A Test. Facility with operating characteristics equivalent to the TRIUMF RF system was used to generate a flat-topped. RF dee voltage at full operating values.
© 1985 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE. IEEE Transactwns DtVELOPMENT T.
OF FLAT-TOPPED
Enegren, L. Durieu, TRIUMF, Vancouver,
D.
RF VOLTAGE
k>n Nuclear Scxnce.
Vol. NS-32. No. 5. October 1985
FOR TRIUMF
Michelson and R.E. Worsham B.C., Canada V6T 2A3
--Summary A Test Facility with operating characteristics equivalent to the TRIUMF RF system was used to generate a flat-topped RF dee voltage at full operating values. The fundamental at 23 MHz, and the third harmonic at 69 MHz were combined in the single resonator. No difficulty was encountered with multipactoring in the addftion of the third harmonic when the fundamental voltage was on at the level of a few kilovolts. Since the TRIUMF dees are flattened coaxial X/4 Lines with uniEorm &e-to-liner spacing, the natural frequencies El and E? fall quite *ear a 3/l ratio. Only a slight warping oE the resonator in two locations that affect fL and f3 differently is required to tune for a given fL and for fj = 3fl, precisely. With the two high power signals (1800 kbi at 23 MHz and -100 kW at 69 MHz in TRIUMF; 45 kW and -4 kW in the Test Facility) comrather large filters in addibined in one resonator, tion to the i;apedsnce matching networks are required in The each drive line for isolation of the transmitters. be results oE the tests and the physical layout will described as well as the control systems for autotuning and for alnplitude and phase of the two voltages.
Since the development, characteristics
TRLUMF operating a test facility equivalent Test
system cannot be used that has operating to those of TRIUMF is
for used.
Facility
The test facility consists of two resonator segments as used in the TRIUMF Dees.* With the addition of fluxguides a X/4 flattened coaxial cavity Is formed. A photograph of the test stand and a cross-section of the cavity are shown in Figs. 1 and 2 respectively. Because of the tip capacitance the resonant frequency of the third mode, f3, that is not exactly three times of the fundamental, fl. Cavity tuning to achieve a 3:L frequency ratio is accomplished through tip and swayback deflection as shown in Fig. 2. Swayback deflection refers to the ground arm deflection at LD. This deflection, harmonic voltage standing where the third wave goes through zero, LD=2/3LT, acts to raise f3 while lowering fl. An example of cavity tuning as a Punction of tip and swayback deElectton is shown in Fig. 3, where LD=LT/3.
-Introduction This paper describes the progress in the development of a system to simultaneously achieve resonance in at both the fundamental and the TRIUMF dee structure’ third harmonic. Thus an accelerating voltage with a Elat top can be realized leading to increased phase acceptance and more precise turn and energy resolution.
TB I
t-em
-:
Fig.
2.
showing
Cross section of RF test stand resonant positions where ground arms are deflected.
21.4
21.2 mDMxT*L
3. Fig. deflection
Tuning is
cavity
of RF test approxillately
RF Power ___-----
Oars
Position stand. LD=LT/3 in this
Test
of swayhack case.
Setup
A bLock diagram oE the RF test setup is shown in Fig. 4, including the feedback system. The RF source consists of a frequency synthesizer for the fundamenta and a frequency tripler to provide the third harmonic frequency. This then feeds the 23 XHz and 69 M!Iz amplifier chains.
Fig.
1.
Photograph
of
test
stand. 0018-9399!85/1000-2936$01
Initial tests at er revealed the eEfects shows frequency scans .OOO 1985 IEEE
low
power using oE snultipactoring. at the fundamental
a network analyzFigure 5 frequency for
293:
Fig.
4.
Block
diagram
of
RF and
phase
and
amplitude
control
system.
1 70KV f
Dee
Fig. 6. flat-topped
voltage waveform.
showing
-g -16
I 23.28
I
I 2330 FREQUENCY (MHz)
I 2332
Fig. 5. Multipactoring at the fundamental resonant Input powers for traces showing multipacfrequency. toring and no multipactoring are .25 watt and .002 respectively.
-g-
02 z -et * ; = oi .5 :.a z; g D z -0; a 0: i: B -; 2 -SF -26 8 P 0 _ g; - :, *” i o= : 8
watt
input powers of .002 watts and .25 watt. For the very low power case the normal resonance curve is seen. As the input power is Lncreased to .25 watts a severe As the flattening of the resonance curve Ls seen. input power IS increased there Is 1fttLe corresponding Similar measurements exist at increase in dee voltage. 69 MHz. At the fundamental frequency the effect of multipactoring Is overcome by using standard puLsing techAt this point with the fundamental on it was niques. not known if the thlrd harmonic could be brought on With just directly or if pulsing would be required. was allowed to warm up the Eundamental on, the system The third harmonic was then brought on and stabilize. With the fundamental on it was possible to in CW mode. bring up the third harmonic voltage to the desired Level without encountering any detectable effect of The ftelds due to the fundamental multipactoring. frequency bias the cavity such as to prevent multipactoring currents from building up with introduction of the third harmonic. The flattopped dee The amplitude and phase is due to panel vibrations. Automatic An expanded The Fig. 7. wedge (swayback) in
voltage noise
is shown present In
in Fig. 6. the waveform
Tuning -___ System
version of the tuning grid structure shows and tip displacements.
diagram is shown lines of constant The desired
-: -
-; ntFLE::EO I 25
PO:,, , .1 l00,
Fig. 7. deadband
Expanded regions
, 0.5 &.“rnW IS/ ,*90102 u7aP
versLon for first
-2
I 21
P 40 NW inwt) I I 13s 111
*I(.at
of
CO......,
tuning diagram showing and third harmonic.
resonant frequencies have been chosen, in this example, The deadband regions to be 23.3 MHz and 69.9 MHz. regions in which the reflected power is below (i.e. accepted limits) are indicated by the dotted lines. The function of the automatic tuning system is to place the resonant frequencies of the first and third This is harmonic in the central rectangular region. done by first measuring the root-loop phase of both the fundamental and third harmonLc to determine present DependFng on where the system is, an tuning status. iterative scheme is embarked upon involving moving either the wedge or tips until the deadband region is entered.
2938
Phase
and
Amplitude
Control
A block diagram of the phase in Fig. 4. system was shown above are : for the control system Fundamental
and amplitude control The specLfications3 AV
--l.
voltage
