HIGH LEVEL PHYSICS APPLICATIONS – THE BIG PICTURE
Day 1, Lecture 2 Relation of High Level Applications to Other Systems
1/27/14 USPAS 1
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
1/27/14 USPAS 2
Accelerator View: Engineer
1/27/14 USPAS 3
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
1/27/14 USPAS 4
Accelerator: Operations View
• A control room with interfaces to whatever is required for seamless accelerator operation.
1/27/14 USPAS 5
Accelerator: Manager’s View
• A device that meets the promises made to the funding sponsor
1/27/14 USPAS 6
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Weeks Since October 1, 2007
Inte
grat
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eam
Pow
er (M
W-h
rs)
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
1/27/14 USPAS 7
EPICS View of the Data Flow
• Here XAL would be a client • Most “MEDM” screens are preconfigured interfaces to hardware
1/27/14 USPAS 8
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.
1/27/14 USPAS 9
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, …
1/27/14 USPAS 10
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
1/27/14 USPAS 11
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
1/27/14 USPAS 12
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
1/27/14 USPAS 13
Beam Position Monitors
• Moving charge induces current in surrounding electrodes
1/27/14 USPAS 14
Zo
beam
electrode
BPM
• BPM
1/27/14 USPAS 15
+
++++++++ - - - - - - -
- - - - - - - 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
1/27/14 USPAS 17
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!)
1/27/14 USPAS 18
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
1/27/14 USPAS 19
-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
1/27/14 USPAS 20
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
1/27/14 USPAS 21
Electric Force in Cavity
Time
accelerated
accelerated
decelerated
10-9 sec
RF System Components
1/27/14 USPAS 22
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
1/27/14 USPAS 24
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.
1/27/14 USPAS 25
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
1/27/14 USPAS 26
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 • …
1/27/14 USPAS 27
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
1/27/14 USPAS 29
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.
1/27/14 USPAS 30