The SLC control system at SLAC is currently used on most of the LINAC. It is the only control system in sectors 20-30, which will be used by the LCLS mostly in tact. LCLS will replace all of the BPM electronics in these sectors to provide higher resolution. The Injector for LCLS will use all new control, except for the high power RF components, which are existing SLC klystrons and modulators. The corrector magnets in the LINAC that will be used for LCLS will all have new EPICS based controllers. From the undulator to the experimental stations, all new controls will be done in EPICS. Note that all SLC data from the existing LINAC will be available to the EPICS environment, but the time stamp information that allows data correlation to beam events is not available at the present.

The motivation to implement an SLC aware, EPICS IOC, is to allow the new elements of the LCLS control system to use EPICS, while still taking advantage of the high level applications on the SLC control systems. These high level applications include:

Correlation plots, energy management, beam steering, beam based alignment, emittance measurements, and slow feedback.

1.1 Assumptions

· The SLC-aware IOCs are to support LCLS beams in the linac. There will be no interleaving of straight-ahead beams from the CID injector with LCLS operation. Straight ahead beams will only be run in a dedicated machine mode when LCLS is not operating. In the event that straight ahead beams are sent down the linac the BPMs in sectors 20 through 30 will be required to measure beam position using the LCLS processors operating on a beam code for the straight ahead beam. The straight ahead beam operation will not require simultaneous reading of both electrons and positrons on a single machine pulse, which used to be the case in the old SLC operation.

· There will be no straight-ahead beam experiments supported by the SLC-aware IOCs or LCLS.

o A bi-pass line will be built for LINAC supported End-Station experiments, or

o existing electronics will remain and be swapped in/out.

· SLC-aware IOCs will be present in the injector and linac portions of the LCLS beam line.

o This allows gated data acquisition and correlation from all parts of the LCLS beam line

o The LTU and Undulator may not require SLC-aware IOCs, as EPICS control may be complete by the time of LTU commissioning.

· There will be only one public calibration setup at one time

o When the experiment changes, a new calibration will be issued or previously stored calibration tables will be loaded.

o Calibration will not be coordinated by SLC / SCP

BPM modules will be acquiring and buffering LCLS beam synchronous data continuously

GADC and TORO modules may do so as well - TBD

2 Use Cases for Beam Synchronous Data

Requirements for the Beam Synchronous Acquisition Facility are derived from existing SLC applications and from expected future applications that will be made available as EPICS clients. Each of these applications requires certain functionality of the BSAC Facility.

The main interface between the SLC applications and the BSAC Facility is the Message Service interface. All requests from the SLC applications are embodied in Message Service request messages, denoted by a function code. The BSAC Facility processes the request and data is returned in a data reply message.

All requests from EPICS clients are issued through the Channel Access interface, and data is returned through this same CA Interface.

The application requests are described in this document as Use Cases. We have divided the Use Cases into two groups, those from the SLC Control System, and those from current and future EPICS Clients.

2.1 System Block Diagram

2.2 SLC Use Cases

All of the gated acquisition based applications available from the SLC Control System have options to acquire data at 120 Hz, or lower rate due to rate-limiting, or due to wire scan range, CPU, user preferences, etc. The PNET broadcast is used to specify a pattern of pulses to exclude/include.

SLC Use Cases originate from the following applications on the VMS system:

· SCP High Level Software Applications

· Standalone Applications

· SCP Diagnostics Panels

· SLC Database Hardware Status and Configuration is stored in the SLC Database

2.2.1 SLC functionality to be used by LCLS

The following table references LCLS application software requirements found in:

Requirements for High-Level Software Applications Packages

by Patrick Krejcik

The first column of the table illustrates which of the required LCLS Software Applications Packages require beam synchronous data. The second column indicates whether the SLC Control system satisfies the LCLS requirement. The third column indicates that all LCLS required SCP applications will be replaced by EDM / EPICS.

Name of LCLS Req’ed App	Requires BSA	SCP/SLC	EDM/EPICS

Diagnostic
Beam Orbit Display	Yes	Yes	future
Wire Scanner	Yes	Yes	future
Profile Monitor	Yes	No	Yes – High Priority
BPM Timing	Yes	No	Yes – High Priority

Tuning-Generic
Multi-knob Facility	Yes	Yes	future
Correlation Plot	Yes	Yes	future
Buffered Acquisition	Yes	Yes	future

Tuning-Specialist
Transverse Emittance	Yes	Yes	future
Beta Matching	Yes	Yes	future
Bunch Length Meas.	Yes	No	Yes – High Priority

Beam Line On-line Modeling
Orbit fitting	Yes	Yes	future

Power Steering	Yes	Yes	future

Linac Energy Management - LEM	Yes	Yes	Yes-High Priority

Fast Feedback	Yes	No	Yes – High Priority

Related Software
Configuration Control		Yes	Yes
Data Archiver		Yes	Yes
Error Logging		Yes	Yes
Orbit Check		No	Yes – High Priority

*future – will be developed in-house or enhanced for LCLS from existing packages.

*Yes – High Priority – is not available thru SCP, required soon for LCLS

2.2.1.1 SLC Software Application to Function Code

The following table addresses the SLC applications that will be used by LCLS. The table shows a mapping of SLC application to Message Service function code. These function codes in effect represent Use Cases that apply to the BSAC Facility. The table shows that the SLC applications required by LCLS have two important Use Cases. They are the Measurement Prep request and the Wire Prep request.

In its simplest form, the Measurement Prep requests beam synchronous data to be provided on one beam pulse across all BPMs. The Wire Prep requests beam synchronous data to be provided on multiple beam pulses in one area along the Linac, such as when doing a wire scan.

There are a few additional Use Cases that support SCP functionality during a beam synchronous acquisition.

Name	SCP Panel	Function Codes	Devices

Diagnostic
Beam Orbit Display	LCLS BPM Measurement	BPMO_MEAS_PREP	BPMS, TORO
	LCLS BPM Diagnostics	BPMO_MEAS_PROC
		BPMO_GETREMDAT

Wire Scanner		BPMO_WIRE_PREP	BPMS, TORO, WIRE, ARRY
		BPMO_WIRE_PROC
		BPMO_GETREMDAT

Tuning-Generic