FEL2012 - List of Authors (Kashiwagi, S.)

Paper	Title	Page
MOPD45	Present Status of Thermionic RF-Gun for Terahertz Source Project at Tohoku University	137
	F. Hinode, H. Hama, N.Y. Huang, S. Kashiwagi, M. Kawai, T. Muto, I. Nagasawa, K. Nanbu, Y. Shibasaki, K. Takahashi Tohoku University, Research Center for Electron Photon Science, Sendai, Japan X. Li TUB, Beijing, People's Republic of China
	Funding: This work is partially supported by the Ministry of Education, Science, Sports and Culture, Grant-in-Aid for Scientific Research (S), Contract #20226003. A thermionic RF gun for an acceleratora-based terahertz source has been commissioned at Electron Light Science Centre, Tohoku University. The RF gun consisting of two independently-tunable cells (ITC RF gun) can be operated so as to optimize the phase space distribution of the extracted electrons for the further manipulation in an alpha magnet and a 3 m accelerating structure for the short pulse generation. Tracking simulations show that very short electron pulse less than 100 fs with a bunch charge of about 20 pC can be obtained by means of the velocity bunching in the accelerating structure. In the early result of the gun commissioning, it was shown that the back-bombardment (B-B) effect was rather serious for the beam quality in spite of the operation with the short pulse length and slow repetition rate. The simulation study for the B-B effect with the 2D heat transfer model turned out that low energy electrons coming back in the cathode cell have the significant contribution for the additional cathode heating rather than the higher energy electrons. We will show the recent results of beam commissioning of the ITC RF gun and the current status of t-ACTS project. H. Hama et al., New J. Phys. 8 (2006) 292, **X. Li et al., Proc. of FEL'11, (2011) THPA17

WEPD64	FEL Gain Measurement with a Novel Method	515
	M. Fujimoto, A. Irizawa, G. Isoyama, F. Kamitsukasa, R. Kato, K. Kawase, H. Ohsumi, M. Yaguchi ISIR, Osaka, Japan S. Kashiwagi Tohoku University, Research Center for Electron Photon Science, Sendai, Japan S. Yamamoto KEK, Tsukuba, Japan
	The FEL gain is an important factor characterizing performance of the FEL. We used to derive the gain of the THz-FEL at Osaka University from the macropulse shape measured using a Ge:Ga detector with the time resolution of ~10 ns. The method was recently found faulty because the response of the detector shows strong non-linearity in amplitude at a high intensity level. We, therefore, have developed a new method for the gain measurement using a silicon bolometer, which has a very high linearity over the wide intensity range. The detector has the time resolution of ~1 ms, which is much longer than the FEL macropulse of a few microseconds, so that it measures energy in the macropluse. In order to derive the temporal revolution of FEL power, the number of amplifications is varied by changing the macropulse length of the electron beam. The sensitivity of the detector is also high, so that we could measure the energy development of the FEL over 6~7 orders of magnitude at a wavelength ~100 micrometers in combination with appropriate absorbers. We will report results of the measurement and analysis of the FEL gain.

Paper

Title

Page

Present Status of Thermionic RF-Gun for Terahertz Source Project at Tohoku University

137

F. Hinode, H. Hama, N.Y. Huang, S. Kashiwagi, M. Kawai, T. Muto, I. Nagasawa, K. Nanbu, Y. Shibasaki, K. Takahashi
Tohoku University, Research Center for Electron Photon Science, Sendai, Japan
X. Li
TUB, Beijing, People's Republic of China

Funding: This work is partially supported by the Ministry of Education, Science, Sports and Culture, Grant-in-Aid for Scientific Research (S), Contract #20226003.
A thermionic RF gun for an acceleratora-based terahertz source has been commissioned at Electron Light Science Centre, Tohoku University*. The RF gun consisting of two independently-tunable cells (ITC RF gun) can be operated so as to optimize the phase space distribution of the extracted electrons for the further manipulation in an alpha magnet and a 3 m accelerating structure for the short pulse generation. Tracking simulations show that very short electron pulse less than 100 fs with a bunch charge of about 20 pC can be obtained by means of the velocity bunching in the accelerating structure. In the early result of the gun commissioning, it was shown that the back-bombardment (B-B) effect was rather serious for the beam quality in spite of the operation with the short pulse length and slow repetition rate. The simulation study for the B-B effect with the 2D heat transfer model turned out that low energy electrons coming back in the cathode cell have the significant contribution for the additional cathode heating rather than the higher energy electrons**. We will show the recent results of beam commissioning of the ITC RF gun and the current status of t-ACTS project.
*H. Hama et al., New J. Phys. 8 (2006) 292,
**X. Li et al., Proc. of FEL'11, (2011) THPA17

WEPD64

FEL Gain Measurement with a Novel Method

515

M. Fujimoto, A. Irizawa, G. Isoyama, F. Kamitsukasa, R. Kato, K. Kawase, H. Ohsumi, M. Yaguchi
ISIR, Osaka, Japan
S. Kashiwagi
Tohoku University, Research Center for Electron Photon Science, Sendai, Japan
S. Yamamoto
KEK, Tsukuba, Japan

The FEL gain is an important factor characterizing performance of the FEL. We used to derive the gain of the THz-FEL at Osaka University from the macropulse shape measured using a Ge:Ga detector with the time resolution of ~10 ns. The method was recently found faulty because the response of the detector shows strong non-linearity in amplitude at a high intensity level. We, therefore, have developed a new method for the gain measurement using a silicon bolometer, which has a very high linearity over the wide intensity range. The detector has the time resolution of ~1 ms, which is much longer than the FEL macropulse of a few microseconds, so that it measures energy in the macropluse. In order to derive the temporal revolution of FEL power, the number of amplifications is varied by changing the macropulse length of the electron beam. The sensitivity of the detector is also high, so that we could measure the energy development of the FEL over 6~7 orders of magnitude at a wavelength ~100 micrometers in combination with appropriate absorbers. We will report results of the measurement and analysis of the FEL gain.