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HG 2017, Valencia, Spain. I. Syratchev, CERN
2
J. CAI, CERNC. Marrelli, ESSA. Baikov, MUFAD. Constable, Lancaster UV. Hill, Lancaster UG. Burt, Lancaster UR. Kowalczyk, SLAC
High Efficiency International klystron activity 2
Since 2013
High efficiency klystron technology.I. Syratchev, CERN
HG 2017, Valencia, Spain. I. Syratchev, CERN
Ch
alle
nge
(a.
u.)
Efficiency, %
Co
mm
on
tu
bes
, 95
% o
f th
e m
arke
t
Ult
imat
e(sp
ace
char
ge –
free
) lim
it
Depressed collector
High efficiency! How high it could/should be!?
Personal outlook and challenges in efficiency reach with single beam klystron amplifiers.
Reducing perveance‘best’ existing tube
We still might do it?
‘Simple” modulatorbreakdown cost model
Efficiency impact on investment cost
~Power~Voltage
Efficiency, %
No
rmal
ized
co
st
Fixed RF power and beam perveance
-16.3%
-2.8%
Installed cooling capacity
Efficiency, %
No
rmal
ized
vo
lum
e
-60%
Klystronlifetime
≈ 𝑒𝑥𝑝 ൗ−𝐼3.4 × 𝑉−0.5
10%
Efficiency, %
No
rmal
ized
ho
urs
New bunching technology
Multi Beam technology. Reduced voltage and perveance. Cost and efficiency.
Gated Cathode (triode gun). No HV switches. Modulator cost and efficiency.
SC or PPM solenoid. Overall efficiency.
Complimentary technologies
MBK
HG 2017, Valencia, Spain. I. Syratchev, CERN
9.3 M Euro
10.7 M Euro
Exce
ssiv
e el
ectr
icit
y b
ill, M
Eu
ro 1 year
Efficiency, %
FCC e+e- at 50 Euro/MWh and 5000 hours/year:
Efficiency impact on operation cost
High efficiency! How high it could/should be!?
Pulsed, 0.7 GHz,92 MW
37 MW, more than twice the overall RF cryogenic power needs
100 MW
HG 2017, Valencia, Spain. I. Syratchev, CERN
Energy storage
switchHV
transformer RF circuit (=0.7)Cathode Collector
Modulator (=0.9)
180 kV
Solenoid 4 KW
20 MW, 50 Hz, 150 sec
150 kW
CLIC 20 MW L-band Multi-beam pulsed klystron.
150 kW + 88 kW
60 KW Total = 0.62
Permanent Magnets:- No power consumption- Potential cost reductionVs. SC solenoid: - More expensive solution
New klystron RF circuit (=0.9)(+) Reduced Collector dissipation (16 kW)
New
/ad
van
ced
tec
hn
olo
gy
Total = 0.95
Lower (<60kV) voltage:- 40 mini-cathodes- No oil tank (cost)- Shorter tube (cost)- Faster switching (efficiency/cost)
Gated mini-cathode:- No switches (cost)- Modulator efficiency ~1.0(+) Improved stability
Power from grid:290 190 MW
Depressed collector (=0.5)
HG 2017, Valencia, Spain. I. Syratchev, CERN
Klystron efficiency vs. perveance
73.5%
RF measurements with directional coupler.
23.04.2017
MBK TH1803
State of the art. Commercial MBK (low perveance) tubes with high efficiency.
After many decades of development the klystron technology was considered to be saturated. The experimental results from hundred’s of different devices have shown that higher efficiency is associated with lower perveance. Accounting for technological and cost reasons (K>0.2), the 75% efficiency was expected to be the utmost limit.
10 beams21 MW1.0 GHz
HG 2017, Valencia, Spain. I. Syratchev, CERN
Bunch saturation issues.
Example of the ‘fully’ saturated bunch in COM tube (Tesla 2D code)
HG 2017, Valencia, Spain. I. Syratchev, CERN
133.8 kV, 12.55 A, 1.4 MW at 0.8 GHz, 80(+)%
High efficiency klystrons. New bunching technologies on one slide.
Core Oscillations Method (5.75 m)
Bunching Alignment Collecting, 2.44 m
Core Stabilization Method
COM
BAC
CSM
High Efficiency International klystron Activity
[email protected] CSM_23B1, 1.72 m
CSM_2L3B3, 1.88 m
HG 2017, Valencia, Spain. I. Syratchev, CERN
From the klystron text book:“For the bunch entering output cavity, the goodbunching (i.e., a high fundamental harmonic ofthe beam current) can only yield high conversionefficiency when the energy spread in stream issmall.”
=1
2
𝐼1
𝐼0
𝐸𝑚𝑖𝑛
𝐸0
Τ1 2(1)
Power conversion efficiency issues.Example: power extraction efficiency from the bunched beam with I1/I0=1.75 and E min=E0 (monochromatic bunch) at the output cavity entrance. The beam and cavity parameters were taken from FCC COM tube.
Output cavity F-Q Loaded phase space. Fully saturated bunch 1D simulations with CERN in-house code CAIman (J. Cai)
85.3%
Unstable area: bouncing/ reflected electrons
F0
Bunch deceleration in the output cavity F=1.00025xF0
85.3%
Equation (1)
Modulation depth, I1/I0
Pow
er c
on
vers
ion
eff
icie
ncy
Fully saturated bunchSimulations (J. Cai)
In a ‘classical’ approach, the highest power conversion efficiency with fully saturated bunch does not exceed 87%.Fully saturated ‘rectangular’ bunchGaussian ‘ideal’ bunch
Ez in the cavity
83.3%
Zoom
accelerated electrons
I1/I0=1.75 I1/I0=1.75
HG 2017, Valencia, Spain. I. Syratchev, CERN
CAIman (1D) vs CST (3D) PIC benchmarking
84.3%
82.8%
Magnetized beam, Bz=20T Bz = 0.07T (CSM tube)
82.8%
Gaussian ‘classical’ bunch
(monochromatic bunch)
bouncing electrons
Magnetized beam, Bz=20T
84.7%
84.5%
Fully saturated ‘rectangular’ bunch
HG 2017, Valencia, Spain. I. Syratchev, CERN
Ultimate high power conversion efficiency conditions:
To avoid migration of the electrons from bunch to anti-bunch during deceleration in the output cavity, the incoming bunch with non-zero length should have certain velocity dispersion: Congregated Bunch, when the leading electrons are slower than the tailing ones.
For the full deceleration, the congregated bunch should be gradually transformed at the cavity exit into monochromatic bunch with least velocity.
Power conversion efficiency issues.
89.4%
Modulation depth, I1/I0
Pow
er c
on
vers
ion
eff
icie
ncy
I1/I0=1.75
Gaussian ‘classical’
saturated
congregated
Equation (1)
bouncing electrons
quick optimisation
Bunch deceleration in the output cavity F=0.999xF0
HG 2017, Valencia, Spain. I. Syratchev, CERN
CAIman (1D) vs CST (3D) PIC benchmarking (congregated bunch)
89.1%
88.4%
PIC simulations confirm that 90% efficiency is with reach for the fully saturated bunch with appropriate congregation.
HG 2017, Valencia, Spain. I. Syratchev, CERN
Power conversion efficiency. Limiting factors.
Applegate diagrams for the electrons emitted at different radius:
r=0 r=0.5 R beamr=0.9 R beam
Harmonic current (bunch length) at different radii.
Example of HE CSM tube (full 3D CST simulations).
• BRS is an effect when the bunch length shows radial dependence.
• It appears as a result of intrinsic radial imbalance between cavities RF impedance and the space charge forces of the beam.
• In 2D simulations this effect is the major source of reflected electrons generation that are not predicted in 1D simulations.
• We are not inefficient (2D vs. 1D), we simply cannot go higher – the reflected electrons collapse power generation.
Efficiency 80%
Bunch Radial Stratification Bz = 0.07T
HG 2017, Valencia, Spain. I. Syratchev, CERN
RBS mitigation in the COM tubes.
Original 8_01 design. Saturated bunch. 79.8%
8_04_08 tube. The new design of ‘gentle’ buncher. Phase focusing method. Radial bunch stratification significantly reduced .
84.6%
8_H02. Hollow beam configuration with optimal beam geometry. BRS effect is almost mitigated!
86%
HG 2017, Valencia, Spain. I. Syratchev, CERN
CSM tube. Second Generation. Tube length 1.72 m at 0.8 GHz. Saturation curve (MAGIC 2D)
Multi-harmonic bunching naturally helps to compensate RBS.
bouncing electrons
85.7%
HG 2017, Valencia, Spain. I. Syratchev, CERN
0.8 GHz, 133.9 kV, 12.551 A, K=0.263 0.704 GHz, 110 kV, 15.272 A, K=0.42
Expected efficiency reduction (AJDisk) 1.9%.
Length 1.72 m Length 1.4 m
GSP/PSP
We have developed special procedure (GSP/PSP) which allows to scale the frequency, power, perveance, voltage, number of beams etc., and to preserve the bunching quality of the original tube:
HG 2017, Valencia, Spain. I. Syratchev, CERN
The choice of bunching technology may drive the applicable frequency range and multi-beam options (cost/performance):
L-band S-band C-band X-band
CSM/modest MBK
BAC/MBK
COM/single beam
LHC,FSS,ESS,ILCCLIC, klystron basedX-band FEL
Medical/industrial
High perveance MBK HE tubes (!?)CLIC, TBA
1/6 MW
10-20 MW
5-10 MW, <60kV
50+ MW
Kladistron
HG 2017, Valencia, Spain. I. Syratchev, CERN
Thanks for your attention!I hope I was efficient.
2
J. CAI, CERNC. Marrelli, ESSA. Baikov, MUFAD. Constable, Lancaster UV. Hill, Lancaster UG. Burt, Lancaster UR. Kowalczyk, SLAC
High Efficiency International klystron activity 2
Since 2013