High efficiency klystron technology. I. Syratchev, CERN › event › 589548 › contributions ›...

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


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


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


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)


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


Bunch saturation issues.

Example of the ‘fully’ saturated bunch in COM tube (Tesla 2D code)


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


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


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


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


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.


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


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%


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%


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:


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


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

High efficiency klystron technology. I. Syratchev, CERN › event › 589548 › contributions ›...

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