Preamble

system linear accelerator injector Nikiforov 1,2,3 Smirnov Fedorov Levichev 1,2,3 Arsentyeva 1,2,3* Sinyatkin Barnyakov Samoilov

1 SRF

SKIF, Nikolsky Koltsovo, Russia

2 Budker

Institute Nuclear Physics Acad. Lavrentyeva Novosibirsk, Russia

3 Novosibirsk

State University, Pirogova Novosibirsk, Russia e-mail:

Abstract

Linear accelerator injector synchrotron radiation facility SKIF) successfully commissioned.

Maximum klystron power values obtained, including klystrons developed Budker Institute Nuclear Physics Siberian Branch Russian Academy Sciences (BINP RAS). performed beamline tuning together measurements waveguides adjusted accelerating field phases, which possible obtain electron energy Measured characteristics after tuned linear accelerator allow proceed stage commissioning, transmission booster ring. words linear accelerator, klystrons, accelerating structures, synchrotron radiation, electrons, radio frequencies

Introduction

synchrotron radiation facility linear accelerator injector successfully commissioned.

Linear accelerator (linac) accelerate electrons beams energy subsequent transport through channel booster synchrotron, which accelerates beams energy 3 GeV.

Accelerated electron beams further injected storage ring. synchrotron facility scheme shown Figure

Scheme linear accelerator (Linac-200) consists particle source based bunching channel, regular accelerating structures magnet system power delivered through waveguides three S-band klystrons operating frequency accelerating structures.

Linac-200 assembled launched injector building Since linac where electron generated formed, commissioning major influence further operation other parts complex. reason necessary obtain parameters suitable operation booster synchrotron shortest possible time, influences optimization tuning process linear accelerator. parameters accelerator total energy gained beam, which depends input power. klystrons, developed manufactured entirely house, klystron Canon 3730A power sources linear accelerator.

Another manufactured klystron provided reserve Despite klystrons preliminarily launched bench, operation working accelerator energy indicators correct klystron functioning.

Thus, system performance designed parameters primarily determine entire linac operation. regard, paper provides layout linac system, measurements parameters, describes tuning process accelerator achieve required output parameters. discussed experience developed klystrons operating accelerator.

Linear accelerator Presented Figure linac scheme linac model shown Figure together transport channel booster synchrotron.

Scheme linear accelerator injector: third harmonic bunching cavity, solenoids, bunching preaccelerator, klystron, regular accelerating structure, quadruple lenses, magnet spectrometer, Faraday reserve klystron model linear accelerator transport channel booster synchrotron Shown Figure assembled linear accelerator injector building together klystron manufactured Parameters linear accelerator shown Table Regular acceleration electron provided constant impedance accelerating structures based loaded waveguide (DLW) operating frequency Parameters single accelerating structure presented Table

Linear accelerator klystrons

Shunt impedance per unit length 51 MOhm/m

Filed attenuation per unit length ( � ) 0.108 1/ m

Waveguide system power three klystrons delivered through waveguide paths temperature stabilization beamline elements.

Waveguide system consist following elements (Figure Vacuum valves Rectangular waveguides coupler couplers Phase shifters Waveguide based attenuator loads Directional measuring couplers (along whole waveguide systems) Waveguide system elements: klystrons, waveguides, vacuum valves, couplers, phase shifters, attenuator, coupler, loads, reserve klystron First waveguide feeds first accelerating structure (AS1) bunching preaccelerator. preaccelerator operation power sufficient, while remaining power supplies first accelerating structure. second third waveguide paths similar designs intended equal distribution power klystron regular accelerating structures.

Thus, klystrons provide power accelerating structure second fifth.

Mechanical phase shifters shown Figure accelerating structure tuning. phase shifter straight waveguide ability variate transverse size, changing wavelength waveguide, therefore phase.

Transverse variations performed stepping motor (STM).

Shown Figure typical phase

dependence number measured phase shifters. phase change there pronounced hysteresis. model phase shifter Characteristic phase shifter couple power preaccelerator power first accelerating structure, waveguide coupler used, shown Figure features plunger, which allows change coupler parameters.

model coupler ports indicated: klystron, waveguide attenuator, plunger already noticed coupler sensitive presence reactive component waveguide path.

Since accelerating structure standing ratio (SWR) about turned sufficient disrupt power balance between branches coupler reflected signal appearance which foreseen during designing tuning.

However, demonstrated possible compensate reactive component waveguide resistance using mechanical phase shifter first accelerating structure. waveguide associated elements already completely manufactured whole linear accelerator, decided redesign unit, according developed design. divide equally klystron power between second third, between fourth fifth structures, respectively, hybrid waveguide couplers used, shown couplers

couplers Figure waveguide attenuator, which finer tuning power supplied preaccelerator. attenuator (Figure waveguide section consisting mirror-symmetrical hybrid couplers connected waveguides, which mechanical phase shifter. principle operation divided output coupler divided phase shift enter mirror-symmetric coupler, original power. phase shift between waves differs completely, leading reduce final power value, while power waveguide load.

Measured coupler characteristics shown Figure model waveguide attenuator Attenuation coefficient Accounting waveguide attenuator, power division between second structure third between fourth fifth ones, hybrid couplers

waveguide system linear accelerator. Measured S-parameters these couplers presented Table

-3.07 ± 0.08 -3.04 ± 0.04 <-25

-3.03 ± 0.04 -3.03 ± 0.02 <-24.5

-3.07 ± 0.02 -3.01 ± 0.04 <-24

-3.04 ± 0.02 -3.06 ± 0.03 <-23.8

Directional couplers power measurements, directional couplers installed along waveguide system, their typical appearance shown Figure directional coupler section waveguide ceramic vacuum windows wall. signal picked front windows coaxial connectors, shown Figure match loop, connectors loaded matched load. coupler design provides possibility adjustment changing angle between waveguide coaxial connector. coupling coefficient adjusted together coupler sensitivity backward wave. measuring directional coupler Linac-200

Drawing coupler measuring Accuracy power measurement couplers determined measurement error coupling coefficient directivity level, which additional measurement error mismatched operation mode. means presence reflected waveguide measured signal value differs obtained using Finding exact error value directional coupler waveguide challenging.

However, based years experience, conclude error measuring power about Klystrons power sources three S-band klystrons operating frequency

2856 MHz

output pulse power First waveguide klystron Canon 3730A second third paths developed klystrons cathode current klystron voltage Canon klystron ones. klystron control induction-type modulators used, consist inductors equipped forming voltage modulators designed manufactured Shown Figure measured signals Canon klystron nominal cathode current output pulse power measured which required value. phenomenon explained after thorough studying klystron magnet system, which turned errors currents solenoid power supplies.

After correcting these errors, repeated measurements showed maximum output power

Canon 3730A klystron characteristics: yellow voltage signal cathode current power pulse envelope After completing conditioning waveguide paths, maximum values power three klystrons achieved.

Figure shows amplitude phase characteristics power signal klystrons, obtained using directional couplers control measurement system linear accelerator Level Radio Frequency (LLRF).Shown klystron output signals, shown right klystron input signals preamplifiers.

According these plots, after phase signals remains practically constant. duration entire bunch sequence injection about Thus, phase stability during electron current pulse, according graphs Figure worse observe signal envelope phase characteristics waveguide paths repeat preamplifier signal shape klystron.

Amplitude phase envelopes klystron output signals, klystron output signals, right klystron preamplifier signals: first waveguide (klystron Canon 3730A), second waveguide (BINP klystron), third waveguide (BINP klystron) power measurements Maximum power values klystrons measured their stable operation directional couplers (Figure worth noting that, according existing expression power propagation constant impedance accelerating structure

� = � 0 ⋅ � − 2 �� ,

power decreases structure factor input power, field attenuation length, structure length.

According structure parameters (Table power decreases structure factor power measurements waveguide system linear accelerator Figure reflected power output klystron power, which significant value. waveguide attenuator, power lost, about

10 MW

reaches preaccelerator. accelerating structure input power power structure which consistent total power which differs measured coupler klystron output. second waveguide path, measured klystron power input power values second third accelerating structures respectively, which agrees output klystron power.

According measurements, meanwhile, power

second structure input value, third structure. regard, reasonable discuss violated calibration measuring coupler output second accelerating structure. third waveguide path, measured power input fourth, input output fifth accelerating structures, looks implausible. indicator incorrect coupler calibration couplers, including violation during waveguide assembling, clarified. third klystron output power measured 55 MW, power after fourth structure which adequate value. this, assume power about enters fourth structure, enters fifth structure based measured klystron power. result, several conclusions. already noted during operation linac facility Linac-20 coupler first waveguide sensitive reactive resistance component waveguide paths located coupler branches. leads violation ratio power entering first accelerating structure entering preaccelerator, appearance significant reflected wave. affect measurement accuracy coupler klystron output, causing difference between measured klystron power total power waveguide According expression maximum potential gained traveling through accelerating structure structure parameters shown Table maximum energy equals which designed value second waveguide path, agreement between measured klystron power total waveguide observed. maximum energy structures, according should second third ones, respectively. issues coupler calibration third waveguide path, complicated discuss accuracy total power klystron measured power.

Assuming power distribution between fourth fifth accelerating structures energy estimated respectively.

final about waveguide paths presented Table measurements given taking account accuracies couplers, discussed earlier.

Based these results, clear maximum energy exceeds required value taking account non-optimized first waveguide path. power values Component Measured power, Estimated energy Designed energy, (with measured power value), energy measurements After commissioning linear accelerator, energy accelerated electrons directly measured. energy measurements performed dipole magnet linac-booster transport channel subsequent fluorescent screen.

Given magnet current displacement transverse plane screen, define energy.

After phase tuning accelerating structures phase shifters, total energy measured partial three accelerating module: case, total energy measured, measurement performed third second klystrons alternately switched accuracy energy measurement dipole magnet determined aperture vacuum chamber, transverse fluorescent screen position monitor, which determine passing charge.

Considering optimal accelerating phase assume phase shift relative optimal smaller energy gain. phase shift defined using

performed measurements theoretical estimates maximum energy.

Summary

energy

results

presented Table Accelerating Maximum energy (estimated Measured Phase deviation module power), energy, optimal value Total According Table third accelerating module configured.

Moreover, closer accelerator beginning, accuracy phase adjustment deteriorates. primarily proximity module channel dipole magnet, which measure energy. further dipole, elements energy passes through, difficult linac elements. worst situation first accelerating structure, which tuned ways. first adjust phase accelerating field using mechanical phase shifter.

method

reflected increase toward klystron influence reactive component waveguide coupler. regard, second

method

used, phase accelerating structure adjusted electronically klystron phase, while preaccelerator phase changed using mechanical phase shifter. complexity

method

higher first leading deterioration tuning accuracy.

Despite possibility further linac operation enhancement energy increase, decided pause tuning process achieved energy value value sufficient proceed transport channel subsequent booster synchrotron. further decision about better energy adjustment after linear accelerator based experience booster synchrotron.

Conclusion

linear accelerator injector assembled launched electron beam. developed conceptual scheme accelerator choice

parameters, including power values accelerating structures, possible perform quickly enough conditioning reach maximum power klystron values.

Measured values klystron output power together power measurements along waveguide paths allow state klystrons, including those developed provide required power least output parameters house developed klystrons, including phase amplitude stability, proven worse these Canon 3730A klystron.

result

linear accelerator adjustment, electron energy achieved, which meets technical requirements.

Additional studies shown possible energy increase about feasibility depends subsequent schedule booster synchrotron.

During linear accelerator operation, number shortcomings miscalculations identified, primarily first waveguide design coupler, which operates stably matched mode. conditions, coupler operate significant level reflected (VSWR 1.4), which coupling characteristics deviate required ones. addition, there issues measuring coupler calibration, which difficult tuned sensitive reactive component waveguide conductivity mechanical impact.

Despite revealed shortcomings, solutions incorporated linac design, available tuning tools, possible launch linear accelerator shortest possible obtain accelerated suitable operation linac-booster transport channel booster synchrotron itself.

Acknowledgements partially supported Ministry Science Higher Education Russian Federation within governmental order Boreskov Institute Catalysis (project FWUR-2025-0004).

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