Emittance growth due to multipole transverse magnetic modes in an rf gun

Chae, Min-Kyun; Hong, Juho; Parc, Yong Woon; Ko, In Soo; Park, S. J.; Qian, Houjun; Huang, Wenhui; Tang, Chuanxiang

doi:10.1103/physrevstab.14.104203

Cited by 30 publications

(23 citation statements)

References 18 publications

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“…However, the bunch length dependent term remains with v xy replaced by v xx . This emittance growth due to bunch length can be mitigated by shaping the rf cavity [21] or introducing additional penetrations into the cavity walls [22] to cancel both normal and skew components of the quadrupole rf field on the beam axis.…”

Section: B the Emittance Due To Rotated Rf-coupler Quadrupole Fieldsmentioning

confidence: 99%

Exact cancellation of emittance growth due to coupled transverse dynamics in solenoids and rf couplers

Dowell

Zhou

Schmerge

2018

Phys. Rev. Accel. Beams

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Weak, rotated magnetic and radio frequency quadrupole fields in electron guns and injectors can couple the beam's horizontal with vertical motion, introduce correlations between otherwise orthogonal transverse momenta, and reduce the beam brightness. This paper discusses two important sources of coupled transverse dynamics common to most electron injectors. The first is quadrupole focusing followed by beam rotation in a solenoid, and the second coupling comes from a skewed high-power rf coupler or cavity port which has a rotated rf quadrupole field. It is shown that a dc quadrupole field can correct for both types of couplings and exactly cancel their emittance growths. The degree of cancellation of the rf skew quadrupole emittance is limited by the electron bunch length. Analytic expressions are derived and compared with emittance simulations and measurements.

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Section: B the Emittance Due To Rotated Rf-coupler Quadrupole Fieldsmentioning

confidence: 99%

Exact cancellation of emittance growth due to coupled transverse dynamics in solenoids and rf couplers

Dowell

Zhou

Schmerge

2018

Phys. Rev. Accel. Beams

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“…To compensate the dipole field component induced by the presence of the coupling hole, a symmetric port (connected to a circular pipe below cut off) has been inserted in the gun [26][27][28]. This port is also used as a pumping port.…”

Section: Electromagnetic Design Of the New Gunmentioning

confidence: 99%

New technology based on clamping for high gradient radio frequency photogun

Alesini

Battisti

Ferrario

et al. 2015

Phys. Rev. ST Accel. Beams

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High gradient rf photoguns have been a key development to enable several applications of high quality electron beams. They allow the generation of beams with very high peak current and low transverse emittance, satisfying the tight demands for free-electron lasers, energy recovery linacs, Compton/Thomson sources and high-energy linear colliders. In the present paper we present the design of a new rf photogun recently developed in the framework of the SPARC_LAB photoinjector activities at the laboratories of the National Institute of Nuclear Physics in Frascati (LNF-INFN, Italy). This design implements several new features from the electromagnetic point of view and, more important, a novel technology for its realization that does not involve any brazing process. From the electromagnetic point of view the gun presents high mode separation, low peak surface electric field at the iris and minimized pulsed heating on the coupler. For the realization, we have implemented a novel fabrication design that, avoiding brazing, strongly reduces the cost, the realization time and the risk of failure. Details on the electromagnetic design, low power rf measurements and high power radiofrequency and beam tests performed at the University of California in Los Angeles (UCLA) are discussed in the paper.

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“…The coupler design intrinsically integrates with complex technical requirements [11][12][13][14][15][16] and requires dedicated methods and techniques [17][18][19]. It is often that complementary devices need to be introduced in order to compensate the undesired effect(s) induced by the coupler [15,16,[20][21][22][23][24][25][26]. In general, the power coupler introduces an asymmetry to the cylindrical symmetry of the fundamental electromagnetic mode of the gun cavity [9,10].…”

Section: Introductionmentioning

confidence: 99%

“…The power coupling is realized through two diametrically opposed, magnetic loop couplers on the cathode back wall of the cavity [34]. At PAL, a four-hole design was proposed [23] for the rf gun to minimize the multipole field, however, the pulsed heating may cause a considerable issue. In [16], an asymmetric vacuum port design [24] and a four-port scheme were applied to a BNL-type rf gun built at Tsinghua University for the SXFEL project [35].…”

Section: Introductionmentioning

confidence: 99%

Frequency-detuning dependent transient coaxial rf coupler kick in an L -band long-pulse high-gradient rf photogun

Chen

Qian

Krasilnikov

et al. 2020

Phys. Rev. Accel. Beams

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A transverse kick resulting from the coaxial rf coupler in the L-band rf gun at the photoinjector test facility at DESY in Zeuthen (PITZ) has been systematically studied in simulations and further characterized in experiments. The used rf macro-pulse for the gun is typically 600 μs long and applied to produce a train of up to 2700 electron bunches. The kick is transient and found to be dependent on the detuning of the resonance frequency of the gun cavity. The frequency detuning within the rf pulse results in a variation in the kick strength along the pulse. This leads to a downstream orbit and size change of individual bunches within the train. Using 3D rf field distributions, calculated at resonant and detuned frequencies of the cavity, particle tracking simulations are performed to evaluate the integral kick location and strength, simulate its transient behaviors with respect to gun launch phase and detuned frequency of the gun cavity, and thereby emulate its impacts onto the electron bunch. In the experiments, the temperature of the cooling water for the gun is tuned, allowing detailed characterization of the frequency detuning within the rf pulse and thus measurements of the kick which are of practical interest for machine operation. The resulting orbit and size change along a 240 μs bunch train have been measured downstream at the injector exit for an rf gun peak power of about 5.7 MW. A measured focusing difference between head and tail of the bunch train is evaluated in terms of the gun solenoid current which provides more relevant information for overall tuning of the FELs. This is exemplarily given for both the under-and over-focusing case. The obtained results will be presented and discussed.

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Emittance growth due to multipole transverse magnetic modes in an rf gun

Cited by 30 publications

References 18 publications

Exact cancellation of emittance growth due to coupled transverse dynamics in solenoids and rf couplers

Exact cancellation of emittance growth due to coupled transverse dynamics in solenoids and rf couplers

New technology based on clamping for high gradient radio frequency photogun

Frequency-detuning dependent transient coaxial rf coupler kick in an L -band long-pulse high-gradient rf photogun

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