High gradient, high average power structure developmentat UCLA and Univ. Romein X- and S- band

High gradient, high average power High gradient, high average power structure developmentstructure developmentat UCLA and Univ. Romeat UCLA and Univ. Romein Xin X-- and Sand S-- band band

May 23May 23--25, 200725, 2007US High Gradient Research Collaboration WorkshopUS High Gradient Research Collaboration Workshop

Atsushi Fukasawa, James Rosenzweig, Brendan OAtsushi Fukasawa, James Rosenzweig, Brendan O’’Shea,Shea,UCLA, Dept. of Physics & Astronomy,UCLA, Dept. of Physics & Astronomy,

Luca Ficcadenti, Andrea Mostacci, Lugi Palumbo,Luca Ficcadenti, Andrea Mostacci, Lugi Palumbo,Rome University La Rome University La SapienzaSapienza,,

David David AlesiniAlesini, Massimo , Massimo FerrarioFerrario, and Bruno , and Bruno SpataroSpataro,,INFN/LNFINFN/LNF

OutlineOutline

- Recent activities of high field guns at UCLA.

- What is “hybrid photoinjector”?

- Beam dynamics of the hybrid photoinjector.

- Measurement of the cold test model.

- Summary

- Future work

Recent activities of high Recent activities of high field guns at UCLAfield guns at UCLA

RF gun for LLNL

- We are going to redesign this type of gun for 100-Hz operation.

BNL/SLAC/UCLA 1.6-cell S-band RF Gun

-25

-20

-15

-10

-5

0

2835 2840 2845 2850 2855 2860

12.33 MHz Mode Separation

S 11 (d

B)

Frequency (MHz)

(S. Anderson, LLNL)

Based on these experience of the gun,we are developing a novel photoinjector at S- and X-band.

A compact A compact photoinjectorphotoinjector

Conventionalphotoinjector

RF Gun TW structure Chicane

Hybridphotoinjector

LoadPhase shifter

Circulator

Load

SW/TW hybrid structure

Injector becomes much simple.

- No circulator. (This is important for X-band case.)- No magnetic bunch compression because of velocity bunching.

SW/TW Hybrid SW/TW Hybrid PhotoinjectorPhotoinjector

SWSW TWTW

SS--bandband(UCLA)(UCLA)

60 MV/m 60 MV/m (peak)(peak)

13.5 MV/m 13.5 MV/m (Average)(Average)

XX--bandband(Rome Univ.)(Rome Univ.)

240 MV/m 240 MV/m (peak)(peak)

54 MV/m 54 MV/m (Average)(Average)

3 m

IC OC

SW TW Velocity Bunching

RF Gun

No ReflectionRF in RF out

Set for the beam to go on proper phase in TW

Laser

- Very week coupling- 90 deg phase differencebetween SW and IC.

π mode

2 π /3 mode

Gun solenoidGun solenoidfor the Sfor the S--band Gunband Gun

Backing solenoid

1st solenoid

2nd solenoid

- Due to the existence of the laser port, it is very difficult to make a strong field in the first solenoid.

Bz along the axisWaveguide

Laser port

Beam dynamics by LANL Beam dynamics by LANL PARMELAPARMELA

- Choose incident phase to obtain shortest bunch length at 4 m.- Make the solenoid field for minimum emittance at 4 m.- Here I do not put downstream solenoid for simplicity.

Strategy to tune

Incident particles

ChargeCharge 1 nC1 nC

ShapeShape Square, uniformSquare, uniform

RadiusRadius 1 mm1 mm

LengthLength 10 10 psps

1.51.5--cell, cell, xxrmsrms and and εεn,rms,xn,rms,x

xrms [mm]

εnrmsx [mm.mrad]ΔE-Δφ

Injection phase: 48 deg.

EmittanceEmittance 3.7 3.7 mm.mradmm.mrad

1.51.5--cell, cell, zzrmsrms

Bunch form

ΔE-Δφ Energy Spectrum

y - x

Bunch length (rms)Bunch length (rms) 95 95 μμmm

Kinetic energyKinetic energy 20.8 20.8 MeVMeV

Energy spread (rms)Energy spread (rms) 1.3 %1.3 %

Bunch length

Scaled to 1 Scaled to 1 pCpC in 1.5 cell in 1.5 cell casecase

All dimensions of x, y, z are scaled down by 1/10.

To keep the charge density as the same before, it is scaled down by 1/1000.

The incident particles

ChargeCharge 1 1 pCpC

ShapeShape Square, uniformSquare, uniform

RadiusRadius 0.1 mm0.1 mm

LengthLength 1 1 psps

In this case, the transverse emittance can be 1/100.

Thermal emittance was not included.

Beam dynamics of 1 Beam dynamics of 1 pCpC, 1.5, 1.5--cellcell

x and εnx

E - φ

EmittanceEmittance 0.095 mm.mrad0.095 mm.mrad

Bunch lengthBunch length 4.6 4.6 μμmm

Energy spreadEnergy spread 0.17 %0.17 %

Bunch length

Scaled to XScaled to X--band frequency band frequency with an ideal solenoid fieldwith an ideal solenoid field

The incident particles

ChargeCharge 250 250 pCpC 0.25 0.25 pCpC

Square, uniformSquare, uniform

0.25 mm0.25 mm

2.5 2.5 psps

ShapeShape Square, uniformSquare, uniform

RadiusRadius 0.025 mm0.025 mm

LengthLength 0.25 0.25 psps

Length: x 1/4 => 75 cmField: x 4 => 240 MV/mCharge: x 1/4 => 250 pC

According to the scaling law,

- For the solenoid field, we used S-band one just by scaling it down.

Thermal emittance was not included.

XX--band, 250 band, 250 pCpC

EmittanceEmittance 2.4 mm.mrad2.4 mm.mrad

Bunch lengthBunch length 13 13 μμmm

Kinetic EnergyKinetic Energy 20.5 20.5 MeVMeV

Energy spreadEnergy spread 1.1 %1.1 %

x and εnx

E - φ

Bunch length

XX--band, 0.25 band, 0.25 pCpC

EmittanceEmittance 0.022 mm.mrad0.022 mm.mrad

Bunch lengthBunch length 0.9 0.9 μμmm

Kinetic EnergyKinetic Energy 20.6 20.6 MeVMeV

Energy spreadEnergy spread 0.16 %0.16 %

εnx

Bunch length

E - φ

Field measurement of the cold test modelField measurement of the cold test model

Beads

S-band Hybrid Structure,which is made of Al.

HFSS model

S11 MeasurementS11 Measurement

- 40

- 35

- 30

- 25

- 20

- 15

- 10

- 5

0

2.74 2.76 2.78 2.8 2.82 2.84 2.86 2.88 2.9 2.92

Frequency [GHz]

S11

[dB]

HFSSExperiment

Experiment agrees with HFSS results.

Fields along the axisFields along the axis

0

0.5

1

1.5

2

2.5

3

- 50 0 50 100 150 200 250 300 350z [mm]

Amp

[a.u

.] HFSSExperiment

- 700- 600- 500- 400- 300- 200- 100

0100200

- 50 0 50 100 150 200 250 300 350z [mm]

Phas

e [d

eg]

HFSSExperiment

(Tuners are out in IC, OC, and the TW cells.)

Peak in SW2Peak in SW2

HFSSHFSS 2.41 (1)2.41 (1)

ExperimentExperiment 0.84 (0.349)0.84 (0.349)

- Field is good except for the amplitude in the standing wave cells.

Amplitude

Phase

Effect of the Bead sizeEffect of the Bead size

0.00

0.20

0.40

0.60

0.80

1.00

1.20

0 50 100 150 200 250 300z

Amp

StandardSmall

- 7 % higher in SW2 in the case of the small bead.

The measurement around the peak could be unreliable as the perturbation of the field becomes large there.

Q factor of the SW cavityQ factor of the SW cavity

0

0.2

0.4

0.6

0.8

1

1.2

- 0.0008 - 0.0006 - 0.0004 - 0.0002 0 0.0002 0.0004 0.0006 0.0008df/ f

Amp

at S

W2

[a.u

.]

HFSSExperiment

Loaded QLoaded Q Peak in SW2Peak in SW2

13,337 (1)13,337 (1) 2.41 (1)2.41 (1)

0.84 (0.349)0.84 (0.349)4,600 (0.345)4,600 (0.345)

HFSS (Cu)HFSS (Cu)

Experiment (Al)Experiment (Al)

The RF contact in the SW could be the problem.

- Redesigned how to clamp the structure.- Make the SW part of copper. Under testing now

Summary of beam Summary of beam dynamicsdynamics

Calculated 1.5-cell S- and X-band hybrid photoinjector.

SS--bandband XX--bandband

ChargeCharge 1 nC1 nC 1 1 pCpC 250 250 pCpC

Normalized Emittance Normalized Emittance (rms)(rms) 3.7 mm.mrad3.7 mm.mrad 0.095 0.095

mm.mradmm.mrad 2.4 mm.mrad2.4 mm.mrad

13 13 μμmm

20.5 20.5 MeVMeV

1.1 %1.1 %

0.022 0.022 mm.mradmm.mrad

4.6 4.6 μμmm

20.6 20.6 MeVMeV

0.17 %0.17 %

0.25 0.25 pCpC

95 95 μμmm 0.9 0.9 μμmm

20.6 20.6 MeVMeV

0.16 %0.16 %

20.8 20.8 MeVMeV

1.3 %1.3 %

Bunch length (rms)Bunch length (rms)

Kinetic energyKinetic energy

Energy spread (rms)Energy spread (rms)

(Thermal emittance was not included.)

- Hybrid photoinjector gave short bunch with low emittance. - In pico Coulomb case, the beam quality became extremely good.- Thermal emittance could limit the emittance minimum.

Summary of Cavity DesignSummary of Cavity Design

- TW section in the Cold test model agrees well with HFSS.

- S11 is almost the same.- Amplitude and phase are basically good in TW section.

- Field in the SW section is smaller than HFSS.

- The bead size were effective to the field amplitude measurement in SW section.- Q value was 0.34 of HFSS result.- The deviation from the simulation could comes from bad RF contact at the SW structure.- We are testing copper model.

Future workFuture work

Beam dynamics

- Take into account of the thermal emittance effect.

Structure design and tests

- Test the copper model.- Review Steele method if it is applicable to a hybrid structure.- Upgrade to 100 Hz gun.- Molybdenum iris for X-band structure.

Others

- Complete the design of a permanent magnet solenoid.