# Presentation: 662265

## Commissioning of the FPGA-Based Transverse and Longitudinal Bunch-by-Bunch Feedback System for Taiwan Light Source

**Commissioning of the FPGA-Based Transverse and Longitudinal Bunch-by-Bunch Feedback System for Taiwan Light Source**
- Kuo-Tung Hsu
- on behalf of the feedback team
- NSRRC
- Hsinchu 30076, Taiwan
- May 2, 2006

**BIW06, FNAL, May 1~4, 2006**

## I.	Introduction

**II.****	****Feedback Processor**
**III.****	****Transverse Feedback System**
**IV.****	****Longitudinal Feedback System**
**V.****	****Summary**

**Outline**

**BIW06, FNAL, May 1~4, 2006**

## I. Introduction

**TLS is a 1.5 GeV light source.**
**Dedication in October 1993.**
**Instabilities are severe in the operation of last decade.**
**SRF upgrade in Dec. 2004.**
**Routine top-up operation is started from Oct. 2005.**
**FPGA-based transverse and longitudinal feedback **
**	****system are deployed in Dec. 2005 and Feb. 2006.**

**BIW06, FNAL, May 1~4, 2006**

## II. FPGA Based Feedback Processor

**Adopted form the design of SPring-8.**
**Minor modification in FPGA code.**
**USB 2.0 interface is supported.**
**Up to 20 taps FIR filter is supported for transverse feedback.**
**Up to 50 taps FIR filter is supported for longitudinal feedback.**
**Up to 10 (20) decimation factor is supported.**
**	****	****=> only useful for longitudinal feedback.**

**BIW06, FNAL, May 1~4, 2006**

## Structure of the Feedback Processor

- DDR F/F

- DDR F/F

- DDR F/F

- DDR F/F

- DDR F/F

**12 Bit**

**12 Bit**

**12 Bit**

**12 Bit**

**12 Bit**

- Delay FIFO

- Delay FIFO

- X 4  PLL

- 499.65 MHz

- 4:1
- MUX

- Delay FIFO

- x2 to 249.83 MHz

- 4:1
- MUX

- 4:1
- MUX

- Delay
- Adj.

- DDR SDRAM, 128 Mega Samples

- fRF/4 = 124.91 MHz

**DAC**
**500 MS/sec**

**ADC**
**125 MS/sec**

**FPGA: Xilinx VirtexII Pro XC2VP70-6FF1517C**

**50-tap FIR Filter**

**20-tap FIR Filter**

**20-tap FIR Filter**

- FIR Filter*

**Structure of the Feedback Processor**

**BIW06, FNAL, May 1~4, 2006**

## Feedback Processor

- Bunch
- Oscillation
- Detector

- Back-end
- Electronic
- and
- Power
- Amplifiers

- USB 2.0 Interface
- => Register access
- => Memory access

- Control Network

- Linux/PC :
- * Feedback Processor Linux Driver support
-    USB 2.0 access
- * Matlab interface
- Control database interface
- Feedback processor register access
- Captured bunch oscillation data access
- Feedback filter design
- Data analysis
- * Control console

- Linux
- (CentOS Distribution)

- Transverse
- Kicker

- Transverse
- and
- Longitudinal
- Pickup

- Longitudinal
- Kicker

**Feedback System Environment**

**BIW06, FNAL, May 1~4, 2006**

## III. Transverse Feedback System

- 1995 	Commissioning of the analog feedback system.
- 		* Only vertical instability is a problem.
- 		* Longitudinal instability is severe.
-  	Second tuner was introduced to RF cavities to shift HOM frequency.
- 		* Longitudinal instability is still severe.
- 		* Transverse instability can be controlled by optimized position of 	 	   the second tuner.
- 2004.12 	SRF put into operation.
- 	 	* Both horizontal and vertical instability are strong.
- 		* Difficult control by over compensated chromaticity.
- 2005.04	Analog transverse feedback loop is put back into service again
- 		* Both plane instability was suppressed, however, tune dependence is 	   strong. It is not easy to operate the machine with 0.1% flux
-                  stability.

**BIW06, FNAL, May 1~4, 2006**

## 2005.10.12 	Start top-up operation @ 200 mA

- 2005.10.12 	Start top-up operation @ 200 mA
- 2005.11.29 	Commissioning of the new transverse feedback system.
- 			* To solve the sensitivity problem of tune dependence.
- 			* To provide better damping for high current operation.
- 			* Increase injection efficiency by reduce chromaticity.
- 			=> High injection efficiency is  essential for top-up operation.
- 2005.11.30 	New digital transverse feedback system commissioning
- 			and put into service immediately.
- 2005.12		Start top-up operation at 300 mA

**BIW06, FNAL, May 1~4, 2006**

## Block Diagram of the New Transverse Feedback System

- A

- B

- C

- D

- ADC

- ADC

- 20tapFIR

- 20tapFIR

- ADC

- ADC

- 20tapFIR

- 20tapFIR

- DACs

- BBF
- Clock Generator

- Clock/4 =
- 124.913 MHz

- Clock/4 =
- 124.913 MHz

- Divider

- # A

- # B

- # B

- FPGA

- Clock

- 124.913 MHz

- fRF
- 499.654 MHz

- 250 W

- AR 250A250

- 10 KHz ~ 250 MHz

- Transverse Kicker

- 2 ns

- D

- 20 dB

- 20 dB

- 53 dB

- 53 dB

- 20 dB

- 20 dB

- 156 MHz
- LPF

**Block Diagram of the New Transverse Feedback System**

- 2 Vp-p

- LVDS

- 933 MHz LPF

- B

- D

- Feedback Processor

- ch 1

- ch 3

- ch 2

- ch 4

- 4 ns

- 4 ns

- 20 dB

- 20 dB

- 46 dB

- LNA

- X 4

- # 1, 5, 9, .. 197

- # 3, 7, 11, .. 199

- # 2, 6, 10, .. 198

- # 4, 8, 12, .. 200

**BIW06, FNAL, May 1~4, 2006**

## Location       x(m)  y(m)    x        y        x(m)

- Target Working Point
- (x, y) = (7.312, 4.168)
- Tunability    ~ 0.05
- C = 120 m
- Trev = 400.2 ns
- Frev = 2.49827 MHz

- Location       x(m)  y(m)    x        y        x(m)
- _R5 BPM1      11.3  5.4   4.876   3.018   0.033_
- _R5 Kicker        4.5  2.7   5.572   3.232   0.397_

- R5

- R4

- R3

- R2

- R1

- R6

- Feedback
- Electronics

- 80 nsec

- 150 nsec

**R5BPM1**
**(B - D)**

** ****Kicker**
**(B - D)**

**Layout of pickup & kicker**

**BIW06, FNAL, May 1~4, 2006**

## Parameters of the Transverse Feedback System

| Parameter | Value |
| --- | --- |
| Energy, E | 1.5 GeV |
| RF frequency, fRF | 499.654 MHz |
| Harmonic number, h | 200 |
| Revolution frequency, frev | 2.49827 MHz |
| Momentum compaction factor | 0.00067 |
| Operating current, IB | 302 mA (March 2006) |
| Betatron frequency, fx/fy | ~ 760 kHz / 450 kHz |
| Betatron tune, x / y  | ~ 0.31 / 0.17 |
| Down-sampling factor, D | 1 |
| Bunch sampling frequency | frev = 2.49827 MHz |
| Working frequency of the betatron oscillation detector | fRF |
| Taps of feedback FIR filter | up to 20 |

**Parameters of the Transverse Feedback System**

**Target Tune**

**Working tune bandwidth (change in arbitrary way)**
******x****: 716 kHz ~ 822 kHz (7.285 ~ 7.328)  =>     ******** > 0.04**
******y****: 400 kHz ~ 480 kHz (4.16 ~ 4.192)    =>****	****   ******** > 0.03**
**Negative chromaticity**
**Nominal setting (SF, SD) = (151 Amp, 124 Amp)**
**=> (SF, SD) = (121 Amp, 114 Amp)   => Beam is still stable**
**=> (SF, SD) = (100 Amp, 100 Amp)   => Beam is still stable**
**However, beam loss suddenly when turn off the feedback loop**

**Feedback Loop Tunability**

**BIW06, FNAL, May 1~4, 2006**

## Beam spectrum observation

**Beam spectrum observation – Feedback OFF and ON**

**Beam spectrum observation**
**(without longitudinal feedback)**

- Feedback OFF

- Feedback ON

**BIW06, FNAL, May 1~4, 2006**

## Loop Closed

- Loop Open

**Snapshot of Synchrotron Radiation Beam Profile**
**(w/o Longitudinal Feedback)**

**Grow/Damp test results @ 300 mA**

- Horizontal

- Vertical

- Vertical

- Horizontal

- Modal
- Spectrum

**BIW06, FNAL, May 1~4, 2006**

## Stable operation have been achieved in users shift.

- Better than 10-3 photon flux stability can be achieved routinely.
- Various feedback filters will be tested in a short-term to probe the possibility to improve system performance.
- Improve various components form operation point of views are under way.

**Current Status of the Transverse Feedback System**

**BIW06, FNAL, May 1~4, 2006**

## IV. Longitudinal Feedback System

-  Longitudinal instability is serve during last decade operation of TLS.
-  Optimized the second tuner position and RF gap voltage modulation is
-     the tools to deal this instability with the cost of large energy
-     oscillation.
-  After SRF upgrade
-     Strength of the longitudinal is weaker than before.
-     Mode pattern are much simple.
-     Longitudinal feedback system are used to lift the residue instabilities.
-  2006.01	New longitudinal kicker installed.
-  2006.02.06 	Longitudinal feedback system commissioning.

**BIW06, FNAL, May 1~4, 2006**

## Adaptation of the SLS Longitudinal Kicker to the TLS LFB System

- Summary of Measured Longitudinal Kicker Performance

-  Modified from the DAΦNE and BESSY kickers (four ridged waveguide damper; nose cone)
-  Center frequency @ 1375 MHz, BW > 250 MHz
-  Highest shunt impedance ~ 1500 Ω
-  A few higher order modes are trapped in the structure and are damped by a hybrid TE/TM coupler
-  Successful operation of the SLS longitudinal kicker
-  Easy adaptation to the TLS storage ring with minor modifications (nearly rectangular 28 x 88 mm beam pipe elliptical, 38 x 80 mm beam pipe)
-  Variation of group delay across the operation bandwidth found (~ 600 ps)
-  Symmetrical excitation to minimize transverse kick due to field non-uniformity

**Adaptation of the SLS Longitudinal Kicker to the TLS LFB System**

**BIW06, FNAL, May 1~4, 2006**

## Response of the Prototype FIR Filter

| Parameter | Value |
| --- | --- |
| Energy, E | 1.5 GeV |
| RF frequency, fRF | 499.654 MHz |
| Harmonic number, h | 200 |
| Revolution frequency, frev | 2.49827 MHz |
| Momentum compaction factor | 0.00067 |
| Operating current, IB | 300 mA (March 2006) |
| Synchrotron frequency, fs | 33.7 kHz |
| Synchrotron tune, s | 0.0136 |
| Down-sampling factor, D | 4 |
| Bunch sampling frequency | frev/4 = 625 kHz |
| Working frequency of the phase detector | 3 fRF (or 6 fRF) |
| Phase detector range | ± 30o (± 15o)  |
| Taps of feedback FIR filter | up to 50 |

**Parameters of the Longitudinal Feedback System**

**Response of the Prototype FIR Filter**

**BIW06, FNAL, May 1~4, 2006**

## s ~ 0.0136

- s ~ 0.0136
- C = 120 m
- Trev = 400.2 ns
- frev = 2.49827 MHz
- fs = frev/4 = 625 kHz

- R5

- R4

- R3

- R2

- R1

- R6

**R5BPM4**
**(A+B+C+D)**

**Longitudinal Kicker**

**Layout of pickup & kicker**

**Beam Position Monitor**
**(Energy Oscillation Detector)**

**Longitudinal Kicker**
**(Energy Correct Kick)**

**Power Amplifier**

- Feedback Electronics

**BIW06, FNAL, May 1~4, 2006**

## Block Diagram of the Longitudinal Bunch-by-Bunch Feedback System

**Block Diagram of the Longitudinal Bunch-by-Bunch Feedback System**

- A

- B

- C

- D

- ADC

- ADC

- 50tapFIR

- 50tapFIR

- ADC

- ADC

- 50tapFIR

- 50tapFIR

- DAC

- FPGA

- Clock

- 124.913 MHz

- 499.654 MHz

- 200 W

- 

- 53 dB

- LVDS

- I-Tech’s
- RF Front-End

- 499.654 MHz

- SSB
- Or
- QPSK
- Modulator

- Milmega AS0814-250R
- 0.8 GHz ~ 1.4 GHz

- 1500 MHz (SSB) or 1375 MHz (QPSK)

- Buffer and Delay Module

- 8 ns

- 4 ns

- 2 ns

- 6 ns

- Longitudinal Kicker

- X 4

- X 3

- BBF
- Clock Generator

- Clock/4 =
- 124.913 MHz

- Clock/4 =
- 124.913 MHz

- # 1, 5, 9, .. 197

- # 3, 7, 11, .. 199

- # 2, 6, 10, .. 198

- # 4, 8, 12, .. 200

**BIW06, FNAL, May 1~4, 2006**

## SSB Modulator

- RF Output

- Monitor

- I

- Q

- Excitation
- On/Off Control

- Correction Signal

- 499.654 MHz

- Frequency
- Multiplier

- 90o

- 0o

- Phase Shifter

- QPSK Modulator

- AD8131
- Differential Amplifier

- MiniCircuits Amplifier

- Sirenza STQ-2016
- 700-2500 MHz Direct Quadrature Modulator

**USB or LSB Selection**

- PULSAR  QE-14-442
- 90o Hybrids  (2~250 MHz)

- Shut-down control

- Beam Spectrum

**BIW06, FNAL, May 1~4, 2006**

## Temporal Behavior of Longitudinal Instability Build-up

- Loop Open 40 msec

**Temporal Behavior of Longitudinal Instability Build-up**

- Loop Open 100 msec

- Longitudinal Instability Signal

**BIW06, FNAL, May 1~4, 2006**

## Beam Phase and Beam Spectrum

**with Feedback Loop Open and Closed**

**Beam Spectrum**
**(Open-Loop  vs. Closed-Loop)**

- 62.5 MHz peak is due to filling pattern with 16 nsec periodicity

- 2nd harmonic
- of 62.5 MHz

**Filling Pattern**

**Beam Phase**
**w/o LFB**

**Beam Phase**
**w LFB**

**Beam Spectrum**
**Details**
**w/o and w LFB**

**BIW06, FNAL, May 1~4, 2006**

## Longitudinal Grow/Damp Experiments

**Longitudinal Grow/Damp Experiments**

- @ 250 mA

**BIW06, FNAL, May 1~4, 2006**

## Streak Camera Observation

**Streak Camera Observation**

**Loop Open**

**Loop Closed**

- One Turn

- One Turn

**Loop Closed -> Open -> Closed**

- One Turn

- Loop Open

**Loop Open**

**Snapshot of the Synchrotron Radiation Beam Profile**

- Loop Closed

- Loop Open

**BIW06, FNAL, May 1~4, 2006**

## Current Status of the Longitudinal Feedback System

- Stable operation have been achieved in users shift.
- Increase the beam brilliance at the results.
- Various feedback filters will be try to improve system performance.
- Improve aspect form operation point of views are same as transverse feedback system.

**BIW06, FNAL, May 1~4, 2006**

## V. Summary

-  Two major upgraded have been completed recently for the TLS.
- 	- SRF cavity
- 	- Top-up operation
-  Transverse feedback system upgrade from analog to digital
-     system in late 2005.
-  Longitudinal feedback system commissioning successful in
-     early 2006.
-  Both the transverse and longitudinal feedback loop adopt the
-     same feedback processor - SPring-8 designed feedback processor.
-  Modified SLS longitudinal kicker is used.
-  SLAC analysis code is adopted for transient signal analysis.
-   Both systems put into service immediately after commissioning.
-  Improved the system performance and functionality is on going.

**BIW06, FNAL, May 1~4, 2006**

## Thank You for Your Attention !

- Many peoples contributed to this project directly or indirectly. Thanks for their help.
- T. Nakamura, K. Kobayashi (JASRI/SPring-8)
- M. Dehler (SLS/PSI)
- M. Tobiyama (KEKB)
- J. Fox, D. Teytelman, S. Prabhakar (SLAC)
- J. Seebek (SSRL),
- G. Strover, J. Byrd (LBNL)

**BIW06, FNAL, May 1~4, 2006**