EnEfficient RF Sources workshop 2014, Cockcroft InstituteEric Montesinos, CERN-RF
TETRODES ARE EFFICIENT !
Eric Montesinos, CERN-RF 2EnEfficient RF Sources workshop, 03-04 June 2014, Cockcroft Institue
OutlineFrequency & Power range of tetrodes & diacrodes
Theoretical and measured efficiency
Availability vs Efficiency, an example with a YL1530 tetrode operated in the CERN SPS
Imposed parameters and their impact to efficiencyOverheadCirculatorsHigh Voltage Power SupplyFundamental Power Coupler
Granularity
Conclusion: Tetrodes are very efficient
Eric Montesinos, CERN-RF 3
0 50 100 150 200 250 300 350 400 450 50010
100
1000
10000Tetrodes & Diacrodes available from
industry
CW
Frequency MHz
Pow
er k
W p
er s
ingl
e tu
be
EnEfficient RF Sources workshop, 03-04 June 2014, Cockcroft Institue
Frequency & Power range of tetrodes
Eric Montesinos, CERN-RF 4
0 50 100 150 200 250 300 350 400 450 50010
100
1000
10000Tetrodes & Diacrodes available from
industry
peak < 1 ms
Frequency MHz
Pow
er k
W p
er s
ingl
e tu
be
EnEfficient RF Sources workshop, 03-04 June 2014, Cockcroft Institue
Frequency & Power range of tetrodes
Eric Montesinos, CERN-RF 5
0 50 100 150 200 250 300 350 400 450 50010
100
1000
10000Tetrodes & Diacrodes available from
industrypeak < 1 msCW
Frequency MHz
Pow
er k
W p
er s
ingl
e tu
be
EnEfficient RF Sources workshop, 03-04 June 2014, Cockcroft Institue
Frequency & Power range of tetrodes
Eric Montesinos, CERN-RF 6EnEfficient RF Sources workshop, 03-04 June 2014, Cockcroft Institue
Theoretical efficiency
RF power in
DC power in
Heat out
RF power out
PRFin + PDCin = PRFout + Heat
As with tetrodes Gain is usually > 13-16 dB
Eric Montesinos, CERN-RF 7
CBABA
EnEfficient RF Sources workshop, 03-04 June 2014, Cockcroft Institue
Amplifier class
InputSignal
OutputSignal
Operative curve
Class A
InputSignal
OutputSignal
Operative curve
Class B
Unsusedarea
InputSignal
Output SignalLess than 180⁰
Operative curve
Class C
Unsusedarea
360⁰2
270⁰3
180⁰ 90⁰Conduction Angle
0⁰0
A AB B C0%25%50%75%100%Efficiency
Amplifier Class Description
Class-A Full cycle 360⁰ of conduction
Class-AB More than 180⁰ of conduction
Class-B Half cycle 180⁰ of conduction
Class-C Less than 180⁰ of conduction
Eric Montesinos, CERN-RF 8EnEfficient RF Sources workshop, 03-04 June 2014, Cockcroft Institue
Theoretical Class B efficiencyDC power isPdc = Vdc Idc
Assuming the tube is linear whilst it is conducting, the dc anode current is found by Fourier analysis of the current waveform and is Idc = Ipk/πIrf = Ipk/2 = Idc π/2And ideal class B, Vrf = VdcSo, RF power isPrf = ½ Vrf IrfPrf = ½ Vdc Idc π/2 = π/4 Vdc Idc
Theoretical efficiencyη = Prf/Pdc = ¼ Vdc Ipk / Vdc Idcη = 78.5 % Vdc
Class B
Ipk
Eric Montesinos, CERN-RF 9EnEfficient RF Sources workshop, 03-04 June 2014, Cockcroft Institue
Class B efficiency in practiceTwo reasons for not achieving this impressive number1. tube is not fully linear whilst
it is conducting2. Anode voltage must be
higher than G2 voltage, VG2 being ~ 10% Vdc
This leads intoPdc = Vdc Idc = Vdc 1.05 Ipk/πPrf = ½ Vrf Irf = ¼ 0.9 Vdc IpkTheoretical efficiency in practiceη = Prf/Pdc = ¼ 0.9 Vdc Ipk / 1.05 Vdc Ipk/πη = 67 %
Class B
UG
2
Ipk
Vdc
Eric Montesinos, CERN-RF 10EnEfficient RF Sources workshop, 03-04 June 2014, Cockcroft Institue
Measurement on a YL1530 tube
0 5 10 15 20 25 30 35 40 45010203040506070
YL1530 @ 200 MHz (Filament – 7.5%)
CW output power [kW]
Effici
ency
RF/
DC Operating point
RF/DC efficiency = 66.4 %
Eric Montesinos, CERN-RF 11EnEfficient RF Sources workshop, 03-04 June 2014, Cockcroft Institue
Overall YL1530 efficiency @ 35 kWOperating conditions for 35 kWGain = 16 dB, PRFin = 0.88 kWPG1 & PG2 = 50 WPfilament = 1.3 kWIpk = 19 AVDC = 10 kVIDC = 1.05 Ipk/π = 6.4 AVRF = 8.5 kVIRF = Ipk/2 = 9.5 A
61 %
Class B
UG
2
Ipk
Vdc
Eric Montesinos, CERN-RF 12EnEfficient RF Sources workshop, 03-04 June 2014, Cockcroft Institue
CERN SPS
SPS1976 (7
km)
Eric Montesinos, CERN-RF 13EnEfficient RF Sources workshop, 03-04 June 2014, Cockcroft Institue
CERN SPS YL1530 Power plantsTwo amplifiers, 64 YL1530 tubes
Frequency 200.2 MHz
One amplifier delivers650 kW with 32 YL1530
-0.2 dB for combiningplant (-4.7 % power)
Each single tube is operated 21.2 kW
Overall Efficiency = 48 %
Eric Montesinos, CERN-RF 14EnEfficient RF Sources workshop, 03-04 June 2014, Cockcroft Institue
Overall YL1530 efficiency @ 21 kWOperating conditions for 21 kW with settings for 21 kWGain = 16 dB, PRFin = 0.58 kWPG1 & PG2 = 50 WPfilament = 1.3 kW de-rated to 1.2 kWIpk = 13 AVDC = 10 kVIDC = 1.03 Ipk/π = 4.3 AVRF = 6.5 kVIRF = Ipk/2 = 6.5 A
48.2 %
Class B
UG
2
Ipk35
Vdc
Ipk21
Eric Montesinos, CERN-RF 15EnEfficient RF Sources workshop, 03-04 June 2014, Cockcroft Institue
SPS Supercycle
SPS1976 (7
km)
North Area
CNGS2006
LHC2008 (27
km)
Eric Montesinos, CERN-RF 16
North Area CNGS LHC
EnEfficient RF Sources workshop, 03-04 June 2014, Cockcroft Institue
SPS SupercycleDuring 2012
Supercycle 48 seconds
19.25 seconds / 650 kW9.6 seconds / 488 kW19.15 seconds / 0 kW
For 7000 hours of operation 2.5 GWh
SPS1976 (7
km)
North Area
CNGS2006
LHC2008 (27
km)
Eric Montesinos, CERN-RF 17EnEfficient RF Sources workshop, 03-04 June 2014, Cockcroft Institue
Operating with ‘OFF Line’ TubesIn normal operation, one tube delivers a maximum power of650 kW + 4.7 % / 32 = 21.2 kW
Systems have been designed (1980) to deliver full voltage into the cavity even with only 24/32 tubes
In case of 8 tubes ‘OFF Line’, remaining tubes shall deliver23 kW x (32/24)^2 = 37.8 kW
32 x 21.2 kW = 18 x 37.8 kW = 680 kW
YL1530 tubes are rated 37.5 kW
32P 18P
Eric Montesinos, CERN-RF 18
1 y 2 y 3 y >= 4 y0
20406080
100120140160180200 YL1530 SPS 200 MHz, 2 x 32 tubes in
parallel(Filament – 7.5 % & 21 kW instead of
35kW)
# years of operation before failure of the tube
# tu
bes
EnEfficient RF Sources workshop, 03-04 June 2014, Cockcroft Institue
Tubes statistics
Total 1980-2013 : 254 tubes
Average lifetime : 32’000 hours
Tubes with > 28’000 hours : 78 %(also true for tubes stored 20 years !)
19EnEfficient RF Sources workshop, 03-04 June 2014, Cockcroft Institue Eric Montesinos, CERN-RF
Amplifiers statistics
Loss of
emission39%
Input re-
flec-tions38%
Un-known
8%
Over temp8%
Arcing7% Reason of
fault# of
faults% of
faultsLoss of emission 99 39
Input reflections 97 38
Unknown 20 8Over Temp 20 8Arcing 18 7We lose 14-16 tubes per year,
that we exchange during Technical Stops 3-4 times a yearUnpredictable : 23 % (equivalent to 4 tubes)Graceful degradation : 77 % (possible to monitor and predict)
YL1530 SPS 200 MHz, 2 x 32 tubes in parallel
Eric Montesinos, CERN-RF 20EnEfficient RF Sources workshop, 03-04 June 2014, Cockcroft Institue
Availability of the CERN SPSWith these operating conditions• - 7.5 % Ufilament → +37.5 %
lifetime• Off Line tubes for the
unpredictable faults• Overall efficiency 48 % during
cavity maximum voltage• Supercycle average power 390
kW
Over 7000 hours of operation in 2012, these two RF Power plants have been responsible for only 16 hours of down time !
2003 2008 20130
1
2
% S
PS d
own
tim
e
Eric Montesinos, CERN-RF 21EnEfficient RF Sources workshop, 03-04 June 2014, Cockcroft Institue
Availability of the CERN SPSAvailability of an Injector is the key parameter
CERN’s total annual electricity consumption is 1.3 TWh, for an operation of almost 7000 hours per year
When SPS is down, electrical bill without physics, costs 4500 CHF / h (minimum, only electricity cost based on 60 CHF / MWh)
20 % for LHC cryogenics + cooling and ventilation10 % for LHC experiments7 % for the North area experiments(http://cds.cern.ch/record/1324541?ln=en)
Eric Montesinos, CERN-RF 22EnEfficient RF Sources workshop, 03-04 June 2014, Cockcroft Institue
Availability of the CERN SPSWe can improve the efficiency from 48 % to 61 % of the RF Power source by• Increasing the filament to the
nominal value (- 37.5% lifetime)
• Reducing the number of tubes in operation(2 x 20 tubes operated 34 kW)
• no additional down time with ‘off line’ operation BUT reduced beam intensity(OR Three hours stop for a tube exchange
Savings 66,000 CHFMoney (electrical bill savings)2.5 GWh at 60 CHF/MWh with
48 % efficiency costs 312,000 CHF61 % efficiency costs 246,000 CHF
Costs 273,000 CHF(money, not taking into account impact to physics)14 additional tube exchanges,42 hours physics lost & electrical bill due to LHC & experiments infrastructure costs
Eric Montesinos, CERN-RF 23EnEfficient RF Sources workshop, 03-04 June 2014, Cockcroft Institue
Availability of the CERN SPSWe can improve the efficiency from 48 % to 61 % of the RF Power source by• Increasing the filament to the
nominal value (- 37.5% lifetime)
• Reducing the number of tubes in operation(2 x 20 tubes operated 34 kW)
• no additional down time with ‘off line’ operation BUT reduced beam intensity(OR Three hours stop for a tube exchange
Savings 66,000 CHFMoney (electrical bill savings)2.5 GWh at 60 CHF/MWh with
48 % efficiency costs 312,000 CHF61 % efficiency costs 246,000 CHF
Costs 186,000 CHF(money, not taking into account impact to physics)14 additional tube exchanges,42 hours physics lost & electrical bill due to LHC & experiments infrastructure costs
Eric Montesinos, CERN-RF 24EnEfficient RF Sources workshop, 03-04 June 2014, Cockcroft Institue
Availability of the CERN SPSWith respect to this CERN SPS example, applicable to all RF plants with smaller energy consumption compare to ‘other’ energy consumers in the machine,
being more efficient with RF power plant with an overall efficiency increased from 48 % → 61 %, and no margin in the RF power plant,
for the same beam qualityWill induce more accelerator stopsCost more electricity at the endEven worse if the kWh cost increases in the coming
years…
Eric Montesinos, CERN-RF 25EnEfficient RF Sources workshop, 03-04 June 2014, Cockcroft Institue
Overhead
0 500 1000 1500 2000 2500 3000 3500 4000 4500 50000
10
20
30
40
50
60
70YL1530, 35 kW @ 200 MHz
Input power W
Out
put p
ower
kW 1 s (x1.4)100 µs (x1.5)
10 µs (x1.7)
CW (x1.2)
35 kWnominal
CourtesyWolfgang Höfle
Eric Montesinos, CERN-RF 26EnEfficient RF Sources workshop, 03-04 June 2014, Cockcroft Institue
Overhead
0 0.5 1 1.5 2 2.5 3 3.5 40
0.20.40.60.8
11.21.41.6
Tetrodes, Klystrons, SSPA
Tetrode
Input power / nominal Input power
Out
put p
ower
/ no
min
al
Out
put p
ower
RF Pulse
Overhead needed for LLRF
operation
klystrons
Eric Montesinos, CERN-RF 27EnEfficient RF Sources workshop, 03-04 June 2014, Cockcroft Institue
HVPS
For tetrodes (and gridded tubes more generally) HVPS is very simpleNo RF -> idle current (can be zero in class B or class C)
Even if HV is drooping, the LLRF will impose output power, and tetrode remains able to deliver requested Power
RF Pulse RF Pulse
time
PdcHV10-20 % tolerant
HVless tolerant
Griddedtubes
klystrons
0 2 4 6 8 10 120
102030405060708090
100RS2004 tetrode
Unominal (8.5 kV)- 10 % U nom-inal-20 % Unominal
Pin kW
Pout
kW
Eric Montesinos, CERN-RF 28EnEfficient RF Sources workshop, 03-04 June 2014, Cockcroft Institue
CirculatorIf the reflected power is not too long, Tetrodes do NOT need a circulator
With a good reflected power protection, Tetrodes can sustain full reflection
We operate the SPS since 1976-1980 without a single failure due to reflected power
Our protection is made with old relays, few milliseconds
Eric Montesinos, CERN-RF 29EnEfficient RF Sources workshop, 03-04 June 2014, Cockcroft Institue
Fundamental power couplerEven if we can imagine cavities able to receive a large amount of power
In the frequency range, Fundamental Power Coupler will limit the maximum power that can be delivered to the cavity
The limit will be~ 1.0 MW peak power~ 0.5 MW average
power(for a stable operation 10-20 years lifetime of a coupler)
Eric Montesinos, CERN-RF 30EnEfficient RF Sources workshop, 03-04 June 2014, Cockcroft Institue
GranularityIn the frequency range, Tetrodes power limit is close to FPC power limit
One (or few) tube per cavity
Redundancy ensured by a small additional number of tubes/cavities
This will ensure to operate with a high efficiency, still having availability
FPC
FPC
FPC
FPC
FPC
Eric Montesinos, CERN-RF 31EnEfficient RF Sources workshop, 03-04 June 2014, Cockcroft Institue
GranularitySingle higher power source
Need a circulator to protect the tube
More losses in circulator & splitting system
No individual control of the cavities
Limited to the weakest cavity
Will lose a large number of cavities in case of source failure
Not easy to have a few spares
FPC
FPC
FPC
FPC
FPC
Eric Montesinos, CERN-RF 32EnEfficient RF Sources workshop, 03-04 June 2014, Cockcroft Institue
GranularityMulti lower power sources
Need a circulator to protect the sources
More losses due to combining system- 0.1 dB is - 2.5 % in PowerAt 352 MHz or 400 MHz
A simple N connector is - 0.01 dB
If redundancy is made by increased number of modules, not anymore the best operating point, efficiency is reduced
If at the efficient operating point, same number of few additional cavities as with tetrodes
FPC
FPC
FPC
FPC
FPC
Eric Montesinos, CERN-RF 33EnEfficient RF Sources workshop, 03-04 June 2014, Cockcroft Institue
Granularity‘New’ way of making the storage of spares
One tube is in ‘stand-by’ mode and can possibly replace any faulty tube within few minutes with a‘OFF line – ON line’ matrix
All four tubes in operation will be operated at their best efficiency point
Still have robustness thanks to the fifth tube
2 MW
2 MW
New SPS power plants: 2 x 2 MW @200 MHz
Four + one diacrodes option scheme
Eric Montesinos, CERN-RF 34EnEfficient RF Sources workshop, 03-04 June 2014, Cockcroft Institue
Conclusion (I/II)Regarding the frequency range & regarding the power range
If AVAILABILITY of the machine is the key criteriaTetrodes are a good choice
Single (few) tubes per cavity with good efficiency & redundancy with few additional cavities (on hold)Multi tubes solution for redundancy operated at a lower power, lower efficiency with nevertheless a very correct final overall cost
If EFFICIENCY is the key criteriaRegarding the arrangement choices, Tetrodes can be operated 60-70 % overall efficiency in operation
Eric Montesinos, CERN-RF 35EnEfficient RF Sources workshop, 03-04 June 2014, Cockcroft Institue
Conclusion (II/II)
If within the frequency & power range
Never neglect a tetrode (diacrode) option
Carefully look at it, and you will see they are very good !
Thank you for your attention
EnEfficient RF Sources workshop, 03-04 June 2014, Cockcroft Institue Eric Montesinos, CERN-RF 36
Eric Montesinos, CERN-RF 37EnEfficient RF Sources workshop, 03-04 June 2014, Cockcroft Institue
Theoretical Class B efficiencyDC power isPdc = Vdc Idc
Assuming the tube is linear whilst it is conducting, the dc anode current is found by Fourier analysis of the current waveform and is Idc = Ipk/πIrf = Ipk/2 = Idc π/2And ideal class B, Vrf = VdcSo, RF power isPrf = ½ Vrf IrfPrf = ½ Vdc Idc π/2 = π/4 Vdc Idc
Theoretical efficiencyη = Prf/Pdc = ¼ Vdc Ipk / Vdc Idcη = 78.5 % Vdc
Class A
Class B
Class C
Ipk
Eric Montesinos, CERN-RF 38EnEfficient RF Sources workshop, 03-04 June 2014, Cockcroft Institue
Tubes costs in the CERN SPS7000 hours operation per year2 x 32 tubes operation
Filament, nominal -7.5 %Lifetime 32000 hoursReduced thermal lossesBroken tubes per year 14Cost 350,000 CHF
Overall efficiency 48 %Electricity 2.5 GWh, 0.125 CHF/kWhCost = 0.06 2.5/0.48Cost = 312,000 CHF
2 x 20 tubes operation
Filament, nominalLifetime 20000 hours (-37.5%)Increased Thermal lossesBroken tubes per year 14Cost 350,000 CHF
Overall efficiency 61 %Electricity 2.5 GWh, 0.06 CHF/kWhCost = 0.06 2.5/0.61Cost = 246,000 CHF
Eric Montesinos, CERN-RF 39EnEfficient RF Sources workshop, 03-04 June 2014, Cockcroft Institue
Pulsed machineOperating frequency 352 MHzPulse duration 3.5 msRepetition rate 14 HzNumber of cavities 26RF Power 400 kWTotal RF peak power 10.4 MWTotal RF average power 510 kW
Redundancy by number of cavities (operation still possible with one/two cavity OFF)Operated at maximum powerSame tetrode being driverPre-driver SSA ~ 600 W
Tetrodes TH595Operating conditions for 200 kWGain = 15 dB, PRFin = 6.3 kWPG1 & PG2 = 500 WPfilament = 1.35 kWIpk = 56 AVDC = 16 kVIDC = 1.05 Ipk/π = 18.7 AVRF = 14.5 kVIRF = Ipk/2 = 28 A
66 %
Eric Montesinos, CERN-RF 40EnEfficient RF Sources workshop, 03-04 June 2014, Cockcroft Institue
Pulsed machineOperating frequency 352 MHzPulse duration 3.5 msRepetition rate 14 HzNumber of cavities 26RF Power 400 kWTotal RF peak power 10.4 MWTotal RF average power 510 kW
Redundancy by number of cavities (operation still possible with one/two cavity OFF)Operated at maximum powerSame tetrode being driverPre-driver SSA ~ 600 W
HVPS