Peter Quigley

Record high-average current from a high-brightness photoinjector

High-power, high-brightness electron beams are of interest for many applications, especially as drivers for free electron lasers and energy recovery linac light sources. For these particular applications, photoemission injectors are used in most cases, and the initial beam brightness from the injector sets a limit on the quality of the light generated at the end of the accelerator. At Cornell University, we have built such a high-power injector using a DC photoemission gun followed by a superconducting accelerating module. Recent results will be presented demonstrating record setting performance up to 65 mA average current with beam energies of 4–5 MeV.

Photocathode behavior during high current running in the Cornell energy recovery linac photoinjector

The Cornell University energy recovery linac (ERL) photoinjector has recently demonstrated operation at 20 mA for approximately 8 hours, utilizing a multialkali photocathode deposited on a Si substrate. We describe the recipe for photocathode deposition, and will detail the parameters of the run. Post-run analysis of the photocathode indicates the presence of significant damage to the substrate, perhaps due to ion back-bombardment from the residual beam line gas. While the exact cause of the substrate damage remains unknown, we describe multiple surface characterization techniques (x-ray fluorescence spectroscopy, x-ray diffraction, atomic force, and scanning electron microscopy) used to study the interesting morphological and crystallographic features of the photocathode surface after its use for high current beam production. Finally, we present a simple model of crystal damage due to ion back-bombardment, which agrees qualitatively with the distribution of damage on the substrate surface.

The cornell erl superconducting 2-cell injector cavity string and test cryomodule

Cornell University is developing and fabricating a SRF injector cryomodule for the acceleration of the high current (100 iriA) beam in the Cornell ERL prototype and ERL light source. Major challenges include emittance preservation of the low energy, ultra low emittance beam, cw cavity operation, and strong HOM damping with efficient HOM power extraction. Prototypes have been completed for the 2-cell niobium cavity with helium vessel, coaxial blade tuner with piezo fine tuners, twin high power input couplers, and beam line HOM absorbers loaded with fer- rites and ceramics. Axial symmetry of HOM absorbers, together with two symmetrically placed input couplers per cavity, avoids transverse on-axis fields, which would cause emittance growth. A one-cavity cryostat has been designed following concepts of the TTF cryostat, and is presently under fabrication and assembly. The cryostat design has been optimized for precise cavity alignment, good magnetic shielding, and high dynamic cryogenic loads from the RF cavities, input couplers, and HOM loads. In this paper we report on the status of the assembly and first test of the one-cavity test cryostat.

Development of superconducting RF for CESR

After the successful CESR beam test of August 1994 the continued development of a superconducting RF system for the CESR luminosity upgrade is in progress at the Laboratory of Nuclear Studies, Cornell University. The system description as well as recent results are presented.

High power tests of first input couplers for cornell erl injector cavities

The first two RF power couplers for the ERL injector, currently under construction at Cornell University, have been fabricated. The couplers were assembled in the liquid nitrogen cryostat, built for their tests. A 15 kW CW IOT transmitter was available for coupler tests. A resonant ring was used for an additional increase of power. The couplers were successfully tested up to the goal power level of 50 kW CW. However, the first pair of couplers showed an excessive temperature rise at some points. Therefore, minor changes in the design have been done to improve cooling.

Instrumentation for the cornell ERL injector test cryostats

Cornell is building a 1.3 GHz Injector Cryomodule for an ERL prototype. The cryomodule consists of five two-cell niobium cavities, each cavity having two coaxial input couplers. Cavity and coupler pairs require acceptance testing at high power prior to assembly in the injector cryomodule. A liquid nitrogen cryostat for testing the couplers at high power has been built and the first input coupler test is complete. In addition, a Horizontal Test Cryostat (HTC) is being built to test input coupler pairs and cavities as a set. The first HTC test is scheduled for summer 2007. Details for instrumentation of the Coupler Test Cryostat (CTC) and HTC are presented.

Design and construction of the main linac module for the superconducting energy recovery linac project at Cornell

Cornell University has been designing and building superconducting accelerators for various applications for more than 50 years. Currently, an energy-recovery linac (ERL) based synchrotron-light facility is proposed making use of the existing CESR facility. As part of the phase 1 R&D program funded by the NSF, critical challenges in the design were addressed, one of them being a full linac cryo-module. It houses 6 superconducting cavities- operated at 1.8 K in continuous wave (CW) mode - with individual HOM absorbers and one magnet/ BPM section. Pushing the limits, a high quality factor of the cavities (2⋅1010) and high beam currents (100 mA accelerated plus 100 mA decelerated) are targeted. We will present the design of the main linac cryo-module (MLC) being finalized recently, its cryogenic features and report on the status of the fabrication which started in late 2012.

Digital cryogenic control system for superconducting RF cavities in CESR

Effective cryomodule control and monitoring are essential components to successful operation of CESR (Cornell Electron Storage Ring). The ability to quickly diagnose system problems can have a dramatic effect on machine down time. The CESR SRF Digital Cryomodule control system, employing a PC and a commercial PLC and user interface, is presented. With these tools, system status is available at a glance or, if needed, detailed system information can be displayed. Straightforward configuration of PID (Proportional Integral Derivative) control loops, safety interlocks, signal display, and data acquisition is the main feature of the system. The SRF cryomodules have several modes of operation. For example, under normal machine running conditions, liquid helium level is regulated using a liquid-level signal as the process variable (PV). For cryostat cool-down, the flow rate of cold helium gas returning to the refrigerator directly reflects cryomodule cooling rate and is a more useful process variable. Both these operational modes use the same control variable (CV): the liquid helium supply valve control signal. Other operational modes include warm-up and RF processing. This control system can be reconfigured quickly to meet the conditions of different operational modes.

High-efficiency, High-current Optimized Main-linac ERL Cryomodule

The Main Linac Cryomodule (MLC) prototype is a key component of the Cornell-BNL ERL Test Accelerator (CBETA) project, which is a 4-turn FFAG ERL currently under construction at Cornell University. This novel cryomodule is the first SRF module ever to be fully optimized simultaneously for high efficient SRF cavity operation and for supporting very high CW beam currents. After a successful initial MLC testing, the MLC has now been moved into its final location for the CBETA ring. For a first beam test of the MLC and CBETA, the Cornell ERL high voltage DC gun and SRF injector cryomodule were connected to MLC via an entry beam line; a beam stop assembly was also installed at the exit line. In this paper, we summarize the performance of this novel ERL cryomodule including the results of the first beam test and the additional tests focused on RF field stability and cavity microphonics.

Performance of the Cornell Main Linac Prototype Cryomodule for the CBETA Project

The Cornell Main Linac Cryomodule (MLC) is a key component in the Cornell-BNL ERL Test Accelerator (CBETA) project, which is a 4-turn FFAG ERL under construction at Cornell University. The MLC houses six 7cell SRF cavities with individual higher order-modes (HOMs) absorbers, cavity frequency tuners, and one magnet/BPM section. Here we present final results from the MLC cavity performance and report on the studies on the MLC HOMs, slow tuner, and microphonics.