Overview of LLRF Developments at the BNL Collider-Accelerator Complex 2011.75 - 2013.75 (What We’ve Been Doing with the RHIC LLRF Platform) Kevin Smith

LLRF 2013, Lake Tahoe, CA, USA October 1, 2013 1

Overview of LLRF Developments at theBNL Collider-Accelerator Complex

2011.75 - 2013.75

(What We’ve Been Doing with the RHIC LLRF Platform)

Kevin Smithfor the C-AD LLRF Group

Tom Hayes, Geetha Narayan, Freddy Severino, Scott Yuan

LLRF 2013, Lake Tahoe, CA, USA October 1, 2013

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Outline of This Presentation

• Overview of the C-AD Complex at BNL• Brief Review of the RHIC LLRF Upgrade Platform

• RHIC Bunch by Bunch Longitudinal Damper (Poster, DSP Tutorial II)• RHIC Periodic Transient Beam Loading Compensation (Poster)• R&D Energy Recovery Linac (ERL) LLRF Commissioning (Poster) • AGS LLRF System Upgrade• Booster LLRF System Upgrade

• Conclusion


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Overview of the C-AD Complex Before We Overview the LLRF Developments

RHIC: Relativistic Heavy Ion Collider• 2.5 – 100 GeV/n Ions

• Symmetric or asymmetric• 250 GeV Polarized Protons• Current RF systems

• 9 MHz, 28 MHz, 197 MHz• Future RF systems

• 56 MHz SRF (Lumi Increase)• 4.5 MHz (Low Energy eCooling)

AGS• Injector for RHIC• RF systems

• 600 kHz, 1.2MHz-4.5MHz

Booster• Injector for AGS• Accelerator for NSRL facility• RF systems

• 400 kHz-4.5MHz

EBIS• Electron Beam Ion Source• Ion source for Booster• RF systems

• 100.125MHz RFQ, Linac and Bunchers R&D Energy Recovery Linac

• First application of SRF systems at C-AD• 703 MHz 1MW SRF Photo-Cathode Gun and 5-Cell ERL Cavity

ERL


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LLRF Developments Throughout C-AD are Based on The RHIC LLRF Platform

RHIC LLRF Platform

• A digital LLRF control platform which is extremely flexible, high performance and readily scalable.

• We designed it to satisfy all the LLRF applications we have across the entire C-AD Complex.• Existing: RHIC, AGS, Booster Upgrades• Development: EBIS, R&D ERL• Unanticipated:

• Bunch by Bunch Longitudinal and Transverse Damping

• RHIC Spin Flipper

• Architecture described in prior LLRF Workshops, PAC 2011.

• Only four major components used to date for LLRF:• Carrier Board• 4CH High Speed DAC and ADC Daughter Boards• Update Link Master

• Deterministic (i.e. fixed latency) gigabit serial link distributing encoded timing and data.• Provides for much of the simplicity and ease of system integration, scaling and synchronization.

Platform Chassis showing Carrier Board, 2 DAC Daughter Boards and 1 ADC Daughter Board.


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RHIC Bunch by Bunch Longitudinal DamperRHIC Bunch by Bunch Longitudinal Damper Background• Polarized Protons in RHIC are captured and accelerated in a 9MHz RF system common to both the BLUE and YELLOW rings.• Above intensities of about 0.5E11/bunch, proton bunches in the RHIC 9MHz system exhibit multiple modes of longitudinal instability.• The existing RHIC LLRF system B2B phase loop damped the coherent dipole oscillations, via 9 MHz “Bouncer” cavities in each ring.• The RHIC Bunch by Bunch Longitudinal Damper was built to damp the incoherent bunch by bunch dipole oscillations.

ADC

DAC

DACs

Arb WFG Table64 KB

X

X

DAC 0 (INSIDE)Bucket By BucketAmplitude Control

Bunch Tracker

DAC

DAC 1 (OUTSIDE)Bucket By BucketAmplitude Control

Update Link Master Chassis

ULR

LLRF Drive Strip Line Kickers(Bunch

byBunch

Damping)

Bunch By BunchPhase Detector

Firmware

BLUE Wall Current Monitor

PPCBBD Loop

UL

DACDDS

ULRDDSPhaseControl

UL

PPCProgram DSP

(Open Loop Frequency Calc)

PPCMain Beam Control Loop

(Includes Coherent Bunch to Bucket Phase Loop)

FPGA

FPGA

LLRF DriveBLUE

Bouncer(Coherent Damping)

(BLUE) DAC Daughter Card in Bunch By Bunch Damper Chassis

DAC Daughter Card in YELLOW Bouncer Cavity Controller Chassis

ADC Daughter Card (BTB Phase & Radial Processor)

DACDDS

ULRDDSPhaseControl

FPGA

DAC Daughter Card in BLUE Bouncer Cavity Controller Chassis

LLRF DriveYELLOW Bouncer

(Coherent Damping)

DAC Daughter Card

BLUE System Controller Chassis(YELLOW is Identical)

Items in RED highlight the Bunch by Bunch Damper extension to the RHIC LLRF System.

FPGA

FPGA

(Identical second DAC card used for

YELLOW Ring)

• A straight forward extension of the existing RHIC LLRF system.

• Takes advantage of key platform capabilities allowing for easy integration and system development.

• Flexibility• Lots of spare resources• Update Link

• Commissioned over several four hour machine development periods. Very quickly made operational.

Damper Off Damper On

One Turn Mountain Range Plots of a 110 bunch RHIC Blue Ring Fill.


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RHIC Bunch by Bunch Longitudinal DamperRHIC Bunch by Bunch Longitudinal Damper Results• The damper had a tremendous impact on the longitudinal stability of the beams in RHIC and the resulting longitudinal emittance.• Ultimately it allowed for an increase in per bunch intensity of roughly a factor of three over the undamped case (without using 197MHz for landau damping).• Operational intensity increase smaller as landau cavities also increase longitudinal stability at higher intensities.

Bunch to Bucket Phase measurement along a RHIC PP energy ramp to 255GeV.

Select measurements for about 10 bunches along the 110 bunch train are shown.

RMS bunch length growth while sitting at injection.

Damper reduces growth from about 140% to 20%. IBS also contributes to growth.

DAMPER OFF DAMPER ON

DAMPER OFF DAMPER ON


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Periodic Transient Beam Loading CompensationRHIC Periodic Transient Beam Loading Compensation Background• The fundamental RF seen by polarized proton bunches in RHIC comprises a “Common” (to both BLUE and YELLOW Beams) 9MHz cavity, and an

individual 9MHz “Bouncer” cavity used for damping coherent dipole motion via the bunch to bucket phase loop.• The beam driven response of RF cavities is affected by the fill pattern. They see transients from the abort gap, and any other empty buckets, that are

periodic at the revolution frequency.• Therefore different bunches along the bunch train see different RF voltages (amplitude and phase), resulting in a shift in the centroid position of each

bunch with respect to the RF reference.RHIC Blue Ring Bunch Fill Pattern (One Turn)

Bunch Phase Shift Due to Transient Beam Loading

Each data point is phase for a particular bunch along 1 turn.

Second transient from twounpopulated buckets in the fill pattern.

Main transient from beam abort gap.

Bunc

h Ph

ase

(Deg

rees

of 9

MH

z)

PTBL leads to longitudinal emittance growth at injection and also at what we refer to as “rebucketing” at RHIC store.

At injection for example, if Bunch 1 is well phase matched to the unloaded RF, subsequent injections will have progressively worse phase mismatches.

The landau voltage required to stabilize the highest intensity fills dominates the particle motion and leads to emittance growth from the phase mismatch that the BBB damper can’t react to.

Note: There is also a 197MHz landau cavity acting on the bunches in this plot and the plot at right. It’s required to

stabilize bunches against intensity driven instabilities.

One Turn Mountain Range of Bunches One Turn Overlay Plots of Bunches

Empty buckets report zero phase.


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Periodic Transient Beam Loading CompensationRHIC Periodic Transient Beam Loading Compensation Technique and Results• The key to measurement and then compensation of transient beam loading was the development (G. Narayan – stay tuned for DSP Tutorial Part II later this week) of a

very flexible piece of firmware for the platform ADC card, in this application generally referred to as the Bucket by Bucket Phase Detector. It is capable of providing filtered turn by turn, bucket by bucket amplitude and phase information on digitized RF signals (bunches via WCM, cavity pickup, bunches via BPM …).

• This firmware coupled with the platform’s intrinsic interconnection and synchronization capabilities (provided by the LLRF Update Link) enabled rapid and very successful development of the RHIC periodic transient beam loading compensation scheme.

• Compensation is applied in the form of bucket by bucket phase modulation of the LLRF drive for the 9 MHz bouncer cavity.

The four larger plots show measured data without PTBL compensation active.

Note that the Bouncer Cavity runs at about 1/7 the voltage of the Common Cavity.

Much larger phase shift than Common, but weighted by 1/7 in the vector sum of the Common and Bouncer Cavities.

The second large transient in the Common Cavity is missing below from the Bouncer Cavity.

The Common sees both Blue and Yellow Beams. This is the Blue abort gap transient.

Inset plot is the vector sum phase with PTBL correction active.

• Although 9MHz vector sum correction was close to “perfect”, only 1/3 of the observed bunch phase shift was corrected.• Recent simulation indicate that the Blue and Yellow 28MHz cavities may be the source of the remaining observed phase shift.


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R&D Energy Recovery LinacR&D Energy Recovery Linac Background• The goal of the R&D ERL is to serve as a platform for R&D into high current ERLs.

• Particularly HOM issues, halo generation and control, and high-power, high-brightness generation and preservation.• Major RF Systems

• 1MW SRF Photo-Cathode Gun @ 703MHz• Strongly HOM Damped 5-Cell SRF Linac Cavity

Extremely difficult to read cutout from impossible to read ERL LLRF System Diagram highlighting major ERL system components (and no LLRF).

The R&D ERL represents the first C-AD LLRF foray into SRF cavity control.


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R&D ERL LLRF Challenges and Results (Gun)

Measured klystron phase modulation with klystron driving a shorting plate.

Y-Axis: Deg

X-Axis: Sec


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R&D ERL LLRF Challenges and Results (5-Cell Cavity)

Moving Forward• Gun conditioning recently began with a blank copper cathode inserted.

• Multipacting in the cathode stalk region has limited duty cycle to 40% at full gradient (22.5 MV/m => 2MeV).• Conditioning will continue once the actual multi-alkalai photocathode is inserted.• Hope to generate first beam later this fall.

• ERL development efforts unfortunately are the lowest priority amongst the many RHIC and C-AD operational requirements.

• Commissioning efforts are therefore sporadic. Most effort put into conditioning, not LLRF performance.


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Upgrade of the AGS LLRF System

• First phase of the upgrade completed prior to RHIC Run 13 (Jan 2013).• Lots of benefits upgrading from a 20+ year old analog system to digital.

• Upgraded Digital LLRF System vs Old Analog LLRF System

• Independent LLRF Drive for all Cavities vs Analog Heterodyne Up/Down Conversion• Direct synthesis of desired harmonic. Low noise. No sideband issues. Trivial to reconfigure harmonic families.• Old system required much kludging of frequency multipliers, dividers, switches, etc. to meet harmonic requirements.

• Digital Cavity IQ Loop vs Analog Magnitude Loop Only• Precision cavity amplitude and phase control and multiple fast protection algorithms.• Precision amplitude and phase particularly helpful for RHIC ion merge schemes.

• Digital Main Tuning Loop vs Analog Phase Detector Loop• Much better resonance control, minimum RF power, fewer tuning faults (RF Station Trips).

• Digital PA Grid Transformer Tuning Loop vs Analog Open Loop F to V Reference• Tremendous improvement in Power Amplifier (Tetrode) Grid Tuning, far fewer Grid Overvoltage faults (RF Station Trips).

• Digital Open Loop AGS to RHIC Synchro vs Analog ATR Synchro PLL• AC coupled BtB phase loop with open loop ramp to target frequency and phase.• Much improved bunch to bucket phase stability for ATR transfers.

• True PPM (Pulse to Pulse Modulation) vs Some true PPM, some pseudo PPM, some not PPM• AGS machine configuration (species, energy, etc.) can change cycle to cycle (typically ~ 4.5s cycle time) => PPM.• Upgraded digital LLRF can trivially reconfigure any and all parameters, functions, loop gains, etc.

(Flexibilty)

(Flexibility, Performance, Reliability)

(Performance, Reliability)

(Performance, Reliability)

(Flexibility,Performance, Reliability)

(Flexibilty)


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Upgrade of the AGS LLRF System

6 Cavity ControllersTwo Cavities Each

(Due to hardware shortage)

IQ Feedback LoopMain Tuning Loop

PA Grid Transformer Tuning Loop

Two System Controllers

Beam Control Loops

Synchro Loops

AuxiliarySynthesizers

for Other Systems

Update LinkMaster

. . . 19 Cavity Controllers

1 per Cavity9 Blue, 9 Yellow, 1 Common


Four System Controllers2 Blue, 2 Yellow

Beam Control Loops

RTR SynchroPTBL Comp.BBB Damper


for Other Systems

Update LinkMaster

AGS LLRF System RHIC LLRF SystemRHIC 4 o’clock

. . .

AGS to RHIC LLRFAbout 1km via fiber

link

Red lines represent

Update Link duplex fiber connections.

RHICLLRF

AGSLLRF

One example benefit of the LLRF Platform and Update Link – AGS to RHIC Synchro• ATR Synchro historically relied on an analog PLL system comprising:

• Analog B&Y synchro references as low as 371kHz from the RHIC LLRF, shipped on analog fiber links to AGS.• An analog synchro loop which was extremely difficult to setup and tune, noisy, and subject to loop closure

transients, drift and occasional loss of lock.• Via the LLRF Platform and the Update Link, ATR synchro becomes trivial, flexible and PPM:

• The only connection between AGS and RHIC are three single mode digital fibers carrying:• The master 100MHz system clock• The Update Link serial data stream.

• Local NCOs in the AGS LLRF serve as synchro phase references• AGS Rev Tick, RHIC Blue and Yellow Rev Ticks• Synchronized to the RHIC system NCOs via hard or soft reset codes on the Update Link.

• On a request to synchro AGS to RHIC:• The AGS LLRF ramps to the RHIC target frequency – this is exact, as it’s an NCO frequency word.• The local AGS and RHIC Rev Tick NCO phases are simultaneously latched.• The AGS LLRF switches to an AC coupled phase loop.• The AGS RF is adiabatically ramped to the target RHIC Blue or Yellow phase. No feedback loop needed.

Bunch by Bunch Damper Controller RHIC 2 o’clock

AGS Booster LLRF SystemUpdate Link Master

RHICBBB

Damper

BOOSTERLLRF


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Upgrade of the AGS Booster LLRF System (Summer 2013)

6 Cavity ControllersTwo Cavities Each

2 DACs, 2 ADCs(Due to hardware shortage)


PA Grid Transformer Tuning Loop


Beam Control Loops

Synchro Loops


for Other Systems

Update LinkMaster

. . . 4 Cavity Controllers

1 per Cavity1 DAC, 1 ADC



Beam Control Loops

Synchro Loops


for Other Systems

Update LinkMaster

AGS LLRF System Booster LLRF System

. . .

Red lines represent

Update Link duplex fiber connections.

To RHIC LLRF System

• Scalability is evident.• Should look fairly familiar at this point.• Same hardware, firmware and software.• Linked to AGS via the LLRF Update Link.• Commissioning system with beam this week.

• Worse places for me to be then Lake Tahoe.

Flexibility


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Conclusion

• The RHIC LLRF Platform has proven to be a tremendous success for us.• An awful lot of hard work by a very talented group of people to get to this point.• Has allowed us to:

• Upgrade, develop and support LLRF systems for a wide variety of machines.• RHIC, AGS, Booster, EBIS, R&D ERL

• Develop and commission capabilities we’ve never had.• RHIC Bunch by Bunch Longitudinal Damper• RHIC Periodic Transient Beam Loading Compensation

• Develop controllers for non-RF systems• RHIC Spin Flipper

• Begin development of yet more new systems and capabilities• RHIC Bunch by Bunch Transverse Damper• RHIC Quad Mode Damper• RHIC 56 MHZ SRF Beam Driven Storage Cavity

• Improved and simplified our ability to troubleshoot operational systems.• Vastly improved diagnostic data capabilities.

• Improved reliability and increased flexibility of all of systems.• Have yet to encounter an application which the Platform could not address.

Thank You for Your Attention

Documents

Overview of LLRF Developments at the BNL Collider-Accelerator Complex 2011.75 - 2013.75 (What We’ve Been Doing with the RHIC LLRF Platform) Kevin Smith