Helmut Wiedemann, 1938 - 2020

Herman Winick:

How Helmut came to SLAC    
Accelerator labs in Europe and the US have had exchanges of personnel for more than 75 years. This included scientists from the US spending a year or more at CERN, DESY, and other European labs and scientists from European labs doing the same at US facilities. One of the earliest such events involved DESY in Hamburg and the Cambridge Electron Accelerator (CEA) at Harvard University. Both were building 5-6 GeV alternating gradient (AG) strong focusing electron synchrotrons. In 1959 DESY was in early stages of designing their facility while CEA was finalizing its design. This was in the early days of AG facilities so there was little experience.

Although DESY and CEA were competitors, these two labs had very good relations, so the Director of DESY (Willibald Jentschke) arranged with the Director of CEA (Stan Livingston) to send Gustav-Adolf Voss, one of his bright young staff members, to Harvard for a year to learn what he can. Voss came to the US in 1959 with his wife and two children. Their travel expenses and salary were paid by DESY with the understanding that they would return to DESY after one year. Voss turned out to contribute so much to the CEA program that, at the end of the year, Livingston offered him a job as head of the CEA accelerator team. By this time Voss and his family were very happy with their experience in the US so Voss wanted to accept the job. DESY director Jentnschke was very disappointed to learn this but could not prevent it from happening.

This experience however led DESY to adopt a new rule, called Lex Voss. This required future DESY staff being sent to US labs at DESY expense to sign an agreement that they would reimburse DESY for the funds DESY paid to support their stay in the US if they did not return to DESY for at least several years after their US visit.

Helmut came under this rule and signed such an agreement when he came to SLAC as a one year visitor from DESY. He contributed so much to the colliding beam program at SLAC that Richter offered him a job at SLAC. Helmut wanted to accept this offer but did not want to reimburse DESY for the many thousands of dollars that DESY paid in support of his visit. When Richter learned this he arranged to pay for this and Helmut stayed at SLAC.

Jeff Corbett:

Herr Doktor Professor Wiedemann was a master of estimation. He could calculate almost anything, by hand, on his feet, at the board, and come very close the exact answer. A true ‘physicist’   

One time I had a question about a section on intrabeam scattering in one of Professor Wiedemann's books. We talked about it and got the formula straightened out but the really important comment Helmut made was 'nobody understands these things the first time through'.

Reza Mansouri:

I am so sorry to hear the unexpected news of passing Helmut. ILSF should remember his contribution to ILSF group and Iran's young scientists.

Javad Rahigi, ILSF:

I was so saddened to hear about Helmut Wiedeman passing away.

I met with him in 2009 when I was visiting NSRRC in Taiwan. He was giving a series of lectures to the NSRRC staff on accelerator physics. I was so impressed with his enthusiasm for teaching, in particular his enormous interest for educating young scientists was so impressive to me. I got to know him rather intimately during the course of my 10 days visit to the NSRRC. I was so excited to have discovered him,that I asked him if he would visit Iran if I invited him to organize a similar educational program for the Iranian scientists.

Soon after I was appointed to set up the Iranian Light Source Facility project in 2010, I invited Helmut to help us with the training of ILSF staff in Tehran.

Helmut visited Iran at more than 10 different occasions , each time staying in Iran for close to a month or longer. He contributed greatly to the education of the Iranian scientists and engineers on the physics and technology of accelerators at ILSF. We at ILSF owe him a lot for the extremely generous efforts he made to give the necessary technological and scientific ability to design a light source in Iran.

Helmut Wiedeman will be always remembered within the scientific community in Iran. He will always be in our heart for his contribution.

Carlo Bocchetta:

A great loss, he was such a wonderful person. Taught me so much, always ready to hear my concerns and helped me understand and see things in a new light. And it wasn't only physics.

Mark Woodley:

Helmut was the person who hired me at SLAC back in 1980 -- a good man to work for, let me aspire to whatever I wanted to do. I remember plotting SLC Damping Ring beta-functions by hand on graph paper for Helmut.

Michael Borland:

Helmut's impact on accelerator physics is immense, from the facilities he helped build to the books he wrote and the students he trained. I consider myself very fortunate to be among the latter. Perhaps it will be of interest to people if I recount some of my experiences as one of Helmut's students.     
When I entered Stanford, accelerator physics was just about the last subject I would have considered. I started out in a group doing solid state physics, but found it more competitive than collegial. I spent the next period in Artie's group, which was very collegial, but somehow the subject didn't click for me. While sitting at the beamline one afternoon, one of the older students told me about a weird bunch of guys who messed around with the accelerator. Some time later, Artie suggested that I speak with Helmut because he thought Helmut's group was a good place for me. Before I knew it, I was one of those weird guys. (Thanks, Artie!)     
Helmut quickly put me to work with Carl Cork and Wilson Ortiz programming magnetic measurement software for the new ring on Stanford campus. A while later, he got me involved in SLC North Arc commissioning, in the process introducing me to Gerry Fisher, Karl Brown, Lenny Rivkin, Andrew Hutton, and other notable people. For a graduate student to be at the controls of a state-of-the-art machine was unheard of, and I later learned that Helmut had fought with SLAC management to make it happen. I also witnessed, somewhat sadly, another student practically begging her supervisor to let her touch the controls instead of passively watching. To this day, I follow Helmut's example.    
I also remember how Helmut took advantage of the SSRL injector project to train his students, for example my thesis designing and simulating the rf gun. He fought considerable resistance to make something new and unproven a part of such a project, but he felt very strongly that it was the right thing to do, both for the field and his students. Such examples of Helmut's intellectual confidence and courage have stayed with me to this day.    
About a year before I finished at Stanford, Helmut got his senior students involved in commissioning a low-emittance lattice for PEP-II, which was then being considered as a possible synchrotron light source. This was, again, a fantastic experience for students, and we worked alongside experts like Martin Donald, John Galayda, Mike Zisman, and Jamie Paterson. Through Jamie Paterson I learned that Helmut's impact a SLAC was significant in ways I hadn't appreciated, e.g., having the idea to accelerate electrons and positrons in the same linac 180 degrees out of phase, thus making SLC feasible, and figuring out a sextupole configuration that made PEP work.    
The connection I made with Zisman and Galayda would later help me start my career at APS. It was only after I got there that I really started to appreciate everything Helmut had done to prepare me for success. Unfortunately, I lost touch with Helmut and didn't see him until many years later, when we both served on the machine advisory committee for the new Taiwan Photon Source. Helmut didn't appear to have aged at all. He was very happy living in Thailand and traveling around the world to teach and help develop light sources.    
On one of these occasions, my wife traveled with me and we sat with Helmut at lunch. He *had* to tell her his favorite story from my student days, about how I had made a mess of the office coffee maker by pouring water in the wrong place. He found it hilarious that I could program computers, but not make coffee. I didn't really mind the story, if it made him laugh.

Yenchieh Huang:

Helmut had a long influence on me as a student in the US and professor in Taiwan. He was the 2nd person who signed my thesis, when I graduated from Prof. Pantell in 1995. My thesis, titled "Sub-Compact Far-IR FEL", utilized the beam facility he built in the end station III of HEPL on the Stanford campus. Initially, he allowed me to work from a trailer at SSRL to learn simulations from Michael Borland. 

Helmut always showed his patience with me as a novice in accelerator research. Helmut's witty humor made me feel comfortable to talk to him with my poor Asian English. In 2002, I had the chance to work with him to clean up the end station III (photo below). He was reluctant to throw away any usable resources. 

Occasionally, he came to the Taiwan Light Source and stopped by my lab to inspect some museum pieces transferred during the end station III cleanup. It was his hope that I could sometime re-use those parts for useful things. 

In Dec. 2017, I traveled to Chang Mai, Thailand, to see him. At that time, he already had some difficulty walking, but he still went up to mountain tribes from time to time to help poor kids. He was a real scholar and human being. I and many other people will always remember him.

Arthur Bienenstock:

Helmut saved SSRL and trained accelerator physicists who have had major impacts. 

It was his idea to build the separate injector when SLC operation threatened SSRL's existence. His faith in his students was remarkable, as they played a major role in its commissioning. 

Similarly, he and his students had the idea and plan for SPEAR's first major rebuild and emittance reduction. 

His textbooks influenced students around the world. I still remember a young graduate student, Cecile Limborg, saying how much she had learned from those texts at the Grenoble meeting at which she announced that a circular machine could not produce the very short, bright pulses of the then-proposed LCLS.

Susan Winchester:

I first met Helmut in the late 80s. The USPAS had a recruiting table at an APS meeting and a group met in the hotel lobby before going to dinner on the night we all arrived. Helmut walked into the hotel after a long flight and overheard our plans and decided to join us. He not only came to dinner, he went dancing with us afterwards too -- despite his long day of travel and the late hour. I soon came to learn that Helmut was always up for anything, he never turned down an invitation for fun. 

Over the years I got to know Helmut quite well as he lectured at our symposium schools, our joint international schools and taught at our university-style schools. He was director of the USPAS from 2002 to 2006. We spent a lot of time together over those 30+ years. When not officially on duty he never wanted to talk shop -- ever. We talked about everything else though, especially our shared love of post-apocalyptic fiction (it really annoyed him when gasoline was still viable 10 or 20 years after the end of the world), travel (he always had the most entertaining stories about his many travels and I kept a running tally of how many times he got mugged in Rio), and food (before I knew what they were, I remember watching in horror as he ate an entire soft-shelled crab). We laughed a lot.

Helmut decided that we should take the USPAS to Baton Rouge, Louisiana for our winter 2003 session. When I asked him why he chose Baton Rouge, especially with New Orleans right next door, he told me a fascinating story about always wanting to visit the area as his German-soldier father was held nearby in a U.S. prisoner-of-war camp in the early 40s. At the time there was a shortage of farm laborers so they turned an old plantation into a camp and made the prisoners work the fields. He visited that plantation while we were there, but declined my offer to go with him. 

Helmut was unflappable and that made him a joy to work with. He didn't sweat either. In 2005 we were in Ithaca for a session with Cornell University and over the weekend he and I decided to hike up one of their beautiful waterfalls. It was a very hot day and by the time we got to the top I was an exhausted sweaty mess and there was Helmut -- absolutely pristine in his dress slacks, crisply ironed shirt and loafers -- as fresh as a daisy (photo below). Not sweaty, not out of breath and not a hair out of place. 

After moving to Thailand, he would tell me stories about how he was treated like a king with a driver and housekeeper who would tie little bags around each piece of fruit on his trees to keep the birds from eating them. He liked to take big groups of students out to dinner and always picked up the tab, they were very impressed with his generosity and it made him laugh when the bill came to the equivalent of something like $12 US. When it first came on TV, he loved the reality show "The Amazing Race" but could only watch it in Thailand a year or two after it aired in the US so he would ask me to watch it and then email a synopsis to him every week. I wouldn't have done that for anyone but Helmut. 

Helmut was a great friend and I will miss him very much.

NSRRC:

Helmut devoted his time, knowledge, experience, and helping hand to the NSRRC (Taiwan) over a period of 4 decades. Highlights of our memory in bits and pieces of time are organized in a PDF file - a tribute from all of us, staff of the NSRRC, Taiwan.