Computer Aided Design of Cavity for a High

8/14/2019 Computer Aided Design of Cavity for a High

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DESIGN & SIMULATION OFDESIGN & SIMULATION OF

RF CAVITY FOR A KLYSTRONRF CAVITY FOR A KLYSTRON

A brief outlineA brief outline

bybyDeepender KantDeepender Kant

Roll No. 09305EN008Roll No. 09305EN008

M.Tech. II sem. I YearM.Tech. II sem. I Year

Electronics Enginnering Department,Electronics Enginnering Department,

IT-BHU, VaranasiIT-BHU, Varanasi


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Introduction to Single beam Klystron

Klystrons are microwave amplifiers based on vacuum electronic

technology. The amplifying medium is a beam of electrons, which is

constrained by a magnetic field.


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Resonant cavity plays an important role in deciding the RFResonant cavity plays an important role in deciding the RFperformance of the Klystron, such as its gain, band width,performance of the Klystron, such as its gain, band width,efficiency etc.efficiency etc.

The above parameters are decided by resonant frequency,The above parameters are decided by resonant frequency,quality factors and shunt resistance of cavity.quality factors and shunt resistance of cavity.

This in turn depends on the geometry of the cavity. HenceThis in turn depends on the geometry of the cavity. Henceproper cavity design is important in the design of theproper cavity design is important in the design of theklystronklystron

Here r0= drift tube radius,

r1= cavity radius,

h = height of cavity,d = gap distance

Half section ofcavity

d

h

r0

r1


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DESIGN APPROACHDESIGN APPROACH


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1.The main parameters involved in the design of1.The main parameters involved in the design ofcavity are height, drift tube radius (a), gapcavity are height, drift tube radius (a), gaplength, shunt impedance (R/Q), quality factorslength, shunt impedance (R/Q), quality factors

(Q0, QL and QE) and resonant frequency.(Q0, QL and QE) and resonant frequency.2. For good interaction of electron beam with RF2. For good interaction of electron beam with RF

field in the cavity, it is necessary that the gapfield in the cavity, it is necessary that the gapdiameter and gap spacing should be small asdiameter and gap spacing should be small as

compared to the distance, an electron travels percompared to the distance, an electron travels percycle.cycle.

3. After fixing the above dimension one can fix3. After fixing the above dimension one can fix

height and diameter to getheight and diameter to get desired resonantdesired resonant

frequency, Qs, R/Q, tunability and coupling tofrequency, Qs, R/Q, tunability and coupling toexternal circuit.external circuit.

4. The approximate dimensions obtained act as the4. The approximate dimensions obtained act as theinput for the softwareinput for the software


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Design Approach

First, a simple pill box type cavity canbe designed and simulated for TM010 mode.

Different cavity parameters such as-drift tube radius, gap length etc canbe calculated from standard

formulae. Simulation of cavity considering all

the cavity parameters.


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SIMULATION SOFTWARES

USED


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MAGIC is an electromagnetic particle-in-cell code, i.e., a finite difference,

time domain code for simulating plasma physics processes, i.e., those

processes that involve interactions between space charge and

electromagnetic fields. Beginning from a specified initial state, the code

simulates a physical process as it evolves in time.

The full set of Maxwells time-dependent equations is solved to obtainelectromagnetic fields. Similarly, the complete Lorentz force equation

is solved to obtain relativistic particle trajectories, and the continuity

equation is solved to provide current and charge densities for

Maxwells equations. This approach, commonly referred to as

electromagnetic particle in cell (PIC), provides self consistence, i.e.,

interaction between charged particles and electromagnetic fields. In

addition, the code has been provided with powerful algorithms to

represent structural geometries, material properties, incoming and

outgoing waves, particle emission processes, and so forth. As a result,

the code is applicable to broad classes of plasma physics problems

MAGIC


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CST MICROWAVE STUDIOCST MICROWAVE STUDIO Computer Simulation Technology Microwave StudioComputer Simulation Technology Microwave Studio isis

fully featured software for electromagnetic analysis andfully featured software for electromagnetic analysis anddesign in the high frequency range. It is based on Finite-design in the high frequency range. It is based on Finite-

Integration method.Integration method.

SOLUTION TYPESSOLUTION TYPES # Transient Solver# Transient Solver

# Eigenmode Solver# Eigenmode Solver

# Frequency Domain Solver# Frequency Domain Solver


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Simulation of resonant

frequency of the cavity 3D View of the Cavity

Simulation Of Cavity Using MAGIC-2D/3D (PIC)


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COLD TEST RESULTSCOLD TEST RESULTS


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Q of the

cavity Cavity frequency Vs. time

Cold Test Simulation Using MAGIC


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R/Q Of cavity Gap Voltage


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Using CST Microwave studio


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Tube Specifications:Tube Specifications:

ParametersParameters SpecificationsSpecifications

Frequency (MHz)Frequency (MHz) 2856.02856.0

Saturated peak power (MW)Saturated peak power (MW) 6.06.0

Average power (kw)Average power (kw) 2424

Gain (dB)Gain (dB) 4545

Band width (MHz)Band width (MHz) 44

Efficiency (%)Efficiency (%) 4545Beam voltage (KV)Beam voltage (KV) 130-140130-140

Beam current (A)Beam current (A) 94-104.794-104.7

Magnetic field ( Gauss)Magnetic field ( Gauss)

11001100


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Fabricated CavityFabricated Cavity


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Cold Test Measurement With Fabricated CavityCold Test Measurement With Fabricated Cavity


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24th July,200824th July,2008

ContinueContinue6. Normalize beam radius (d')=6. Normalize beam radius (d')=

7. Plasma frequency7. Plasma frequency

Charge density ()=I/(.bCharge density ()=I/(.b22.U.U00 ))

taking e/m = 1.758 x 1011 c/kg andtaking e/m = 1.758 x 1011 c/kg and 00 = 8.854 x10-12= 8.854 x10-12 farad/mfarad/m

8. Reduced plasma frequency8. Reduced plasma frequency

R = plasma reduction factorR = plasma reduction factor9. Reduced plasma wavelength (q) = 2..Uo/q9. Reduced plasma wavelength (q) = 2..Uo/q10. Typical length of one Drift tube = q/410. Typical length of one Drift tube = q/411. Cavity radius (a):11. Cavity radius (a):

f = c/2f = c/2

[(Xnp)/a][(Xnp)/a]22

12. Gap length12. Gap length e * d = 0.9e * d = 0.9

WhereWhere e is beam coupling coefficiente is beam coupling coefficient

er b

0

p

e

m

=

q pR =

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Computer Aided Design of Cavity for a High