IPAC2012 - List of Keywords (accelerating-gradient)

Paper	Title	Other Keywords	Page
TUPPD063	Interpretation of Dark Current Experimental Results in HZB SC RF Gun	cavity, simulation, gun, HOM	1545
	V. Volkov BINP SB RAS, Novosibirsk, Russia R. Barday, T. Kamps, J. Knobloch, A.N. Matveenko, A. Neumann HZB, Berlin, Germany
	Funding: Work supported by Bundesministerium für Bildung und Forschung, Land Berlin, and grants of Helmholtz Association VH-NG-636 and HRJRG-214. The experimental dark current measurement results are obtained on HZB SC RF gun. The field emitters are considered to be random defects on the back wall of the cavity. Conducting wires with 1 micron length, blobs of 200 micron diameter and ”tip on tip” combination of them are taken as dark current emitters in the cavity. RF fields were calculated with CLANS program. The dynamic simulation of dark currents from these emitters fit experimental data. The emitter heating power by RF induced current is four orders of magnitude larger than by the field emitted dark current. The RF induced emitter temperature is proportional to ω1/2 which explains the accelerating gradient limit of a cavity like Kilpatrik law. The RF processing by high order modes seems to be promising.

WEPPC013	Progress of High Gradient Performance in STF 9-cell Cavities at KEK	cavity, status, laser, HOM	2233
	Y. Yamamoto, H. Hayano, E. Kako, S. Noguchi, T. Shishido, K. Watanabe KEK, Ibaraki, Japan
	Vertical tests for ILC have been carried out since 2008 at KEK-STF. Measured cavities are from MHI#5 to MHI#22 (not yet for MHI#18-#22 at the end of November 2011), and MHI#12, #13 and #17 reached the ILC specification of 0.8x10¹⁰ at 35MV/m. The MHI cavity was added into the “qualified vendor” for the cavity yield. These three cavities (#12, #13 and #17) had no defect on every EBW seam of equator, iris and beampipe. On the other hand, the other cavities had a few or several defects on EBW seam. Especially, defect on the EBW seam of the equator is the worst case, and cavity performance is limited “certainly”. MHI#10, #15 and #16 cavities were limited by this kind of defect. As for iris region, MHI#14 had large defect at the iris between cell #8 and #9, and the performance was limited by the heavy field emission with “explosive event”. However, after the locally mechanical grind for this defect, the cavity performance was drastically improved with no field emission at 37MV/m. In this paper, the recent progress of the cavity performance at KEK-STF will be reported with the “detailed” defect analysis.

WEPPC051	Multipactor Simulation in SC Elliptical Shape Cavities	cavity, simulation, electron, multipactoring	2327
	S. Kazakov, I.V. Gonin, V.P. Yakovlev Fermilab, Batavia, USA
	Typically multipactor exists near equator region in elliptical shape superconductive cavities. If the multipactor power zone dose not coincide with operating power, it is often the cavity has to pass through it before it reaches operating level of field. Results of multipactor simulations for several shapes of elliptical cavity are presented. New shape, which significantly suppresses multipactor, is found.

WEPPC078	Recent Developments in the Cornell Nb3Sn Initiative	cavity, niobium, linac, SRF	2390
	S. Posen, G.H. Hoffstaetter, M. Liepe, Y. Xie CLASSE, Ithaca, New York, USA
	Superconducting accelerator cavities coated with Nb3Sn have already demonstrated significantly higher unloaded quality factors than standard niobium cavities at surface magnetic fields <30 mT. Theoretical predictions suggest that the maximum critical field of such cavities could be twice that of niobium cavities. Significant facilities have been developed at Cornell University to fabricate Nb3Sn using the vapor diffusion technique. In this paper, recent progress is presented from our Nb3Sn program. The first RF results from a test of a Nb3Sn sample in a TE pillbox sample cavity are presented as well as first images of the newly constructed apparatus for coating full 1.3 GHz single cell cavities.

WEPPC079	Residual Resistance Studies at Cornell	cavity, SRF, linac, simulation	2393
	S. Posen, D. Gonnella, G.H. Hoffstaetter, M. Liepe CLASSE, Ithaca, New York, USA J. Oh Cornell University, Ithaca, New York, USA
	The Cornell single-cell temperature mapping system has been adapted for use with ILC and Cornell ERL-shape superconducting accelerator cavities. The system was optimized for low-noise, high-precision measurements with the goal of measuring resistances as low as 1 nohms. Using this system, a T-map of an ILC single cell was obtained at accelerating fields below the onset of Q-slope and at temperatures at which BCS resistance is small, producing a measurement of the distribution of residual resistance over the surface of the cavity. Standard procedures were used in preparing the cavity to avoid Q-disease and trapped flux caused by cooling the cavity through its transition in the presence of magnetic fields. Studying the T-map gives clues to the source of residual resistance, so that steps can be taken to reduce it, thereby lowering losses and increasing Q0. The temperature map noise-reduction studies as well as the residual resistance results are presented in this paper.

WEPPC091	A Path to Higher Q0 with Large Grain Niobium Cavities	cavity, SRF, niobium, induction	2426
	P. Dhakal, G. Ciovati, G.R. Myneni JLAB, Newport News, Virginia, USA
	The improvement of the quality factor Q0 of superconducting radio-frequency (SRF) cavities at medium accelerating gradients (~ 20 MV/m) is important in order to reduce the cryogenic losses in continuous wave accelerators for a variety of applications. In recent years, SRF cavities fabricated from ingot niobium have become a viable alternative to standard high-purity fine-grain Nb for the fabrication of high-performing SRF cavities with the possibility of significant cost reduction. Initial studies,, demonstrated the improvement of Q0 at medium field in cavities heat treated at 800-1000 °C without subsequent chemical etching. To further explore this treatment procedure, a new induction furnace with an all-niobium hot-zone was commissioned. A single-cell 1.5 GHz cavity fabricated from ingot material from CBMM, Brazil, with RRR~200, was heat treated with the new furnace in the temperature range 600-1400 °C for several hours. Residual resistance values below 5 nano Ω have been consistently achieved on this cavity as well as Q0 values above 4.5×1010 at 2 K and 100 mT peak surface magnetic field. Q0-values of the order of 1011 have been measured at 1.5 K. G. Ciovati, et al., Phys. Rev. ST Accel. Beams 13, 022002 (2010). ** G. Ciovati, et al., Proc. of the 15th Int. Conf. on RF Superconductivity, Chicago, July 25-29, 2011, paper TUPO051

THPPC039	Study of RF Breakdown in Normal Conducting Cryogenic Structure	cryogenics, impedance, klystron, lattice	3368
	V.A. Dolgashev, J.R. Lewandowski, D.W. Martin, S.G. Tantawi, S.P. Weathersby, A.D. Yeremian SLAC, Menlo Park, California, USA
	Funding: *Work supported by DoE, Contract No. DE-AC02-76SF00515. RF Breakdown experiments on short accelerating structures at SLAC have shown that properties of rf breakdown probability are reproducible for structures of the same geometry. At a given rf power and pulse shape, the rf breakdown triggers continuously and independently at a constant average rate. Hypotheses describing the properties of the rf breakdown probabilities involve defects of metal crystal lattices that move under forces caused by rf electric and magnetic fields. The dynamics of the crystal defects depend on the temperature of the structure. To study the dependence we designed and built an experimental setup that includes a cryogenically cooled single-cell, standing-wave accelerating structure. This cavity will be high power tested at the SLAC Accelerator Structure Test Area (ASTA).

THPPC047	Fabrication and Initial Tests of an Ultra-High Gradient Compact S-Band (HGS) Accelerating Structure	coupling, klystron, linac, vacuum	3392
	L. Faillace, R.B. Agustsson, P. Frigola, A.Y. Murokh RadiaBeam, Santa Monica, USA V.A. Dolgashev SLAC, Menlo Park, California, USA J.B. Rosenzweig UCLA, Los Angeles, California, USA V. Yakimenko BNL, Upton, Long Island, New York, USA
	Funding: Work supported by US DOE grant # DE-SC000866. RadiaBeam Technologies reports on the RF design and fabrication of a ultra-high gradient (50 MV/m) S-Band accelerating structure (HGS) operating in the pi-mode at 2.856 GHz. The compact HGS structure offers a drop-in replacement for conventional S-Band linacs in research and industrial applications such as drivers for compact light sources, medical and security systems. The electromagnetic design (optimization of the cell shape in order to maximize RF efficiency and minimize surface fields at very high accelerating gradients) has been carried out with the codes HFSS and SuperFish while the thermal analysis has been performed by using the code ANSYS. The initial cold tests are presented together with the plans for high-power tests currently ongoing at Lawrence Livermore National Laboratory (LLNL).

THPPR005	The Preliminary Test of a Digital Control System Based on the FPGA for a PEFP 120-keV RF Cavity	cavity, controls, resonance, proton	3975
	Y.M. Li, S. Cha UST, Daejeon City, Republic of Korea Y.-S. Cho, J.-H. Jang, H.S. Kim, H.-J. Kwon, Y.M. Li, K.T. Seol, Y.-G. Song KAERI, Daejon, Republic of Korea
	Funding: Proton Engineering Frontier Project, Korea Atomic Energy Research Institute, Ministry of Education, Science and Technology of the Republic of Korea. PEFP developed a 120-keV RF cavity for their ion implantation applications. Due to ambient disturbances, the cavity’s resonance frequency may vary in long-term test. We designed a digital control system to change the frequency of the RF sources for tracking the cavity’s frequency variations. The digital control system has functions such as, phase shift, phase comparison, proportional-integral compensation, waveform generation and frequency/pulse modulation, and driving signal generator. Most of them are implemented digitally in a Virtex II 4000 Field Programmable Gate Array (FPGA). In this research we show the design and the preliminary test results of the digital control system. * Work supported by the Ministry of Science and Technology

Paper

Title

Other Keywords

Page

TUPPD063

Interpretation of Dark Current Experimental Results in HZB SC RF Gun

cavity, simulation, gun, HOM

1545

V. Volkov
BINP SB RAS, Novosibirsk, Russia
R. Barday, T. Kamps, J. Knobloch, A.N. Matveenko, A. Neumann
HZB, Berlin, Germany

Funding: Work supported by Bundesministerium für Bildung und Forschung, Land Berlin, and grants of Helmholtz Association VH-NG-636 and HRJRG-214.
The experimental dark current measurement results are obtained on HZB SC RF gun. The field emitters are considered to be random defects on the back wall of the cavity. Conducting wires with 1 micron length, blobs of 200 micron diameter and ”tip on tip” combination of them are taken as dark current emitters in the cavity. RF fields were calculated with CLANS program. The dynamic simulation of dark currents from these emitters fit experimental data. The emitter heating power by RF induced current is four orders of magnitude larger than by the field emitted dark current. The RF induced emitter temperature is proportional to ω1/2 which explains the accelerating gradient limit of a cavity like Kilpatrik law. The RF processing by high order modes seems to be promising.

WEPPC013

Progress of High Gradient Performance in STF 9-cell Cavities at KEK

cavity, status, laser, HOM

2233

Y. Yamamoto, H. Hayano, E. Kako, S. Noguchi, T. Shishido, K. Watanabe
KEK, Ibaraki, Japan

Vertical tests for ILC have been carried out since 2008 at KEK-STF. Measured cavities are from MHI#5 to MHI#22 (not yet for MHI#18-#22 at the end of November 2011), and MHI#12, #13 and #17 reached the ILC specification of 0.8x10¹⁰ at 35MV/m. The MHI cavity was added into the “qualified vendor” for the cavity yield. These three cavities (#12, #13 and #17) had no defect on every EBW seam of equator, iris and beampipe. On the other hand, the other cavities had a few or several defects on EBW seam. Especially, defect on the EBW seam of the equator is the worst case, and cavity performance is limited “certainly”. MHI#10, #15 and #16 cavities were limited by this kind of defect. As for iris region, MHI#14 had large defect at the iris between cell #8 and #9, and the performance was limited by the heavy field emission with “explosive event”. However, after the locally mechanical grind for this defect, the cavity performance was drastically improved with no field emission at 37MV/m. In this paper, the recent progress of the cavity performance at KEK-STF will be reported with the “detailed” defect analysis.

WEPPC051

Multipactor Simulation in SC Elliptical Shape Cavities

cavity, simulation, electron, multipactoring

2327

S. Kazakov, I.V. Gonin, V.P. Yakovlev
Fermilab, Batavia, USA

Typically multipactor exists near equator region in elliptical shape superconductive cavities. If the multipactor power zone dose not coincide with operating power, it is often the cavity has to pass through it before it reaches operating level of field. Results of multipactor simulations for several shapes of elliptical cavity are presented. New shape, which significantly suppresses multipactor, is found.

WEPPC078

Recent Developments in the Cornell Nb3Sn Initiative

cavity, niobium, linac, SRF

2390

S. Posen, G.H. Hoffstaetter, M. Liepe, Y. Xie
CLASSE, Ithaca, New York, USA

Superconducting accelerator cavities coated with Nb3Sn have already demonstrated significantly higher unloaded quality factors than standard niobium cavities at surface magnetic fields <30 mT. Theoretical predictions suggest that the maximum critical field of such cavities could be twice that of niobium cavities. Significant facilities have been developed at Cornell University to fabricate Nb3Sn using the vapor diffusion technique. In this paper, recent progress is presented from our Nb3Sn program. The first RF results from a test of a Nb3Sn sample in a TE pillbox sample cavity are presented as well as first images of the newly constructed apparatus for coating full 1.3 GHz single cell cavities.

WEPPC079

Residual Resistance Studies at Cornell

cavity, SRF, linac, simulation

2393

S. Posen, D. Gonnella, G.H. Hoffstaetter, M. Liepe
CLASSE, Ithaca, New York, USA
J. Oh
Cornell University, Ithaca, New York, USA

The Cornell single-cell temperature mapping system has been adapted for use with ILC and Cornell ERL-shape superconducting accelerator cavities. The system was optimized for low-noise, high-precision measurements with the goal of measuring resistances as low as 1 nohms. Using this system, a T-map of an ILC single cell was obtained at accelerating fields below the onset of Q-slope and at temperatures at which BCS resistance is small, producing a measurement of the distribution of residual resistance over the surface of the cavity. Standard procedures were used in preparing the cavity to avoid Q-disease and trapped flux caused by cooling the cavity through its transition in the presence of magnetic fields. Studying the T-map gives clues to the source of residual resistance, so that steps can be taken to reduce it, thereby lowering losses and increasing Q0. The temperature map noise-reduction studies as well as the residual resistance results are presented in this paper.

WEPPC091

A Path to Higher Q0 with Large Grain Niobium Cavities

cavity, SRF, niobium, induction

2426

P. Dhakal, G. Ciovati, G.R. Myneni
JLAB, Newport News, Virginia, USA

The improvement of the quality factor Q0 of superconducting radio-frequency (SRF) cavities at medium accelerating gradients (~ 20 MV/m) is important in order to reduce the cryogenic losses in continuous wave accelerators for a variety of applications. In recent years, SRF cavities fabricated from ingot niobium have become a viable alternative to standard high-purity fine-grain Nb for the fabrication of high-performing SRF cavities with the possibility of significant cost reduction. Initial studies*,**, demonstrated the improvement of Q0 at medium field in cavities heat treated at 800-1000 °C without subsequent chemical etching. To further explore this treatment procedure, a new induction furnace with an all-niobium hot-zone was commissioned. A single-cell 1.5 GHz cavity fabricated from ingot material from CBMM, Brazil, with RRR~200, was heat treated with the new furnace in the temperature range 600-1400 °C for several hours. Residual resistance values below 5 nano Ω have been consistently achieved on this cavity as well as Q0 values above 4.5×1010 at 2 K and 100 mT peak surface magnetic field. Q0-values of the order of 1011 have been measured at 1.5 K.
* G. Ciovati, et al., Phys. Rev. ST Accel. Beams 13, 022002 (2010).
** G. Ciovati, et al., Proc. of the 15th Int. Conf. on RF Superconductivity, Chicago, July 25-29, 2011, paper TUPO051

THPPC039

Study of RF Breakdown in Normal Conducting Cryogenic Structure

cryogenics, impedance, klystron, lattice

3368

V.A. Dolgashev, J.R. Lewandowski, D.W. Martin, S.G. Tantawi, S.P. Weathersby, A.D. Yeremian
SLAC, Menlo Park, California, USA

Funding: *Work supported by DoE, Contract No. DE-AC02-76SF00515.
RF Breakdown experiments on short accelerating structures at SLAC have shown that properties of rf breakdown probability are reproducible for structures of the same geometry. At a given rf power and pulse shape, the rf breakdown triggers continuously and independently at a constant average rate. Hypotheses describing the properties of the rf breakdown probabilities involve defects of metal crystal lattices that move under forces caused by rf electric and magnetic fields. The dynamics of the crystal defects depend on the temperature of the structure. To study the dependence we designed and built an experimental setup that includes a cryogenically cooled single-cell, standing-wave accelerating structure. This cavity will be high power tested at the SLAC Accelerator Structure Test Area (ASTA).

THPPC047

Fabrication and Initial Tests of an Ultra-High Gradient Compact S-Band (HGS) Accelerating Structure

coupling, klystron, linac, vacuum

3392

L. Faillace, R.B. Agustsson, P. Frigola, A.Y. Murokh
RadiaBeam, Santa Monica, USA
V.A. Dolgashev
SLAC, Menlo Park, California, USA
J.B. Rosenzweig
UCLA, Los Angeles, California, USA
V. Yakimenko
BNL, Upton, Long Island, New York, USA

Funding: Work supported by US DOE grant # DE-SC000866.
RadiaBeam Technologies reports on the RF design and fabrication of a ultra-high gradient (50 MV/m) S-Band accelerating structure (HGS) operating in the pi-mode at 2.856 GHz. The compact HGS structure offers a drop-in replacement for conventional S-Band linacs in research and industrial applications such as drivers for compact light sources, medical and security systems. The electromagnetic design (optimization of the cell shape in order to maximize RF efficiency and minimize surface fields at very high accelerating gradients) has been carried out with the codes HFSS and SuperFish while the thermal analysis has been performed by using the code ANSYS. The initial cold tests are presented together with the plans for high-power tests currently ongoing at Lawrence Livermore National Laboratory (LLNL).

THPPR005

The Preliminary Test of a Digital Control System Based on the FPGA for a PEFP 120-keV RF Cavity

cavity, controls, resonance, proton

3975

Y.M. Li, S. Cha
UST, Daejeon City, Republic of Korea
Y.-S. Cho, J.-H. Jang, H.S. Kim, H.-J. Kwon, Y.M. Li, K.T. Seol, Y.-G. Song
KAERI, Daejon, Republic of Korea

Funding: Proton Engineering Frontier Project, Korea Atomic Energy Research Institute, Ministry of Education, Science and Technology of the Republic of Korea.
PEFP developed a 120-keV RF cavity for their ion implantation applications. Due to ambient disturbances, the cavity’s resonance frequency may vary in long-term test. We designed a digital control system to change the frequency of the RF sources for tracking the cavity’s frequency variations. The digital control system has functions such as, phase shift, phase comparison, proportional-integral compensation, waveform generation and frequency/pulse modulation, and driving signal generator. Most of them are implemented digitally in a Virtex II 4000 Field Programmable Gate Array (FPGA). In this research we show the design and the preliminary test results of the digital control system.
* Work supported by the Ministry of Science and Technology