cavities auto recovery with beam rf&linac section - alba accelerators division francis perez...
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Cavities Auto Recovery with BeamRF&Linac Section - ALBA Accelerators Division
Francis Perez
Angela Salom
ALBA Overview ALBA Accelerators RF plants of Booster and SR LLRF Conceptual Design
Automatic Recovery with beam Automatic startup without beam Automatic recovery with beam Trips postmortem analysis
Future Upgrade: Feedforward loops
Outline
Cavities autorecovery with beam – LLRF Workshop – October 2013 2/21
ALBA Overview
ALBA is a 3rd generation synchrotron light source, located at 20 km from Barcelona, Spain.
History2004. Start Acc + Building design2008 Linac Installation (turnkey system)2009 Booster Installation2010 Booster Commissioning and SR Installation2011 SR Commissioning2012 Operation with users
ALBA Overview
Cavities autorecovery with beam – LLRF Workshop – October 2013 4/21
LINAC100MeV
BoosterRamping at 3Hz
SR3GeV
ALBA Overview
Accelerators Main Parameters
Energy 3GeV
Circumference 268m
Beam Current 400mA
Emittance 4nm.rad
Lifetime ≈10h
RF Freq 500MHz
Beamlines up to 34
Cavities autorecovery with beam – LLRF Workshop – October 2013 5/21
RF Plants
Booster RF Plant
Ramping from 100MeV to 3GeV at 3Hz
Petra Cavity type (5 Cells)
Normal Conducting
500MHz
80kW CW - IOT
Injection Extraction
Cavity voltage 55kV 1000kV
Energy loss 0.001keV/turn 627keV/turn
Cavity power 0.1kW 33kW
Beam Power 0kW 2.5kW
Sync. Freq 13.7kHz 9.4kHz
Cavities autorecovery with beam – LLRF Workshop – October 2013 7/21
Storage Ring RF Plants
6 RF Plants of 160kW at 500 MHz
2 IOT Transmitters per RF cavity. Power combined in CaCo
Dampy CavityNormal ConductingSingle cell, HOM damped3.3 MΩ
Digital LLRF System based on IQ mod/demod
RF Parameters
U0 1.3MeV/turn
Vtotal 3.6 MV
q ≈ 2.5
fs ≈ 9kHz
PRF 960kW
Cavities autorecovery with beam – LLRF Workshop – October 2013 8/21
LLRF Conceptual Design
ALBA LLRF
Main Characteristics Based on digital technology using a
commercial cPCI board with FPGA
Signal processing based on IQ demodulation technique
Main loops: Amplitude, phase and tuning
RF diagnostics: Circular buffer for post-mortem analysis (0.5s)
Extra utilities Automatic conditioning for cavities Automatic soft start
Loops Resolution and bandwidth (adjustable parameters) Resolution Bandwidth Dynamic Range
Amplitude Loop < 0.1% rms [0.1, 50] kHz 30dB
Phase Loop < 0.1º rms [0.1, 50] kHz 360º
Tuning < ± 0.5º -- < ± 75º
Digital board: VHS-ADC from Lyrtech
Cavities autorecovery with beam – LLRF Workshop – October 2013 10/21
Analog Front End
Down Conversion
FPGA
Digital IQ Demodulation
Analog Front End
UpConversion
IOT2
RF Cavity Voltage (500MHz)
IF
RF Forward Cavity Voltage(500MHz)
Analog Timing System520MHz 500MHz
80MHz80MHz
CAVITY
Tuning Control Loop
Digital Timing SystemPCI Bus
DIGITAL LLRF - HARDWARE SCHEME
ICEPAPMotor Controller
13 RF Diagnostic Signals (500MHz)
IOT1CACO
DC
500MHz
8 ADCs80MHz
8 ADCs80MHz
FPGA
Digital IQ Demodulation and Control Loops
Control Inputs
Diagnostics Inputs
IQ Ctrl IOT1& IOT2
8DACs80MHz
Analog Front End
Down Conversion
FPGA
Digital IQ Demodulation
Analog Front End
UpConversion
IOT2
RF Cavity Voltage (500MHz)
IF
RF Forward Cavity Voltage(500MHz)
Analog Timing System520MHz 500MHz
80MHz80MHz
CAVITY
Tuning Control Loop
Digital Timing SystemPCI Bus
DIGITAL LLRF - HARDWARE SCHEME
ICEPAPMotor Controller
13 RF Diagnostic Signals (500MHz)
IOT1CACO
DC
500MHz
8 ADCs80MHz
8 ADCs80MHz
FPGA
Digital IQ Demodulation and Control Loops
Control Inputs
Diagnostics Inputs
IQ Ctrl IOT1& IOT2
8DACs80MHz
IQ Ctrl IOT1& IOT2
Analog Front End
Down Conversion
FPGA
Digital IQ Demodulation
Analog Front End
UpConversion
IOT2
RF Cavity Voltage (500MHz)
IF
RF Forward Cavity Voltage(500MHz)
Analog Timing System520MHz 500MHz
80MHz80MHz
CAVITY
Tuning Control Loop
Digital Timing SystemPCI Bus
DIGITAL LLRF - HARDWARE SCHEME
ICEPAPMotor Controller
13 RF Diagnostic Signals (500MHz)
IOT1CACO
DC
500MHz
8 ADCs80MHz
8 ADCs80MHz
FPGA
Digital IQ Demodulation and Control Loops
Control Inputs
Diagnostics Inputs
8DACs80MHz
Commercial Digital Board: cPCI
Commercial Digital Board: cPCI
LLRF Conceptual Design
Conceptual Design and Prototype
Analog Front Ends for Downconversion (RF to IF) and Upconversion (DC to RF)
Digital Commercial Board: cPCI with 16 ADCs, 8 DACs and Virtex-4 FPGA
Timing systems: 520MHz (500 + 20 MHz) for downconversion synchronized with digital 80MHz clock for digital acquisition
Analog Front End
Down Conversion
FPGA
Digital IQ Demodulation
Analog Front End
UpConversion
IOT2
RF Cavity Voltage (500MHz)
IF
RF Forward Cavity Voltage(500MHz)
Analog Timing System520MHz 500MHz
80MHz80MHz
CAVITY
Tuning Control Loop
Digital Timing SystemPCI Bus
DIGITAL LLRF - HARDWARE SCHEME
ICEPAPMotor Controller
13 RF Diagnostic Signals (500MHz)
IOT1CACO
DC
500MHz
8 ADCs80MHz
8 ADCs80MHz
FPGA
Digital IQ Demodulation and Control Loops
Control Inputs
Diagnostics Inputs
IQ Ctrl IOT1& IOT2
8DACs80MHz
Cavities autorecovery with beam – LLRF Workshop – October 2013 11/21
Automatic Recovery with Beam
One cavity -out of six- trips
Beam is not lost
One wants to recover the tripped cavity with heavy beam loading
RF Autorecovery with beam
Automatic Start up – Initial version:
- When RF trips LLRF Standby:- Low RF drive- Disable tuning - Open loops (I&Q)
- When RF ON LLRF smooth startup- Minimum RF Drive (low power to avoid high reflected power)- Tuning enabled- Amplitude and phase loops closed
- Smooth power increase
Main Inconvenients when applying this startup with beam:- After a trip, the cavity remains tuned it steals power from beam and
in some cases make it unstable
- Recovering the cavity with beam, when tuning the cavity, the beam induces more voltage in the cavity than the IOT Tuning loop becomes crazy
Cavities autorecovery with beam – LLRF Workshop – October 2013 13/21
RF Autorecovery with beam
New Automatic Start up – to take into account beam loading:
- When RF trip- Open loops (I&Q)- Disable tuning - Detune cavity (parking) by moving the plunger 30,000 steps up
- When RF ON:- IOT power high enough to induce more voltage in the cavity than the
beam loading after unparking- Amplitude and phase loops open because cavity is completely detuned
- Phase and amplitude of LLRF adjusted to have very similar conditions in open loop and close loop
- Plunger moved back 30,000 steps to tune cavity (unparking)- Tuning enabled
- Amplitude and phase loops closed- Smooth power increase
- Tested in all cavities at 130mA
Cavities autorecovery with beam – LLRF Workshop – October 2013 14/21
RF Autorecovery with beam
Cavity 10B trip:Other 5 cavities increase power
10B steals -20kW power to the
beam
After trip Parking Process starts
After 15s, 10B power = 0kW
1.552 1.554 1.556 1.558 1.56 1.562
x 104
-20
-15
-10
-5
0
5
10
15
20
25
30
t (s)
Pow
er to
the
beam
(kW
)
Cavity 10B trip
PBeam 06A
PBeam 06B
PBeam 10APBeam 10B
PBeam 14A
PBeam 14B
There are 6 cavities: 06A - 06B – 10A – 10B – 14A – 14B
1.5805 1.581 1.5815 1.582 1.5825 1.583 1.5835 1.584 1.5845 1.585
x 104
-15
-10
-5
0
5
10
15
20
25
t (s)
Pow
er to
the
beam
(kW
)
Cavity 10B autorecovery with beam
PBeam 06A
PBeam 06B
PBeam 10A
PBeam 10B
PBeam 14A
PBeam 14B
RF Autorecovery with beam
Cavity 10B autorecoveryRF ON in 10B: some power to the beamUnparking Process startsAfter unparking, 10B steals power to the beamTuning Loop Enable (10B power > 0kW)Amplitude and phase loop enable and power increased
10B RF ON Unparking Tuning
1485 1490 1495 1500 1505 1510 1515 1520-100
-50
0
50
t(s)
Tu
nin
gD
ep
ha
se (
º)
Cavity 10B Autorecovery with beam
TunDephase-10B
Tuning Dephase during autorecoveryRF ON : TuningDephase = -90ºUnparking Process starts → Tuning dephase approaching 0º and then overpasses this value
Cavities autorecovery with beam – LLRF Workshop – October 2013 16/21
1.581 1.582 1.583 1.584 1.585 1.586 1.587
x 104
140
160
180
200
220
240
t(s)
Bea
m P
hase
(º)
BeamPhase-06A
BeamPhase-06B
BeamPhase-10A
BeamPhase-10B
BeamPhase-14A
BeamPhase-14B
Cavity 10B autorecovery with beam
RF Autorecovery with beam
Cavity 10B autorecoveryRF ON: 10B Beam phase ~ 140ºUnparking Process finishes: 10B Beam phase ~ 230ºConclusion: the unparking process should move the plunger less steps than the parking process
10B RF ON Unparking Tuning
Beam Phase respect to RF ~ 150º
Cavities autorecovery with beam – LLRF Workshop – October 2013 17/21
0 0.5 1 1.5 2 2.5 3 3.5 4
x 10-3
100
110
120
130
140
150Beam Phase
t(s)
(º)
Beam Phase (º)
0 0.5 1 1.5 2 2.5 3 3.5 4
x 10-3
0
2
4
6
8
10
12Cav Dis - RvCav - Beam Power
t(s)
kW
Cav DisBeamPowerRvCav
Trips Post Mortem Analysis
Sometimes beam does not survive after RF trip
- The less # of cavities, the more likely to have beam dump due to RF trips- The higher the current, the higher reflected power in other cav. after a RF
trip
Will the beam survive at 400mA after a RF trip?
Transient of 06B after trip in 10A
Behaviour of 06B after a trip in 10B and no beam dump (61mA)Power to the beam increasesBeam phase gets reducedFrequency oscillations ~ 6kHz (synchrotron freq)Stabilization time ~ 3ms (longitudinal damping time)
Effect on beam trajectory (BPMs reading after RF ITCK – Data provided by A. Olmos)Cavities autorecovery with beam – LLRF Workshop – October 2013 18/21
Trips Post Mortem Analysis
Behavior of 06B after a trip in 10A and Beam Dump (100mA)Power to the beam starts to increaseBeam phase starts to get reducedBUT Reflected power reaches interlock level: 16kW
0 0.2 0.4 0.6 0.8 1 1.2 1.4
x 10-3
100
150
200
250Beam Phase
t(s)
(º)
Beam Phase (º)
0 0.2 0.4 0.6 0.8 1 1.2 1.4
x 10-3
-20
-15
-10
-5
0
5
10
15Cav Dis - RvCav - Beam Power
t(s)
kW
Cav DisBeamPowerRvCav
Provisional solution:Reflected power interlock level increased up to 23kWCavities detuned to avoid Robinson instability and to reduce the amplitude of reflected power in active cavities when one RF cavity trips
Maximum reflected power calculated when working at 400mA (data provided by Bea Bravo)Cavities β adjusted to have minimum reflected power at 400mAWorking with 6 Cavities, 600kV/cav, 400mA → RF trip causes:
Reflected Power transient of 73kW per cavity Circulator incapable to react against fast transients Reflected power will reach IOTsWill beam survive at 400mA after RF trip? Still don’t know, but not likely
Cavities autorecovery with beam – LLRF Workshop – October 2013 19/21
Future upgrade: Feedforward loops
Feedforward Loop
Feedforward loop to compensate transient when RF cavity tripsWhen cavity trips
- Cavity Voltage oscillates with frequency equal to synchrotron tune
- Transient time equal to damping time of machine
Compensation- Amplitude modulation triggered when
one cavity trips- Frequency, amplitude and phase of
modulation are adjustable parameters
Tests with beam still pending
Cavity Voltage & Beam Phase transient after RF trip
Cavity voltage, Power to Beam and Cavity Reverse Power
19 19.5 20 20.5 21 21.5 22 22.5 235000
5500
6000
6500
7000
7500
8000
8500
t(ms)
VC
av (
a.u.
)
Amplitude Modulation of Cavity after fake interlock
Cavities autorecovery with beam – LLRF Workshop – October 2013 21/21
Thanks for your attentionQuestions?