BNL, Upton, Long Island, New York
Omega-P, Inc., New Haven, Connecticut
Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.
A novel tuner has been developed by the Omega-P company to achieve fast control of the accelerator RF cavity frequency. The tuner is based on the ferroelectric property which has a variable dielectric constant as function of applied voltage. Tests using a Brookhaven National Laboratory (BNL) 1.3 GHz RF cavity have been carried out for a proof-of-principle experiment of the ferroelectric tuner. Two different methods were used to determine the frequency change achieved with the ferroelectric tuner. The first method is based on a S11 measurement at the tuner port to find the reactive impedance change when the voltage is applied. The reactive impedance change then is used to estimate the cavity frequency shift. The second method is a direct S21 measurement of the frequency shift in the cavity with the tuner connected. The estimated frequency change from the reactive impedance measurement due to 5 kV is in the range between 3.2 kHz and 14 kHz, while 9 kHz is the result from the direct measurement. The two methods are in reasonable agreement. The detail description of the experiment and the analysis will be discussed in the paper.
Fermilab, Batavia
Omega-P, Inc., New Haven, Connecticut
Yale University, Physics Department, New Haven, CT
Funding: Sponsored in part by US Department of Energy, Office of High Energy Physics.
A preliminary design is presented for a two-cavity 7th harmonic multiplier, intended as a high-power RF source for use in experiments aimed at developing high-gradient structures for a future collider. The harmonic multiplier is to produce power in K-band using as an RF driver an XK-5 S-band klystron (2.856 GHz). The device is to be built with a TE111 rotating mode input cavity and interchangeable output cavities, a principal example of which is a TE711 mode cavity running at 19.992 GHz. Design of the harmonic multiplier is described that uses a 250 kV, 20 A injected laminar electron beam. With 10 MW of S-band drive power, 4.7 MW of 20-GHz output power is predicted. Details are described of the gun beam optics, beam dynamics in the RF system, and of the magnetic circuit. The theory of an azimuthally distributed coupler for the output cavity is presented, as well as the conceptual design of the entire RF circuit.
Omega-P, Inc., New Haven, Connecticut
KEK, Ibaraki
Fermilab, Batavia
Measurements are reported for a one-third version of a L-band high-power ferroelectric phase shifter. The device is designed to allow fast adjustments of cavity coupling in an accelerator where microphonics, RF source fluctuations, or another uncontrolled fluctuations could cause undesired emittance growth. Experimental measurements of switching speed, phase shift and insertion loss vs. externally-applied voltage are presented. An average switching rate of 0.5 ns or better for each degree of RF phase has been observed.
Omega-P, Inc., New Haven, Connecticut
Columbia University, New York
Yale University, Beam Physics Laboratory, New Haven, Connecticut
NSC/KIPT, Kharkov
Funding: US Department of Energy, Office of High Energy Physics, Advanced Accelerator R & D.
A rectangular two-beam dielectric wakefield accelerator (DWA) module is described which, when energized by a 14 MeV, 50 nC drive bunch moving in one channel, is shown to deflect a test bunch which originates from an independent source moving in a parallel channel. We show that such a module, 30 cm in length, can deflect transversely a 1 GeV electron by ~ 1 mrad in 1 ns, after which a following bunch can pass undeflected. Apparatus required to accomplish this task consists of a laser-cathode RF gun and an optional linac to generate the drive bunch. The associated DWA components could be used for kicker applications in a storage ring or a more energetic electron linear accelerator. An example we describe is tailored to a DWA demonstration project underway at the Argonne Wakefield Accelerator, but the design can be altered to allow for changes including a lower-energy but still relativistic drive bunch. The kicker, through appropriate design, can deflect one out of several bunches in a storage ring, leaving the remaining bunches essentially unaffected by the structure.
BINP SB RAS, Novosibirsk
Yale University, Physics Department, New Haven, CT
KEK, Ibaraki
Fermilab, Batavia
Funding: Sponsored in part by US Department of Energy, Office of High Energy Physics.
Conceptual design of a multi-beam klystron (MBK) for ILC and Project X application is presented. The chief distinction between the MBK design and existing 10-MW MBK’s is the low operating voltage of 60 kV. There are at least four compelling reasons that justify development of a low-voltage MBK, namely (i) no pulse transformer would be required; (ii) no oil tank would be required for the tube socket; (iii) modulator would be a compact 60-kV IGBT switching circuit. The proposed klystron consists of four clusters that contain six beams each. The tube has common input and output cavities for all 24 beams, and individual gain cavities for each cluster. A closely related optional configuration for a 10 MW tube would involve a design having four totally independent cavity clusters and four 2.5 MW output ports, all within a common magnetic circuit. This option has appeal because the output waveguides would not require a controlled atmosphere and because it would be easier to achieve phase and amplitude stability as required in individual SC cavities.
IAP/RAS, Nizhny Novgorod
Yale University, Physics Department, New Haven, CT
Yale University, Beam Physics Laboratory, New Haven, Connecticut
Funding: Research sponsored by US Department of Energy, Office of High Energy Physics
Experimental investigations of an active Ka-band microwave pulse compressor are presented. The compressor is based on a running wave three mirror quasi-optical resonator utilizing a diffraction grating whose channels embody plasma discharge tubes as the active switch. The principle of compression is based on quickly changing the output coupling coefficient (Q-switching) by initiating plasma discharges in the grating channels. Excitation of the resonator was achieved with a few 100 kW of 34.29 GHz microwaves in 700 nS pulses from the magnicon in the Yae Ka-band Test Facility. A power gain of at least 7:1 in the compressed pulse with a duration of 10-15 nS was achieved.
IAP/RAS, Nizhny Novgorod
Yale University, Physics Department, New Haven, CT
Omega-P, Inc., New Haven, Connecticut
Funding: Sponsored in part by US Department of Energy, Office of High Energy Physics.
A multi-mode cavity design for a two-beam accelerator aimed to achieve an accelerating gradient exceeding 150 MeV/m is reported. The cavity has a square cross section which allows excitation in several equidistantly-spaced eigen modes by a bunched drive beam in such a way that the RF fields reach peak values only during time intervals that can be much shorter than for excitation of a single mode, thus exposing the cavity surfaces to strong fields for shorter times. This feature is expected to raise the breakdown and pulse heating thresholds. In order to measure an increase in breakdown threshold surface electric field due to this reduction of exposure time during each RF period, a high-power experiment is planned. Preliminary calculations show that such a study in which comparison of breakdown threshold would be made of a conventional single-mode cavity with a multi-mode cavity can in principle be carried out using the drive beam of the CTF-3 test stand at CERN.
NSC/KIPT, Kharkov
Yale University, Physics Department, New Haven, CT
Omega-P, Inc., New Haven, Connecticut
Yale University, Beam Physics Laboratory, New Haven, Connecticut
Funding: The research was supported by US Department of Energy, Office of High Energy Physics, Advanced Accelerator R & D.
A new scheme for a dielectric wakefield accelerator is proposed that em-ploys a cylindrical multi-zone dielectric structure configured as two concentric dielectric tubes with outer and inner vacuum channels for drive and accelerated bunches. Analytical and numerical studies have been carried out for such coaxial dielectric-loaded structures (CDS) for high-gradient acceleration. An analytical theory of wakefield excitation by particle bunches in a multi-zone CDS has been formulated. Numerical calculations were made for an example of a CDS using dielectric tubes of material with dielectric permittivity 5.7, having external diameters of 2.121 mm and 0.179 mm with inner diameters of 2.095 mm and 0.1 mm. An annular 5 GeV, 5 nC electron bunch with RMS length of 0.14 mm energizes a wakefield on the structure axis having an accelerating gradient of ~600 MeV/m with a transformer ratio ~8. The period of the accelerating field is ~0.38 mm. Full numerical simulation using a PIC code has confirmed results of the linear theory and furthermore has shown the important influence of the quenching wave. The simulation also has shown stable transport of drive and accelerated bunches through the CDS.
Yale University, Beam Physics Laboratory, New Haven, Connecticut
Yale University, Physics Department, New Haven, CT
Omega-P, Inc., New Haven, Connecticut
Fermilab, Batavia
Funding: Supported by US Department of Energy, Office of High Energy Physics
A detailed analysis is presented of a new concept for a high current, high gradient proton beam accelerator in a normal conducting (i.e. room temperature) structure. The structure consists of a cascade of RF cavities in a nearly uniform magnetic axial field. The proton energy gain mechanism relies upon cyclotron resonance acceleration in each cavity. In order to check the concept and determine its limits, an engineering design is presented of a four cavity electron counterpart test accelerator under construction that will mimic parameters of the multi-cavity proton accelerator.