Development of a Compact Dielectric-Loaded Test Accelerator at 11.4 GHz* S.H. Gold, a) A.K. Kinkead, b) W. Gai, c) J.G. Power, c) R. Konecny, c) C. Jing,

Development of a Compact Dielectric-Loaded Test

Accelerator at 11.4 GHz*

S.H. Gold,a) A.K. Kinkead,b) W. Gai,c) J.G. Power,c) R. Konecny,c) C. Jing,c,d) and A.W. Flifleta)

a) Plasma Physics Division, Naval Research Laboratory, Washington, DC 20375b) Icarus Research, Bethesda, MD 20814

c) Argonne National Laboratory, Argonne, IL 60439d) Euclid TechLabs, Solon, OH 44139

Presented at13th Advanced Accelerator Concepts Workshop

Santa Cruz, CA27 July – 2 August 2008

*DoE Interagency Agreement #DE–AI02–01ER41170

NRL Magnicon Facility

• Magnicon Facility offers a flexible venue for hands-on experiments requiring high power 11.4 GHz radiation, with reasonable work and safety rules and minimal red tape

• Magnicon properties: high power (10–20 MW), adjustable pulse length (200-ns FWHM– 1-µs), repetition rate up to 10 Hz, stable gain, a modest (~0.1%) tuning range, phase stability, and stable operation into resonant loads

• Magnicon facility has been used for two series of collaborative experiments over the past 5 years:

– Sixteen tests of DLA Structures– Eight tests of Active Pulse Compressors

• It is now being used to power a 5-MeV injector, the first stage of a compact test accelerator to study acceleration in DLA structures

Magnicon Facility Schematic

Magnicon

Power Combiner/Splitter Load

5 MeV Injector DLA Structure Spectrometer

X-Band Test Accelerator

Magnicon

Power Combiner/Splitter Load

5 MeV Injector 20 MeV Dielectric-Loaded Accelerator Spectrometer

Accelerator

Section

Focusing

Quads

Cathode

Assembly

Device

under test

X-Band Test Accelerator

ICT YAG

Design Parameters

Energy 5.2 MeVCharge/Bunch >5 pC RF Frequency 11.430 GHzRF Power in ~2 MWQ ~1000Norm.Emittance 3.1 mm mradEnergy Spread ~6%

MatchingQuads

Injector

NRL X-Band Injector

LaB6 Cathode

Accelerator Lab of Tsinghua University 胡源 (Y. Hu, Student), 杜晓福 (X. Du),唐传祥 (Prof. C. Tang), and 林郁正 (Prof. Y. Lin)

Measured Axial Field Profile and PARMELA Results

Temperature Tuning the Injector

Linear Fit

Experimental Data

Cavity filling comparison

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.0E+00 2.0E-07 4.0E-07 6.0E-07 8.0E-07 1.0E-06

Time (s)

Normalized RF Power

0.E+00

5.E-09

1.E-08

2.E-08

2.E-08

3.E-08

3.E-08

4.E-08

4.E-08

5.E-08

5.E-08

Stored Energy for 1 W drive (J)

Pforward

Wref

W

Injector Cavity Filling Calculation

P forward, P injected, P reflected vs time

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

0.E+00 2.E-07 4.E-07 6.E-07 8.E-07 1.E-06

Time (s)

Normalized RF Power

PforwardPinjectedPreflected

Q0 = 9700

Qe = 1115

= 8.7

1.0E+03

1.0E+04

1.0E+05

1.0E+06

1.0E+07

1.0E+03 1.0E+04 1.0E+05 1.0E+06 1.0E+07

Forward Power (W)

Reflected Power (W)

Conditioning the Injector

y = 0.65x

Pforward

(6 MW)Preflected

ICT

4 mm

(0.5 mA)

Initial Accelerator Operation

Beam Deflection Measurement

~ 7.5

• Injector installed with rf window, gate valve, ICT, YAG, focusing quads, steering magnet

• RF conditioning completed

• Dark current electrons observed; energy of ~3–5 MeV, based on electron range in Al and bending in 1.2 kG magnetic field

• Initial operation with hot cathode at rated rf drive (~2 MW injected) produced ~1 mA, ~3.2 MeV, 4-mm-diam beam

• Low cathode temperature, apparent cathode poisoning limited beam current from LaB6 cathode

• Temperature gradient along 24-cell structure may have limited beam energy

• These problems will be addressed in the near future

Compact Accelerator Summary