plenty of room for problems in the digitizer to control system interface as well

•  Timing triggers are always an issue

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1.05MHz ( Δf) RING Ref. 1.05MHz RING Ref PLL and TIMING

67MHz Clock

14 Bits

CIR

CU

LAR

D

ATA

MEM

ORY

FI

FO

8 Bits

GA

IN &

SE

TTIN

GS

M

EMO

RY

Gate Control

1mS GATE PC

INTE

RFA

CE

EVENT TRIGGER

LOC

AL

CO

MPU

TER

DIG

ITIZ

ER

DATA

Data Timing Out Data Timing In

TIM

ING

Timing

DATA DATA

RF Systems

• Use Oscillating Electric Fields to Accelerate a Charged Particle •  High Voltage Convertor Modulators •  High Power RF •  Low Level RF

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Electric Force in Cavity

Time

accelerated

accelerated

decelerated

10-9 sec

RF System Components

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Klystrons

Linac LLRF Transmitter

Ring Cavity Klystrons

Reference Line System

Ring LLRF

Klystrons

Typical LLRF Control Rack 1/27/14 USPAS 23

Typical LLRF control rack installation in the superconducting linac.

The VXI crate contains:

•  Input/Output Controller: PowerPC running VxWorks

•  Utility Module: Decodes events from Real Time Data Link (Global Timing System)

•  Timing Module: Generates RF Gate timing signal

•  Two FCM/HPM pairs – generates the patterns for the high power RF, includes feedback, feed-forward, interfaces to the control system, etc.

Block Diagram of the SNS Linac LLRF Control System

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Down-Conversion & Distribution Chassis

RF Reference Line402.5 MHz – NC Linac805.0 MHz – SC Linac

Cavity Field Probe

Fundamental Power Coupler

RF Cavity

TunnelKlystron Gallery

Higher Order Mode Couplers(SCL Only)

Klystron

Pf PrDirectional

Coupler

Local Oscillator352.5 MHz – NC Linac755.0 MHz – SC Linac

IOC

(VxW

orks

OS)

Util

ity M

odul

e

Tim

ing

Mod

ule

Fiel

d C

ontro

l Mod

ule

Hig

h-Po

wer

Pro

tect

ion

Fiel

d C

ontro

l Mod

ule

Hig

h-Po

wer

Pro

tect

ion

VXI Cratex5x5

Master Oscillator2.5 MHz10 MHz352.5 MHz402.5 MHz755.0 MHz805.0 MHz(locate in DTL6 rack row)

Down-Conversion & Distribution ChassisDown-Conversion & Distribution Chassis

RF Reference Line402.5 MHz – NC Linac805.0 MHz – SC Linac

Cavity Field Probe

Fundamental Power Coupler

RF Cavity

TunnelKlystron Gallery

Higher Order Mode Couplers(SCL Only)

Klystron

Pf PrDirectional

Coupler

Local Oscillator352.5 MHz – NC Linac755.0 MHz – SC Linac

IOC

(VxW

orks

OS)

Util

ity M

odul

e

Tim

ing

Mod

ule

Fiel

d C

ontro

l Mod

ule

Hig

h-Po

wer

Pro

tect

ion

Fiel

d C

ontro

l Mod

ule

Hig

h-Po

wer

Pro

tect

ion

IOC

(VxW

orks

OS)

Util

ity M

odul

e

Tim

ing

Mod

ule

Fiel

d C

ontro

l Mod

ule

Hig

h-Po

wer

Pro

tect

ion

Fiel

d C

ontro

l Mod

ule

Hig

h-Po

wer

Pro

tect

ion

VXI Cratex5x5

Master Oscillator2.5 MHz10 MHz352.5 MHz402.5 MHz755.0 MHz805.0 MHz(locate in DTL6 rack row)

Field Control Module (FCM)

•  Regulates frequency control , field amplitude and phase regulation

•  Corrects for correlated and uncorrelated errors

•  Adaptive feed-forward control used for correction of repetitive field errors caused by beam loading and Lorentz force detuning

•  RF Sequencer is used for normal operations – startup, warming up cavities, tuning cavities, etc.

•  Primary interface to the Control system, e.g. what phase and ampltiude does the user want the cavity to run at.

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High-power Protection Module (HPM) • Responsible for protection of the RF systems

•  Monitors up to 7 RF inputs

• Detects cavity and klystron arc faults utilizing the AFT FOARC chassis

• Vacuum interface is connected to LLRF via HPM •  Soft interlocks from Cryo, Water, HPRF and Coupler Cooling • Chatter faults are expert settable to fine tune individual channels • History plots are available to monitor any two input channels

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Timing Systems (Master) • Master Timing system

generates event signals and propagates these throughout the accelerator to be used as triggers for systems •  Pulsed magnets •  Diagnostics •  RF •  …

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Real-TimeData Link

(RTDL)

ExtractMPS FPAR

EventLink

End Injection

0 2 ms1 ms 6 ms4 ms 7 ms5 ms 8 ms3 ms

AnytimeAnytime

Informational Events, non critical timingTime Critical Events, (soft events disabled)

RTDLTransmit

Snapshot, 1Hz, 6Hz,

etc… RTDL Valid

RTDL parameter transmission

(for next cycle)

RF & High Voltage Events

MPS FPL

System xxx Trigger Events

(Alternate) Cycle Start

Machine

+60 Hz ZeroCrossing

Line-SynchReference

Clock

Beam OnCycle Start

Mostly Stable Triggers

Beam On Range

Allowed Range for Variable Triggers

Extraction Kicker Charge

beam accumulation

Timing Systems (Clients) 1/27/14 USPAS 28

•  A difficulty is that different systems receive separate triggers and handle the triggers differently

Timing Signals from Multiple Sources

•  Providing common units and ways of providing information amongst disparate groups is important

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Putting it All Together – The Big Picture • We want to know what the beam is doing where and when (the

beam state) • We want to control the magnets, RF, hardware, etc. with “physically meaningful units” relative to the beam

• We want to adjust the controllable parameters in a predictable manner

•  Lots of things can go wrong: “trust but verify” all information that you use.

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