SNS Timing System
EPICS Workshop
April 28, 2005
Coles Sibley
Dave Thompson
SNS Global Controls
SNS Integrated Control System
Design Decisions

MPS and Timing systems are tightly integrated. Timing systems should
“RESPECT” machine protection system beam power and pulse width
limits to not “challenge” MPS system.

Timing system will run at 60 Hz. (but don’t preclude the possibility of
120 Hz).

Super cycle will be 10 seconds (600 cycles, 0.1 Hz rep-rate resolution).

As much as possible should be done in hardware.

As little as possible should be relegated to the client IOCs.

Synchronous with Ring RF, not linac RF

System hardware design from RHIC
SNS Integrated Control System
Machine / Beam Mode Definitions


Machine mode selected by Key switch in control room,
Beam Mode selected by Key or software. Switches read
by MPS PLC system and distributed through timing
system.
Machine Mode defines
where the beam goes
–
–
–
–
–
–
–
MEBT Beam Stop
CCL Beam Stop
Linac Dump
Injection Dump
Ring
Extraction Dump
Target
SNS Integrated Control System

Beam Mode defines allowable
beam charge or power
–
–
–
–
–
Pilot pulse (10 usec)
Diagnostics pulse (50 usec)
Tuning pulse (100 usec)
Full Pulse Width (1 msec)
Full Power (Depends on Dump)
Timing System Components
RTDL
Master
Timing IOC
Event
Link
Experimental
Halls
10 MHz
Crystal
Osc.
SNS Real
Time Data
Link
Master
Timing
Slave
(V124S)
*32 PLL
(33 MHz)
SNS Event
Link
Master
Machine
Protection
System
SNS Time Stamps
Beam data
RF Gates
Extraction Kickers
TxHV Gates
High resolution timestamps
Machine Modes
Ring RF
AC
Line
ICS IOC's
Timing
Reference
Generator
SNS Utility
Module
LEBT
Chopper
Neutron
Choppers
Timing System
Hardware
Diagnostics
Subsystem Hardware
Timing System Users Experimental Systems
SNS Integrated Control System
SNS Timestamps
Remote Reset
Synchronous ISR’s
*4 PLL
(64 MHz)
Beam Delay
Beam Phase
Micro pulse width
Macro pulse width
SNS Time stamps
Delays
Gates
Triggers
Timeline (from the timing system point of view)
Time Critical Events, (soft events disabled)
Informational Events, non critical timing
RTDL parameter
transmission
(for next cycle)
Real-Time
Data Link
(RTDL)
Beam On
Cycle Start
System xxx
Trigger Events
Extract
MPS Inhibit
MPS Fault
RF & High
Voltage Events
End
Injection
RTDL
Transmit
Extraction
Kicker Charge
Snapshot,
1Hz, 6Hz,
etc…
(Alternate)
Cycle Start
RTDL Valid
Event
Link
Beam On Range
Beam On Range
Allowed Range for Variable Triggers
Anytime
Anytime
Machine
Line-Synch
Reference
Clock
+60 Hz Zero
MPS Post
Mortem
beam
accumulation
-60 Hz Zero
Crossing
Crossing
0
1 ms
2 ms
SNS Integrated Control System
3 ms
4 ms
5 ms
6 ms
7 ms
8 ms
RTDL Sequencer

Runs at 60 Hz. Driven by the “RTDL Valid” Event interrupt.

Loads the RTDL frames for the next cycle (the cycle after the upcoming
“Cycle Start” event, including:
–
–
–
–
–
–

Time of next Cycle Start (From GPS + ~162/3 msec) for time stamps
Ring revolution frequency (from counter module)
Line crossing phase error (from timing reference generator)
Beam flavor parameters (Beam profile)
Machine and Beam Mode (MPS Mode Masking)
Last frame is 24-bit CRC on all RTDL data.
Writes correction term (based on measured event-link clock speed) to
timing reference generator.
SNS Integrated Control System
Event Link Sequencer

Runs at 60 Hz, driven by the “RTDL Valid” event.

Enables gates for variable rep-rate events that are scheduled to fire on
the next machine cycle.

Handles the “bookeeping” tasks required for setting new rep-rates.
Rep-Rate Pattern Generator

Actually, a set of EPICS “genSub” records.

Computes the rep-rate “patterns” used by the Event Link Sequencer to
schedule which events should occur on each cycle.

Can also be used on “Client” IOC’s to do local rep-rates.
SNS Integrated Control System
Variable Rep-Rates — genSub Record
Inputs
Outputs
A.
Desired Rep-Rate (double)
A. Actual Rep-Rate (double)
B.
Constraint Pattern (structure)
B. Rep-Rate Pattern (structure)
C. V124S Gate Address (card &
signal)
D. Mode selector
•
•
E.
0 = “Fixed” (ignore pattern)
1 = “Variable” (use pattern)
Offset from Constraint Pattern
(long)
–n: Precede constraint pattern by
n pulses
+n: Follow constraint pattern by n
pulses
0: No offset (pattern must be
coincident with constraint
pattern)
SNS Integrated Control System
Note: Constraint pattern can come from
another “repRate” genSub record (e.g.
for the gate this gate depends on) or
from a combination of patterns
(computed by another genSub record).
Application: Beam Control
Hardware interface between MPS and Timing
V124S
Trigger Control Chassis
Event Link
Auto Reset
Latched
}
MPS Inputs
MPS PLC
To Source
Cycle Start
Beam On
To RFQ
Source RF
Delayed Source RF
RFQ
From RFQ LLRF Controller
SNS Integrated Control System
To Chopper
Event Link Monitor

Monitors event in a supercycle

Compare with event link sequence, fault on difference

Hardware check against software errors

Hardware read back for pattern generators
SNS Integrated Control System
Application: Ion Source Control
Source RF
Warm Linac
LLRF
Beam On
End
Injection
Extract
Cycle Start
Event Link
Growth
Source On
Growth
Delayed Source On
RFQ
Cycle Start
Beam On
0
1 ms
2 ms
SNS Integrated Control System
3 ms
4 ms
5 ms
6 ms
7 ms
8 ms
Application: Linac RF Control
Requirements

RF Gates should always end at “End Injection” event. Increasing the
gate width decreases the delay (and vice versa).

Low-level RF gate should come on about 100 mSec before beam (300
mSec in super-conducting linac).

HV power supplies should come on about 100 mSec before Low-Level
RF.

Variable rep rates replaced with fixed events
– 1, 2, 5, 10, 20, 30, and 60 Hz
– Modulator HV Power supplies need an upgrade before 31 Hz or higher
permitted

Individual RF gate widths adjustable but sets a constraint on
maximum beam pulse width
SNS Integrated Control System
Application: Linac RF Control
RF Gate Relationships
Source RF
Cycle Start
Beam On
RF & High
Voltage Events
End
Injection
Extract
Event Link
Beam On
Source On
Warm LLRF
Warm HPRF
Cold LLRF
Cold HPRF
0
1 ms
2 ms
SNS Integrated Control System
3 ms
4 ms
5 ms
6 ms
7 ms
8 ms
Typical User Defined Beam Flavors

Reconfiguration requires beam off, flavor integrated charge and power
recomputed, beam scheduled power calculated against machine/beam
modes.

Flavors used by LLRF and Ring RF for feed forward loops.

1 - Beam Off

2 - 10 usec, (Chopped) (Fast faraday cup)

3 - 50 usec , (Chopped) (All wire scanners, faraday cups)

4 - 100 usec , (Chopped)

5 - Physics , (Unchopped)

6 – Arbitrary 1 msec gates, 50 usec beam

7 - Reserved

8 - Normal, ie. 1060 turns, 50 usec ramp up
SNS Integrated Control System
LEBT Chopper Pattern Generator
16.67 msec
1 msec
Phase
delay
Ring RF PLL Signal
Cycle
Start
Macro
Delay
50 usec
Start Width
Mini Pulse
duty factor
645 nsec
Mini Pulse
Width
945 nsec
Ramp up
Time
divide by "n"
n=2, I = I0/2
75 %
65 %
Macro
Pulse Width
SNS Integrated Control System
End Width
Ramp down
Time
Beam Profile Requirements

Ring Commissioning
–
–
–
–
10 turns, 1 per 100usec (next generation of chopper)
Nominal beam to Linac Dump (Beam flavor 1)
Single turn (beam flavor 2)
Chopped beam to ring (beam flavor 3)
SNS Integrated Control System
Pattern Generator – CD4 in 2006
Fixed RF rep rates limited to < 30
Hz

1 Hz beam, < 50 usec gate width
thru Dec 2005

LEBT Chopper commissioned,
Beam gate < 1msec, integrated
pulse width < 50usec

(LEBT fails with fulll width beam)

Beam RR and PW must fall in
safe operating envelope (May
2006)
SNS Integrated Control System
Safe Operating Limits
100
1.4 MW envelope (Target)
10
Beam Rate

200 KW envelope
(Injection Dump)
Safe Operation
7.5 KW MEBT_BS, CCL_BS
LDmp, Ring, EDmp
1
Beam Diagnostics
0.1
0
200
400
600
800
Turns (945 nsec / turn)
1000
1200
Beam Scheduling Post CD4

SNS runs in loss limited mode (<10-4), Scale back in power until loss
limits met.

All beam on after trip of > 5(?) min, pilot pulse and power ramp up
required

Target has limits on machine trips, 25(?) fast and 5(?) slow per day.
Requirements not defined for bad machine days.

Target Requirements
– < 100 kW, no restrictions
– > 100 kW and beam off < 30 min, no restrictions
– > 100 kW and beam off > 30 min, linear ramp in power for 10 min.

One diagnostics pulse per super cycle allowed (Monitor injection phase
painting) implies pulse to pulse scheduling.

Second target station, More pulse to pulse beam mode scheduling
required
SNS Integrated Control System
SNS AC Line is being Characterized using Filter for
Neutron Chopper Response
Line synch installed in controls
lab timing system for
distribution to neutron
chopper lab.
60.1 Hz
Six day line frequency measurement
60.0 Hz
Limiting Slew Rate results
in wide frequency range
59.9 Hz
GPS-based filter with slew rate
limit being studied
500usecs
Deviation from Grid in usecs
Deviation in slew rate in mHz/sec
Beam Phase with line delay from 0 to 800 usec in 50
usec increments (2 beam trips) +/- 10deg RFQ
Minimal Effect on Beam from 0 to 800usec delay
SNS Integrated Control System
New Requirements

Use SLS and Diamond timing
hardware (Timo Korhonen)

3 – D beam bunch shape
measurements

12 degree longitudinal length,
402.5 MHz (83 psec)

Need ~1 psec stability,

1 to10 psec resolution

Use 402.5 or 805 MHz LLRF
Reference line as input clock

Synchronize Beam-On pulse
using SLS Hardware
SNS Integrated Control System