Digital Low-Level RF control system for Accumulator Ring at Advanced Light Source Upgrade Project

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Digital Low-Level RF control system for

Accumulator Ring at Advanced Light Source

Upgrade Project

Qiang Du∗, Shreeharshini Murthy, Michael Betz, Kevin Bender, Wayne Lewis, Najm Us Saqib,

Sergio Paiagua, Lawrence Doolittle, Carlos Serrano, Benjamin Flugstad, Kenneth Baptiste

Lawrence Berkeley National Laboratory

1 Cyclotron Rd, Berkeley, CA, 94720 USA

Email: QDu@lbl.gov

Abstract—Currently ALS is undergoing an upgrade to ALS-

U to produce 100 times brighter soft X-ray light. The LLRF

system for Accumulator Ring (AR) is composed of two identical

LLRF stations, for driving RF ampliﬁers. The closed loop RF

amplitude and phase stability is measured as <0.1% and

<0.1◦respectively, using the non-IQ digital down conversion

together with analog up/down conversion, under a system-on-

chip architecture. Realtime interlock system is implemented

with <2µs latency, for machine protection against arc ﬂash

and unexpected RF power. Control interfaces are developed to

enable PLC-FPGA-EPICS communication to support operation,

timing, cavity tuning, and interlock systems. The LLRF system

handles alignment of buckets to swap beams between AR and

Storage Ring by synchronous phase loop ramping between the

two cavities. The system also includes an optimization routine to

characterize the loop dynamics and determine optimal operating

point using a built-in network analyzer feature. A cavity emulator

of 31 kHz bandwidth is integrated with the LLRF system to

validate the performance of the overall system being developed.

I. INTRODUCTION

The Advanced Light Source (ALS) at Lawrence Berkeley

National Laboratory is a U.S. Department of Energy’s syn-

chrotron light source user facility that is operational since

1993. With circumference of 196.8 m, the ALS Storage Ring

(SR) keeps electron beam current of 500 mA at 1.9 GeV under

multi–bunch mode user operation to deliver synchrotron X-

rays to surrounding 40 experimental end stations. [1]

There is an ongoing ALS upgrade project (ALS-U), sched-

uled to upgrade towards 2 orders of magnitude increase in

brightness and ﬂux of 1keV soft X-rays at diffraction limit.

The ALS-U project involves a new 2.0 GeV Storage Ring

(SR) in existing tunnel optimized for low emittance, and add

a new 2.0 GeV Accumulator Ring (AR) for full energy swap-

out injection and bunch train recovery, as shown in Fig. 1.

The AR is a triple-bend-achromat (TBA) lattice, very similar

to the current ALS SR lattice. The RF system requirements

for the TBA lattice can be found in Table I. Two normal

conducting RF cavities have been selected for AR. Each RF

cavity is driven by an identical chain from a high power solid-

state ampliﬁer (SSA) and low-level RF (LLRF) control system,

together with personnel safety interlocks, equipment protection

interlocks, etc.

Fig. 1: ALS Upgrade with both Accumulator and Storage

Rings

ALS SR ALS-U SR ALS-U AR

Cavity RF Frequency 499.64 500.394 500.394 MHz

Number of Cavities 2 2 2

Q(ea) 4.9 4.9 3.4–3.5 MΩ

Cavity voltage 671 300 500 kV

β2.9 10.6 1.18

Energy loss per trun 329 347 270 keV

BM Beam Power 141 125 13.3 kW

ID Beam Power 42 35 kW

3HC Beam Power 7.3 13.8 kW

Parasitic Beam Power 2.9 (est.) 2.6 (est.) 0.2 kW

Total Beam Power 192.9 176.4 13.5 kW

Cavity Power(no beam) 46 9.2 36.0 kW

Cavity Power(beam) 142.5 97.4 42.7 kW

High Power Ampliﬁer 294.0 197.5 60 kW

TABLE I: ALS and ALS-U AR and SR RF parameters

II. HARDWARE DESIGN

The AR LLRF system consists of two identical stations,

each controlling one SSA and RF cavity, but sharing communi-

cation interface with a central interlock PLC and both stations

are coordinated By common timing events for synchronous

operations. Each LLRF station consists of an analog frontend

chassis and a digital chassis. The analog chassis receives ALS-

U master oscillator and generates local oscillator (LO) signal,

and provides frequency conversions including 6 channels of

down-conversion and 2 channels of up-conversion between

arXiv:2210.05095v1 [physics.acc-ph] 11 Oct 2022

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DigitalLow-LevelRFcontrolsystemforAccumulatorRingatAdvancedLightSourceUpgradeProjectQiangDu,ShreeharshiniMurthy,MichaelBetz,KevinBender,WayneLewis,NajmUsSaqib,SergioPaiagua,LawrenceDoolittle,CarlosSerrano,BenjaminFlugstad,KennethBaptisteLawrenceBerkeleyNationalLaboratory1CyclotronRd,Berkeley,CA,947...

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Digital Low-Level RF control system for Accumulator Ring at Advanced Light Source Upgrade Project

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