BNL-94194-2011-CP

RHIC 10 Hz global orbital feedback system

R. Michnoff, L. Arnold, L. Carboni, P. Cerniglia, A. Curcio, L. DeSanto, C. Folz, C. Ho, L. Hoff, R. Hulsart, R. Karl, C. Liu,

Y. Luo, W. W. MacKay, G. Mahler, W. Meng, K. Mernick, M. Minty, C. Montag, R.H. Olsen, J. Piacentino, P. Popken,

R. Przybylinski, V. Ptitsyn, J. Ritter, R. Schoenfeld, P. Thieberger, J. Tuozzolo, A. Weston, J. White,

P. Ziminski, P. Zimmerman

Presented at the 2011 Particle Accelerator Conference (PAC’11) New York, N.Y.

March 28 – April 1, 2011

Collider-Accelerator Department

Brookhaven National Laboratory

U.S. Department of Energy Office of Science Notice: This manuscript has been authored by employees of Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy. The publisher by accepting the manuscript for publication acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. This preprint is intended for publication in a journal or proceedings. Since changes may be made before publication, it may not be cited or reproduced without the author’s permission.

DISCLAIMER

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or any third party’s use or the results of such use of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof or its contractors or subcontractors. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

RHIC 10 HZ GLOBAL ORBIT FEEDBACK SYSTEM*

R. Michnoff#, L. Arnold, L. Carboni, P. Cerniglia, A. Curcio, L. DeSanto, C. Folz, C. Ho, L. Hoff,

R. Hulsart, R. Karl, C. Liu, Y. Luo, W. W. MacKay, G. Mahler, W. Meng, K. Mernick, M. Minty,

C. Montag, R.H. Olsen, J. Piacentino, P. Popken, R. Przybylinski, V. Ptitsyn, J. Ritter, R.

Schoenfeld, P. Thieberger, J. Tuozzolo, A. Weston, J. White, P. Ziminski, P. Zimmerman

BNL, Upton, NY 11973, U.S.A.

Abstract Vibrations of the cryogenic triplet magnets at the

Relativistic Heavy Ion Collider (RHIC) are suspected to

be causing the horizontal beam perturbations observed at

frequencies around 10 Hz. Several solutions to counteract

the effect have been considered in the past, including a

local beam feedback system at each of the two

experimental areas [1], reinforcing the magnet base

support assembly, and a mechanical servo feedback

system [2]. However, the local feedback system was

insufficient because perturbation amplitudes outside the

experimental areas were still problematic, and the

mechanical solutions are very expensive. A global 10 Hz

orbit feedback system consisting of 36 beam position

monitors (BPMs) and 12 small dedicated dipole corrector

magnets in each of the two 3.8 km circumference counter-

rotating rings has been developed and commissioned in

February 2011. A description of the system architecture

and results with beam will be discussed.

DESCRIPTION OF ARCHITECTURE

The RHIC 10 Hz global orbit feedback system is

composed of the following main components:

• 72 (36 for each ring) standard RHIC BPM Integrated

Front End (IFE) electronic modules [3] with new

daughter card for ~10 kHz position data distribution.

• Dedicated 1 gigabit BPM data distribution network

using off-the-shelf Netgear Ethernet switches [4].

• 6 Xilinx Virtex-5 based ML-510 data processing

modules including on-board power PC running

vxWorks operating system as control system front

end computer.

• 24 Kepco Model BOP-36-12M (+/- 36 V, +/- 12 A)

magnet power supplies (12 for each ring).

• 24 small corrector magnets (12 in each ring) [5].

• 6 Modicon programmable logic controllers (PLCs)

for Kepco power supply on/off control.

Block diagrams are shown in Fig. 1 and 2. Each ML-

510 receives data from all 72 BPMs every 8 beam

revolutions (~103 microseconds), and uses a matrix and

control loop filter to generate the power supply setpoints

for each of the 4 local corrector magnets (2 for each ring).

One ML-510 processing module, four power supplies,

and related control equipment are located in each of 6

service buildings around the RHIC complex (Fig. 3). The

BPM IFE modules are located in the same service

buildings as well as in alcoves in the tunnel.

Figure 1: Hardware block diagram.

Figure 2: Software/firmware block diagram.

DESIGN DETAILS

BPM Daughter Card

A daughter card was designed for the standard RHIC

BPM IFE module (Fig. 4) to send position data to the

ML-510 processing modules via a dedicated 1 gigabit

Ethernet network. The daughter card uses an Altera Arria

GX EP1AGX35 gate array to calculate the position for a

single selected bunch every turn, average 8 consecutive

Controls Ethernet Network

BPM Ethernet Network (72 BPMs updated every 100 microseconds)

Power supply

ON/OFF control PLC

ADO

DAC board

4-chan 16-bit serial DAC

(AD5754R)

Analog outputs to power supplies

PM1 Connector

DAC data write state

machine

BPM

data buffer

BPM data receiver state

machine

Power supply setpoint data buffer

ML-510 Xilinx Virtex-5 gate array board

with dual core Power PC

BPM data ADO

Matrix

values

Power supply

setpoint ADO

Control loop ADO

Control loop processing

RJ-45 RJ-45

BPM BPM BPM …

copper

BPM BPM BPM

Ethernet Switch (Netgear GS724AT)

…

copper

BPM BPM BPM …

Ethernet Switch (Netgear GS724AT)

copper fiber

fiber Alcove Alcove

Service

Building

(typ. 1 of 6)

fiber

Ethernet Switch (Netgear GSM7212)

ML-510 Xilinx Virtex-5

Processing Module (including front end computer)

Power Supply

Power Supply

Power Supply

Power Supply

copper Analog

outputs

1005S

Hub room

fiber

…

copper

Control system Ethernet network

To other service buildings (6 total)

fiber

fiber

Magnet

Magnet

Magnet

Magnet

Setpoint, current, voltage readbacks to control system

Ethernet Switch (Netgear GS724AT)

____________________________________________

*Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the

U.S. Department of Energy. #michnoff@bnl.gov

turns, and send the 8-turn average to the ML-510

processing modules located in the 6 service buildings.

Figure 3: Typical equipment rack layout (1012A)

showing BPM modules with Ethernet connection for

BPM position data distribution, power supply control

PLC panel, Kepco power supplies, and Xilinx Virtex-5

ML-510 processing and analog output module.

Figure 4: RHIC BPM hardware board with daughter card.

Figure 5: Control loop filter response.

BPM Data Distribution Network [4]

The standard Ethernet low level packet structure was

selected for distributing BPM data in order to allow off-

the-shelf network switch hardware to be used. After

evaluation of several network switches, Netgear models

GS724AT (24 RJ-45 connections, with 4 SFP ports) and

GSM7212 (12 SFP ports) 1 gigabit switches were selected

for their low latency performance (~2 microseconds).

The BPM daughter cards connect to the local network

switch via RJ-45 CAT-6 cables, and fiber optic cables are

used to interconnect the network switches between

alcoves and service buildings (Fig. 1). The service

buildings are interconnected in a star configuration

through a main hub room in building 1005S.

ML-510 Software/Firmware

The software/firmware block diagram for the ML-510

processing module is provided in figure 2. The on-board

Xilinx Virtex-5 has a dual core Power PC 440, one of

which is running the vxWorks real-time operating system

and RHIC accelerator device object (ADO) software for

interfacing with the higher level control system via the

controls Ethernet network. The other Power PC is

unused. The remaining software blocks shown in the

diagram are implemented in VHDL gate array code.

Each ML-510 generates setpoints for 4 local magnet

power supplies (2 per ring). A 36 x 1 matrix calculations

is performed every 103 microseconds to calculate each

power supply setpoint using up to 36 BPM measurements

per ring. The SVD matrix output value [6] is processed

by the control loop filter with the frequency and phase

response shown in Fig. 5. This filter has proven very

effective in correcting frequencies around 10 Hz while

ignoring slow orbit shifts as occur during application of

slow orbit feedback [7] and actions such as removal of

separation bumps to bring beams into collision.

The corrector magnet power supply setpoints are

generated by an AD475R +/-10V 16-bit DAC (Fig. 6).

SMA connectors interface to the Kepco power supplies.

Corrector Magnets [5]

Each magnet coil pair is wired in parallel, and in series

with a 7-turn reverse coil installed on the magnet in the

other ring. The reverse coil is used to counteract the

fringe field affects on the other beam. Figures 7 and 8

show a typical magnet installation in the RHIC tunnel.

Twenty four magnets are installed in total, 12 in each

ring, and are located near each of the triplet magnets that

are driving the 10 Hz perturbations.

Figure 6: ML-510 processing module with DAC card.

BPM

Modules Kepco power

supplies

Power supply control PLC

ML-510 processing module

Figure 7: Typical installation of 10 Hz corrector magnets.

Figure 8: Corrector magnets in sector 12.

RESULTS WITH BEAM

The 10 Hz global orbit feedback system has recently

been commissioned and has routinely been turned on

during normal physics stores since Feb. 19, 2011.

Position data for a single BPM are shown in Fig. 9,

comparing 10 Hz feedback off vs. on. The perturbations

are dramatically reduced from about 3000 to about 250

microns peak-peak. Reductions of the same order are

evident at all BPMs used for 10 Hz orbit feedback.

The amplitude variations noted when the feedback is

off are due to the beating of several frequencies around 10

Hz as the different triplet magnets vibrate at slightly

different frequencies [8].

The effect on the experimental collision rates and beam

loss rates is shown in Fig. 10. The 10 Hz feedback

clearly improves the collision rates and decreases beam

loss rates.

Although luminosity lifetime is also expected to

improve, additional studies are required in order to prove

this expectation. Ideally a store with 10 Hz feedback on

would be compared to a store with 10 Hz feedback off,

but continuously changing beam conditions make this

comparison very challenging.

Figure 9: Typical BPM measurement with 10 Hz feedback

OFF vs. ON (1000 data points per second).

Figure 10: Effect on experimental collision rates and beam

loss rates with 10 Hz feedback OFF vs. ON.

REFERENCES

[1] C. Montag, et al., “Status of Fast Orbit Feedback at

RHIC,” Proc. EPAC 2006, Edinburgh, Scotland.

[2] P. Thieberger, et al., “Recent Triplet Vibration

Studies in RHIC,” Proc. IPAC 2010, Kyoto, Japan.

[3] R. Michnoff, et al., RHIC BPM System Average

Orbit Calculations,” Proc. PAC 2009, Vancouver.

[4] R. Hulsart, et al., “Fast BPM data distribution for

global orbit feedback using commercial gigabit

Ethernet technology,” Proc. PAC 2011, New York.

[5] P. Thieberger, et al., “The Dipole Corrector Magnets

for the RHIC Fast Global Orbit Feedback System,”

Proc. PAC 2011, New York.

[6] C. Liu, et al., “Near Real-time ORM Measurements

and SVD Matrix Generation for 10 Hz Global Orbit

Feedback in RHIC,” Proc. PAC 2011, New York.

[7] M. Minty, et al., “Global Orbit Feedback at RHIC,”

Proc. IPAC 2010, Kyoto, Japan.

[8] C. Montag, et al., Nucl. Instr. Meth. A 564, 26-31

(2006)

10 Hz feedback OFF 10 Hz feedback ON

March 2, 2011

(250 GeV polarized protons)

Triplet magnet

cryostat

suspected of

vibrating and

causing 10 Hz

beam

oscillations.

10 Hz corrector

magnets

Magnet

stand

7-turn coil to

compensate fringe

field from magnet

in other ring

10 Hz feedback OFF 10 Hz feedback ON

March 2, 2011

10 Hz feedback OFF 10 Hz feedback ON

2 second period 2 second period

BPM bi5-bh3

Mic

ron

s M

icro

ns

4 minute period

Time of day

Time of day Time of day

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