J. Haimson and B. Mecklenburg Haimson Research Corporation FG02-05ER84362 Work performed under the auspices of the U.S. Department of Energy SBIR Grant.

J. Haimson and B. Mecklenburg

Haimson Research Corporation

Work performed under the auspices of the U.S. Department of Energy SBIR Grant No. DE-FG02-05ER84362FG02-05ER84362

DESIGN FEATURES AND INITIAL RF DESIGN FEATURES AND INITIAL RF PERFORMANCE OF A GRADIENT PERFORMANCE OF A GRADIENT

HARDENED 17 GHz LINACHARDENED 17 GHz LINAC

1 AAC 08

To Prevent Surface Erosion During High Gradient Operation To Prevent Surface Erosion During High Gradient Operation and to Assist inand to Assist in Studying RF Breakdown, the Gradient Studying RF Breakdown, the Gradient

Hardened 17 GHz Linac StructureHardened 17 GHz Linac Structure was Designed to havewas Designed to haveBrazed and Machined Stainless Steel Surfaces in the High Brazed and Machined Stainless Steel Surfaces in the High

Field Regions of the Circuit.Field Regions of the Circuit.

AAC 08

HAIMSON RESEARCH CORPORATION

2

Topics to be PresentedTopics to be Presented1.1. DESIGN PARAMETERS AND SPECIAL FEATURES OF DESIGN PARAMETERS AND SPECIAL FEATURES OF

THE GRADIENT HARDENED LINAC AND THE HIGH THE GRADIENT HARDENED LINAC AND THE HIGH POWER DUAL RESONANT RING SYSTEM USED FOR POWER DUAL RESONANT RING SYSTEM USED FOR RF TESTING.RF TESTING.


2.2. THE STATUS OF THE SST/CU LINAC STRUCTURE PRESENTLY BEING RF PROCESSED AT MIT.

3

3. RF WAVEFORM DYNAMICS RECORDED WHILE RF RF WAVEFORM DYNAMICS RECORDED WHILE RF PROCESSING AT HIGH SURFACE GRADIENTS AND PROCESSING AT HIGH SURFACE GRADIENTS AND LOW REPETITION RATES. LOW REPETITION RATES.

AAC 08

To Prevent Surface Erosion During High Gradient Operation To Prevent Surface Erosion During High Gradient Operation and to Assist inand to Assist in Studying RF Breakdown, the Gradient Studying RF Breakdown, the Gradient

Hardened 17 GHz Linac StructureHardened 17 GHz Linac Structure was Designed to havewas Designed to haveBrazed and Machined Stainless Steel Surfaces in the High Brazed and Machined Stainless Steel Surfaces in the High

Field Regions of the Circuit.Field Regions of the Circuit.

AAC 08


PAC 2007

4

The Filling Time, Insertion Loss and Physical The Filling Time, Insertion Loss and Physical Dimensions of the Gradient Hardened (SST/Cu) Dimensions of the Gradient Hardened (SST/Cu) Structure were Specifically Chosen to Match the Structure were Specifically Chosen to Match the

Requirements of an existing Dual Resonant Ring High Requirements of an existing Dual Resonant Ring High Power Amplifying System (having an RF Bridge Ratio Power Amplifying System (having an RF Bridge Ratio

of 3) that had been Used Previously with a Similar of 3) that had been Used Previously with a Similar Geometry 17 GHz All-Copper Structure.Geometry 17 GHz All-Copper Structure.

AAC 08


5

DC – High Directivity Directional Coupler FC – Faraday Cup M – Motor DrivePSh – Phase Shifter W – Ceramic RF Window

DC

SPECTROMETER

R F

W

FC

FC

TRIPLE HYBRID

M

17 GHz TWRK

94 CAVITY TW LINACINJECTOR

LOAD

DCR

F

M

PSh

LOADHYBRID

DC

22 CAVITY TEST LINAC

F R

LOADHYBRID

R

FDC

DCF

RF R

DC

(A)

(B)


AAC 086

(b)0

0.2

0.4

0.6

0.8

1.0

0 50 100 150 200 2500

1

2

3

4

5

= 1.65 dB

TEST DATA


f = 17.1 GHzn = 3.0c = 0.5 = Total Loss in Feedback Loop

(PL/P

S)

(PA/P

S)

= 1.35 dB = 1.25 dB

= 1.15 dB

ELAPSED TIME (ns)

RF

LO

AD

PO

WE

R (

PL/P

S)

LIN

AC

IN

PU

T P

OW

ER

(P

A/P

S)

ms11cfsh5.epw

Frequency . . . . . . . . . . . . . . . . 17.140 GHz Frequency . . . . . . . . . . . . . . . . 17.140 GHz

Number of Cavities Number of Cavities . . . . . . . . . . . 22. . . . . . . . . . . 22

Phase Advance . . . . . . . . . . . . . 120Phase Advance . . . . . . . . . . . . . 120

Linac Structure Beam Aperture (a/Linac Structure Beam Aperture (a/λλ). . . 0.1715). . . 0.1715

Linac Structure Disc Thickness (t/Linac Structure Disc Thickness (t/λλ). . . 0.0835 ). . . 0.0835

Group Velocity Group Velocity . . . . . . . . . . . . . . 0.044c . . . . . . . . . . . . . . 0.044c

Cavity Phase Velocity . . . . . . . . . . 4 at c, 2 at 1.005c, Cavity Phase Velocity . . . . . . . . . . 4 at c, 2 at 1.005c, 2 at 1.010c, and 14 at1.015c2 at 1.010c, and 14 at1.015c

Structure Attenuation Parameter . . . . 0.178 NpStructure Attenuation Parameter . . . . 0.178 Np

Resonant Ring Loop Loss Resonant Ring Loop Loss . . . . . . . . . . . . . . . . 1.65 dB1.65 dB

RF Power Buildup [= C/(1-TcTf)] . . . . . . 3.1RF Power Buildup [= C/(1-TcTf)] . . . . . . 3.1

DESIGN AND OPERATING PARAMETERS DESIGN AND OPERATING PARAMETERS OF OF THE 17 GHz THE 17 GHz SST/CU LINAC STRUCTURE AND RESONANT RINGSST/CU LINAC STRUCTURE AND RESONANT RING


7 AAC 087

AAC 08


8


9 AAC 08

AAC 08


10

NORMAL LINAC OPERATION

RF Source PowerBridge Load Power

Linac Input PowerLinac Reflected Power

High Power RF Waveforms of the Bridge Protected High Gradient 17 GHz Linac

Frequency = 17137 MHz. Time Base = 50 ns/div.

“A Linear Accelerator Power Amplification System for High Gradient Structure Research,” in Advanced Accelerator Concepts, AIP Conf. Proc., No. 472, pp. 1003–1013, 1998.

Showing that when an Arc Occurs in the Linac, the Linac Input Power (blue) is Rapidly Truncated and, for

the Remaining Portion of the Klystron RF Pulse the Bridge Input Power (red) is Automatically Directed into

the Bridge Load (green). Thus, the Linac Power Amplifying Bridge Assists in Automatically Protecting

both the RF Source and the High Gradient Linac Structure.

WITH ARC IN LINAC


11 AAC 08

BECAUSE THE RING LIMITS THE ENERGY DEPOSITION IN THE BECAUSE THE RING LIMITS THE ENERGY DEPOSITION IN THE STRUCTURE DURING THE BREAKDOWN, AND BECAUSE THE STRUCTURE DURING THE BREAKDOWN, AND BECAUSE THE

KLYSTRON POWER IS SIMULTANEOUSLY SWITCHED INTO THE KLYSTRON POWER IS SIMULTANEOUSLY SWITCHED INTO THE LOAD ARM AND DISSIPATED OUTSIDE THE HIGH VACUUM LOAD ARM AND DISSIPATED OUTSIDE THE HIGH VACUUM ENVELOPE, BREAKDOWNS CAN BE TOLERATED WITHOUT ENVELOPE, BREAKDOWNS CAN BE TOLERATED WITHOUT

TRIPPING OR SWITCHING OFF THE SYSTEM, AND BY REDUCING TRIPPING OR SWITCHING OFF THE SYSTEM, AND BY REDUCING THE REP RATE TO ½ or 1Hz, THE SYSTEM CAN BE RUN THE REP RATE TO ½ or 1Hz, THE SYSTEM CAN BE RUN

CONTINUOUSLY WHILE OBSERVING THE PULSE BY PULSE CONTINUOUSLY WHILE OBSERVING THE PULSE BY PULSE PROGRESSION OF THE RF CONDITIONING PROCESS.PROGRESSION OF THE RF CONDITIONING PROCESS.

AAC 08


893

894

895

896

AAC 08


13

ARC

SPARK

SIZZLE

AFTER THE PULSE WIDTH IS INCREASED BY ONLY 10 ns,AFTER THE PULSE WIDTH IS INCREASED BY ONLY 10 ns,IT TAKES ONLY 1 (0R 2) PULSES AT THE NEW WIDTH TO IT TAKES ONLY 1 (0R 2) PULSES AT THE NEW WIDTH TO ERASE THE SURFACE MEMORY OF THE PRIOR PROCESSING ERASE THE SURFACE MEMORY OF THE PRIOR PROCESSING HOLD -OFF LEVEL AND FOR THE BREAKDOWN TO DEFAULT HOLD -OFF LEVEL AND FOR THE BREAKDOWN TO DEFAULT TO A MUCH LOWER LEVEL.TO A MUCH LOWER LEVEL.

AAC 0814


17 GHz Data Attained After17 GHz Data Attained After 1.5e05 Pulses1.5e05 Pulses

Input Power from RF Source (160ns) . . . Input Power from RF Source (160ns) . . .

Linac Input Power . . . . . . . . . . . . . Linac Input Power . . . . . . . . . . . . .

EESMSM / E / EAA . . . . . . . . . . . .

Maximum Accelerating Gradient. . . . . . Maximum Accelerating Gradient. . . . . .

Maximum Surface Gradient Maximum Surface Gradient . . . . . . . . . . . . . .

SST/CuSST/Cu

16 MW16 MW

50 MW50 MW

2.222.22

84 MV/m 84 MV/m

186 MV/m 186 MV/m

(RF Processing(RF ProcessingStill in Progress)Still in Progress)

0

20

40

60

80

100

0 10 20 30 40 50 60

IN DUAL RING

IN DUAL RING

1.2 e +

05 pulses

1.5 e+05 pulses(still processing)

f = 17136 MHzT = 160 ns

Em

= 11.8

P

0

1/2

07-13-08 pt71177125 pwr.epw

SST/Cu STRUCTURE

Em

= 13.2

P

0

1/2

ALL-Cu STRUCTURE

LINAC INPUT POWER, P0 (MW)M

AX

IMU

M A

CC

EL

ER

AT

ING

GR

AD

IEN

T,

Em

(M

V/m

)

AAC 08


15


16 AAC 08

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

-360 -270 -180 -90 0 90 180 270 360

PACCEL

TEST DATA

PLOAD

TEST DATA

75 MHz87 MHz

n = 3 = 1.1 dB

PSOURCE

PLOAD

PACCEL

06-03-02FEEDBACK PHASE WRT SOURCE PHASE

ST

EA

DY

ST

AT

E P

OW

ER

RA

TIO

(PA/P

S a

nd

PL/P

S)

b11cfdat.epw

Observations During High Gradient Testing Observations During High Gradient Testing of the 22 Cavity SST/Cuof the 22 Cavity SST/Cu LinacLinac


• A notable difference in the processing behavior of the ring A notable difference in the processing behavior of the ring driven linac structures was the absence of retrogressive driven linac structures was the absence of retrogressive breakdown thresholds, even after heavy discharges duringbreakdown thresholds, even after heavy discharges duringwide pulse operation.wide pulse operation.

• A gradient of 84 MV/m has been achieved after 1.5x10A gradient of 84 MV/m has been achieved after 1.5x105 5

pulses,pulses, and RF processing is still in progress.and RF processing is still in progress.

AAC 0817

Observations During High Gradient Testing Observations During High Gradient Testing of the 22 Cavity SST/Cuof the 22 Cavity SST/Cu LinacLinac

• Because the resonant ring automatically limits energy Because the resonant ring automatically limits energy deposition during RF breakdown events, it is possible to deposition during RF breakdown events, it is possible to continue operating at threshold values of surface gradient continue operating at threshold values of surface gradient without trip interruptions. Thus, by also operating at a low without trip interruptions. Thus, by also operating at a low pulse repetition rate, the pulse by pulse progression of the RF pulse repetition rate, the pulse by pulse progression of the RF processing mechanism can be continually monitored and processing mechanism can be continually monitored and studied as the RF pulse parameters are varied.studied as the RF pulse parameters are varied.

AAC 08


• This low pulse repetition mode of operation continues to This low pulse repetition mode of operation continues to provide interesting data related to structure BD and is provide interesting data related to structure BD and is

influencing the planning and direction of future R&D efforts.influencing the planning and direction of future R&D efforts.

DC – High Directivity Directional Coupler FC – Faraday Cup M – Motor DrivePSh – Phase Shifter W – Ceramic RF Window

DC

SPECTROMETER

R F

W

FC

FC

TRIPLE HYBRID

M

17 GHz TWRK

94 CAVITY TW LINACINJECTOR

LOAD

DCR

F

M

PSh

LOADHYBRID

DC

22 CAVITY TEST LINAC

F R

LOADHYBRID

R

FDC

DCF

RF R

DC

(A)

(B)


AAC 0819


This is to acknowledge contributions of the MIT Plasma Science and Fusion Center Staff, especially the assistance of Ivan MastovskyIvan Mastovsky,

Roark MarshRoark Marsh and Brian MunroeBrian Munroe with the Ongoing RF Testing of the Gradient Hardened

17GHz Linac Structure.

AAC 0820

J. Haimson and B. Mecklenburg

Haimson Research Corporation

Work performed under the auspices of the U.S. Department of Energy SBIR Grant No. DE-FG02-05ER84362FG02-05ER84362

DESIGN FEATURES AND INITIAL RF DESIGN FEATURES AND INITIAL RF PERFORMANCE OF A GRADIENT PERFORMANCE OF A GRADIENT

HARDENED 17 GHz LINACHARDENED 17 GHz LINAC

21 AAC 08

J. Haimson and B. Mecklenburg Haimson Research Corporation FG02-05ER84362 Work performed under the auspices of the U.S. Department of Energy SBIR Grant.

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