Timing Requirements for Spallation Neutron Sources

• Timing system clock synchronized to the storage ring’s revolution frequency.– LANSCE: 2.7951389 MHz (1/72 of the 201.25 MHz Acclerator RF

frequency)

– SNS: Variable. 1.027323 - 1.097502 MHz. Not derived from the Accelerator RF.

Timing Requirements for Spallation Neutron Sources

• The end of the cycle is more important than the beginning of the cycle.– Large, high inertia, “T0” neutron choppers define when the

beam is extracted from the ring. Most of the other important timing signals (beam and RF gates) end at the “Extraction Time” and derive their starting times by working backwards from the Extraction Time.

– Multiple beam lines require multiple choppers to be synchronized by the timing system.

– Compromise between keeping a stable “Extraction” reference signal for the choppers and not drifting too far away from the AC line phase for the RF system.

Basic Characteristics of SNS Timing System

• Event System.– 256 events possible. 25 events currently in use.

• ~5 millisecond machine cycle. 60 Hz.– Option to go to 120 Hz. when second target added.

• 10 second super-cycle.• Clock synchronized with ring RF.

– Ring RF is 1.057767 Mz at 1 GeV

– Clock is 32 X Ring RF

Timing System Components of SNS Timing System

Ring RF

TimingReferenceGenerator

NeutronChoppers

ACLine

SNS EventLink

Master

X32 PLL(33 MHz)

SNS RealTime Data

LinkMaster

10 MHzCrystal

Osc.

TimingSlave

(V124S)

MachineProtection

System

ICS IOC'sSNS Utility

Module

LEBTChopper

*4 PLL(64 MHz)

ExperimentalHalls

Diagnostics

RTDLEventLink

MasterTiming IOC

GPS

SNS Time StampsBeam data

RF GatesExtraction KickersTxHV Gates

High resolution timestampsMachine Modes

SNS TimestampsRemote ResetSynchronous ISR’s

Beam DelayBeam PhaseMicro pulse widthMacro pulse width

SNS Time stampsDelaysGatesTriggers

Timing SystemHardware

Timing System Users Experimental Systems

Subsystem Hardware

Two SNS Transmission Links

• Event Link– Transmits the timing events that define a machine cycle.– Each event is 8 bits plus parity (256 events maximum).– Clock is variable and derived from the ring revolution

frequency (32 * Frev).– Events 0 – 63 are generated by the timing system hardware.– Events 64 – 255 are generated by software (no fixed times).

• Real-Time Data Link (RTDL)– Transmits machine parameters and data prior to every new

cycle.– 128 frames possible (expandable to 255).– Each frame contains an 8-bit frame number, 24-bits of data,

and an 8-bit CRC.– Clock is 10 MHz.

Sample SNS RTDL Data Frames

Frame Number Data1 – 3 Time of day

4 Event link period 5 MPS mode 6 60 Hz phase error

7 Beam Width15 IOC Reset Address17 Pulse Flavor

18-21 RF Gate Widths24 Previous Pulse

Status25 Cycle

255 24-bit CRC (calculated)

Real-TimeData Link

(RTDL)

ExtractMPS FPAR

EventLink

End Injection

SNS Machine Cycle Timeline

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

-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

Basic Characteristics of LANSCE Timing System

• “Gate” rather than “Event” driven system.

• 96 independent timing gates 82 gates in use.

• 8.3 millisecond machine cycle (120 Hz).

• 1 second super-cycle.

• Clock synchronized with ring RF.

– 2.7951389 MHz.

Current Architecture of LANSCE Timing System

• Star configuration

• 4 redundant gate generator sets in 2 CAMAC crates.

• Gate generators are loaded by Master Timer computer, then run independently.

• Master Timer computer checks the output of the gate generators and automatically switches to another set when a discrepancy is seen.

RICE

CAMAC

ISS DATACONCENTRATOR

RICE

CAMAC

ISS DATACONCENTRATOR

Master Timer

MUX

TimingDistribution

Timing Gates

TimingGate

Generators