Creating an EPICS Based Test Stand Development System

for the BPM Digitizer

Farah MemonSan Jose State University

SULI, Science Undergraduate Laboratory InternshipAugust 12, 2010

Linac Coherent Light Source (LCLS)

Provides movies of molecular activities.

X-ray pulses are short in wavelength.

Photon energy ranges from 540eV to 9.0keV.

Highest x-ray pulse energy is 3mJ.

Advances in medicine, chemistry, and materials science.

BPM Digitizer Beam Position Monitor (BPM) Digitizer is used to obtain the location

of the electron bunches in the LCLS. 4 different input channels capture signals from four different sides

of the beam. The signals are converted at a low intermediate frequency (IF). –

Radio Frequency (RF). The RF signals are digitized using analog to digital converters

(ADC). The Digitizer has four 16K by 18 bit buffers; one for each channel. The ADC acquires data at each rising each of the clock where the

external clock rate is 119MHz and internal clock rate is125 MHz.

BPM Digitizer

The process of acquiring RF signals and keeping them as digitized samples in the buffer.

Monitoring the Digitizer

The IOC is the VME 64x Crate with the Motorola Microprocessor.

Consists of EPICS Core and Application Database.

The OPI is a Dell Linux Machine (Service Tag: GGQXPDI).

Allows the user to view process variables on iocConsole or EDM (EPICS GUI).

Controlled using an IOC (Input/Output Controller) and an OPI (Operator Interfaces)

LAN

Monitoring the Digitizer

Example of a record:

record(waveform, "$(digi):WAV"){

field(DESC, "Raw VMEDIGI Data")field(DTYP, "VMEDigi-Waveform")field(INP, "#C$(card)S0@")field(FTVL, "SHORT")field(EGU, "Counts")field(HOPR, "32768")field(LOPR, "-32767")

}

Each field of a record is called a Process Variable (PV).

Project Guidelines

Matlab is currently used to test the digitizer with Matlab Guide being the GUI.

Similar as well as advanced functionalities need to be transferred over to EPICS to develop an improved test stand development system.

All the previous functionalities need to be provided.

Added functionality of logging of data also needs to be incorporated.

The GUI for Matlab Scripts

The Matlab Guide providing the existing functionalities.

Setting up Equipment

Hardware Equipments: Power-One Hybricon VME

64x crate with VME 64100 Microcontroller in Slot 1 and the BPM Digitizer in Slot 4.

Cisco Systems Catalyst 3750 Series Switch

Digi Port Server TS 16 serial port

HP Signal Generator (Model 8648C

Stanford Research Systems Digital Delay Generator (Model DG645). Power-One Hybricon VME 64x crate, Cisco

Systems Catalyst 3750 Series Switch, and

digi Port Server TS 16 serial port below.

Equipment

HP Signal Generator (Model 8648C) below.

Stanford Research Systems Digital Delay Generator (Model DG645) above.

Driver Code:R5-3-0 of BPM Application Code was used.

Simulation functions of the driver code were neglected.

Functionalities by the driver code

The following EDM Panel was provided with R5-3-0 vmeDigi driver code

Implementation in EPICS

genSub Record employed for illustrating the four different waveform signals.

The genSub module was incorporated into the IOC. The record allows easy passage of PVs as inputs. The genSub record was invoked periodically and

called a subroutine, written in C language, to perform division of the combined waveform signal.

In the subroutine, the genSub record is passed as a pointer to a structure.

The outputs of the function, the four distinct input signals, were displayed onto the EDM panel.

Displaying four waveforms

Implementation in EPICSThe four input signals are clearlyillustrated on the main EDM panel.

Implementation in EPICSMathematical Calculations

waveProc1-0 module was incorporated with the existing source code.

Four instances of waveAnl records are added. Each waveform is passed as an input to the

record. The mathematical and statistical data relevant

to the waveform are contained in the PVs. All the PVs are exposed on the Wave Analysis

Record panels. These panels are attached to the main EDM panel via a button.

Implementation in EPICSThe Wave Analysis Record panel is linked to the main EDM panel.

Implementation in EPICSFast Fourier Transform

Matlab labCA is utilized. Matlab Client intefaces with the IOC through

Channel Access and has access to the PVs. Matlab is used to perform the fast Fourier

transform (FFT) and compute the power spectrum of the four waveforms. The program also finds the carrier frequency.

Matlab labCA commands obtain the waveform signals and change the contents of the four power spectrum signals.

The four power density signals are displayed on a separate EDM panel and linked to the main panel via the button ‘FFT’.

Implementation in EPICSThe FFT EDM Panel displaying the power density of he four waveform signals with respect to the frequency.

Implementation in EPICS

Logging functionality

Six different files created for logging: Four files for the RF signals from four

input channels. One file for the combined waveform. One generic log file for hardware-specific

information, i.e, serial, firmware, and hardware revision number.

Files are created on demand – upon a click of a button

For data corresponding to waveforms, a function in the wavAnl record was written.

For the generic log file, a subroutine was created.

Implementation in EPICSLogging functionality – waveform log files

Implementation in EPICSLogging functionality – generic log file

Future Work

Add buttons that bring up PDF files that assist the user in configuring the BPM digitizer.

Ability to change between engineering units; currently the default units are ‘samples’.

For example: going from samples to volts. The test stand system can be used as a template to

design test stand systems for other types of digitizers, including the PAD digitizer.

References[1] J. Frisch et al. Beam Position in LCLS [Online]. Available: http://www.als.lbl.gov/biw08/papers-final/MOIOTIO02.pdf[2] LCLS FAQ [Online]. Available: https://slacportal.slac.stanford.edu/sites/lclscore_public/Lists/LCLS_FAQ/FAQ.aspx[3] R. Lill et al. Design and Performance of the LCLS Cavity BPM System[Online]. Available: http://accelconf.web.cern.ch/accelconf/p07/PAPERS/FRPMN111.PDF[4] W. Ross, “SLAC BPM Digitizing Module 144-045-1 Programming Module” [5] (2008, March 10). EPICS I[Online]. Available: https://confluence.slac.stanford.edu/download/attachments/67503315/LCLS-EPICS-Intro.pdf?version=1&modificationDate=1257093082000[6] B. Dalesio. (1999). Channel Access Concepts [Online]. Available: http://www.slac.stanford.edu/comp/unix/package/epics/training/documents/02_CA_Concepts.pdf [7] A. Foster. (2003, March 12). The EPICS genSub Record Reference Manual [Online]. Available: http://www.slac.stanford.edu/grp/ssrl/spear/epics/site/genSub/genSubManual.pdf[8] E. Norum. WaveProc [Online]. Available: http://www.aps.anl.gov/epics/modules/soft/waveProc/index.html[9] E. A. Medvedko et al. LCLS Stripline BPM System Commissioning [Online]. Available: http://trshare.triumf.ca/~pac09proc/Proceedings/papers/th6rep036.pdf