Hu Kesong

A method for frequency measurements of submillimeter wave using Josephson effect

A method for directly measuring the absolute frequency of a long pulse period and ultrashort pulse duration in the submillimeter band using a superconducting technique is presented. The frequency of these pulses cannot be measured by the AC Josephson effect, because their frequency spectrum is very complex. The method makes use of superconductive active and passive devices, namely, tapped delay lines, Josephson junctions for switching, and Josephson junctions for measuring frequency, and all devices constitute a whole. This method can directly accomplish real time frequency measurement of the submillimeter wave pulse signal.

A microwave FEL amplifier experiment

Abstract An extremely high power gain true free-electron-laser-amplifier experiment on a pulseline accelerator is described, in which an intense electron beam (700 kV, 500 A) with low axial velocity spread ( Δβ ‖ β ‖ ⋍ 0.2% ) is used and a narrow band 34.5 GHz microwave signal is coherently amplified to several megawatts. An extended interaction oscillator (EIO) is used as the microwave signal source. The signals are sent into the FEL interaction tube through a quasi-optical cavity. Specific efforts are made to optimize the experimental parameters in order to obtain higher power gain.

RF photoinjector in CAEP

An RF photoinjector is a type of high-brightness electron beam source. Improved experimental results have been made on the CAEP photoinjector. A 70 A electron beam of 2 MeV energy is made: 10 ps micropulse width of 81.25 MHz repetition and 2.5 /spl mu/s macropulse width of 3 Hz repetition. The system operates stably, and is made up of driving laser, the RF cavity, the vacuum chamber for Cs/sub 2/Te fabrication, high microwave power system, etc. The driving laser is very important in the system: the output of the driving laser can reach 1 /spl mu/J/micropulse at fourth harmonics, and the timing jitter is below 2 ps.

L band, 1+1/2 cell microwave gun with a LaB 6 thermionic cathode

Abstract A L-band, 1+1/2 cell microwave gun (i.e.RF gun) with a LaB 6 thermionic cathode is being developed in CAEP. The RF gun had been first tested and produced electron beam in May. 1995. These results are very satisfactory. When input microwave power into the RF gun is about 2.4MW, the parameters of the RF gun are following: electron energy is approximately 1.8 MeV. macropulse current is 1A, maximum macropulse current is 1.7A, macropulse-width is 7μ5, RF frequency is 1.3GHz, repetition rate is 1∼50 Hz, An estimate of electron beam normalized emittance is 20πmm.mrad.

Investigation of Photocathode

ABSTRACT The experimental studies of photocathode driven by laser are reported in the paper. The experimental systems including the D-C voltage vacuum chamber and measurement apparatus are given. Also we will present the experimental results and discussions of LaB 6 , pure metals (Cu,Sm) and semiconductor Cs 2 Te photocathodes. The quantum efficiencies of photocathodes are 6 × 10 −4 , 3.8 × 10 −4 , 11.6 × 10 −4 and 2 − 6 × 10 −2 respectively, the corresponding photocurrent densities are 70 A/cm 2 , 50 A/cm 2 , 102 A/cm 2 and 257 A/cm 2 are obtained. Using the pepper pot method, the normalized beam emittances for these materials are about 10 π.mm.mrad and the corresponding normalized brightness are about 10 10 A/m 2 rad 2

The relativistic klystron amplifier with a single output gap [pulsed power applications]

A relativistic klystron amplifier at X-band with a single gap output cavity is designed and tested. The klystron is operated with a pencil beam of 450 keV, 200A extracted from a field immersed diode connected to the electron pulsed accelerator EPA-74, and the pulse width is about 40 ns. The focus magnetic field is about 1 Tesla, generated by an RLC circuit. The width of discharge is about 15 ms. At the first step, with the input RF of 500 W level, more than 1 MW radiation is detected. The authors have found that the RF breakdown was the biggest problem to overcome. The problem came from both the output cavity and the vacuum (the vacuum pressure near the output cavity was about /spl sim/5/spl times/10/sup -3/ Torr). Then, the authors developed a new output cavity with lower Q and improved the vacuum pressure near the output gap, and more than 10 MW radiation is detected with the input RF of /spl sim/kW level. The efficiency is about 10%, the gain is about 40 dB.

End effects and focusing ability of a double bifilar helix linear wiggler

Abstract The end effects and focusing ability of a double bifilar helix linearly polarized wiggler are analyzed and demonstrated. The period of the wiggler used in experiments is 3.2 cm. On EPA-74, with 600 keV electron energy, the transported beam, with no external focusing, is 30 A at 23 wiggler periods. The results show that the fields at both ends of the wiggler, with no tapering, can be reasonably smooth and helically symmetric, and the wiggler is capable of focusing an intense relativistic electron beam.

The Relativistic Klystron Amplifier Experiment

We are investigating the high power operation of the Relativistic Klystron Amplifier (RKA). An intense relativistic electron beam (200 A, 600 Kv, 40 ns) is generated by EPA-74 pulseline accelerator. The electron beam is modulated by an external microwave source at a frequency of 9.375 GHz. The mutual interation between the resonant cavity and the modulated electron beam results in boosting the more intense current in the beam. The radiated Power level of 1 MW at a 9.375 GHz in the two cavity arrangement and 10 MW in the three cavity arrangement is predicted.

Brightness measurements of electron beam photoemitted multicrystalline I/sub a/B/sub 6/

Lanthanum hexaboride has been tested as a photoemitter when irradiated by a KrF eximer laser. Measured current, from 0.4cm/sup 2/ emitting area, was 10 A at irradiating wavelength of 248 nm; current density was about 25 A/cm/sup 2/. Beam normalized rms emittance measured with pepper pot method was 20 mm-mrad. The corresponding normalized rms brightness was about 2.5 X 10/sup 10/ A/cm/sup 2/-rad/sup 2/. The quantum efficiency was about 1.0 X 10/sup -4/ . The chamber pressure radius was better than 2 X 10/sup -6/ torr. Further research is underway.