steven h. gold naval research laboratory · 2007. 5. 30. · development and testing of advanced...
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Development and Testing of Advanced Accelerator Structures and Technologies
at 11.424 GHz
Interagency Agreement #DE–AI02–01ER41170
Steven H. GoldNaval Research Laboratory
US High Gradient Research Collaboration WorkshopStanford Linear Accelerator Center
23–25 May 2007
Program Overview
Dielectric-Loaded Accelerator (DLA) Program (NRL, ANL, SLAC, Euclid)Program: DLA Structure Development and High Power TestingGoal: A compact 20-MeV Dielectric-Loaded Test Accelerator
High Power RF Component Development (NRL, Omega-P, IAP, …)Program: Active pulse compressors using plasma discharge switch tubes or ferroelectrics; high-power component testing; etc.
NRL Magnicon Facility (developed jointly with Omega-P, Inc.)Goal: A dedicated X-band facility for collaborative accelerator research
11.424-GHz Magnicon Amplifier
Magnicon Facility Summary
• 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 flattop), moderate repetition rate (up to 10 Hz), stable gain, precise frequency control, very narrow bandwidth, a modest (~0.1%) tuning range, phase stability, and stable operation into resonant or mismatched loads; power limited by pulse-shortening effects
• Magnicon facility has been used for two series of collaborative experiments since 2001:
• Twelve high-power tests of DLA Structures (3 since last Workshop)• Seven high-power tests of Active Pulse Compressors
fdrive = 5716 MHz
Magnicon Response vs Drive Frequency
fdrive = 5714 MHz
fdrive = 5716 MHz
Magnicon Response vs Drive Frequency
fdrive = 5714 MHz
11.432 GHz
11.428 GHz
fdrive = 5716 MHz RADLAB vol. 18
Magnicon Response vs Drive Frequency
fdrive = 5714 MHz
y = 0.1242x + 1001111428
11428.5
11429
11429.5
11430
11430.5
11431
11431.5
11432
11432.5
11415 11420 11425 11430 11435 11440 11445
Drive Frequency x 2 (MHz)
Gun Voltage = 472 kVPulse Length = 200 ns
Frequency vs Drive Frequency
y = -0.1667x + 11508
11425
11426
11427
11428
11429
11430
11431
11432
11433
11434
11435
440 450 460 470 480 490 500
Gun Voltage (kV)
fdrive = 5712 GHz
Frequency vs Voltage
-47 dB
-51 dB
2.382”0.900”
-177.6°
-87.6°
matchphase
2.143”
0.500”
9.765”
sliding piece
Circular TE01 In-Line Phase Shifter
New Magnicon Power Combiner(To combine magnicon output arms, and split power with
continuous control of power ratio and relative phase)
Rectangular TE10 Hybrid
Basic Circuitwaveguide hybrid
mode converters
phaseshifter
Mode Converter
height taper (.400” .800”) planar
TE10 TE20converter
rect.-to-circ.TE20 TE01mode converter
C. Nantista & S.Tantawi
C. Nantista
V. Dolgashev
WR90
WC150
WC150
10.82 degrees/turn
Tuning
TE01 Phase Shifter Cold Test Results at SLACS21
S11
y = -10.566x - 31.696
-70
-60
-50
-40
-30
-20
-10
0
10
-4 -3 -2 -1 0 1 2 3 4
Position (cm)
Cold Test of Power Combiner at NRL
Phase Angle vs Positio
y = -10.778x - 52.65-90.00
-80.00
-70.00
-60.00
-50.00
-40.00
-30.00
-20.00
-10.00
0.00-4 -3 -2 -1 0 1 2 3 4
Position (cm)
Phase Angle vs Positio
y = -10.798x + 128.8
80.00
90.00
100.00
110.00
120.00
130.00
140.00
150.00
160.00
170.00
-4 -3 -2 -1 0 1 2 3 4
Position (cm)
Power Split vs Positio
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
-4 -3 -2 -1 0 1 2 3 4
Position (cm
Power Split vs Positio
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
-4 -3 -2 -1 0 1 2 3 4
Position (cm
Test of Power Combiner Using Magnicon Output
Normal Magnetic Field Reversed Magnetic Field
Magnicon Output Power Combiner Output
LeftRight
LeftRight
20 MW, 200 ns
Power Combiner Traces
Magnicon Output Power Combiner Output
LeftRight
LeftRight
20 MW, 200 ns
Power Combiner Traces
LeftRight
LeftRight
10 MW, 1 µs
Power Combiner Traces
Magnicon Output Power Combiner Output
16 MW, 350 ns, 11.424 GHz
Power Combiner Traces
Power Combiner Summary
• Power combiner is conditioned and has produced up to 21 MW, 200-ns and 10 MW, 1-μs pulses into a single load
• Phase adjust of ~65º permits adjustment of power split ratio from approx. 99:1 to 65:35
• Reversing magnicon magnetic fields permits interchange of power between two output waveguides
• Waveguides have been fabricated to bring power to experimental stations, and soon to bunker
• Power combiner has now been operated into first external experiment, a TiN-coated silica DLA structure
Dielectric-Loaded Accelerator Program
Goals: Study RF acceleration in dielectric structures; Develop a compact 20 MeV test accelerator
Collaboration: Argonne National LaboratoryStanford Linear Accelerator CenterEuclid Techlabs LLC
Experimental Setup for High Power DLA Structure Tests
Modular DLA Structure
Faint Light (can be conditioned away)
Bright Light
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Recent Resultsfrom TiN-Coated Quartz Structure
First Day Second Day
DLA Progress to Date
Three different dielectric materials (Alumina, Silica, MCT) tested at gradients up to 8 MV/m, the first two with and without TiN-coatings.Strong multipactor loading observed in most cases, but
substantially less for TiN-coated silicaNo dielectric breakdown observed, but breakdown at dielectric joints frequently a gradient limitA new paper (L. Wu and L.K. Ang, Phys. Plasmas 14, 013105, 2007) suggests that multipactor may vanish at high accelerating gradients, when electron impact energy is above second crossoverof secondary emission curve
Dielectric-LoadedTest Accelerator
Magnicon
Power Combiner/Phase Shifter Load
5 MeV Injector 20 MeV Dielectric-Loaded Accelerator Spectrometer
Planned Accelerator Layout
(1) (2) (3) (4) (5) (6)(8)
(7)
ParametersEnergy 5.2 MeVCharge/Bunch >5 pC RF Frequency 11.434 GHzRF Power in ~2 MWNorm.Emittance 3.1 π 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
Frequency –Temperature Curves1×10−9~3×10−9Torr
DLA Program Plans
• Continue study of ceramic structures, with goal of reducing multipactor and eliminating joint breakdown
– jointless DLA structures (to avoid joint breakdown)– smaller i.d. structures (to reduce multipactor loading
and increase accelerating gradient)– dual layer structures (to reduce rf attenuation); – TiN-coated and other structures to further explore
multipactor issues
• Complete installation and commissioning of 5 MeV electron injector
High Power RF Component Development and Testing
Recent Program: Active pulse compressors using plasma discharge switch tubes
Collaboration: Omega-P, Inc. Institute of Applied Physics
Active Pulse Compressor Summary
• Series of seven 6–8 week experiments on different pulse compressor configurations, addressing problems of switching stability, multipactor, self-breakdown
• The best result was ~50 MW, 43-ns output pulse at ~10x compression from a two-channel, single-mode compressor in the reflection configuration
• An improved dual mode configuration, designed for higher power, was limited by self-breakdown of the gas switch tube
• Next experiment in series, an improved dual-mode configuration to produce >100 MW compressed pulse using 10 MW, 1 μs drive pulse,scheduled for August–October 2007
• Program transitions to SLAC for tests of an active SLED II configuration
Dual-Mode Reflection Configuration
Energy Storage
Traces from Two-ChannelDual-Mode Reflection Experiment
Pinc = 1.8 MWPcom = 16.5 MWGain = 9.2Efficiency = 55%
• Power limited by self-breakdown (believed due to rf field nonuniformities near electrodes)
• No breakdown during switching
11/16/04–12/23/04
Improved Switch for Pulse Compressor
Calculations suggested that self-breakdown in previous switch resulted from excitation of non-axially symmetric modes in the cavity due to the presence of holes in the switch tube wall needed to feed the electrodes of the gas discharge tubes. In the redesigned cavity, the holes are set in a groove in the cylindrical wall of the switch to eliminate this problem.
RF Test of Axisymmetric X-Band Gun(October 12–20, 2006)
RF Conditioning Normal Pulse Breakdown
240 MV/m
H. Bluem
I. High-power pulse compressor using plasma switch tubes—100 MW test (Omega-P—DoE Phase II SBIRs)
II. High-power pulse compressor using ferroelectric switch—first test (Omega-P—DoE Phase II SBIRs)
III. RF tests of advanced DLA structures—tests of gapless structure
IV. Commissioning of 5-MeV X-band injector for DLA experiments
Planned Near-Term Projects
Longer-Term Goals
• Operate compact X-band accelerator as test bed for study of DLA and other advanced structures (ANL, Euclid, SLAC)
• Continue collaboration with Omega-P on development and testing of high-power RF components, advanced pulse compression schemes, etc.
• Make NRL Magnicon Facility and test accelerator available to other users for high-power X-band experiments
• Experiments can transition to SLAC for higher-power tests, once initial success has been demonstrated